City Council and Authorities Concurrent
August 27, 2024

The OA has a 40.3 percent foreign-born population. Other than English, the most commonly spoken languages in the OA are Chinese, Vietnamese, and Tagalog, followed by Spanish.18F 19 Figure 14: Race Distribution in the Operational Area19F 20 5.6.4 Education
Understanding educational attainment of the population is important when developing appropriate outreach and educational materials. The U.S. Census estimates that 28 percent of the population OA 25 years and older has attained a bachelor’s degree, and 27 percent a graduate or professional degree.

Seventy-six percent of the population has attended college for some period, and 10 percent have not achieved a high school or equivalent degree.20 F
21 19 United States Census Bureau. (2020). Santa Clara County, California. https://data.census.gov/profile?g=050XX00US06085
20 United States Census Bureau. (2020). Santa Clara County, California. https://data.census.gov/profile?g=050XX00US06085
21 United States Census Bureau. (2020). Santa Clara County, California. https://data.census.gov/profile?g=050XX00US06085
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 46

5.6.5 Individuals with Disabilities or with Access or Functional Needs The U.S. Census estimates that over 42 million non-institutionalized people with disabilities live in the U.S. Individuals with disabilities are more likely to have difficulty with resilience and responding to a hazard event than the general population.21F
22 Local government may be the first level of response to assist these individuals, and coordination of efforts to meet their access and functional needs is paramount to life safety efforts. It is important for emergency and incident managers to distinguish between functional and medical needs in order to plan for incidents that require evacuation and sheltering. Knowing the percentage of population with a disability will allow emergency management personnel and first responders to have personnel available who can provide services needed by those with access and functional needs.

According to the U.S. Census 2021 American Community Survey 1-Year Estimates, 169,467, or 9 percent, of individuals have some form of disability in the OA.2 F 23 5.6.6. Social Vulnerability
The Social Vulnerability Index provides a visual representation of the potential negative effects on communities that natural hazards or other external stresses on human health. The index is based on 16 variables from the U.S. Census to indicate areas that may need additional support before, during or after disasters. These indices include measures of socioeconomic status, household characteristics, racial and ethnic minority status, and housing type and transportation. The overall social vulnerability for Santa Clara County is shown in Figure 14. A summary of the four categories of indices that contribute to the overall index is shown in Figure 15. The darker toned colors indicate areas with potentially higher vulnerability.
22 United States Census Bureau. (2020). United States. https://data.census.gov/profile/United_States?g=010XX00US 23 United States Census Bureau. (2020). Santa Clara County, California. https://data.census.gov/profile?g=050XX00US06085
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 47 Figure 15: Santa Clara County Social Vulnerability Index Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 48 Figure 16: Social Vulnerability Index Themes
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 49

5.7 Economy

5.7.1 Income
In the United States, individual households are expected to use private resources to prepare for, respond to and recover from disasters to some extent. This means economically disadvantaged households are automatically disadvantaged when confronting hazards. Additionally, those who are economically disadvantaged typically occupy more poorly built and inadequately maintained housing. Mobile or modular homes, for example, are more susceptible to damage in earthquakes and floods than other types of housing. In urban areas, those who are economically disadvantaged often live in older houses and apartment complexes, which are more likely to be made of un-reinforced masonry, a building type that is particularly susceptible to damage during earthquakes. Furthermore, those who are economically disadvantaged are less likely to have insurance to compensate for losses incurred from natural disasters.

This means they may have a great deal to lose during an event and may be the least prepared to deal with potential losses. The events following Hurricane Katrina in 2005 illustrated that personal household economics significantly impact people’s decisions on evacuation. Individuals who cannot afford gas for their cars will likely decide not to evacuate.

A living wage calculator developed at the Massachusetts Institute of Technology estimates the hourly living wage needed to support different types of families. The calculator takes into consideration basic needs such as health, housing, transportation, and other necessities and interprets the living wage as a geographically specific hourly rate required to acquire basic minimum necessities cost. Table 13 presents summary information from the living wage calculator for 2022. Each hourly rate is adjusted per each working adult.

Table 13: Hourly Living Wage Calculation for Santa Clara County, California (2022)23F 24 Wage Level One Adult One Adult + Two
Children Two Adults Two Adults + One Child
Living Wage $26.86 $68.69 $38.42 $46.79
Poverty Wage $6.53 $11.07 $8.80 $11.07
Minimum Wage $15.50 $15.50 $15.50 $15.50
Based on 2022 U.S. Census Bureau estimates, the median household income in Santa Clara County was $141,562. It is estimated that about 16 percent of households receive an income between $100,000 and $149,999 per year and over 47 percent of household incomes are above $150,000 annually. About 9 percent of the households in the OA make less than $25,000 per year. The poverty threshold for a family of four in 2022 was $30,186; for a family of three, $22,892; for a family of two under 65 years, $19,597 and for unrelated individuals under 65 years, $15,225.24 F 25 The 2015 living wage calculations cited in the 2017 Hazard Mitigation Plan were notably different than the current estimates. For example, the living wage for one adult was $14.52 and $11.30 for two adults.

When incomes do not match the cost-of-living increase, households may be forced to reduce household on nonessential items. Hazard mitigation measures, such as flood insurance and voluntary structural retrofitting, are not usually considered essential despite their demonstrated long-term cost effectiveness. 24 Massachusetts Institute of Technology. (2023). Living Wage Calculator, Santa Clara County. https://livingwage.mit.edu/counties/06085
25 United States Census Bureau. (2020). Santa Clara County, California. https://data.census.gov/profile?g=050XX00US06085
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5.8 Industry, Businesses, and Institutions
The county’s economy is strongly based in the professional, scientific, and management, and administrative and waste management services industry, followed by educational services and health care and social assistance, manufacturing, and retail trade. Figure 16 shows the breakdown of industry types in the OA. Santa Clara County is part of one of the state’s busiest urbans areas.

The OA benefits from a variety of business activity. Major businesses include Apple, Inc, Alphabet Inc. (Google), Netflix, Roku, Inc. Shockley Semiconductor Laboratory, eBay Inc., Cisco Systems Inc., Applied Materials Inc., Flextronics International, Intel Corp, Kaiser Permanente Medical Center, Liberty Tax Service, Lockheed Martin Space Systems, NASA, Phillips Lumileds Lighting Company, Santa Clara Valley Medical Center, and many others.

Major educational and research institutions in the OA include Stanford University, San José State University, Santa Clara University, Mission College, De Anza College, Foothill College, West Valley College, Mission College, Evergreen Valley College, San José City College, and Gavilan College.

Figure 17: Industry in Santa Clara County

5.8.1 Employment Trends and Occupations
According to the Census Bureau, 66.6 percent of the Santa Clara County population 16 years and over is in the labor force. Management, business, science, and arts occupations make up 59 percent of jobs in the County. Other major occupations include sales and office (15 percent) and service (13 percent).

Multiple major employers in California are located in Santa Clara County, including Apple, Cisco Systems, Advanced Micro Devices Inc, Amazon, Apple, Applied Materials Inc, California’s Great America, Cisco Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 51 Systems, Intel Corp, Intuit, Hewlett Packard Enterprise, Alphabet Inc. (Google), and Nvidia Corp., and Yahoo. The largest of these are Applied Materials Inc, Apple, Cisco Systems, Intel Inc, Hewlett Packard Enterprise, Google, and Yahoo each with 10,000 or more employees. The others employ between 1,000- 4,999 employees.25F
26 Figure 18: Occupations in Santa Clara County
The figure below compares the California and the Santa Clara County unemployment trends from 2017 to 2021. According to the State of California’s Employment Development Department, the Santa Clara County unemployment rate was trending downward prior to 2020 when it spiked upward, likely in part due to the COVID-19 pandemic. By 2021, the unemployment rates started to fall again. They continued to fall below pre-pandemic estimates in 2022. Overall, Santa Clara County experienced less unemployment than the rest of the State throughout this time period.26 F 27 26 United States Census Bureau. (2021). American Community Survey, Selected Economic Characteristics Santa Clara County, California.
https://data.census.gov/table?q=employment+in+Santa+Clara+County,+California&tid=ACSDP1Y2021.DP03 27 State of California Employment Development Department. (2023). Economic Development Data Library. https://data.edd.ca.gov/
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 52 Figure 19: California and Santa Clara County Unemployment Rate27F 28 5.9 Laws and Ordinances
Existing laws, ordinances, and plans at the federal, state, and local level can support or impact hazard mitigation actions identified in this plan. Hazard mitigation plans are required to include a review and incorporation, if appropriate, of existing plans, studies, reports, and technical information as part of the planning process (44 CFR, Section 201.6(b)(3)). The following federal and state programs have been identified as programs that may interface with the actions identified in this plan. Each program enhances capabilities to implement mitigation actions or has a nexus with a mitigation action in this plan.

Information presented in this section can be used in addition to local capabilities to implement the actions found in the jurisdictional and special district annexes of Volume 2 of this plan. Each planning partner has individually reviewed existing local plans, studies, reports, and technical information in its jurisdictional or special district annexes, presented in Volume 2 of this plan.

5.9.1 Federal
Stafford Act
The Stafford Disaster Relief and Emergency Assistance Act (“Stafford Act”) is the statutory authority for most Federal disaster response activities for FEMA and FEMA programs. The Stafford Act initially provided limited resources mitigation and pre-disaster community resilience. It did include the PresDisaster Hazard Mitigation (PDM) program however, funding was often ad hoc and historically much less than traditional disaster spending. Subsequent legislation has since amended the Stafford Act, opening the doors to additional mitigation opportunity.
28 State of California Employment Development Department. (2023). Economic Development Data Library. https://data.edd.ca.gov/
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 53 Disaster Mitigation Act
The DMA is the current federal legislation addressing hazard mitigation planning. It emphasizes planning for disasters before they occur. It specifically addresses planning at the local level, requiring plans to be in place before certain hazard mitigation funds are available to communities. This plan is designed to meet the requirements of DMA, improving eligibility for future hazard mitigation funds.

Disaster Recovery Reform Act
The Disaster Recovery Reform Act of 2018 amended the Stafford Act and provided 56 provisions for FEMA policy or regulation changes. Crucially, the Act set aside 6 percent of the total aid amount awarded in the previous year for pre-disaster mitigation. FEMA estimates this mean $300-500 million dollars will be available for mitigation annually.28F
29 This creates a much more consistent, reliable stream of pre-disaster mitigation dollars than ever seen before. Additionally, the Act expanded language for the Hazard Mitigation Grant Program (HMGP) to include an increased focused on resilience and reducing future damage in the post-disaster environment which may encourage proactive mitigation measures. It also provided states, tribes, and local jurisdictions with additional authority to use FEMA funding to rebuild to the latest building codes to reduce future risk to the Nation.

National Environmental Policy Act
The National Environmental Policy Act (NEPA) requires federal agencies to consider the environmental impacts of proposal actions and reasonable alternatives to those actions, alongside technical and economic considerations. NEPA established the Council on Environmental Quality (CEQ), whose regulations (40 CFR Parts 1500-1508) set standards for NEPA compliance. Consideration and decisionmaking regarding environmental impacts must be documented in an environmental impact statement or environmental assessment. Environmental impact assessment requires the evaluation of reasonable alternatives to a proposed action, solicitation of input from organizations and individuals that could be affected, and an unbiased presentation of direct, indirect, and cumulative environmental impacts. FEMA hazard mitigation project grant applications require full compliance with applicable federal acts. Any action identified in this plan that falls within the scope of this act will need to meet its requirements.

Endangered Species Act
The federal Endangered Species Act (ESA) was enacted in 1973 to conserve species facing depletion or extinction and the ecosystems that support them. The act sets forth a process for determining which species are threatened and endangered and requires the conservation of the critical habitat in which those species live. The ESA provides broad protection for species of fish, wildlife and plants that are listed as threatened or endangered. Provisions are made for listing species, as well as for recovery plans and the designation of critical habitat for listed species. The ESA outlines procedures for federal agencies to follow when taking actions that may jeopardize listed species and contains exceptions and exemptions.

It is the enabling legislation for the Convention on International Trade in Endangered Species of Wild Fauna and Flora. Criminal and civil penalties are provided for violations of the ESA and the Convention. 29 Federal Emergency Management Agency (FEMA). (2020). Hazard Mitigation Assistance. https://sgp.fas.org/crs/homesec/IN11187.pdf
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 54 Federal agencies must seek to conserve endangered and threatened species and use their authorities in furtherance of the ESA’s purposes. The ESA defines three fundamental terms:29F 30  Endangered means that a species of fish, animal or plant is “in danger of extinction throughout all or a significant portion of its range.” (For salmon and other vertebrate species, this may include subspecies and distinct population segments.)
 Threatened means that a species “is likely to become endangered within the foreseeable future.” Regulations may be less restrictive for threatened species than for endangered species.  Critical habitat means “specific geographical areas that are…essential for the conservation and management of a listed species, whether occupied by the species or not.” Five sections of the ESA are of critical importance to understanding it:
 Section 4: Listing of a Species—The National Oceanic and Atmospheric Administration (NOAA) Fisheries Service is responsible for listing marine species; the U.S. Fish and Wildlife Service is responsible for listing terrestrial and freshwater aquatic species. The agencies may initiate reviews for listings, or citizens may petition for them. A listing must be made “solely on the basis of the best scientific and commercial data available.” After a listing has been proposed, agencies receive comment and conduct further scientific reviews for 12 to 18 months, after which they must decide if the listing is warranted. Economic impacts cannot be considered in this decision, but it may include an evaluation of the adequacy of local and state protections. Critical habitat for the species may be designated at the time of listing.
 Section 7: Consultation—Federal agencies must ensure that any action they authorize, fund, or carry out is not likely to jeopardize the continued existence of a listed or proposed species or adversely modify its critical habitat. This includes private and public actions that require a federal permit. Once a final listing is made, non-federal actions are subject to the same review, termed a “consultation.” If the listing agency finds that an action will “take” a species, it must propose mitigations or “reasonable and prudent” alternatives to the action; if the proponent rejects these, the action cannot proceed.
 Section 9: Prohibition of Take—It is unlawful to “take” an endangered species, including killing or injuring it or modifying its habitat in a way that interferes with essential behavioral patterns, including breeding, feeding, or sheltering.
 Section 10: Permitted Take—Through voluntary agreements with the federal government that provide protections to an endangered species, a non-federal applicant may commit a take that would otherwise be prohibited as long as it is incidental to an otherwise lawful activity (such as developing land or building a road). These agreements often take the form of a “Habitat Conservation Plan.”
 Section 11: Citizen Lawsuits—Civil actions initiated by any citizen can require the listing agency to enforce the ESA’s prohibition of taking or to meet the requirements of the consultation process.

FEMA hazard mitigation project grant applications require full compliance with applicable federal acts.

Any action identified in this plan that falls within the scope of this act will need to meet its requirements. 30 National Oceanic and Atmospheric Administration. (n.d.). Glossary: Endangered Species Act. https://www.fisheries.noaa.gov/laws-and-policies/glossary-endangered-speciesact#:~:text=A%20threatened%20species%20is%20defined%20under%20the%20ESA,threatened%20or%20endange red%20are%20called%20%E2%80%9C%20listed%20species.%E2%80%9D Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 55 The Clean Water Act
The federal Clean Water Act (CWA) employs regulatory and non-regulatory tools to reduce direct pollutant discharges into waterways, finance municipal wastewater treatment facilities, and manage polluted runoff. These tools are employed to achieve the broader goal of restoring and maintaining the chemical, physical, and biological integrity of the nation’s surface waters so that they can support “the protection and propagation of fish, shellfish, and wildlife and recreation in and on the water.” Evolution of CWA programs over the last decade has included a shift from a program-by-program, source-by-source, and pollutant-by-pollutant approach to more holistic watershed-based strategies.

Under the watershed approach, equal emphasis is placed on protecting healthy waters and restoring impaired ones. A full array of issues is addressed, not just those subject to CWA regulatory authority.

Involvement of stakeholder groups in the development and implementation of strategies for achieving and maintaining water quality and other environmental goals is a hallmark of this approach.

FEMA hazard mitigation project grant applications require full compliance with applicable federal acts.

Any action identified in this plan that falls within the scope of this act will need to meet its requirements.

National Flood Insurance Program
The National Flood Insurance Program (NFIP) provides federally backed flood insurance in exchange for communities enacting floodplain regulations. Participation and good standing under NFIP are prerequisites to grant funding eligibility under the Robert T. Stafford Act. Santa Clara County and all of the partner cities for this plan participate in the NFIP and have adopted regulations that meet the NFIP requirements. At the time of the preparation of this plan, all participating jurisdictions in the partnership were in good standing and in full compliance with the minimum requirements of the NFIP.

Community Rating System
The Community Rating System (CRS) is a voluntary incentive program for communities that participate in the NFIP and adopt and enforce floodplain management practices that exceed minimum requirements.

Flood insurance premium discounts reflect the ways in which the community meets the following goals of the program:
 Reduce and avoid flood damage to insurable property.
 Strengthen and support the insurance aspects of the National Flood Insurance Program.  Foster comprehensive floodplain management.

Participating in the CRS program not only encourages communities to reduce the risk to life and property from flooding through a proactive floodplain management program, but provides a clear, monetary incentive for residents for supporting mitigation activities. Many planning partners participate in the CRS.

Many planning partners participate in the CRS. The planning partners discussed using this plan to meet CRS requirements as well. Ultimately, it was decided that Santa Clara Valley Water will lead the development of a separate Floodplain Management Plan specifically dedicated towards this goal, allowing planning partners that participate in the CRS program to maintain or enhance their CRS classifications. Relevant information from this Hazard Mitigation Plan will be incorporated into the Floodplain Management Plan.

Coastal Zone Management Act
The national Coastal Zone Management Act requires federal agencies to conduct their planning, management, development, and regulatory activities in a manner consistent to the maximum extent practicable with the policies of state Coastal Zone Management (CZM) programs. State CZM lead agencies have the authority to review federal actions for consistency with their federally approved CZM programs.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 56 In California, the California Coastal Commission, the Bay Conservation and Development Commission, and the California Coastal Conservancy are the three CZM agencies empowered to conduct federal consistency reviews. The informational and procedural requirements for CZM federal consistency reviews are prescribed by federal regulations (15 CFR 930). Any action identified in this plan that falls within the scope of this act will need to meet its requirements.

National Incident Management System
The National Incident Management System is a systematic approach for government, nongovernmental organizations, and the private sector to work together to manage incidents involving hazards. The system provides a flexible but standardized set of incident management practices. Incidents typically begin and end locally, and they are managed at the lowest possible geographical, organizational, and jurisdictional level. In other instances, success depends on the involvement of multiple jurisdictions, levels of government, functional agencies, and emergency-responder disciplines. These instances necessitate coordination across this spectrum of organizations. Communities using the National Incident Management System follow a comprehensive national approach that improves the effectiveness of emergency management and response personnel across the full spectrum of potential hazards (including natural hazards, terrorist activities, and other human-caused disasters) regardless of size or complexity.

Although participation is voluntary, federal departments and agencies are required to make adoption of NIMS by local and state jurisdictions a condition to receive federal preparedness grants and awards. The content of this plan is considered to be a viable support tool for any phase of emergency management.

The NIMS program is considered as a response function, and information in this hazard mitigation plan can support the implementation and update of all NIMS-compliant plans within the planning area.

Americans with Disabilities Act and Amendments
The Americans with Disabilities Act (ADA) seeks to prevent discrimination against people with disabilities in employment, transportation, public accommodation, communications, and government activities. The most recent amendments became effective in January 2009 (P.L. 110-325). Title II of the ADA deals with compliance with the act in emergency management and disaster-related programs, services, and activities. It applies to state and local governments as well as third parties, including religious entities and private nonprofit organizations.

The ADA has implications for sheltering requirements and public notifications. During an emergency alert, officials must use a combination of warning methods to ensure that all residents have any necessary information. Those with hearing impairments may not hear radio, television, sirens, or other audible alerts, while those with visual impairments may not see flashing lights or visual alerts. Two stand-alone technical documents have been issued for shelter operators to meet the needs of people with disabilities. These documents address physical accessibility as well as medical needs and service animals.

The ADA also intersects with disaster preparedness programs in regard to transportation, social services, temporary housing, and rebuilding. Persons with disabilities may require additional assistance in evacuation and transit (such as vehicles with wheelchair lifts or paratransit buses). Evacuation and other response plans should address the unique needs of residents. Local governments may be interested in implementing a special-needs registry to identify the home addresses, contact information, and needs for residents who may require more assistance.

FEMA hazard mitigation project grant applications require full compliance with applicable federal acts.

Any action identified in this plan that falls within the scope of this act will need to meet its requirements.

Civil Rights Act of 1964
The Civil Rights Act of 1964 prohibits discrimination based on race, color, religion, sex, or national origin and requires equal access to public places and employment. The act is relevant to emergency management and hazard mitigation in that it prohibits local governments from favoring the needs of one population group over another.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 57 Local government and emergency response must ensure the continued safety and well-being of all residents equally, to the extent possible. FEMA hazard mitigation project grant applications require full compliance with applicable federal acts. Any action identified in this plan that falls within the scope of this act will need to meet its requirements.

Rural Development Program
The mission of the U.S. Department of Agriculture (USDA) Rural Development Program is to help improve the economy and quality of life in rural America. The program provides project financing and technical assistance to help rural communities provide the infrastructure needed by rural businesses, community facilities, and households. The program addresses rural America’s need for basic services, such as clean running water, sewage and waste disposal, electricity, and modern telecommunications and broadband. Loans and competitive grants are offered for various community and economic development projects and programs, such as the development of essential community facilities including fire stations. Some of the actions identified in this plan may be eligible for funding available under this program.

Community Development Block Grant Disaster Resilience Program In response to disasters, Congress may appropriate additional funding for the U.S. Department of Housing and Urban Development Community Development Block Grant programs to be distributed as Disaster Recovery grants (CDBG-DR). These grants can be used to rebuild affected areas and provide seed money to start the recovery process. CDBG-DR assistance may fund a broad range of recovery activities, helping communities and neighborhoods that otherwise might not recover due to limited resources. CDBG-DR grants often supplement disaster programs of FEMA, the Small Business Administration, and the U.S. Army Corps of Engineers. Housing and Urban Development generally awards noncompetitive, nonrecurring CDBG-DR grants by a formula that considers disaster recovery needs unmet by other federal disaster assistance programs. To be eligible for CDBG-DR funds, projects must meet the following criteria:
 Address a disaster-related impact (direct or indirect) in a presidentially declared county for the covered disaster.
 Be a CDBG-eligible activity (according to regulations and waivers).  Meet a national objective.

Incorporating preparedness and mitigation into these actions is encouraged, as the goal is to rebuild in ways that are safer and stronger. CDGB-DR funding is a potential alternative source of funding for actions identified in this plan.

Community Development Block Grant Mitigation
The Community Development Block Grant Mitigation (CDBG-MIT) program was developed to support communities impacted by recent disasters in carrying out strategic and high-impact mitigation actions to reduce losses from future events. Congress may appropriate additional CDBG-MIT funding for the U.S.

Department of Housing and Urban Development following a disaster event. The goals of CDBG-MIT funding are:
 Support data-informed investments, focusing on repetitive loss of property and critical infrastructure;
 Build capacity to comprehensively analyze disaster risks and update hazard mitigation plans;  Support the adoption of policies that reflect local and regional priorities that will have long-lasting effects on community risk reduction, including risk reduction to community lifelines and decreasing future disaster costs; and
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 58  Maximize the impact of funds of encouraging leverage, private/public partnerships, and coordination with other federal dollars.

This would be a potential post-disaster financial capability of jurisdictions covered in this plan which could be put towards implementing the identified mitigation actions.

Emergency Watershed Program
The USDA Natural Resources Conservation Service administers the Emergency Watershed Protection Program, which responds to emergencies created by natural disasters. Eligibility for assistance is not dependent on a national emergency declaration. The program is designed to help people and conserve natural resources by relieving imminent hazards to life and property caused by floods, fires, windstorms, and other natural occurrences. The Emergency Watershed Protection is an emergency recovery program.

Financial and technical assistance are available for the following activities:30 F 31  Remove debris from stream channels, road culverts, and bridges.  Reshape and protect eroded banks.
 Correct damaged drainage facilities.
 Establish cover on critically eroding lands.
 Repair levees and structures.
 Repair conservation practices.

This federal program could be a possible funding source for actions identified in this plan.

Presidential Executive Orders 11988 and 13690
Executive Order 11988 requires federal agencies to avoid to the extent possible the long and short-term adverse impacts associated with the occupancy and modification of floodplains and to avoid direct and indirect support of floodplain development wherever there is a practicable alternative. It requires federal agencies to provide leadership and take action to reduce the risk of flood loss, minimize the impact of floods on human safety, health, and welfare, and restore and preserve the natural and beneficial values of floodplains. The requirements apply to the following activities31F 32:
 Acquiring, managing, and disposing of federal lands and facilities.  Providing federally undertaken, financed, or assisted construction and improvements.  Conducting federal activities and programs affecting land use, including but not limited to water and related land resources planning, regulation, and licensing.

Executive Order 13690 expands Executive Order 11988 and acknowledges that the impacts of flooding are anticipated to increase over time due to the effects of climate change and other threats. It mandates a federal flood risk management standard to increase resilience against flooding and help preserve the natural values of floodplains. This standard expands management of flood issues from the current base flood level to a higher vertical elevation and corresponding horizontal floodplain when federal dollars are involved in a project.
31 National Resources Conservation Service. (n.d.). Emergency Watershed Protection. https://www.nrcs.usda.gov/programs-initiatives/ewp-emergency-watershed-protection/kentucky/emergencywatershed-protection 32 Federal Emergency Management Agency. (2015, October 8). Guidelines for Implementing Executive Order 11988. https://www.fema.gov/sites/default/files/documents/fema_implementing-guidelines-EO11988-13690_10082015.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 59 The goal is to address current and future flood risk and ensure that projects funded with taxpayer dollars last as long as intended.32F
33 All actions identified in this plan will seek full compliance with all applicable presidential executive orders.

Presidential Executive Order 11990
Executive Order 11990 requires federal agencies to provide leadership and take action to minimize the destruction, loss, or degradation of wetlands, and to preserve and enhance the natural and beneficial values of wetlands. The requirements apply to the following activities:3 F 34  Acquiring, managing, and disposing of federal lands and facilities.  Providing federally undertaken, financed, or assisted construction and improvements.  Conducting federal activities and programs affecting land use, including but not limited to water and related land resources planning, regulation, and licensing.

All actions identified in this plan will seek full compliance with all applicable presidential executive orders.

Emergency Relief for Federally Owned Roads Program
The U.S. Forest Service’s Emergency Relief for Federally Owned Roads Program was established to assist federal agencies with repair or reconstruction of tribal transportation facilities, federal lands transportation facilities, and other federally owned roads that are open to public travel and have suffered serious damage by a natural disaster over a wide area or by a catastrophic failure. The program funds both emergency and permanent repairs.34F
35 Eligible activities under this program meet some of the goals and objectives for this plan and the program is a possible funding source for actions identified in this plan.

U.S. Army Corps of Engineers Programs
The U.S. Army Corps of Engineers has several civil works authorities and programs related to flood risk and flood hazard management:
 Floodplain Management Services are 100-percent federally funded technical services such as development and interpretation of site-specific data related to the extent, duration, and frequency of flooding. Special studies may be conducted to help a community understand and respond to flood risk. These may include flood hazard evaluation, flood warning and preparedness, or flood modeling.
 For more extensive studies, the Corps of Engineers offers a cost-shared program called Planning Assistance to States and Tribes. Studies under this program generally range from $25,000 to $100,000, with the local jurisdiction providing 50 percent of the cost.  The Corps of Engineers has several cost-shared programs (typically 65 percent federal and 35 percent non-federal) aimed at developing, evaluating, and implementing structural and nonstructural capital projects to address flood risks at specific locations or within a specific watershed:
33 Obama White House. (2015, January 30). Executive Order – Establishing a Federal Flood Risk Management Standard and a Process for Further Soliciting and Considering Stakeholder Input. https://obamawhitehouse.archives.gov/the-press-office/2015/01/30/executive-order-establishing-federal-flood-riskmanagement-standard-and34 National Archives. (n.d.). § 9.4 Definitions. https://www.ecfr.gov/current/title-44/chapter-I/subchapter-A/part9/section-9.4 35 Federal Highway Administration. (n.d.). Fact Sheets, Emergency Relief Program. https://www.fhwa.dot.gov/bipartisan-infrastructurelaw/er_fact_sheet.cfm#:~:text=The%20BIL%20continues%20the%20Emergency%20Relief%20program%2C%20whi ch,disasters%20or%20catastrophic%20failure%20from%20an%20external%20cause.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 60 ▪ The Continuing Authorities Program for smaller-scale projects includes Section 205 for Flood Control, with a $7 million federal limit and Section 14 for Emergency Streambank Protection with a $1.5 million federal limit. These can be implemented without specific authorization from Congress.
▪ Larger scale studies, referred to as General Investigations, and projects for flood risk management, for ecosystem restoration or to address other water resource issues, can be pursued through a specific authorization from Congress and are cost-shared, typically at 65 percent federal and 35 percent non-federal.
▪ Watershed Management planning studies can be specifically authorized and are cost-shared at 50 percent federal and 50 percent non-federal.
 The Corps of Engineers provides emergency response assistance during and following natural disasters. Public Law 84-99 enables the Corps to assist state and local authorities in flood fight activities and cost share in the repair of flood protective structures. Assistance afforded under PL 84-99 is broken down into the following categories:
▪ Preparedness: The Flood Control and Coastal Emergency Act establishes an emergency fund for preparedness for emergency response to natural disasters; for flood fighting and rescue operations; for rehabilitation of flood control and hurricane protection structures.

Funding for Corps of Engineers emergency response under this authority is provided by Congress through the annual Energy and Water Development Appropriation Act. Disaster preparedness activities include coordination, planning, training and conduct of response exercises with local, state, and federal agencies.
▪ Response Activities: PL 84-99 allows the Corps of Engineers to supplement state and local entities in flood-fighting for urban and other non-agricultural areas under certain conditions (Engineering Regulation 500-1-1 provides specific details). All flood-fight efforts require a Project Cooperation Agreement (PCA) signed by the public sponsor and a requirement for the sponsor to remove all flood-fight material after the flood has receded. PL 84-99 also authorizes emergency water support and drought assistance in certain situations and allows for “advance measures” assistance to prevent or reduce flood damage conditions of imminent threat of unusual flooding.
▪ Rehabilitation: Under PL 84-99, an eligible flood protection system can be rehabilitated if damaged by a flood event. The flood system would be restored to its pre-disaster status at no cost to the federal system owner, and at 20-percent cost to the eligible non-federal system owner. All systems eligible for PL 84-99 rehabilitation assistance have to be in the Rehabilitation and Inspection Program prior to the flood event. Acceptable operation and maintenance by the public levee sponsor are verified by levee inspections conducted by the Corps on a regular basis. The Corps has the responsibility to coordinate levee repair issues with interested federal, state, and local agencies following natural disaster events where flood control works are damaged.

All of these authorities and programs are available to the planning partners to support any intersecting mitigation actions.

5.9.2 State
Alquist-Priolo Earthquake Fault Zoning Act
The Alquist-Priolo Earthquake Fault Zoning Act was enacted in 1972 to mitigate the hazard of surface faulting to structures for human occupancy. The Alquist-Priolo Earthquake Fault Zoning Act’s main purpose is to prevent construction of buildings used for human occupancy on the surface trace of active faults. Before a new project is permitted, cities and counties require a geologic investigation to demonstrate that proposed buildings will not be constructed on active faults.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 61 The act addresses only the hazard of surface fault rupture and is not directed toward other earthquake hazards, such as liquefaction or seismically induced landslides. The law requires geologists from the State of California to establish regulatory zones around the surface traces of active faults and to issue appropriate maps. The maps are distributed to all affected cities, counties, and state agencies for their use in planning and controlling new or renewed construction. Local agencies must regulate most development projects within the zones. Projects include all land divisions and most structures for human occupancy. All seismic hazard mitigation actions identified in this plan will seek full compliance with the Alquist-Priolo Earthquake Fault Zoning Act.

California General Planning Law
California state law requires that every county and city prepare and adopt a comprehensive long-range plan to serve as a guide for community development. The general plan expresses the community’s goals, visions, and policies relative to future land uses, both public and private. The general plan is mandated and prescribed by state law (Cal. Gov. Code §65300 et seq.) and forms the basis for most local government land use decision-making.

The plan must consist of an integrated and internally consistent set of goals, policies, and implementation measures. In addition, the plan must focus on issues of the greatest concern to the community and be written in a clear and concise manner. City and county actions, such as those relating to land use allocations, annexations, zoning, subdivision and design review, redevelopment, and capital improvements, must be consistent with the plan.

All municipal planning partners to this plan have general plans that are currently compliant with this law and have committed to integrating this mitigation plan with their general plans through provisions referenced below (AB-2140 and SB-379).

California Environmental Quality Act
The California Environmental Quality Act (CEQA) was passed in 1970, shortly after the federal government enacted the National Environmental Policy Act, to institute a statewide policy of environmental protection. CEQA requires state and local agencies in California to follow a protocol of analysis and public disclosure of the potential environmental impacts of development projects. CEQA makes environmental protection a mandatory part of every California state and local agency’s decisionmaking process.

CEQA establishes a statewide environmental policy and mandates actions all state and local agencies must take to advance the policy. Jurisdictions conduct analysis of the project to determine if there are potentially significant environmental impacts, identify mitigation measures, and possible project alternatives by preparing environmental reports for projects that requires CEQA review. This environmental review is required before an agency takes action on any policy, program, or project.

Santa Clara County has sought exemption from CEQA for the Hazard Mitigation Plan based on four different sections of the CEQA Guidelines:
 Section 15183(d): “The project is consistent with…a general plan of a local agency, and an EIR was certified by the lead agency for the...general plan.”  Section 15262: “A project involving only feasibility or planning studies for possible future actions which the agency, board or commission has not approved, adopted, or funded does not require the preparation of an EIR or negative declaration but does require consideration of environmental factors. This section does not apply to the adoption of a plan that will have a legally binding effect on later activities.”
 Section 15306: “(Categorical Exemption) Class 6 consists of basic data collection, research, experimental management, and resource evaluation activities which do not result in a serious or major disturbance to an environmental resource. These may be strictly for information gathering Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 62 purposes, or as part of a study leading to an action which a public agency has not yet approved, adopted, or funded.”
 Section 15601(b)(3): “...CEQA applies only to projects which have the potential for causing a significant effect on the environment. Where it can be seen with certainty that there is no possibility that the activity in question may have a significant effect on the environment, the activity is not subject to CEQA.”
Planning partners may seek exemption at their discretion.

California Coastal Management Program
The California Coastal Management Program under the California Coastal Act requires each city or county lying wholly or partly within the coastal zone to prepare a local coastal plan. The specific contents of such plans are not specified by state law, but they must be certified by the Coastal Commission as consistent with policies of the Coastal Act (Public Resources Code, Division 20). The Coastal Act has provisions relating to geologic hazards but does not mention tsunamis specifically. Section 30253(1) of the Coastal Act states that new development shall minimize risks to life and property in areas of high geologic, flood, and fire hazard. Development should be prevented or limited in high hazard areas whenever possible. However, where development cannot be prevented or limited, land use density, building value, and occupancy should be kept at a minimum.

There are identified coastal zones in the Santa Clara County Operational Area and affected planning partners have developed local coastal plans to address them. Any mitigation project identified in this plan that intersects the mapped coastal zone will be consistent with the recommendations of the local coastal plan.

California State Assembly Bills
Assembly Bill 162: Flood Planning, Chapter 369, Statutes of 2007 This California State Assembly Bill (AB) passed in 2007 requires cities and counties to address floodrelated matters in the land use, conservation, and safety and housing elements of their general plans.

The land use element must identify and annually review the areas covered by the general plan that are subject to flooding as identified in floodplain mapping by either FEMA or the Department of Water Resources (DWR). During the next revision of the housing element on or after January 1, 2009, the conservation element of the general plan must identify rivers, creeks, streams, flood corridors, riparian habitat, and land that may accommodate floodwater for groundwater recharge and stormwater management. The safety element must identify information regarding flood hazards, including:
 Flood hazard zones;
 Maps published by FEMA, DWR, the U.S. Army Corps of Engineers, the Central Valley Flood.

Protection Board, and CalOES;
 Historical data on flooding; and
 Existing and planned development in flood hazard zones.

The general plan must establish goals, policies, and objectives to protect from unreasonable flooding risks, including:
 Avoiding or minimizing the risks of flooding new development;  Evaluating whether new development should be located in flood hazard zones; and  Identifying construction methods to minimize damage.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 63 Assembly Bill 2140: General Plans—Safety Element, Chapter 739, Statutes of 2006 This bill allows jurisdictions to be eligible for state funding to cover the local match of public assistance costs for recovery activities after hazard events if the local jurisdiction incorporates their Local Hazard Mitigation Plan into the safety element of their general plan. In addition, this bill requires Cal OES to give preference for federal mitigation funding to cities and counties that have adopted local hazard mitigation plans. The intent of the bill is to encourage cities and counties to create and adopt hazard mitigation plans.

The County OEM has worked with the safety element team throughout 2022 and 2023 in updating the Safety Element, to ensure the County is maximizing their future funding opportunities to reduce risk in the County and comply with Assembly Bill 2140 (2006), which affords the county additional benefits under the California Disaster Assistance Act. The Multi-Jurisdictional Hazard Mitigation Plan will be incorporated into the Safety Element as the Safety Element update comes to a completion and is presented to the Board of Supervisors for Adoption.

Assembly Bill 70: Flood Liability, Chapter Number 367, Statutes of 2007 This bill provides that a city or county may be required to contribute a fair and reasonable share to compensate for property damage caused by a flood to the extent that it has increased the state’s exposure to liability for property damage by unreasonably approving new development in a previously undeveloped area that is protected by a state flood control project, unless the city or county meets specified requirements.

Assembly Bill 32: The California Global Warming Solutions Act This bill addresses greenhouse gas emissions. It identifies the following potential adverse impacts of global warming:
the exacerbation of air quality problems, a reduction in the quality and supply of water to the state from the Sierra snowpack, a rise in sea levels resulting in the displacement of thousands of coastal businesses and residences, damage to marine ecosystems and the natural environment, and an increase in the incidences of infectious diseases, asthma, and other human health-related problems.

AB 32 establishes a state goal of reducing greenhouse gas emissions to 1990 levels by 2020 (a reduction of approximately 25 percent from forecast emission levels), with further reductions to follow. The law requires the state Air Resources Board to do the following:35F 36  Establish a program to track and report greenhouse gas emissions.  Approve a scoping plan for achieving the maximum technologically feasible and cost-effective reductions from sources of greenhouse gas emissions.
 Adopt early reduction measures to begin moving forward.  Adopt, implement, and enforce regulations—including market mechanisms such as “cap andtrade” programs—to ensure that the required reductions occur.

The Air Resources Board recently adopted a statewide greenhouse gas emissions limit and an emissions inventory, along with requirements to measure, track, and report greenhouse gas emissions by the industries it determined to be significant sources of greenhouse gas emissions. 36 California Air Resources Board. (2018, September 28). AB 32 Global Warming Solutions Act of 2006. https://ww2.arb.ca.gov/resources/fact-sheets/ab-32-global-warming-solutions-act-2006 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 64 Assembly Bill 2800: Climate Change: Infrastructure Planning This California State Assembly bill, in effect through July 1, 2020, requires state agencies to consider the current and future impacts of climate change when planning, designing, building, operating, maintaining, and investing in state infrastructure. The bill requires the agency to establish a climate-safe infrastructure working group by July 1, 2017, to examine how to integrate scientific data concerning projected climate change impacts into state infrastructure engineering.

Assembly Bill 38: Fire Safety: Low-Cost Retrofits: Regional Capacity Review: Wildfire Mitigation
The Governor approved assembly bill 38 in October 2019 expanding pre-existing obligations to review regional capacity to improve forest health, fire resilience, and safety as well as provide a prescribed disclosure notice to buyers of property informing them of their fire home hardening options. In addition, it authorized Cal OES and CALFIRE to jointly develop a wildfire mitigation program now known as the “Home Hardening Program.” This effort is intended to encourage cost-effective wildfire resilience measures by providing financial assistance for retrofits, hardening, and the creation of defensible space. 1998 Natural Hazard Disclosure Act
The Natural Hazard Disclosure Act, which became effective in June 1998, requires sellers to provide home buyers with a natural hazard disclosure report (NHD) in order to sell a home in a natural hazard zone. Failure to comply with this act may result in the buyer or agent being liable for any damage experienced by the buyer. There are six main hazards required to be disclosed in an NHD:36F 37  A special flood hazard area
 An area of potential flooding on a dam failure inundation map  A very high fire severity zone
 A wildland area that may contain substantial forest fire risks and hazards  An earthquake fault zone
 A seismic hazard zone
California State Senate Bills
Senate Bill 97
Senate Bill 97, enacted in 2007, amends CEQA to clearly establish that greenhouse gas emissions and the effects of greenhouse gas emissions are appropriate subjects for CEQA analysis. It directs the Governor’s Office of Planning and Research to develop draft CEQA guidelines for the mitigation of greenhouse gas emissions or their effects by July 1, 2009, and directs the California Natural Resources Agency to certify and adopt the CEQA Guidelines by January 1, 2010.

Senate Bill 1000 General Plan Amendments: Safety and Environmental Justice Elements Senate Bill 1000 amends California’s Planning and Zoning Law in two ways:
 The original law established requirements for initial revisions of general plan safety elements to address flooding, fire, and climate adaptation and resilience. It also required subsequent review and revision as necessary based on new information. Senate Bill 1000 specifies that the 37 California Association of Realtors. (n.d.). Natural Hazard Disclosure Statement. https://www.car.org/- /media/CAR/Documents/Transaction-Center/PDF/QUICK-GUIDES/Quick-Guide--Natural-Hazard-Disclsoure-NHDStatement-REVISED-52022.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 65 subsequent reviews and revision based on new information are required to address only flooding and fires (not climate adaptation and resilience).
 Senate Bill 1000 adds a requirement that, upon adoption or revision of any two other general plan elements on or after January 1, 2018, an environmental justice element be adopted for the general plan or environmental justice goals, policies and objectives be incorporated into other elements of the plan.

Senate Bill 1241: General Plans: Safety Element—Fire Hazard Impacts In 2012, Senate Bill 1241 was enacted, requiring that all future General Plans address fire risk in state responsibility areas and very high fire hazard severity zones in their safety element. In addition, the bill requires cities and counties to make certain findings regarding available fire protection and suppression services before approving a tentative map or parcel map.

Senate Bill 379: General Plans: Safety Element—Climate Adaptation Senate Bill 379 builds on the flood planning inclusions into the safety and housing elements and the hazard mitigation planning safety element inclusions in General Plans outlined in AB 162 and AB 2140.

Senate Bill 379 specifically focuses on a new requirement that cities and counties include climate adaptation and resiliency strategies in the safety element of their General Plans beginning January 1, 2017. In addition, this bill requires general plans to include a set of goals, policies, and objectives, and specified implementation measures based on the conclusions drawn from climate adaptation research and recommendations.

This update process for this hazard mitigation plan was conducted with the intention of full compliance with this bill. However, at the time of the update, there was no clear guidance from the state on what constitutes full compliance or what protocol is to be used to determine compliance. When such guidance has been established, the planning partners will submit this plan or its subsequent updates to the state for review and approval.

Senate Bill 190: Fire Safety: Building Standards: Defensible Space Program In October 2019, Senate Bill 190 amended the Government Code and Health and Safety Code to build a common understanding of site and structure fire risk reduction measures. Among other things, the bill authorized the Office of the State Fire Marshall to develop a model defensible space program which would be available for city and county code enforcement officials to utilize. Additionally, it directed the Office of the State Fire Marshall to develop and make publicly available a Wildland-Urban Interface Fire Safety Building Standards compliance training intended for local building officials, builders, and fire service personnel.37 F
38 California State Building Code
California Code of Regulations Title 24 (CCR Title 24), also known as the California Building Standards Code, is a compilation of building standards from three sources:
 Building standards that have been adopted by state agencies without change from building standards contained in national model codes.
 Building standards that have been adopted and adapted from the national model code standards to meet California conditions.
 Building standards authorized by the California legislature that constitute extensive additions not covered by the model codes adopted to address particular California concerns. 38 California Legislative Information. (2019, October 2). SB-190 Fire Safety: Building Standards: Defensible Space Program. Bill Text - SB-190 Fire safety: building standards: defensible space program. (ca.gov) Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 66 The state Building Standards Commission is authorized by California Building Standards Law (Health and Safety Code Sections 18901 through 18949.6) to administer the processes related to the adoption, approval, publication, and implementation of California’s building codes. These building codes serve as the basis for the design and construction of buildings in California. The national model code standards adopted into Title 24 apply to all occupancies in California, except for modifications adopted by state agencies and local governing bodies. Since 1989, the Building Standards Commission has published new editions of Title 24 every 3 years. All municipal planning partners to this plan have adopted building codes that are in full compliance with the California State Building Code.

California has also passed the first green building code in the Nation, known as the California Green Building Standards Code (CALGreen). CALGreen establishes new green building standards in order to promote sustainable development. The goals of the program include:
 Reduce greenhouse gas emissions from buildings.
 Promote environmentally responsible, cost-effective, healthier places to live and work.  Reduce energy and water consumption.
 Respond to the environmental directives of the administration.

Standardized Emergency Management System
CCR Title 19 establishes the Standardized Emergency Management System to standardize the response to emergencies involving multiple jurisdictions. The system is intended to be flexible and adaptable to the needs of all emergency responders in California. It requires emergency response agencies to use basic principles and components of emergency management. Local governments must use the Standardized Emergency Management System by December 1, 1996, to be eligible for state funding of responserelated personnel costs under CCR Title 19 (Sections 2920, 2925 and 2930). The roles and responsibilities of individual agencies contained in existing laws or the state emergency plan are not superseded by these regulations. This hazard mitigation plan is considered to be a support document for all phases of emergency management, including those associated with SEMS.

California State Hazard Mitigation Plan
Under the DMA, California must adopt a federally approved state multi-hazard mitigation plan to be eligible for certain disaster assistance and mitigation funding. California has elected to develop an enhanced plan, which makes it eligible for additional mitigation funding. The State Hazard Mitigation Plan (SHMP) is the State’s primary hazard mitigation guidance. It incorporates:
 An updated analysis of the state’s historical and current hazards.  Hazard mitigation goals and objectives.
 Hazard Mitigation strategies and actions.

The California Governor’s Office of Emergency Services (Cal OES) is responsible for leading the plan update in coordination with key planning stakeholders and sources of information. The 2018 SHMP is being updated at the time of this plan’s update to reflect changing conditions and add new information as well as incorporate the new FEMA planning policy guidance.

Under 44 CFR Section 201.6, local hazard mitigation plans must be consistent with their state’s hazard mitigation plan. In updating this plan, the Steering Committee reviewed the California State Hazard Mitigation Plan to identify key relevant state plan elements.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 67 Governor’s Executive Order S-13-08
Governor’s Executive Order S-13-08 enhances the state’s management of climate impacts from sea level rise, increased temperatures, shifting precipitation and extreme weather events. There are four key actions in the executive order:
 Initiate California’s first statewide climate change adaptation strategy to assess expected climate change impacts, identify where California is most vulnerable, and recommend adaptation policies by early 2009. This effort will improve coordination within state government so that better planning can more effectively address climate impacts on human health, the environment, the state’s water supply and the economy.
 Request that the National Academy of Science establish an expert panel to report on sea level rise impacts in California, to inform state planning and development efforts.  Issue interim guidance to state agencies for how to plan for sea level rise in designated coastal and floodplain areas for new projects.
 Initiate a report on critical infrastructure projects vulnerable to sea level rise.

5.9.3 Local
Plans, Reports, and Codes
Plans, reports, and other technical information were identified and provided directly by participating jurisdictions and stakeholders or were identified through independent research by the planning consultant. These documents were reviewed to identify the following:
 Existing jurisdictional and special district capabilities.  Needs and opportunities to develop or enhance capabilities, which may be identified within the local mitigation strategies.
 Mitigation-related goals or objectives considered during the development of the overall goals and objectives.
 Proposed, in-progress, or potential mitigation projects, actions, and initiatives to be incorporated into the updated mitigation strategies.
 The following local regulations, codes, ordinances, and plans were reviewed in order to develop complementary and mutually supportive goals, objectives, and mitigation strategies that are consistent across local and regional planning and regulatory mechanisms:
▪ General Plans (Housing Elements, Safety Elements).
▪ Building Codes.
▪ Zoning and Subdivision Ordinances.
▪ NFIP Flood Damage Prevention Ordinances.
▪ Stormwater Management Plans.
▪ Emergency Management and Response Plans.
▪ Land Use and Open Space Plans.
▪ Climate Action Plans.
▪ Capability Assessment.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 68 All participating jurisdictions and special districts compiled an inventory and analysis of existing authorities and capabilities called a “capability assessment.” A capability assessment creates an inventory of a jurisdiction’s mission, programs, and policies, and evaluates its capacity to carry them out.

This assessment identifies potential gaps in the jurisdiction’s capabilities and opportunities to expand and improve upon existing capabilities.

The planning partners views all core jurisdictional and special district capabilities as fully adaptable to meet an organization’s needs. Every code can be amended, and every plan can be updated. Such adaptability is itself considered to be an overarching capability. If the capability assessment identified an opportunity to add a missing core capability or expand an existing one, then doing so has been selected as an action in the jurisdiction’s action plan, which is included in the individual annexes presented in Volume 2 of this plan.

Capability assessments for each planning partner are presented in the jurisdictional and special district annexes in Volume 2 of this plan. The sections below describe the specific capabilities evaluated under the assessment.

Legal and Regulatory Capabilities
Jurisdictions have the ability to develop policies and programs and to implement rules and regulations to protect and serve residents. Local policies are typically identified in a variety of community plans, implemented via a local ordinance, and enforced through a governmental body.

Jurisdictions regulate land use through the adoption and enforcement of zoning, subdivision, and land development ordinances, building codes, building permit ordinances, floodplain, and stormwater management ordinances. When effectively prepared and administered, these regulations can lead to hazard mitigation.

Fiscal Capabilities
Assessing a jurisdiction’s or special district’s fiscal capability provides an understanding of the ability to fulfill the financial needs associated with hazard mitigation projects. This assessment identifies both outside resources, such as grant-funding eligibility, and local authority to generate internal financial capability, such as through impact fees.

Administrative and Technical Capabilities
Legal, regulatory, and fiscal capabilities provide the backbone for successfully developing a mitigation strategy; however, without appropriate personnel, the strategy may not be implemented. Administrative and technical capabilities focus on the availability of personnel resources responsible for implementing all the facets of hazard mitigation. These resources include technical experts, such as engineers and scientists, as well as personnel with capabilities that may be found in multiple departments, such as grant writers.

NFIP Compliance
Flooding is the costliest natural hazard in the United States and, with the promulgation of recent federal regulation, homeowners throughout the country are experiencing increasingly high flood insurance premiums. Community participation in the NFIP opens up opportunity for additional grant funding associated specifically with flooding issues. Assessment of the jurisdiction’s current NFIP status and compliance provides planners with a greater understanding of the local flood management program, opportunities for improvement, and available grant funding opportunities.

Public Outreach Capability
Regular engagement with the public on issues regarding hazard mitigation provides an opportunity to directly interface with community members. Assessing this outreach and education capability illustrates Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 5: Santa Clara County Operational Area Profile 69 the connection between the government and community members, which opens a two-way dialogue that can result in a more resilient community based on education and public engagement.

Participation in Other Programs
Other programs, such as the Community Rating System, StormReady, and Firewise, enhance a jurisdiction’s ability to mitigate, prepare for, and respond to natural hazards. These programs indicate a jurisdiction’s desire to go beyond minimum requirements set forth by local, state, and federal regulations in order to create a more resilient community. These programs complement each other by focusing on communication, mitigation, and community preparedness to save lives and minimize the impact of natural hazards on a community.

Development and Permitting Capability
Identifying previous and future development trends is achieved through a comprehensive review of permitting since completion of the previous plan and in anticipation of future development. Tracking previous and future growth in potential hazard areas provides an overview of increased exposure to a hazard within a community.

Adaptive Capacity
An adaptive capacity assessment evaluates a jurisdiction’s ability to anticipate impacts from future conditions. By looking at public support, technical adaptive capacity, and other factors, jurisdictions identify their core capability for resilience against issues such as sea level rise. The adaptive capacity assessment provides jurisdictions with an opportunity to identify areas for improvement by ranking their capacity high, medium, or low.

Expanding and Improving Mitigation Capabilities
Both pre- and post-disaster mitigation capabilities change over time. The intent of this mitigation plan is to evaluate current mitigation capabilities and identify if there are any gaps which could be further addressed. In Volume 2 of this plan, in addition to an individual capability assessment, there is a discussion of the capabilities which could be expanded upon for each participant. County items, such as increasing funding for community education and outreach including translated materials as well as funding regional planning and coordination, serve as examples of what this looks like. If there are any challenges or limitations for each participant, they have stated so in the in their respective annex.

Integration Opportunity
The assessment looked for opportunities to integrate this mitigation plan with the legal/regulatory capabilities identified. Capabilities were identified as integration opportunities if they can support or enhance the actions identified in this plan or be supported or enhanced by components of this plan.

Planning partners considered actions to implement this integration as described in the jurisdictional and special district annexes in Volume 2 of this plan.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 70 6 Identified Hazards of Concern and Risk
Assessment
Risk assessment is the process of measuring the potential loss of life, personal injury, economic injury, and property damage resulting from identified hazards. It allows emergency management personnel to establish early response priorities by identifying potential hazards and vulnerable assets. The process focuses on the following elements:
 Hazard identification: Use all available information to determine what types of hazards may affect a jurisdiction, how often they can occur, and their potential severity.  Exposure identification: Estimate the total number of people and properties in the jurisdiction that are likely to experience a hazard event if it occurs.
 Vulnerability identification and loss estimation: Assess the impact of hazard events on the people, property, environment, economy, and lands of the region, including estimates of the cost of potential damage or cost that can be avoided by mitigation. 
The risk assessment for this hazard mitigation plan update evaluates the risk of natural hazards prevalent in the OA and meets requirements of the Disaster Mitigation Act (44 CFR, Section 201.6(c)(2)).

To protect individual privacy and the security of critical facilities, information on properties assessed is presented in aggregate, without details about specific individual personal or public properties.

6.1 Identified Hazards of Concern
The Core Planning Group considered the full range of natural hazards that could affect the OA and then listed hazards that present the greatest concern. The process incorporated a review of state and local hazard planning documents as well as information on the frequency of, magnitude of, and costs associated with hazards that have struck the OA or could do so. Anecdotal information regarding natural hazards and the perceived vulnerability of the OA’s assets to them was also used. Based on the review, this plan addresses the following hazards of concern (presented in order of the hazard risk index results; the order of listing does not indicate the hazards’ relative severity):
 Earthquake
 Wildfire
 Inclement Weather
 Drought
 Climate Change
 Dam and Levee Failure
 Flood
 Landslide
 Tsunami
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 71 In addition to the hazards of concern for which full risk assessments were performed, other hazards of interest were identified for inclusion in this plan: intentional hazards, technological hazards, and epidemic and pandemic. These hazards are of interest because they present risk to the OA. However, no methodologies are currently available to perform risk assessments on them that are equivalent to those used for the natural hazards of concern addressed in detail in this plan.

6.2 Hazard Risk Index
FEMA requires all hazard mitigation planning partners to have jurisdiction-specific mitigation actions based on local risk, vulnerability, and community priorities (FEMA, 2011). This plan included a risk index procedure for each planning partner, in which the degree of risk posed by each hazard was calculated based on a set of factors.

Risk index factors were assigned a numerical degree of risk level based on information presented in the hazard profiles and planning partner annexes. This number was then weighted, and a formula was used to aggregate the values into an overall hazard risk index number. The weight given to each factor was based on a review of best practices and agreed upon by the Core Planning Team.

All planning partners calculated risk for their own jurisdiction or special district following the same methodology. The higher the overall risk index number, the greater the hazard risk. This methodology does not compare hazards to each other or rank hazards against one another. Instead, this process provides a sense of hazard priorities or relative risk and allows comparison of the same hazard across participants. It provides planning participants with a sense of hazard priorities, or relative risk. By doing this analysis, mitigation planning and initiatives can focus on the greatest risk. While hazards occur together or as a consequence of others (e.g., dam failure may cause flooding and earthquakes may cause landslides), participants considered hazards as a singular event for the purposes of rating. This approach is part of a holistic hazard risk analysis that includes complementary qualitative and quantitative elements and provides a consistent metric across different hazards.

This hazard analysis methodology can:
 Help establish priorities for planning, capability development, and hazard mitigation;  Serve as a tool in the identification of hazard mitigation measures;  Be one tool in conducting a hazard-based needs analysis;  Serve to educate the public and public officials about hazards and vulnerabilities; and  Help communities make objective judgments about acceptable risk.

The factors and their corresponding numeric indices and weight factors are detailed in Table 14.

Individual and OA-level hazard risk indices were used to inform the action plan development process and mitigation priorities for each planning partner. Each annex presents the risk indices for each planning partner.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 72 Table 14: Probability of Hazards
Risk Index
Factor
Degree of Risk
Level Criteria
Factor
Weight for
Degree of
Risk Level
Probability of
Future Events
0 Unlikely
Less than 1 percent probability of occurrence
in the next year or a recurrence interval of
greater than every 100 years.
30%
1 Occasional
1 to 10 percent probability of occurrence in
the next year or a recurrence interval of 11 to
100 years.
2 Likely
11 to 90 percent probability of occurrence in
the next year or a recurrence interval of 1 to
10 years.
3 Highly Likely
91 to 100 percent probability of occurrence in
the next year or a recurrence interval of less
than 1 year.

Life Impact
0 Minor Very few injuries, if any at all.
35%
1 Limited Minor injuries.
2 Critical Multiple deaths and/or injuries.
3 Catastrophic High number of deaths and/or injuries.

Property Impact
0 Minor
Only minor property damage and minimal
disruption of life. Temporary shutdown of
critical facilities.
25%
1 Limited
More than 10 percent of property in affected
area damaged/destroyed. Complete
shutdown of critical facilities for more than
one day.
2 Critical
More than 25 percent of property in affected
area damaged/destroyed. Complete
shutdown of critical facilities for more than
one week.
3 Catastrophic
More than 50 percent of property in affected
area damaged/destroyed. Complete
shutdown of critical facilities for 30 days or
more.

Percentage of
Area Impacted
0 Negligible Less than 10 percent of planning area or
isolated single-point occurrences.
10%
1 Minimal 10 to 25 percent of the planning area or
limited single-point occurrences.
2 Significant 26 to 74 percent of planning area or frequent single-point occurrences.
3 Extensive 75 to 100 percent of planning area or
consistent single-point occurrences.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 73 Table 15: Hazard Risk Ranking by Jurisdiction
Earthquake Wildfire Inclement
Weather Drought Climate Change
Dam and
Levee Failure Flood Landslide Tsunami
Campbell 2 0.9 1.7 0.7 0 1.75 0.55 0 0
Cupertino 2.7 1.9 1.1 1.45 1.55 0.45 0.5 0.4 0
Gilroy 2.9 1.05 1.25 0.9 0.3 2 0.4 0 0
Los Altos 2 1.95 2.05 1.8 1.6 0.95 0.65 0 0
Los Altos Hills 2 2.1 1.4 1.95 1.3 0 0.65 1.3 0
Los Gatos 1.45 2.55 1.15 0.6 1.2 0.35 0.35 0.65 0
Milpitas 2.3 2.05 0.9 1.2 2.3 1.85 1.8 0.6 0
Monte Sereno - - - - - - - - -
Morgan Hill 2.9 1.05 1.25 0.9 0.3 2 1.25 0 0
Mountain
View
2 0.65 1.4 2 1.3 0 2 0 0
Palo Alto 2 1.95 2.05 2.05 1.85 0.95 0.65 0 0
San Jose 1.25 1.6 1.8 1.45 0 1.9 1.9 0 0
Santa Clara
City
3 1.3 1.7 1.45 1.4 1.8 2 0 0.35
Saratoga 2.7 2 0.95 0.8 0.4 0 0 0.85 0
Sunnyvale 2.9 1.05 1.25 0.9 0.3 2 0.3 0 0
Santa Clara
County

2.1 1.7 1.55 0.8 1.6 1.75 0.65 0.4 0
SCC 2.1 1.7 1.55 0.8 1.6 1.75 0.65 0.4 0
MidPen 1.35 3 1.3 1.2 1.8 0.25 1.2 1.55 0
SCCFD 2.7 1.7 1.55 0.8 1.6 1.75 0.65 0.4 0

SCVWD - - - - - - - - -
Average 2.24 1.68 1.44 1.21 1.13 1.19 0.90 0.36 0.02
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 74

6.2.1 Average Overall Hazard Risk Index Results
The overall hazard risk index results based on an average of partner indices is shown in Table 16. These results show which hazards pose the highest overall risk to the Operational Area.

Table 16: Average Overall Hazard Risk Index Results
Hazard Risk Order Hazard Average Overall Hazard Risk
Index Result
1 Earthquake 2.24
2 Wildfire, smoke, and air quality 1.68
3 Inclement weather* 1.44
4 Drought 1.21
5 Climate change, including sea-level
rise

1.13 6 Dam and levee failure 1.19
7 Flood .90
8 Landslide and mass movement .36
9 Tsunami .02
*Listed as separate hazards in the hazard profile and annexes: heavy precipitation, high wind, extreme heat, extreme cold, and space weather.

Based on the average overall hazard risk index results from planning partner risk indices:
• The earthquake hazard has the highest risk results, followed by wildfire/smoke/air quality.  The inclement weather, drought, climate change hazards were a moderate risk to the Operational Area.
 The dam failure, flood, and landslide/mass movement hazards were a lower risk to the Operational Area.
 The tsunami hazard poses the lowest risk to the Operational Area, as not all planning partners can be impacted by this hazard due to geographic location.

6.3 Risk Assessment Tools

6.3.1 Mapping
National, state, and county databases were reviewed to locate available spatially based data relevant to this planning effort. Maps were produced using geographic information system (GIS) software to show the spatial extent and location of hazards when such datasets were available. These maps are included in the hazard profile sections and planning partner annexes of this MJHMP.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 75

6.3.2 Hazus
Overview
In 1997, FEMA developed the standardized Hazards U.S. (Hazus) model to estimate losses caused by earthquakes and identify areas that face the highest risk and potential for loss. Hazus was later expanded into a multi-hazard methodology with new models for estimating potential losses from hurricanes and floods.

Hazus is a GIS-based software program used to support risk assessments, mitigation planning, and emergency planning and response. It provides a wide range of inventory data, such as demographics, building stock, critical facility, transportation and utility lifeline, and multiple models to estimate potential losses from natural disasters. The program maps and displays hazard data and the results of damage and economic loss estimates for buildings and infrastructure. Its advantages include the following:
 Provides a consistent methodology for assessing risk across geographic and political entities.  Provides a way to save datasets so that they can readily be updated as population, inventory, and other factors change and as mitigation planning efforts evolve.  Facilitates review of mitigation plans because it helps to ensure that FEMA methodologies are incorporated.
 Supports grant applications by calculating benefits using FEMA definitions and terminology.  Produces hazard data and loss estimates that can be used in communication with local stakeholders.
 Is administered by the local government and can be used to manage and update a hazard mitigation plan throughout its implementation.

Levels of Detail for Evaluation
Hazus provides default data for inventory, vulnerability, and hazards; the default data can be supplemented with local data to provide a more refined analysis. The model can carry out three levels of analysis, depending on the format and level of detail of information about the OA:
 Level 1: All of the information needed to produce an estimate of losses is included in the software’s default data. These data are derived from national databases and describe in general terms the characteristic parameters of the OA.
 Level 2: More accurate estimates of losses require more detailed information about the OA. To produce Level 2 estimates of losses, detailed information is required about local geology, hydrology, hydraulics, and building inventory, as well as data about utilities and critical facilities.

This information is needed in a GIS format.
 Level 3: This level of analysis generates the most accurate estimate of losses. It requires detailed engineering and geotechnical information to customize it for the OA.

6.4 Risk Assessment Approach
The risk assessments in this plan describe the risks associated with each identified hazard of concern.

The following steps were used to define the risk of each hazard:
 Identify and profile each hazard: The following information is given for each hazard:
▪ Geographic areas most affected by the hazard.
▪ Event frequency estimates.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 76 ▪ Severity estimates.
▪ Warning time likely to be available for response.
 Define probability: probability of future events was identified utilizing the following terms:
▪ Unlikely – less than 1 percent probability of occurrence in the next year or a recurrence interval of greater than every 100 years.
▪ Occasional – 1 to 10 percent probability of occurrence in the next year or a recurrence interval of 11 to 100 years.
▪ Likely – 11 to 90 percent probability of occurrence in the next year or a recurrence interval of 1 to 10 years.
▪ Highly Likely – 91 to 100 percent probability of occurrence in the next year or a recurrence interval of less than 1 year.
 Determine exposure to each hazard: Exposure was assessed by overlaying hazard maps with an inventory of structures, facilities, and systems to decide which of them would be exposed to each hazard.
 Assess the vulnerability of exposed facilities: Vulnerability of exposed structures and infrastructure was evaluated by interpreting the probability of occurrence of each event and assessing structures, facilities, and systems that are exposed to each hazard. Tools such as GIS and Hazus were used for this assessment for the flood and earthquake hazards. Outputs similar to those from Hazus were generated for other hazards, using data generated through GIS.

6.4.1 Earthquake and Flood
The following hazards were evaluated using Hazus:
 Flood: A Level 1 user-defined analysis was performed for general building stock in flood zones and for critical facilities and infrastructure. Digital Elevation Models (DEM) for the OA was used to delineate flood hazard areas and estimate potential losses from the 10-percent-annual-chance, 1- percent-annual-chance, and 0.2-percent-annual-chance flood events. To estimate damage that would result from a flood, Hazus uses pre-defined relationships between flood depth at a structure and resulting damage, with damage given as a percent of total replacement value.

Curves defining these relationships have been developed for damage to structures and for damage to typical contents within a structure. By inputting flood depth data and known property replacement cost values, dollar-value estimates of damage were generated.  Earthquake: A Level 2 analysis was performed to assess earthquake exposure and vulnerability for three scenario events and two probabilistic events:
▪ A Magnitude-7.0 event on the Hayward Fault with an epicenter approximately 25 miles north of the City of Palo Alto.
▪ A Magnitude-7.0 event on the Calaveras Fault with an epicenter approximately 25 miles north of the City of Milpitas.
▪ A Magnitude-7.8 event on the San Andreas Fault with an epicenter approximately 148 miles northwest of the City of Palo Alto.
▪ The standard Hazus 100- and 500-year probabilistic events.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 77

6.4.2 Drought
The risk assessment methodologies used for this plan focus on damage to structures. The risk assessment for drought was more limited and qualitative than the assessment for the other hazards of concern because drought does not affect structures.

6.4.3 All Other Assessed Hazards
Historical datasets were not adequate to model future losses for most of the hazards of concern.

However, areas and inventory susceptible to some of the hazards of concern were mapped by other means and exposure was evaluated. A qualitative analysis was conducted for other hazards using the best available data and professional judgment.

6.5 EMAP Consequence Analysis
A consequence analysis of the potential for detrimental impacts of hazards is included in this 2023 plan update for the Emergency Management Accreditation Program (EMAP). Each hazard identified in this plan is followed by the Consequence Analysis result.

In this analysis all nine natural hazards profiled for Santa Clara County have been addressed, with the impacts that each will have on the following:
 Impact on the Public: What is the scope of impact on the health and safety of people in the area of the incident?
 Impact on Responders: What is the scope of impact on health and safety of responders (i.e., firefighters, law enforcement, emergency management personnel, etc.) in the area responding to the incident?
 Continuity of Operations: Will the organization need to relocate in order to fulfill duties? Will any other continuity measures be implemented?
 Impact on Property, Facilities, and Infrastructure: What are potential damages to structures (private and public), utilities, treatment plants, electric grid, roads, and bridges?  Delivery of Services: What impacts occur to the delivery of services such as food, medical, or any other life sustaining entities?
 Impact on the Environment: How has the incident affected the surrounding environment, i.e., contamination (water, soil, or air), erosion, crop damage, etc.?  Impact on the Economy: Are there any affects to the economy due to loss of revenue, cleanup efforts, and reconstruction?
 Impact of the Public Confidence in the Jurisdiction’s Governance: How has the hazard affected public confidence?
The Consequence Analysis includes ranking determinations for each of the above elements. The ranking elements are categorized as Minimal, Moderate, or Severe. The Risk Assessment portion of the MJHMP was used to ascertain prior damages in an effort to estimate ratings on future impacts. The ratings are meant to be a guide, and not all inclusive, due to the variances that could apply such as population, location, time, hazard type, and the number of jurisdictions within the hazard area.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 78

6.6 Sources of Data Used in Hazus Modeling

6.6.1 Building and Cost Data
Replacement cost values and detailed structure information and census data are included within Hazus

6.0. This recently updated version of Hazus uses 2020 census data and dasymetric census blocks for improved floodplain model accuracy. The stock building inventory data is from the National Structure Inventory (NSI), a point-based dataset developed by the U.S. Army Corps of Engineers (USACE). When available, updated data provided by Santa Clara County was used in place of the Hazus defaults for critical facilities and infrastructure.

Replacement cost is the cost to replace the entire structure with one of equal quality and utility.

Replacement cost is based on industry-standard cost-estimation models published in RSMeans Square Foot Costs.38F
39 It is calculated using the RSMeans square foot cost for a structure, which is based on the Hazus occupancy class (i.e., multi-family residential or commercial retail trade), multiplied by the square footage of the structure from the tax assessor data. The construction class and number of stories for single-family residential structures also factor into determining the square foot costs.

6.6.2 Hazus Data Inputs
The following hazard datasets were used for the Hazus Level 2 analysis conducted for the risk assessment:
 Flood: A USGS 10-meter Digital Elevation Model for the OA was used to delineate flood hazard areas and generate flood depth grids that are integrated into the Hazus model. These depth grids are used to estimate potential losses from the 10-percent-annual-chance, 1-percent-annualchance, and 0.2-percent-annual-chance flood events.  Earthquake: Earthquake ShakeMaps and probabilistic data prepared by the USGS were used for the analysis of this hazard. A National Earthquake Hazard Reduction Program soils map from the California Department of Conservation, USGS liquefaction susceptibility data and susceptibility to deep-seated landslide from the California Geological Survey were also integrated into the Hazus model. Hazus uses classifications within these datasets to derive probabilities that ground deformation can occur in areas of higher liquefaction or landslide susceptibility. It should be noted that deep-seated landslides are generally large landslides that are slow moving during rainfall induced movement, but some can be fast moving and may occur during earthquakes. However, this dataset does not specifically measure earthquake induced landslides. Inclusion of liquefaction and landslide data in Hazus represent ground deformation that may occur during an earthquake that can contribute to structural damage. As such, inclusion of these datasets tends to increase the amount and cost of damage modeled by Hazus.

6.6.3 Other Local Hazard Data
Locally relevant information on hazards was gathered from a variety of sources. Frequency and severity indicators include past events and the expert opinions of geologists, emergency management specialists, and others. Data sources for specific hazards were as follows:
 Landslide: Susceptibility to deep-seated landslide data were provided by the California Geological Survey.
39 RSMeans data from Gordian. (2023). Estimating Square Foot Cost. https://www.rsmeans.com/estimating-squarefoot-cost Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 79  Sea Level Rise: Sea level rise data were provided by the San Francisco Bay Conservation and Development Commission. A sea level rise of 6 feet above current mean higher high water was used for the exposure analysis.
 Dam Inundation: Dam inundation exposure areas were acquired from the California Department of Water Resources Division of Safety of Dams. Many of these are owned by the Santa Clara Valley Water District.
 Levee Inundation: Levee inundation exposure areas were defined with boundaries provided by Santa Clara County.
 Severe Storm: No GIS format severe storm area datasets were identified for the OA.  Tsunami: Tsunami inundation map was prepared by California Department of Conservation in cooperation with the University of Southern California, California Geological Survey, and California Emergency Management Agency.
 Wildfire: Wildfire Hazard Classification and Structures at Risk data were provided by Tukman Geospatial. Additional fire severity data was acquired from California Department of Forestry and Fire Protection (CAL FIRE).

6.6.4 Data Source Summary
Table 17 summarizes the data sources used for the risk assessment for this plan.

Table 17: Hazus Model Data Documentation
Data Source Date Format
Building information such as area,
occupancy, date of construction,
and stories
FEMA Hazus version 6.0,
National Structure Inventory
(NSI), Santa Clara County
2023 Digital (tabular)
format
Building replacement cost FEMA Hazus version 6.0 2023 Digital (GIS and tabular) format
Population data FEMA Hazus version 6.0, US
Census Bureau
2020 Digital (GIS and
tabular) format
Flood hazard data FEMA 2016 Digital (GIS)
format
Tsunami CGS (State of California) 2021 Digital (GIS)
format
Earthquake ShakeMaps USGS, provided via Hazus
version 6.0
Downloaded
2023
Digital (GIS)
format
Liquefaction susceptibility USGS (via ABAG) 2006 Digital (GIS) format
National Earthquake Hazard
Reduction Program
California Department of
Conservation, California
Geological Survey
Downloaded
2023
Digital (GIS)
format
Dam Inundation Areas California Department of
Water Resources, Division of
Safety of Dams
Varies
2019-2021
Digital (GIS)
format
Landslide California Geological Survey 2011 Digital (GIS) format
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 80 Data Source Date Format
Sea Level Rise Adapting to Rising Tides -
San Francisco Conservation
and Development
Commission
2018 Digital (GIS)
format
Wildfire Tukman Geospatial, CAL
FIRE
2022, 2007 Digital (GIS)
format
Digital Elevation Model USGS Downloaded
2023
Digital (GIS)
format
Critical Facilities and Assets Hazus version 6.0, Santa Clara County
2023 Digital (GIS)
format
Emergency operation centers,
airport facilities, bus facilities, light
rail facilities, rail facilities,
communication facilities, electric
power facilities, potable water
facilities, wastewater facilities
FEMA Hazus version 6.0
Default Critical Facilities Data
2023 Digital (GIS)
format
Points of interest (city halls,
community centers, other county
facilities, child day care facilities)
Santa Clara County 2023 Digital (GIS)
format
Santa Clara County critical facilities
(fire stations, hospitals, skilled
nursing facilities and clinics, police
stations, public / private schools,
universities, and colleges)
FEMA Hazus version 6.0,
Santa Clara County
2023 Digital
(spreadsheet)
format
Superfund sites (hazardous material
sites)
EPA 2022 Digital (GIS)
format
Toxic release inventory facilities
(hazardous material facilities,
designated communications
centers, electric power, and
petroleum facilities)
Environmental Protection
Agency (EPA)
Downloaded
2023
Digital (GIS)
format
State and local bridges (highway
bridges, light rail bridges, rail
bridges, includes pedestrian
bridges)
Hazus 6.0 Inventory, Santa
Clara County
2023 Digital (GIS)
format

6.7 Limitations
Loss estimates, exposure assessments, and hazard-specific vulnerability evaluations rely on the best available data and methodologies. Uncertainties are inherent in any loss estimation methodology and arise in part from incomplete scientific knowledge concerning natural hazards and their effects on the built environment. Uncertainties also result from the following:
 Approximations and simplifications necessary to conduct a study.  Incomplete or outdated inventory, demographic or economic parameter data.  The unique nature, geographic extent, and severity of each hazard.  Mitigation measures already employed.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 6: Identified Hazards of Concern and Risk Assessment 81  The amount of advance notice residents have to prepare for a specific hazard event.  Lack of a standardized model for assessing sea level rise impacts. Multiple models provide multiple results. Not all models were run in the development of the sea level rise analysis.

These factors can affect loss estimates by a factor of two or more. Therefore, potential exposure and loss estimates are approximate and should be used only to understand relative risk. Over the long term, Santa Clara County will collect additional data to assist in estimating potential losses associated with other hazards.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 82
7 Earthquake
Definitions
 Earthquake: The shaking of the ground caused by an abrupt shift of rock along a fracture in the earth or a contact zone between tectonic plates.
 Epicenter: The point on the earth’s surface directly above the hypocenter of an earthquake. The location of an earthquake is commonly described by the geographic position of its epicenter and by its focal depth.
 Fault: A fracture in the earth’s crust along which two blocks of the crust have slipped with respect to each other.
 Hypocenter: The region underground where an earthquake’s energy originates.  Liquefaction: Loosely packed, water-logged sediments losing their strength in response to strong shaking, causing major damage during earthquakes.

7.1 General Background
An earthquake is the vibration of the earth’s surface following a release of energy in the earth’s crust. This energy can be generated by a sudden dislocation of the crust or by a volcanic eruption. Most destructive quakes are caused by dislocations of the crust. The crust may first bend and then, when the stress exceeds the strength of the rocks, break and snap to a new position. In the process of breaking, vibrations called “seismic waves” are generated. These waves travel outward from the source of the earthquake at varying speeds.

Geologists have found that earthquakes tend to reoccur along faults, which are zones of weakness in the earth’s crust. Even if a fault zone has recently experienced an earthquake, there is no guarantee that all the stress has been relieved. Another earthquake could still occur. In fact, relieving stress can increase stress in other parts of the affected fault and other faults. Additional earthquakes, called aftershocks, are common after a large earthquake.

California is seismically active because of movement of the North American Plate, east of the San Andreas Fault, and the Pacific Plate to the west, which includes the state’s coastal communities.

Movement of the tectonic plates against one another creates stress, which is released as energy that moves through the earth as seismic waves.

Faults are classified in terms of their activity level; “active,” “potentially active,” or “inactive.” Most seismic activity occurs along faults that are known to have geologic evidence of activity. However, inactive faults, where no such displacements have been recorded, also have the potential to reactivate or experience displacement along a branch sometime in the future. An example of a fault zone that has been reactivated is the Foothills Fault Zone. The zone was considered inactive until evidence of an earthquake (approximately 1.6 million years ago) was found near Spenceville, California. Then, in 1975, an earthquake occurred on another branch of the zone near Oroville, California (now known as the Cleveland Hills Fault). The State Division of Mines and Geology indicates that increased earthquake activity throughout California may cause tectonic movement along currently inactive fault systems.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 83

7.1.1 Damage from Earthquakes
A direct relationship exists between a fault’s length and location and its ability to generate damaging ground motion at a given site. Small, local faults produce lower magnitude quakes, but ground shaking can still be strong, and damage can be significant in areas close to the fault. In contrast, large regional faults can generate earthquakes of great magnitudes but, because of their distance and depth, they may result in only moderate shaking in an area.

Earthquakes can last from a few seconds to over five minutes; they may also occur as a series of tremors over a period of several days. Aftershocks may be felt for months or years after the mainshock. The actual movement of the ground in an earthquake is seldom the direct cause of injury or death. People that fall over during the quake may experience more mild injuries like broken bones. Casualties generally result from falling objects and debris, because earthquakes shake, damage, or demolish furnishings and buildings and other structures. Disruption of communications and internet, electrical power, gas, sewer, and water services should be expected in the affected area. Earthquakes may trigger dam failures and landslides. Their damage may cause fires and releases of hazardous material, compounding the disastrous effects.

7.1.2 Earthquake Classifications
Earthquakes are typically classified in one of two ways: by the amount of energy released, measured as magnitude; or by the impact on people and structures, measured as intensity.

Magnitude
An earthquake’s magnitude is a measure of the energy released at the source of the earthquake. It is commonly expressed by ratings on either of two scales (Michigan Tech University)39F 40:
 The Richter scale measures magnitude of earthquakes based on the amplitude of the largest energy wave released by the earthquake. Richter scale readings are suitable for smaller earthquakes; however, because it is a logarithmic scale, the scale does not distinguish clearly the magnitude of large earthquakes above a certain level. Richter scale magnitudes and corresponding earthquake effects are as follows:
▪ 2.5 or less: Usually not felt, but can be recorded by seismograph. ▪ 2.5 to 5.4: Often felt, but causes only minor damage. ▪ 5.5 to 6.0: Slight damage to buildings and other structures. ▪ 6.1 to 6.9: May cause a lot of damage in very populated areas. ▪ 7.0 to 7.9: Major earthquake; serious damage.
▪ 8.0 or greater: Great earthquake; can totally destroy communities near the epicenter. 40 Michigan Tech University. (n.d.) How do we measure Earthquake Magnitude? https://www.mtu.edu/geo/community/seismology/learn/earthquake-measure/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 84
 While the Richter scale may be well known, the most commonly used scale today is the moment magnitude (Mw) scale. The moment magnitude scale is based on the total moment release of the earthquake (the product of the distance a fault moved, and the force required to move it).

Moment magnitude roughly matches the Richter scale but provides more accuracy for larger magnitude earthquakes. The scale is as follows:
▪ Great: Mw > 8.
▪ Major: Mw = 7.0 - 7.9.
▪ Strong: Mw = 6.0 - 6.9.
▪ Moderate: Mw = 5.0 - 5.9.
▪ Light: Mw = 4.0 - 4.9.
▪ Minor: Mw = 3.0 - 3.9.
▪ Micro: Mw < 3.

Intensity
For an earthquake, intensity varies across the area. Intensity will be larger near the fault rupture, in the direction of the rupture, and in sedimentary basins. Sedimentary basins are depressions in the earth’s surface that consist of alluvial deposit and sedimentary rocks, which are geologically younger and have slower seismic wave velocities.40F
41 Sedimentary basins like the Evergreen basin, which lies beneath the northeastern margin of the Santa Clara Valley near the south end of the San Francisco Bay, amplify the ground shaking during an earthquake, increasing the intensity of the quake. Currently the most commonly used intensity scale is the Modified Mercalli Intensity (MMI) Scale, with ratings defined in Figure 19.41F 42 41 U.S. Geological Survey. (2020). Earthquake Science Center Seminars, Sedimentary basin effects in ground motions from empirical models and simulation platforms. https://earthquake.usgs.gov/contactus/menlo/seminars/1297#:~:text=Sedimentary%20basins%20are%20depressions %20in,in%20thickness%20towards%20their%20margins.
42 U.S. Geological Survey. (n.d.). The Modified Mercalli Intensity (MMI) Scale assigns intensities as…. https://www.usgs.gov/media/images/modified-mercalli-intensity-mmi-scale-assigns-intensities Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 85
Figure 20: Modified Mercalli Intensity Scale42F
43 7.1.3 Ground Motion
Earthquake hazard assessment is also based on expected ground motions. During an earthquake when the ground is shaking, it experiences acceleration. The peak ground acceleration (PGA) is the largest increase in velocity recorded by a particular station during an earthquake. PGA indicates the severity of an earthquake and is a measure of how hard the earth shakes, or accelerates, in a given geographic area. It is measured in g (the acceleration due to gravity), expressed as a percentage of that acceleration (%g). Horizontal and vertical PGA varies with soil or rock type. Instruments called accelerographs record levels of ground motion due to earthquakes at stations throughout a region. These readings are recorded by state and federal agencies that monitor and predict seismic activity. Earthquake hazard assessment involves estimating the annual probability that certain ground motion accelerations will be exceeded, and then summing the annual probabilities over the time period of interest.

National maps of earthquake shaking hazards, which have been produced since 1948, provide information for creating and updating seismic design requirements for building codes, insurance rate structures, earthquake loss studies, retrofit priorities and land use planning. After thorough review of the studies, professional organizations of engineers update the seismic-risk maps and seismic design requirements contained in building codes, the USGS updated the National Seismic Hazard Maps in 2018. 43 U.S. Geological Survey. (n.d.). The Modified Mercalli Intensity (MMI) Scale Assigns Intensities as... https://www.usgs.gov/media/images/modified-mercalli-intensity-mmi-scale-assigns-intensities Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 86
New seismic, geologic, and geodetic information on earthquake motion, soil amplification factors, and local seismic velocity models was incorporated into the revised maps, allowing the USGS, for the first time, to calculate probabilistic seismic hazard curves for an expanded time period and site classes as well as account for long-period ground motions in deep sedimentary basins like the San Francisco Bay region.43F
44 The USGS is currently working on updating this model with a targeted release later in 2023.

These maps influence earthquake insurance rates and support government official, emergency managers, community planners, and the public in understanding the potential risks to their community.

Building codes that include seismic provisions specify the horizontal force due to lateral acceleration that a building should be able to withstand during an earthquake. Buildings, bridges, highways, and utilities built to meet modern seismic design requirements are typically able to withstand earthquakes better, with less damage and disruption. PGA values are directly related to these lateral forces that could damage “short period structures” (e.g., single-family dwellings). Longer-period response components determine the lateral forces that damage taller structures with longer natural periods (apartment buildings, factories, high-rises, bridges). Figure 20 lists damage potential and perceived shaking by PGA factors, compared to the Mercalli scale.

Figure 21: Peak Acceleration (%g) with 10% Probability of Exceedance in 50 Years4F 45 44 U.S. Geological Survey. (2021, September 23). Data Release for Additional Period and Site Class Data for the 2018 National Seismic Hazard Model for the Conterminous United States. https://www.usgs.gov/data/data-releaseadditional-period-and-site-class-data-2018-national-seismic-hazard-model 45 U.S. Geological Survey. (2018). 2018 Long-term National Seismic Hazard Map. https://www.usgs.gov/media/images/2018-long-term-national-seismic-hazard-map Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 87
Table 18: Mercalli Scale and Peak Ground Acceleration Comparison45F 46 Modified
Mercalli
Scale
Perceived
Shaking
Potential Structure Damage
Estimated PGAa
Resistant (%g)
Buildings
Vulnerable
Buildings
I Not Felt None None <0.17%
II-III Weak None None 0.17% - 1.4%
IV Light None None 1.4% - 3.9%
V Moderate Very Light Light 3.9% - 9.2%
VI Strong Light Moderate 9.2% - 18%
VII Very Strong Moderate Moderate/Heavy 18% - 34%
VIII Severe Moderate/Heavy Heavy 34% - 65%
IX Violent Heavy Very Heavy 65% - 124%
X - XII Extreme Very Heavy Very Heavy >124%
a PGA measured in percent of g, where g is the acceleration of gravity.

7.1.4 Effect of Soil Types
The impact of an earthquake on structures and infrastructure is largely a function of ground shaking, distance from the source of the quake, and liquefaction, a secondary effect of an earthquake in which soils lose their shear strength and flow or behave as liquid, thereby damaging structures that derive their support from the soil. Liquefaction generally occurs in soft, unconsolidated sedimentary soils and shallow water table.

A program called the National Earthquake Hazard Reduction Program (NEHRP) creates maps based on soil characteristics to help identify locations subject to liquefaction. Table 19 summarizes NEHRP soil classifications. NEHRP Soils B and C typically can sustain ground shaking without much effect, dependent on the earthquake magnitude. The areas that are commonly most affected by ground shaking have NEHRP Soils D, E, and F. In general, these areas are also most susceptible to liquefaction.

Table 19: National Earthquake Hazard Reduction Program Soil Classification System46F 47 NEHRP Soil Type Description
Mean Shear
Velocity to 30 m
(m/s)
A Hard Rock 1,500
B Firm to Hard Rock 760–1,500
C Dense Soil/Soft Rock 360–760
D Stiff Soil 180–360
E Soft Clays < 180
46 SanAndreasFault.org. (2010). Did you feel it? http://www.sanandreasfault.org/feelit.html 47 National Earthquake Hazard Reduction Program. (n.d.). Seismic Site Classification. https://www.masw.com/files/NEHRP.pdf
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 88
NEHRP Soil Type Description
Mean Shear
Velocity to 30 m
(m/s)
F Special Study Soils (liquefiable soils, sensitive clays, organic soils, soft clays >36 m thick)
The USGS has created a soil type map for the San Francisco Bay area that provides rough estimates of site effects based on surface geology. NEHRP soil types were assigned to a geologic unit based on the average velocity of that unit, and the USGS notes that this approach can lead to some inaccuracy. For instance, a widespread unit consisting of Quaternary sand, gravel, silt, and mud has been assigned as Class C soil types; however, some of the slower soil types in this unit fall under Class D. USGS does not have any way of differentiating units for slower-velocity soils in its digital geologic dataset.47F 48 7.2 Hazard Profile
The Bay region is located within the active boundary between the Pacific and the North American tectonic plates. The western edge of the Santa Clara County OA is on the Pacific Plate, which is constantly moving northwest past the North American Plate at a rate of about 2 inches per year.48F 49 Earthquakes in
the San Francisco Bay region result from strain energy constantly accumulating across the region because of the motion of the Pacific Plate relative to the North American Plate. The San Andreas Fault, on which earthquakes of magnitude 7.8 and 7.9 have occurred in historical time, including the 1906 San Francisco earthquake, is the fastest slipping fault along the plate boundary.

7.2.1 Past Events
The last major earthquake with an epicenter in the Santa Clara County OA was the 1984 Morgan Hill Earthquake (Magnitude 6.2). The epicenter of the 1989 Loma Prieta Earthquake (Magnitude 7.1) was just a few miles outside the OA. Since then, there have been no significant seismic events in Santa Clara County.49F
50 Other significant earthquakes in California include the 1906 earthquake in San Francisco, the 1971 San Fernando Earthquake, the 1994 Northridge earthquake, the 2014 Napa earthquake, and the 2019 Ridgecrest earthquake.

The Morgan Hill Earthquake of April 24, 1984, was a moderate size earthquake on the Calaveras Fault. It caused moderate damage that extended southward from the epicenter. In the Santa Clara County OA, where most of the damage occurred, more than 550 structures experienced minor damage. Major structural damage was mostly confined to a small area on two streets in the Jackson Oaks subdivision east of Morgan Hill. There were numerous reports of fires resulting from the earthquake. Minor damage was also reported in San Martin and Coyote. Twenty-seven people were injured.50 F 51 This event led to a
FEMA major disaster declaration (DR-845).
48 U.S. Geological Survey. (2006). Geologic Map of the San Francisco Bay Region. https://pubs.usgs.gov/sim/2006/2918/sim2918_geolposter-stdres.pdf 49 U.S. Geological Survey. (n.d.). Earthquake Facts & Earthquake Fantasy. https://www.usgs.gov/programs/earthquake-hazards/earthquake-facts-earthquakefantasy#:~:text=The%20Pacific%20Plate%20moves%20northwestward%20past%20the%20North,tiny%20shocks%2 0and%20a%20few%20moderate%20earth%20tremors.
50 Association of Bay Area Governments. (n.d.). Resilience. https://abag.ca.gov/our-work/resilience 51 Association of Bay Area Governments. (2011). Bay Area Local Hazard Mitigation Plan Taming Natural Hazards. https://abag.ca.gov/2011-bay-area-hazard-mitigation-plan Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 89
The Loma Prieta Earthquake on October 17, 1989, occurred near Loma Prieta in the Santa Cruz Mountains along the San Andreas Fault. Thousands of landslides across the area blocked roads and highways, impacting rescue efforts and damaging structures. In Santa Clara County, collapsed and damaged buildings were reported in Gilroy, Los Gatos, and San José.51F 52 California has been included in 13 FEMA major disaster (DR) or emergency (EM) declarations for earthquakes. Santa Clara County was included in only one declaration: DR-845 for the Loma Prieta Earthquake, which occurred in 1989. The declaration for this event covered Alameda, Contra Costa, Marin, Monterey, Sacramento. Table 20 and Figure 21 summarize recent earthquakes of magnitude of

5.0 or greater within a 100-mile radius of the OA.

Table 20: Recent Earthquakes Magnitude 5.0 or Larger Within a 100-Mile Radius of the Operational Area
Date Magnitude Epicenter Location
10/25/2022 5.1 9 miles east-southeast of Alum Rock, California 4/5/2018 5.3 19 miles southwest of Santa Cruz, California 8/24/2014 6.0 South Napa, California
10/21/2012 5.3 15 miles east-northeast of King City, California 10/31/2007 5.5 San José, California
5/14/2002 5.0 Northern California
9/3/2000 5.0 Northern California
8/12/1998 5.2 Central California
4/18/1990 5.4 Northern California
10/17/1989 6.9 Loma Prieta, California Earthquake
10/18/1989 5.1 4 miles southwest of Monte Sereno, California 8/8/1989 5.4 Northern California
6/27/1989 5.3 Northern California
6/13/1988 5.3 San Francisco Bay Area, California
2/20/1988 5.1 Central California
3/31/1986 5.7 Northern California
1/26/1986 5.4 Central California
52 Association of Bay Area Governments. (2011). Bay Area Local Hazard Mitigation Plan Taming Natural Hazards. https://abag.ca.gov/2011-bay-area-hazard-mitigation-plan Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 90
Figure 22: Historic Earthquakes in the Operational Area

7.2.2 Location
Santa Clara County is exposed to three major regional faults: Hayward, Calaveras, and San Andreas.

The Hayward and Calaveras faults are in the central portion of Santa Clara County and present the greatest earthquake threat to the OA. The San Andreas Fault is on the northwestern boundary of the OA and runs through hills separating Santa Clara County from Santa Cruz County. The primary seismic hazard for the OA is potential ground shaking from these three large faults.52F 53 The Greenville fault in the
northeastern portion of the county presents less risk than these three major faults. Figure 22 provides 53 Association of Bay Area Governments. (n.d.). Earthquake. https://abag.ca.gov/our-work/resilience/dataresearch/earthquake Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 91
location and probability of area fault lines. The three major faults are described further in the following sections.

Hayward Fault
The Hayward Fault runs parallel to and east of the San Andreas Fault. It extends from San José about 74 miles northward along the base of the East Bay Hills to San Pablo Bay. The fault is a right-lateral slip fault. The Hayward Fault extends through some of the Bay Area’s most populated areas. Communities on or near the fault include San José, Oakland, Fremont, Richmond, Berkeley, Hayward, San Leandro, San Lorenzo, El Cerrito, Emeryville, Kensington, and Milpitas. Among other sites, the fault runs directly under the now-abandoned old city hall in downtown Hayward, the University of California-Berkeley football stadium, the Mira Vista Golf Course near Berkeley, Lake Temescal, Contra Costa College, and Port Pinole Shoreline Regional Park. It is the single most urbanized earthquake fault in the United States.53F 54 The Hayward Fault is becoming a hazard priority throughout the Bay Area because of its increased chance for activity and its intersection with multiple highly populated areas and critical infrastructure.

According to the Uniform California Earthquake Rupture Forecast, Volume 3, released in March 2015, the probability of experiencing a Magnitude 6.7 or greater earthquake along the Hayward Fault in the next 30 years (starting from 2014) is 14.3 percent.54 F
55 An earthquake of this magnitude has regional implications for the entire Bay Area, as the Hayward Fault crosses transportation and resource infrastructure, including multiple highways, regional gas and water pipelines, electrical transmission lines, and the Hetch-Hetchy Aqueduct. Disruption of the Hetch-Hetchy system has the potential to severely impair water service to the Santa Clara County OA.

An important difference between the Hayward and San Andreas faults is “aseismic creep.” The San Andreas Fault is locked in many places; much of its energy is released in the form of earthquakes.

However, creep occurs in spots along the Hayward Fault. The ground moves a few millimeters each year, pulling apart sidewalks, pipelines and other structures that sit astride the fault. At Memorial Stadium at the University of California Berkeley, which was built in 1923, creep has caused the two sides of the stadium to be offset more than a foot, requiring retrofitting with expansion joints. Creep accounts for a small part of the total motion that takes place on a fault over geologic time; earthquakes account for the rest.5F 56 54 California Office of Emergency Services. (2016, July 6). Bay Area Earthquake Plan. https://www.caloes.ca.gov/wpcontent/uploads/Preparedness/Documents/BayAreaEQConopsPub_Version_2016.pdf. 55 U.S. Geological Survey. (2015, March). UCEFR3: A New Earthquake Forecast for California’s Complex Fault System. https://pubs.usgs.gov/fs/2015/3009/pdf/fs2015-3009.pdf 56 California Department of Conservation. (2008, October 7). Hayward Fault Fact Sheet. https://www.conservation.ca.gov/index/Pages/HaywardFaultFactSheet.aspx Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 92
Figure 23: Significant Known Faults in the Bay Area56F
57 57 U.S. Geological Survey. (2016, August). Earthquake Outlook for the San Francisco Bay Region 2014-2043. https://pubs.usgs.gov/fs/2016/3020/fs20163020.pdf
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Calaveras Fault
The Calaveras Fault is a major branch of the San Andreas Fault, located to the east of the Hayward Fault. It extends 76 miles from the San Andreas Fault near Hollister to Danville at its northern end. The Calaveras Fault is one of the most geologically active and complex faults in the Bay Area. Recent research from the University of Berkeley suggests that the Hayward fault is essentially an offshoot of the Calaveras Fault.57F
58 This means that they could go off together, potentially creating a larger event as an earthquake’s magnitude is relative to its length. In a worst case scenario, a rupture along the Hayward fault could extend to the Calaveras Fault and south to where the Calaveras Fault meets the San Andreas Fault. The probability of experiencing a Magnitude 6.7 or greater earthquake along the Calaveras Fault in the next 30 years is 7.4% percent.

San Andreas Fault
The San Andreas Fault extends 810 miles from the East Pacific rise in the Gulf of California through the Mendocino fracture zone off the shore of northern California. The fault is estimated to be 28 million years old. The San Andreas Fault is an example of a transform boundary exposed on a continent. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip.

The San Andreas Fault is typically referenced in three segments. The southern segment extends from its origin at the East Pacific Rise to Parkfield, California, in Monterey County. The central segment extends from Parkfield to Hollister, California. The northern segment extends northwest from Hollister, through Santa Clara County, to its ultimate junction with the Mendocino fracture zone and the Cascadia subduction zone in the Pacific Ocean. The probability of experiencing a Magnitude 6.7 or greater earthquake along the San Andreas Fault within the next 30 years is 6.4 percent.

Maps of Earthquake Impact on the OA
The impact of an earthquake is largely a function of the following components:
 Surface fault rupture
 Ground shaking (ground motion accelerations)
 Liquefaction (soil instability)
Impacts vary with distance from the source (both horizontally and vertically). Mapping that shows the impacts of these components was used to assess the risk of earthquakes within the OA, as described in the sections below.

Probabilistic Seismic Hazard Map
A probabilistic seismic hazard map shows the hazard from earthquakes that geologists and seismologists agree could occur. The maps are expressed in terms of probability of exceeding a certain ground motion, such as the 10-percent probability of exceedance in 50 years. This level of ground shaking has been used for designing buildings in high seismic areas.58F
59 58 University of California Berkley. (2015, April 2). https://news.berkeley.edu/2015/04/02/calaveras-hayward-fault-linkmeans-potentially-larger-quakes/ 59 Probabilistic Seismic Hazard Assessment, Association of Bay Area Government Resilience Program (2018, February 22) https://www.arcgis.com/home/item.html?id=c3a21989363b484ca6f9c0730e14d9f6.

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Figure 24: 500-Year Probabilistic Earthquake Scenario Peak Ground Acceleration

7.2.3 ShakeMaps
A ShakeMap is a representation of ground shaking produced by an earthquake. The information it presents is different from the earthquake magnitude and epicenter that are released after an earthquake because ShakeMaps focus on the ground shaking resulting from the earthquake, rather than the parameters describing the earthquake source. An earthquake has only one magnitude and one epicenter, but it produces a range of ground shaking at sites throughout the region, depending on the distance from the earthquake, the rock and soil conditions at sites, and variations in the propagation of seismic waves from the earthquake due to complexities in the structure of the earth’s crust. A ShakeMap shows the extent and variation of ground shaking in a region immediately following significant earthquakes.

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Ground motion and intensity maps are derived from peak ground motion amplitudes recorded on seismic sensors (accelerometers), with interpolation based on estimated amplitudes where data are lacking, and site amplification corrections. Color-coded instrumental intensity maps are derived from empirical relations between peak ground motions and Modified Mercalli intensity.

There are two types of scenario ground motion maps: a ShakeMap of median shaking for a fault rupture; and a map of simulated ground motions for a specified earthquake hypocenter and fault rupture. The latter is more like an earthquake event and presents more variability in ground motions than a scenario ShakeMap.

Earthquake scenario maps describe the expected ground motions and effects of hypothetical large earthquakes for a region. The following scenarios were chosen for this plan:
• A Magnitude 7.0 on the Hayward Fault with an epicenter approximately 25 miles north of the City of Palo Alto. 59F
60 • A Magnitude 7.0 on the Calaveras Fault with an epicenter approximately 25 miles north of the City of Milpitas. 60F
61 • A Magnitude 7.8 on the San Andreas Fault with an epicenter approximately 148 miles northwest of the City of Palo Alto. 61F
62 60 U.S. Geological Survey Shakemap Scenario. (n.d.) M 7.0 Scenario Earthquake – Hayward – Rodgers Creek. https://earthquake.usgs.gov/scenarios/eventpage/nclegacyhaywardrodgerscreekhnhsm7p0_se/executive. 61 U.S. Geological Survey Shakemap Scenario (n.d.) M 7.0 Scenario Earthquake – Calaveras North + Central+ South. https://earthquake.usgs.gov/scenarios/eventpage/nclegacycalaverascncccsm7p0_se/executive. 62 USGS Shakemap Scenario (n.d.) M 7.8 Scenario Earthquake – N. San Andreas; North Coast + Peninsula + Santa Cruz Mountain.
https://earthquake.usgs.gov/scenarios/eventpage/nclegacynpsanandreassansapsasm7p8_se/executive.

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
Figure 25: Hayward Magnitude 7.0 Fault Scenario Peak Ground Acceleration Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 97
Figure 26: Calaveras Magnitude 7.0 Fault Scenario Peak Ground Acceleration Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 98
Figure 27: San Andreas Magnitude 7.8 Fault Scenario Peak Ground Acceleration Liquefaction Maps
Soil liquefaction maps are useful tools to assess potential damage from earthquakes. When the ground liquefies, sandy or silty materials saturated with water behave like a liquid, causing pipes to leak, roads and airport runways to buckle, and building foundations to be damaged. In general, areas with NEHRP Soils D, E, and F are also susceptible to liquefaction. If there is a dry soil crust, excess water will sometimes come to the surface through cracks in the confining layer, bringing liquefied sand with it, creating sand boils. Figure 27 shows the liquefaction susceptibility in the Santa Clara County OA.

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Figure 28: Liquefaction Susceptibility
Alquist-Priolo Zone Maps
The sliding movement of earth on either side of a fault is called fault rupture. Fault rupture begins below the ground surface at the earthquake hypocenter, typically between 3 and 12 miles below the ground surface in California. If an earthquake is large enough, the fault rupture will travel to the ground surface, potentially destroying structures built across its path.

California’s Alquist-Priolo Zone maps define regulatory zones for potential surface fault rupture where fault lines intersect with future development and populated areas. The purpose of these maps is to assist in the geologic investigation before construction begins to ensure that structures will not be located on an active fault.

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Cities and counties affected by the zones must regulate certain development projects while sellers of real estate must disclose at the time of sale that the property lies within such a zone. The Santa Clara County OA is located in a designated Alquist-Priolo Zone for the Hayward Fault.62 F 63 Alquist-Priolo maps were referenced, but not specifically used, in the assessment of risk for this plan. This plan assumes that the studies conducted and information provided by the State of California are the best available data for surface rupture risk and could not be improved through a separate assessment for this plan. Alquist-Priolo maps are available to the public on the California Department of Conservation website.63F
64 7.2.4 Frequency
California experiences hundreds of earthquakes each year, most with minimal damage and magnitudes below 3.0 on the Richter Scale. Earthquakes that cause moderate damage to structures occur several times a year. According to the USGS, a strong earthquake measuring greater than 5.0 on the Richter Scale occurs every 2 to 3 years and major earthquakes of more than 7.0 on the Richter Scale occur once a decade.

The USGS estimated in 2016 that there is a 72-percent probability of at least one earthquake before 2043 with a magnitude of 6.7 or greater that could cause widespread damage in the San Francisco Bay area.64F 65 According to the Third Uniform California Earthquake Rupture Forecast, the probability of moderate-sized earthquakes (magnitude 6.5 to 7.5) is lower than previously forecasted, whereas that of larger events is higher.65F
66 This is because the new study took into account the possibility of ruptures along multiple faults simultaneously. Probabilities for earthquakes on major fault lines in the San Francisco Bay Area have been estimated by the USGS in its 2016 report, as summarized in Table 21.

A major earthquake could happen at any time. Both the San Andreas and the Hayward Faults have the potential for experiencing major to great events. Large earthquakes along the Hayward Fault have occurred on average every 150 years – the last being in 1868.6F 67 USGS describe the fault as a “tectonic
time bomb.”.67F
68 Any seismic activity of 6.0 or greater on faults within the OA would have significant impacts throughout the OA. Bay Area communities can use the likelihood of a 6.8-7.0 earthquake near San Francisco as a predictive model of what to prepare for.

Further information on the impact of climate change on the probability of earthquakes is included in Section 11.

Probability in OA: Likely
63 California Department of Conservation. (2008). Hayward Fault Fact Sheet. https://www.conservation.ca.gov/index/Pages/HaywardFaultFactSheet.aspx 64 California Department of Conservation. (2023). The California Seismic Hazards Program. https://www.conservation.ca.gov/cgs/sh
65 U.S. Geological Survey. (2016, August). Earthquake Outlook for the San Francisco Bay Region 2014-2043. https://pubs.usgs.gov/fs/2016/3020/fs20163020.pdf
66 Southern California Earthquake Center. (2017). Third Uniform California Earthquake Rupture Forecast. https://www.scec.org/ucerf#:~:text=UCERF3%20shows%20the%20likelihood%20of%20moderatesized%20earthquakes%20%28magnitude,may%20occasional%20rupture%20together%20to%20cause%20larger%2 0earthquakes.
67 California Earthquake Authority. (2020, July 8). What to Expect from an Earthquake along the Hayward Fault. https://www.earthquakeauthority.com/Blog/2019/hayward-fault-earthquake-prediction 68 U.S. Geological Survey. (2008). The Hayward Fault – Is it Due for a Repeat of the Powerful 1868 Earthquake? https://pubs.usgs.gov/fs/2008/3019/
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Table 21: Earthquake Probabilities for the San Francisco Bay Area Region, 2014–204368F 69 Fault Probability of One or More M ≥ 6.7 Quake
2014–2043
Hunting Creek 16%
Green Valley 16%
Concord 16%
Greenville 16%
Berryessa 16%
Calaveras 26%
Maacama 8%
Rodgers Creek Fault 33%
Hayward 33%
San Andreas 22%
San Gregorio 6%

7.2.5 Severity
The severity of an earthquake can be expressed in terms of intensity or magnitude:
 Intensity represents the observed effects of ground shaking at any specified location. The intensity of earthquake shaking lessens with distance from the earthquake epicenter. Tabulated peak ground accelerations for listed “maximum credible earthquakes” are a measure of how a site will be affected by seismic events on distant faults.  Magnitude represents the amount of seismic energy released at the hypocenter of the earthquake. It is based on the amplitude of the earthquake waves recorded on instruments.

Magnitude is thus represented by a single, instrumentally determined value. 69 U.S. Geological Survey. (2017). Map of Known Active Faults and Earthquake Probabilities. https://www.usgs.gov/media/images/map-known-active-faults-and-earthquake-probabilities Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 102
Figure 29: Peak Ground Acceleration with 10-percent Probability of Exceedance in 50 Years ABAG estimates a potential loss of 159,000 housing units in Bay Area communities after a large earthquake. This loss would have disastrous effects on local and regional economies. Recovery, repair, and rebuilding time for each household would be lengthy because of the number of homes that would need repair or replacement.

Annual losses also represent a sizable economic burden on the OA. According to FEMA 2023 report Hazus Estimated Annualized Earthquake Losses for the United States, the annualized earthquake loss ratio (AELR)—or the estimated building loss value as a fraction of the building inventory replacement value—for the San José metro area is the second highest in California69F

70. The metro areas include San
José, Sunnyvale, and Santa Clara. This finding emphasizes the fact that the severity of more frequent, non-catastrophic earthquakes is still significant enough to warrant further seismic risk reduction actions.

7.2.6 Warning Time
There is no current reliable way to predict when an earthquake will occur at any given location. Research and beta testing are being done with warning systems that use telecommunications that can travel faster than an earthquake’s high energy waves, called S waves. 70 FEMA. (April 2023). Hazus Estimated Annualized Earthquake Losses for the United States. Hazus Estimated Annualized earthquake losses for the United States, FEMA P-366 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 103
The warning is generated by a rupture at an earthquake’s hypocenter and telecommunicated to provide a warning for shaking before the S waves arrive. These potential earthquake early warning systems could give up to approximately 40 seconds’ notice of peak earthquake shaking. In 2019, California became the nation’s first state to have a statewide earthquake early warning system. Early Warning California is able to provide alerts to the public seconds before an earthquake is felt. The warning time is very short, but it could allow for someone to get under a desk, step away from a hazardous material, or shut down a computer system.

7.3 Cascading Impacts
Earthquakes can cause a variety of cascading hazards including landslides, tsunamis, fires, dam failures, and hazardous material releases. Earthquakes cause large and sometimes disastrous landslides and mudslides. River valleys are vulnerable to slope failure, often as a result of loss of cohesion in clay-rich soils. Soil liquefaction occurs when water-saturated sands, silts, or gravelly soils are shaken so violently that the individual grains lose contact with one another and “float” freely in the water, turning the ground into a pudding-like liquid. Building and road foundations lose load-bearing strength and may sink quicksand-like into what was previously solid ground. Unless properly secured, hazardous materials can be released, causing considerable damage to the environment and people.

Depending on the location, earthquakes can also trigger tsunamis. Most tsunamis are caused by underwater earthquakes. The tsunami hazard is furthered described in Section 13. Earthen dams and levees are highly susceptible to seismic events, and the impacts of their eventual failures can be considered secondary risk exposure to earthquakes. Dams do not have to be destroyed in an earthquake for there to be devastating consequences. Dams can be cracked due to embankment deformation induced by ground shaking, experience foundation damage, or be impacted by an earthquake-cased landslide. Dam failures can result in significant downstream flooding. This hazard is further described in Section 12.

Additionally, fires can result from gas lines or power lines that are broken or downed during the earthquake. It may be difficult to control a fire, particularly if the water lines feeding fire hydrants are also broken. After the 1906 earthquake in San Francisco, for example, a fire burned for three days, destroying much of the city and leaving 200,000 people houseless.70F 71 Fires in urban areas present unique firefighting
and public health challenges. They would be a considerable concern after a major earthquake event.

7.4 Exposure

7.4.1 Population
The entire population of the OA is potentially exposed to direct and indirect impacts from earthquakes.

The degree of exposure is dependent on many factors, including the age and construction type of the structures people live in, the soil their homes are constructed on, their proximity to fault location, etc.

Whether directly impacted or indirectly impact, the entire population will have to deal with the consequences of earthquakes to some degree. Business interruption could keep people from working, road closures could isolate populations, and loss of functions of utilities could impact populations that suffered no direct damage from an event itself.
71 The U.S. National Archives and Records Administration. (n.d.). San Francisco Earthquake, 1906. https://www.archives.gov/legislative/features/sf#:~:text=On%20the%20morning%20of%20April%2018%2C%201906 %2C%20a,three%20days%20and%20destroyed%20nearly%20500%20city%20blocks..

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7.4.2 Property
According to Santa Clara County Tax Assessor records, there are 535,391 buildings in the OA, with a total replacement value of $381 billion. Since all structures in the OA are susceptible to earthquake impacts to varying degrees, this total represents the property exposure to seismic events. Table 22 shows the exposure value breakdown by jurisdiction with the OA.

Table 22: Earthquake Exposure by Jurisdiction
Jurisdiction Number of Buildings Total Building Value:

Structure and Contents
Campbell 14,494 $9,337,059,000
Cupertino 17,460 $14,466,910,000
Gilroy 11,597 $7,140,035,000
Los Altos 13,433 $9,697,438,000
Los Altos Hills 3,342 $4,077,127,000
Los Gatos 10,467 $7,634,327,000
Milpitas 20,912 $13,830,811,000
Monte Sereno 1,078 $986,431,000
Morgan Hill 21,044 $5,547,035,000
Mountain View 6,545 $14,501,750,000
Palo Alto 19,914 $16,233,190,000
San José 25,5703 $168,553,959,000
Santa Clara (city) 32,978 $26,584,014,000
Saratoga 10,214 $8,348,159,000
Sunnyvale 41,941 $28,567,428,000
Unincorporated County 54,269 $46,077,151,000
Total 535,391 $381,582,824,000

7.4.3 Loss Potential
Property losses were estimated through the Level 2 Hazus analysis for the 100-year and 500-year earthquakes and the three scenario events. Table 23 through Table 27 show the results for two types of property loss:
 Structural loss, representing damage to building structures.  Contents loss, representing the value of lost contents and inventory.  Total loss, representing a combination of direct (structural and content) and indirect costs such as relocation, income loss, rental loss, and wage loss.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 105
Table 23: Loss Estimates for 100-Year Probabilistic Earthquake Jurisdiction
Estimated Loss Associated with Earthquake
% of Total
Replacement
Value
Structure Contents Total
Campbell $83,411,720 $147,383,480 $714,842,110 6.42
Cupertino $110,113,070 $202,728,570 $944,296,790 5.58
Gilroy $111,762,750 $186,420,740 $919,308,810 10.87
Los Altos $60,407,350 $105,705,000 $516,809,420 4.75
Los Altos Hills $15,337,870 $32,413,630 $143,905,510 3.27 Los Gatos $52,214,200 $97,964,100 $469,109,470 5.21
Milpitas $229,633,340 $366,547,460 $1,792,104,770 10.79 Monte Sereno $5,582,230 $9,912,830 $48,082,010 4.59
Morgan Hill $85,693,050 $144,753,610 $647,026,030 9.86
Mountain View $138,215,630 $228,950,290 $1,135,921,470 6.55 Palo Alto $123,276,450 $234,519,070 $1,143,458,680 5.89 San José $2,271,729,230 $3,804,754,590 $18,548,766,290 9.19 Santa Clara (city) $371,540,110 $623,137,970 $2,922,510,780 9.07 Saratoga $46,922,910 $87,663,150 $411,758,710 4.52
Sunnyvale $277,402,330 $471,198,590 $2,271,326,290 6.81 Unincorporated
County
$491,709,760 $847,476,000 $4,002,857,370 7.40
Total $4,474,952,000 $7,597,529,080 $36,632,084,510 8.07 Table 24: Loss Estimates for 500-Year Probabilistic Earthquake Jurisdiction
Estimated Loss Associated with Earthquake % of Total
Replacement
Structure Contents Total Value
Campbell $332,939,800 $514,222,930 $2,637,075,050 23.67 Cupertino $483,321,680 $773,618,650 $3,846,779,640 22.62 Gilroy $325,070,990 $496,300,090 $2,565,057,320 30.59
Los Altos $253,325,050 $368,045,620 $1,957,493,570 17.73 Los Altos Hills $79,356,360 $139,360,770 $675,309,730 14.98 Los Gatos $237,262,800 $375,686,540 $1,937,596,360 21.33 Milpitas $868,837,200 $1,284,918,220 $6,491,226,210 39.92 Monte Sereno $24,465,000 $32,498,890 $181,964,270 17.12 Morgan Hill $278,620,680 $446,000,140 $2,045,968,380 31.44 Mountain View $554,403,710 $860,895,660 $4,359,290,900 25.19 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 106
Jurisdiction
Estimated Loss Associated with Earthquake % of Total
Replacement
Structure Contents Total Value
Palo Alto $508,699,590 $904,493,750 $4,518,057,520 23.11 San José $7,547,645,640 $12,175,341,680 $60,078,192,300 30.15 Santa Clara (city) $1,281,702,680 $2,143,040,010 $10,023,437,510 31.60 Saratoga $215,118,140 $317,501,240 $1,672,277,590 18.05 Sunnyvale $1,022,240,280 $1,620,535,330 $8,017,810,470 24.07 Unincorporated County $1,834,740,210 $2,763,641,700 $13,914,201,350 25.85 Total $15,847,749,810 $25,216,101,220 $142,921,738,170 27.77 Table 25: Loss Estimates for San Andreas Fault Scenario Earthquake Jurisdiction
Estimated Loss Associated with Earthquake % of Total
Replacement
Structure Contents Total Value
Campbell $49,214,560 $92,236,240 $432,374,280 3.91
Cupertino $81,301,810 $153,677,230 $710,419,020 4.24
Gilroy $33,481,560 $61,301,010 $280,483,670 3.24
Los Altos $55,804,220 $90,175,700 $462,202,090 4.27
Los Altos Hills $10,926,300 $20,917,530 $97,960,120 2.25 Los Gatos $27,424,860 $45,440,870 $234,302,660 2.58
Milpitas $296,969,340 $464,378,390 $2,282,091,580 13.76 Monte Sereno $2,727,410 $4,081,180 $21,982,080 2.10
Morgan Hill $24,995,170 $42,475,860 $184,472,540 2.78
Mountain View $132,855,600 $217,121,870 $1,083,896,690 6.22 Palo Alto $97,695,850 $200,178,300 $936,127,860 4.90
San José $1,868,771,120 $3,118,303,370 $14,933,844,800 7.34 Santa Clara (city) $325,662,720 $591,625,640 $2,655,220,690 8.28 Saratoga $27,814,510 $48,360,240 $237,674,840 2.62
Sunnyvale $260,122,500 $429,175,020 $2,076,576,830 6.17 Unincorporated County $288,238,330 $481,595,870 $2,294,416,020 4.20 Total $3,584,005,860 $6,061,044,320 $28,924,045,770 6.34 Table 26: Loss Estimates for Hayward Fault Scenario Earthquake Jurisdiction
Estimated Loss Associated with Earthquake % of Total
Replacement
Structure Contents Total Value
Campbell $40,301,090 $98,620,250 $409,079,960 3.76
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 107
Jurisdiction
Estimated Loss Associated with Earthquake % of Total
Replacement
Structure Contents Total Value
Cupertino $76,928,120 $182,120,770 $752,020,960 4.56
Gilroy $30,147,280 $73,497,000 $305,747,590 3.72
Los Altos $45,091,440 $101,276,690 $433,600,270 4.03
Los Altos Hills $25,102,370 $58,726,440 $246,663,700 5.56 Los Gatos $49,681,050 $105,154,360 $470,871,870 5.23
Milpitas $22,068,720 $68,614,250 $254,995,140 1.61
Monte Sereno $4,912,510 $10,456,710 $45,981,960 4.41
Morgan Hill $17,740,240 $47,816,600 $177,511,110 2.78
Mountain View $65,744,520 $161,424,770 $669,374,410 3.94 Palo Alto $74,475,780 $202,860,830 $827,014,160 4.32
San José $412,039,580 $1,243,445,510 $4,732,726,140 2.46 Santa Clara (city) $78,077,550 $242,884,660 $886,193,970 2.89 Saratoga $48,918,390 $105,223,740 $456,057,380 5.04
Sunnyvale $97,943,980 $261,626,210 $1,041,138,290 3.22
Unincorporated
County
$206,686,640 $460,193,440 $1,944,849,460 3.66
Total $1,295,859,260 $3,423,942,230 $13,653,826,370 3.13 Table 27: Loss Estimates for Calaveras Fault Scenario Earthquake Jurisdiction
Estimated Loss Associated with Earthquake % of Total
Replacement
Structure Contents Total Value
Campbell $40,939,680 $86,487,180 $386,261,760 3.56
Cupertino $71,012,520 $146,392,880 $651,211,640 3.95
Gilroy $19,238,740 $45,359,670 $188,770,670 2.26
Los Altos $50,620,630 $86,562,830 $431,369,830 4.03
Los Altos Hills $10,762,060 $20,780,700 $96,841,280 2.23 Los Gatos $23,993,340 $43,003,930 $213,109,080 2.40
Milpitas $209,898,010 $374,708,150 $1,728,857,450 10.54 Monte Sereno $2,665,370 $4,043,610 $21,636,660 2.08
Morgan Hill $15,897,370 $34,459,240 $137,948,090 2.14
Mountain View $105,347,590 $194,639,980 $921,924,650 5.39 Palo Alto $84,410,530 $188,043,650 $842,872,700 4.49
San José $1,354,935,210 $2,533,808,530 $11,560,267,970 5.78 Santa Clara (city) $250,185,320 $521,829,550 $2,208,182,000 6.99 Saratoga $26,733,350 $47,643,880 $231,358,470 2.57
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 108
Jurisdiction
Estimated Loss Associated with Earthquake % of Total
Replacement
Structure Contents Total Value
Sunnyvale $198,860,640 $368,380,050 $1,711,126,870 5.17 Unincorporated
County
$211,495,100 $406,336,080 $1,828,500,120 3.42
Total $2,676,995,460 $5,102,479,910 $23,160,239,240 5.16 A summary of the property-related loss results is as follows:
 For a 100-year probabilistic earthquake shaking, the estimated damage potential is $36.6 billion, or 8 percent of the total replacement value for the OA.  For a 500-year probabilistic earthquake shaking, the estimated damage potential is $142.9 billion, or 27.8 percent of the total replacement value for the OA.  For a 7.8-magnitude event on the San Andreas Fault, the estimated damage potential is $28.9 billion, or 6.3 percent of the total replacement value for the OA.  For a 7.0-magnitude event on the Hayward Fault, the estimated damage potential is $13.7 billion or 5 percent of the total replacement value for the OA.  For a 7.0-magnitude event on the Calaveras Fault, the estimated damage potential is $23.2 billion, or 5.6 percent of the total replacement value for the OA.

The Hazus analysis also estimated the amount of earthquake-caused debris in the OA for the 100-year and 500-year earthquakes and the three scenario events, as summarized in Table 28: .

Table 28: Estimated Earthquake-Caused Debris
Scenario Debris to Be Removed (Thousands of Tons)
100-Year Earthquake 4,589
500-Year Earthquake 17,862
San Andreas Fault Scenario 3,902
Hayward Fault Scenario 1,106
Calaveras Fault Scenario 2,638

7.4.4 Critical Facilities and Infrastructure
All critical facilities in the OA are exposed to the earthquake hazard. Table 29: Number of Critical Facilities Exposed to Earthquakes lists the number of each type of facility by jurisdiction. Additionally, communities in the Bay Area are serviced by infrastructure that is susceptible to damage from earthquakes, as nearly all the infrastructure connection that the area depends on for water, electric power, fuel, and transportation services cross a fault.71F 72 Hazardous materials releases can occur during an
earthquake from fixed facilities or transportation-related incidents. Transportation corridors can be disrupted during an earthquake, leading to the release of materials to the surrounding environment. 72 California Office of Emergency Services. (2016, July 6). Bay Area Earthquake Plan. https://www.caloes.ca.gov/wpcontent/uploads/Preparedness/Documents/BayAreaEQConopsPub_Version_2016.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 109
Facilities holding hazardous materials are of particular concern because of possible isolation of neighborhoods surrounding them. During an earthquake, structures storing these materials could rupture and leak into the surrounding area or an adjacent waterway, having a disastrous effect on the environment, or emit chemicals in a toxic plume.

Table 29: Number of Critical Facilities Exposed to Earthquakes Jurisdiction
Number of Facilities by Jurisdiction
Critical
Facilities Transportation Utilities Community Assets
Hazardous
Materials Total
Campbell 21 23 0 7 6 57
Cupertino 26 26 2 16 5 75
Gilroy 25 34 2 13 7 81
Los Altos 22 8 0 11 0 41
Los Altos Hills 6 21 0 2 0 29
Los Gatos 20 35 0 6 1 62
Milpitas 32 66 1 19 60 178
Monte Sereno 1 1 0 1 0 3
Morgan Hill 22 14 1 10 8 55
Mountain View 37 52 1 29 20 139
Palo Alto 49 42 4 46 26 167
San José 370 498 18 191 135 1,212
Santa Clara (city) 53 63 9 36 103 264
Saratoga 18 32 0 11 0 61
Sunnyvale 40 49 3 27 51 170
Unincorporated
County
35 187 17 48 4 291
Total 777 1151 58 473 426 2885

7.4.5 Environment
The entire OA is a seismically active area and could be exposed to ground shaking from several different faults. According to the Alquist-Priolo Earthquake Fault Zones map for the San Francisco Bay Region, all of the OA is likely to experience very strong, severe, or violent shaking. Environmental problems as a result of an earthquake could occur anywhere in the OA. Cascading hazards will likely have some of the most damaging effects on the environment.

7.5 Vulnerability
Earthquake vulnerability data was generated using a Level 2 Hazus analysis. Once the location and size of a hypothetical earthquake are identified, Hazus estimates the intensity of the ground shaking, the number of buildings damaged, the number of casualties, the damage to transportation systems and utilities, the number of people displaced from their homes, and the estimated cost of repair and cleanup.

Changes in conditions: No change in vulnerability
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 110
• Overall, the OA is in a seismically active area with multiple fault sources. • The OA has a significant population and number of assets exposed to damage from earthquake which constitutes a high risk.
• Population and building development has grown but at a very slow rate and new buildings are built in accordance with seismic codes.

7.5.1 Population
Impacts on persons and households in the OA were estimated for the 100-year and 500-year shaking from earthquakes and the three scenario events through the Level 2 Hazus analysis. One of the primary impacts on population is being displaced from their homes and seeking alternative shelter. Table 30:

Estimated Earthquake Impact on Persons summarizes the results. People can also experience physical injury or death, be impacted by disruptions to transportation and utility systems, loss or wages or other loss of services from business interruptions.

There are estimated to be 29,329 people in 10,010 households living on soils with high to very high liquefaction potential in the OA, or about 1.52 percent of the total population. Higher liquefaction potential contributes to structural damage and subsequent displacement of people from their residences.

A summary analysis of demographics using the Hazus data identified populations with additional factors that add to their vulnerability to earthquake hazard. The Hazus model does not provide results for how specific demographic categories will be impacted by the different earthquake scenarios. This only provides a general indication of the number of people who may have a more difficult time recovering from the impacts of an earthquake.
 Economically Disadvantaged Populations: It is estimated that 2.45 percent of the people within the OA are economically disadvantaged, defined as having household incomes of $20,000 or less.
 Population over 64 Years Old: It is estimated that 260,705 persons or 13.5 percent of the population in the OA are over 64 years old.
 Population under 16 Years Old: It is estimated that 422,719 persons or 21.8 percent of the population within the OA under 18 years of age.
 Racial and ethnic minorities comprise a significant proportion of the population: 39% are Asian and 25% are Hispanic.

Table 30: Estimated Earthquake Impact on Persons
Scenario Number of Displaced
Households
Number of Persons Requiring
Short-Term Shelter
100-Year Shaking from Earthquakes 16,071 8,076
500-Year Shaking from Earthquakes 77,037 38,242
San Andreas ShakeMap Scenario 4,364 2,047
Calaveras ShakeMap Scenario 8,199 4,047
Hayward ShakeMap Scenario 2,708 1,282
The 100-year shaking results are less than the 500-year shaking results because stronger shaking occurs less often and is more likely to occur in a 500-year period than a 100-year period.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 111

7.5.2 Property
Building Age
Table 31 identifies significant milestones in building and seismic code requirements that directly affect the structural integrity of development. Using these time periods, the Core Planning Group used the National Structure Inventory to identify the number of structures in the OA by date of construction. The NSI provided limited data on the number of structures built between 2005 and 2016.

Table 31: Age of Structures in Operational Area
Time Period
Number of Current
OA Structures
Built in Period
Significance of Time Frame
1939-1940 7,853 In 1940, the first strong motion recording was made. 1941-1960 96,753 In 1960, the Structural Engineers Association of California published guidelines on recommended earthquake provisions. 1961-1975 224,356 In 1975, significant improvements were made to lateral force requirements.
1976–1993 141,510 In 1994, the Uniform Building Code was amended to include provisions for seismic safety.
1994–present 65,144 Seismic code is currently enforced. Please note that data on more recent structures are limited.

Total 535,616
The number of structures does not reflect the number of total housing units, as many multi-family units and attached housing units are reported as one structure.

Approximately 38.5 percent of the OA’s structures were constructed after the Uniform Building Code was amended in 1994 to include seismic safety provisions.

Soft-Story Buildings
A soft-story building is a multi-story building with one or more floors that are “soft” because of structural design. If a building has a floor that is 70-percent less stiff than the floor above it, it is considered a softstory building. This soft story creates a major weak point in an earthquake. Since soft stories are typically associated with retail spaces and parking garages, they are often on the lower stories of a building. When they collapse, they can take the whole building down with them, causing serious structural damage that may render the structure totally unusable.

These floors can be especially dangerous in earthquakes because they cannot cope with the lateral forces caused by the swaying of the building during a quake. As a result, the soft story may fail, causing what is known as a soft-story collapse. Soft-story collapse is one of the leading causes of earthquake damage to private residences.

Loss estimation and vulnerability analyses based on models with specified fragility curves for soft-story construction in the OA are not currently available to support quantitative analyses of risk. There are qualitative reports on risk available within the OA. These reports were not used for this analysis due to their lack of quantitative data. ABAG and other agencies in the Bay Area have programs generating this type of data, but it is not known when such data will be available for the Santa Clara County OA. This type of data will need to be generated to support future risk assessments of the earthquake hazard.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 112
Unreinforced Masonry Buildings
Unreinforced masonry buildings are constructed from materials such as adobe, brick, hollow clay tiles, or other masonry materials and do not contain an internal reinforcing structure, such as rebar in concrete or steel bracing for brick. Unreinforced masonry poses a significant danger during an earthquake because the mortar holding masonry together is typically not strong enough to withstand significant earthquakes.

Additionally, the brittle composition of these houses can break apart and fall away or buckle, potentially causing a complete collapse of the building.

In the Santa Clara County OA, unreinforced masonry buildings are generally brick buildings that were constructed before modern earthquake building codes and designs were enacted. The State of California enacted a law in 1986 that required all local governments in Seismic Zone 4 (nearest to active earthquake faults) to inventory unreinforced masonry buildings. The law encourages local governments to adopt local mandatory strengthening programs, delineate seismic retrofit standards, and put into place measures to reduce the number of people in unreinforced masonry buildings.

According to ABAG, housing units in unreinforced masonry buildings account for only 1-percent of the total Bay Area housing stock.72F
73 7.5.3 Critical Facilities and Infrastructure
Level of Damage
Hazus classifies the vulnerability of critical facilities to earthquake damage in five categories: no damage, slight damage, moderate damage, extensive damage, or complete damage. Hazus also classifies facilities in terms of loss-of-function and possible restoration times. The model was used to assign a vulnerability category to each critical facility category in the OA.

The analysis was performed for the 100-year and 500-year events and for all three fault scenarios.

Selected results are summarized in Table 32 through Table 37.

Table 32: Estimated Damage to Critical Facilities from 100-Year Earthquake Type of Critical Facility Total
With
Moderate
Damage
With
Complete
Damage
With
Functionality
>50% on Day 1
With
Functionality
>50% on Day 7
Essential Facilities 777 151 0 257 N/A
Transportation 1154 12 0 1146 1154
Utilities 58 49 0 30 57
Community Assets 515 N/A N/A N/A N/A
Hazardous Materials 426 N/A N/A N/A N/A
Overall 2927 212 0 1433 1211
Notes: Damage level represents the highest-probability damage state for each facility. Values shown are accurate for comparison of results in this plan. See Section 6.7 for discussion of data limitations.

This scenario modeled significant impacts to essential facilities. Loss of functionality of these services will result in difficult response in the immediate aftermath of an earthquake. Furthermore, of the 656,063 73 Association of Bay Area Governments. (2016, March). Resilience Policy Guidance Document Soft Story Retrofit Program Development. https://abag.ca.gov/sites/default/files/soft_story_report_web_version_v2.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 113
households, 203,485 are expected to be without potable water, and 358,285 without electric power on day one. Transportation systems will mostly remain functional.

Table 33: Essential Facility Functionality in 100-Year Probabilistic Earthquake Facility Total With >50% Functionality on
Day 1
Hospital 20 7
Schools 617 195
EOCs 7 4
Police Stations 35 12
Fire Stations 98 39
Table 34: Estimated Damage to Critical Facilities from 500-Year Earthquake Type of Critical
Facility Total
With
Moderate
Damage
With
Complete
Damage
With
Functionality
>50% on Day 1
With
Functionality
>50% on Day 7
Essential Facilities 777 654 62 0 N/A
Transportation 1154 599 23 607 942
Utilities 58 58 14 0 31
Community Assets 515 N/A N/A N/A N/A
Hazardous Materials 426 N/A N/A N/A N/A
Overall 2957 1311 99 607 973
Notes: Damage level represents the highest-probability damage state for each facility. Values shown are accurate for comparison of results in this plan. See Section 6.7 for discussion of data limitations.

Table 35: Estimated Damage to Critical Facilities from Hayward Fault Type of Critical
Facility Total
With
Moderate
Damage
With
Complete
Damage
With
Functionality
>50% on Day 1
With
Functionality
>50% on Day 7
Essential Facilities 777 25 0 704 N/A
Transportation 1154 0 0 1153 1154
Utilities 58 32 0 33 58
Community Assets 515 N/A N/A N/A N/A
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 114
Type of Critical
Facility Total
With
Moderate
Damage
With
Complete
Damage
With
Functionality
>50% on Day 1
With
Functionality
>50% on Day 7
Hazardous Materials 426 N/A N/A N/A N/A
Overall 2927 57 0 1890 1212
Notes: Damage level represents the highest-probability damage state for each facility. Values shown are accurate for comparison of results in this plan. See Section 6.7 for discussion of data limitations.

Table 36: Estimated Damage to Critical Facilities from San Andreas Fault Type of Critical
Facility Total
With
Moderate
Damage
With
Complete
Damage
With
Functionality
>50% on Day 1
With
Functionality
>50% on Day 7
Essential Facilities 777 124 0 531 N/A
Transportation 1154 10 0 1151 1154
Utilities 58 29 0 33 58
Community Assets 515 N/A N/A N/A N/A
Hazardous Materials 426 N/A N/A N/A N/A
Overall 2927 163 0 1715 1212
Notes: Damage level represents the highest-probability damage state for each facility. Values shown are accurate for comparison of results in this plan. See Section 6.7 for discussion of data limitations.

Table 37: Estimated Damage to Critical Facilities from Calaveras Type of Critical
Facility Total
With
Moderate
Damage
With
Complete
Damage
With
Functionality
>50% on Day 1
With
Functionality
>50% on Day 7
Essential Facilities 777 45 0 579 N/A
Transportation 1154 10 0 1150 1154
Utilities 58 29 0 33 53
Community Assets 515 N/A N/A N/A N/A
Hazardous Materials 426 N/A N/A N/A N/A
Overall 2927 84 0 1762 1207
Notes: Damage level represents the highest-probability damage state for each facility. Values shown are accurate for comparison of results in this plan. See Section 6.7 for discussion of data limitations.

Hazardous Materials
An earthquake can cause hazardous material releases from fixed facilities and transportation-related releases. The Bay Area includes numerous oil refineries, chemical plants, tank farms, pipelines, high tech and biotechnology laboratories and production facilities and other industrial facilities.73F 74 74 California Office of Emergency Services. (2016, July 6). Bay Area Earthquake Plan. https://www.caloes.ca.gov/wpcontent/uploads/Preparedness/Documents/BayAreaEQConopsPub_Version_2016.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 115
Additionally, there are there are multiple highways and railroads which transport HAZMAT, oil, and natural gas products in the OA. Although the Hazus scenarios did not include specific damage estimates for hazardous materials facilities, any facility could experience damage from severe ground shaking that could result in a HAZMAT incident.

Transportation
Liquefaction, landslides, and fault surface rupture during an earthquake can significantly damage roads.

Access to major roads is crucial to life and safety after a disaster event as well as to response and recovery operations. Disruptions in transportation systems are of particular concern in areas with limited access via transportation corridors, as a major event has the potential to isolate these communities from critical assistance and aid. Several communities in the OA extend into the foothills, where narrow and dead-end spur roads are common. Landslide susceptibility is also higher in these areas. Although the Hazus models did not indicate significant functional disruption to transportation network, past events indicate transportation damage should be expected that will disrupt response and recovery, and also require costly repairs.

Bridges
Earthquake shaking, liquefaction and landslides can significantly damage bridges, which often provide the only access to some neighborhoods. Since soft soil regions generally follow floodplain boundaries, those bridges that cross water courses are considered vulnerable. Key factors in the degree of vulnerability are the facility’s age and type of construction and soil classification at the bridge support structure, which indicate the standards to which the bridge was built. An example of the location of bridges in the OA with potential damage in the Calaveras Hazus Scenario is shown in Figure 29.

Figure 30: Highway Bridge Percentage Damage Exceeds Moderate: Calaveras Scenario Water and Sewer Infrastructure
Water and sewer infrastructure would likely suffer considerable damage in the event of an earthquake. If water and wastewater treatment plants were damaged, there could be a lack of potable water and spilling of raw sewage into bays or rivers.74F
75 Distribution systems with older brittle pipes are vulnerable to shaking 75 California Seismic Safety Commission. (1999). Earthquake Risk Management: A Toolkit for Decision-Makers. https://ssc.ca.gov/wp-content/uploads/sites/9/2020/08/ssc_1999-04_risk_toolkit.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 116
and liquefaction in particular. Water and sewer restoration generally takes longer than other critical infrastructure. There would be significant regional needs for water after a Bay Area earthquake. Table 38 and Table 39 give more details on potential damage to these systems based on Hazus models. These indicate a significant number of residents across the OA without essential services for an extended time.

Table 38: Damage to Potable Water Systems by Hazus Scenario Potable Water Total Pipelines
Length
Number of
leaks
Number of
Breaks
Households
without service
at Day 7
100 Year 7,119 2,050 777 147,285
500 Year 7,119 13,762 4,974 625,830
San Andreas 7119 4,717 1,457 362,907
Calaveras 7119 4,696 1,375 342,397
Hayward 7,119 2,947 839 170,876
Table 39: Damage to Waste Water Systems by Hazus Scenario Waste Water Total Pipelines
Length
Number of
leaks
Number of
Breaks
100 Year 4,272 1,030 390
500 Year 4,272 6,913 2,498
San Andreas 4,272 2,369 733
Calaveras 4,272 2,359 691
Hayward 4,272 1,480 421

7.5.4 Environment
Environmental problems as a result of an earthquake can be numerous. Earthquakes can cause ground shaking, soil liquefaction, landslides, fissures, fires, dam failures, and tsunamis. Cascading hazards will likely have some of the most damaging effects on the environment. Earthquake-induced landslides in landslide-prone areas can significantly damage surrounding habitat. It is also possible for streams to be rerouted after an earthquake. Rerouting can change the water quality, possibly damaging habitat and feeding areas. There is a possibility that streams fed by groundwater wells will dry up because of changes in underlying geology. Hazardous material releases, including through transportation incidents, damage to sewers, and natural gas lines, as well as other infrastructure could seriously impact the environment.

7.5.5 Economic Impact
Earthquake events can severely disrupt the economy of the affected area. Economic impact will be largely associated with the disruption of power, gas, telecommunication, water, and wastewater services caused by an earthquake event. In general, major events may cause damage to land, buildings, transportation infrastructure, and businesses. With an event of such significance, economic recovery could take years, depending on available recovery funds.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 117
The total economic impact of a major earthquake is likely to spread well beyond the impacted area, especially in a population center like the Santa Clara County OA. This is often referred to the “ripple effect.”75F
76 The United States has a highly developed, specialized, interdependent, money economy. While those features make the economy productive and resilient, they also mean that a large magnitude earthquake will not be just a regional event. It has the potential to impact the national economy. An earthquake can result in impacts to the national economy including through disruptions to supply chains, shocks to financial markets, and drain on the insurance system.

Various sectors of the OA economy would be impacted differently. For example, tourism would likely be impacted over a long term while the impacted area recovers. The retail sector would likely recover quickly to support recovery, and the construction sector would eventually experience growth. Businesses would experience different levels of damage to property, loss of revenues, loss of market share and/or reputation. Business interruptions in recent California earthquakes have caused the failure of a number of small and medium-sized businesses.76F
77 Failed businesses impact the sales, property, and other tax revenue for local governments. Recovery of the economy is a key sign of a community’s resilience.

7.6 Future Trends in Development
Since all of the Santa Clara County Operational Area is located within an earthquake hazard zone, all future development will, to some extent, be exposed to the earthquake hazard. In the 30 years since the Loma Prieta earthquake, the bay region has invested about $80 billion (in 2016 U.S. dollars) in seismic strengthening of transportation, water, and other critical infrastructure; hospitals, schools, and governments facilities; and unreinforced masonry, soft story, and other types of buildings.7F 78 More work
needs to be done to prepare the region for the next major event. A key part of that is adopting and enforcing land use practices and building codes that consider seismic hazards.

Land use planning is directed by general plans adopted under California’s General Planning Law.

Municipal planning partners are encouraged to establish General Plans with policies directing land use and dealing with issues of geologic and seismic safety. These plans provide the capability at the local municipal level to protect future development from the impacts of earthquakes. All planning partners reviewed their general plans under the capability assessments performed for this effort. Deficiencies identified by these reviews can be identified as mitigation actions to increase the capability to deal with future trends in development.

Unincorporated Santa Clara County and the development departments in participating jurisdictions will strictly enforce all seismic building codes and design standards to prevent loss of life and property caused by earthquake. Public education, cooperation with the development community, and individual preparedness are essential as the OA welcomes thousands of new residents and hundreds of new businesses to each year. It will take a whole community approach to prepare for the next seismic event.

Kaiser Permanente, a health care organization, was highlighted by FEMA as a mitigation best practice for its work to seismically retrofit or replace its existing hospitals and buildings, including the Santa Clara Medical Center, in accordance with California Senate Bill 1953. ABAG’s Resilience Program assists Bay Area local governments and residents in planning and preparing for earthquakes through data, planning, policy, and implementation tools. Plan Bay Area 2050 proposes long-term strategies for minimizing damage from a major earthquake.
76 National Academies of Since, Engineering and Medicine. (1992). The Economic Consequences of a Catastrophic Earthquake. https://nap.nationalacademies.org/catalog/2027/the-economic-consequences-of-a-catastrophicearthquake-proceedings-of-a 77 California Seismic Safety Commission. (1999). Earthquake Risk Management: A Toolkit for Decision-Makers. https://ssc.ca.gov/wp-content/uploads/sites/9/2020/08/ssc_1999-04_risk_toolkit.pdf 78 U.S. Geological Survey. (2021, October). They HayWired Earthquake Scenario. https://pubs.usgs.gov/fs/2021/3054/fs20213054.pdf
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 118
It aims to provide means-based financial support for the retrofit of existing residential buildings. These investments would ensure higher seismic standards to protect residents, especially those with lowincome, from earthquakes.

7.7 Scenario
With the abundance of fault exposure in the Bay Area, the potential scenarios for earthquake activity are many. An earthquake does not have to occur within the OA to have a significant impact on the people, property, and economy of the OA. In 2018, the USGS in partnership with the Southern California Earthquake Center shared hypothetical earthquake scenario known as the HayWired Earthquake Scenario which imagined a M7.0 earthquake centered in Oakland, California rupturing the Hayward fault along its length for about 52 miles. In this scenario, the entire OA would experience ground shaking and severe impacts. A screenshot from the computer simulation of the earthquake shows the region that would be impacted in Figure 30.

If this type of event were to occur, there would be significant impacts through the OA, region, and nation.

More than a million Bay Area homes would be impacted.78F 79 Potential warning systems would be able to
provide mere seconds or tens of seconds of warning time. This would not provide adequate time for preparation. There would be immediate need for first responder assistance. Many thousands of people could be stranded in elevators or under debris. Models predict hundreds of deaths and thousands of injuries. There would be massive structural failure of property on NEHRP C, D, E, and F soils. Levees and revetments built on these poor soils would likely fail, representing a loss of critical infrastructure. Fires could be started and, in worse case scenarios, turn into to firestorms, devastating urban areas. Electricity may not return for days. Water restoration may take up to a month. Many homes, particularly those built to older building code standards, would be considered unsafe to return to. Tens of thousands of households could be displaced. Aftershocks would continue to rock the area, causing more damage than the main shock in communities like Palo Alto.79F
80 Aftershocks would be felt for months to years after the earthquake event. Cascading impacts, like landslides and mudslides, could further damage structures.

River valley hydraulic-fill sediment areas are also vulnerable to slope failure, often as a result of loss of cohesion in clay-rich soils. Soil liquefaction would occur in water-saturated sands, silts, or gravelly soils.

The long-term impacts of an earthquake like this would be enormous. The estimated financial loss to residential, commercial, and infrastructure would be over $100 billion around the Bay Area. 79 California Earthquake Authority. (2020, July 8). What to Expect from an Earthquake along the Hayward Fault. https://www.earthquakeauthority.com/Blog/2019/hayward-fault-earthquake-prediction 80 U.S. Geological Survey. (2018). The HayWired Scenario: An Urban Earthquake in a Connected World. https://geonarrative.usgs.gov/haywired_vol1/#:~:text=The%20U.S.%20Geological%20Survey%20%28USGS%29%2 0HayWired%20scenario%20considers,fact%2C%20the%20HayWired%20earthquake%20will%20probably%20never %20occur.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 119
Figure 31: Hayward Fault Earthquake Scenario80F
81 7.8 Issues
Important issues associated with an earthquake include the following:
 More quantitative information is needed on the exposure and performance of soft-story construction within the OA.
 Approximately 29 percent of the OA’s building stock was built prior to 1975, when seismic provisions became uniformly applied through building code applications.  Based on the modeling of critical facility performance performed for this plan, a portion of facilities in the OA is expected to have complete or extensive damage from scenario events. These facilities are prime targets for structural retrofits.
 Critical facility owners should be encouraged to create or enhance continuity of operations plans using the information on risk and vulnerability contained in this plan.  Geotechnical standards should be established that consider the probable impacts from earthquakes in the design and construction of new or enhanced facilities.  There are a large number of high risk dams within the OA. Dam failure warning and evacuation plans and procedures should be reviewed and updated to reflect the dams’ risk potential associated with earthquake activity in the region.
81 U.S. Geological Survey. (2018, January 18). HayWired Scenario. https://www.usgs.gov/programs/scienceapplication-for-risk-reduction/science/haywiredscenario#:~:text=The%20HayWired%20earthquake%20scenario%20is%20a%20magnitude%207.0,Ma%20By%20Ea rthquake%20Hazards%20Program%20June%2016%2C%202020
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 120
 Earthquakes could trigger other natural hazard events such as liquefaction, dam failures and landslides, and fire which could severely impact the OA.  A worst-case scenario would be the occurrence of a large seismic event during a flood or highwater event. Levee failures would happen at multiple locations, increasing the impacts of the individual events.
 Citizens are expected to be self-sufficient up to 3 days after a major earthquake without government response agencies, utilities, private-sector services, and infrastructure components.

Education programs are currently in place to facilitate development of individual, family, neighborhood, and business earthquake preparedness. Government alone can never make this region fully prepared. It takes individuals, families, and communities working in concert with one another to truly be prepared for disaster.
 After a major seismic event, the Santa Clara County Operational Area is likely to experience disruptions in the flow of goods and services resulting from the destruction of major transportation infrastructure across the broader region.
 The Santa Clara County OA is home to multiple tech centers that provide goods and services to the nation and world. A major earthquake in the region would disrupt these service providers and severely impact the economic and functional stability of the region and potentially the country.

Table 40: EMAP Consequence Analysis: Earthquake
Subject Ranking Impacts/Earthquake
Public Minimal to
severe
Depending on the size and location of the earthquake, the public may be at significant risk from an earthquake event.

They could sustain injuries from falls, collapsing building, fall items, and damaged utilities, as well as any number of cascading impacts. Loss of life is possible. There could be significant disruption to normal life following an event.

People with disabilities and access/functional needs, as well as other diverse characteristics that may impact their ability to respond and recover from an event, will need additional assistance.

Responders Minimal to
severe
First responders would be relied upon during the
aftermath of an earthquake and potentially exposed to
increased risk of injury and loss of life, particularly from aftershocks.

Continuity of
Operations (including
continue delivery of
services)
Minimal to
severe
Earthquakes can damage buildings, roads, utilities, and other critical infrastructure necessary for normal
operations. Government facilities may be impacted.

Records and systems may be damaged or destroyed.

Damages may take a long time to repair. Delivery of
services may be disrupted.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 7: Earthquakes 121
Subject Ranking Impacts/Earthquake
Property, Facilities, and
Infrastructure
Minimal to
severe
Depending on the location and magnitude of the
earthquake, buildings be damaged or destroyed; bridges, highways, dams, and other public infrastructure may fail; utilities would be interrupted; and community lifelines would be impacted. There would be debris to clean-up.

There may be additional cascading impacts, like
landslides, tsunamis, fires, or dam failures which
compound the event. Medical facilities, mass-care
shelters, and essential food and water supply chains
would be critical to quickly restore post-event.

Environment  Minimal to
severe
Earthquake-caused cascading impacts could negatively
impact the environment. Landslides, tsunamis, fires, and dam failures can occur after an earthquake. Disruption to waterways, such as through rerouting streams and debris, could possibly damage habitat and feeding areas.

Hazardous materials release would be a serious concern.

Economic Conditions Minimal to
severe
Impacts to the economy will largely depend on the amount of damage and destruction to facilities, infrastructure, and transportation lifelines. Major damage or significant delays in recovery could severely impact the local, state, national, and even global economy.

Public Confidence in
the Government
Minimal to
severe
The public’s confidence in the government will depend on how it handles response and recovery efforts to the event.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 122
8 Wildfire
Definitions
 Interface Area: An area susceptible to wildfires and where wildland vegetation and urban or suburban development occur together. An example would be smaller urban areas and dispersed rural housing in forested areas.
 Wildfire: Fires that result in uncontrolled destruction of forests, brush, field crops, grasslands, and real and personal property in non-urban areas. Because of their distance from firefighting resources, they can be difficult to contain and can cause a great deal of destruction.

8.1 General Background
A wildfire is any uncontrolled fire occurring on undeveloped land that requires fire suppression. Wildfires can be ignited by lightning or by human activity such as smoking, campfires, equipment use, sparks from power lines, and arson.

Fire hazards present a considerable risk to vegetation and wildlife habitats. Short-term loss caused by a wildfire can include the destruction of timber, wildlife habitat, scenic vistas, and watersheds. Long-term effects include smaller timber harvests, reduced access to affected recreational areas, and destruction of cultural and economic resources and community infrastructure. The potential for significant damage to life and property exists in areas designated as “wildland urban interface areas,” where development is adjacent to densely vegetated areas.

There are a few different types of wildfires:
 Ground Fires: Fires that burn when surface fuels, such as organic soils, duff, decomposing litter, buried logs, roots, and the below-surface portion of stumps ignite and burn under the ground.

Ground fires may eventually burn through the ground surface and become surface fires.  Surface Fires: Fires that burn on the surface of the ground and are primarily fueled by low-lying vegetation such as leaf and needle litter, dead branch material, downed logs, bark, trees bones, and low statute living plants.
 Ladder Fuels: Dead or live vegetation such as low-lying tree branches, shrubs, and trees under the tree canopy that allows an active fire to spread from the forest floor into the tree canopy to become crown fires.
 Crown Fires: Fires that spread from treetop to treetop, typically at a rapid pace. They are often pushed by wind and can become extremely intense and difficult to put out.  Spotting Fires: Fires that involve burning embers which are thrown ahead of the main fire. This type of fire can be produced by crown fires depending on wind and topography. Once they begin, spotting fires are difficult to control.

The Santa Clara County Community Wildfire Protection Plan was used to inform parts of this risk assessment and can be accessed for an in-depth look at the County’s wildfire risk and other supporting data. The plan can be found online with the following link:
https://www.sccfd.org/santa-clara-county-community-wildfire-protection-plan/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 123

8.2 Hazard Profile

8.2.1 Past Events
Wildfire poses a significant risk to public health and safety, economies, infrastructure, and irreplaceable cultural and natural resources within the OA.81F
82 Wildfire is an annual risk in Santa Clara County.82F83 The following are wildfires of over 10 acres that have been recorded in or near the OA before February 2023.83F
84 Table 41: Past Wildfire Events
Event Name
Event Period
Additional Information
From To
Lexington Fire 6/26/1985 7/19/1985 FEMA-739-DR-CA. This federal wildfire disaster included six counties. In Santa Clara County, the worst of the fires affected the Santa Cruz Mountains south of the City of San José, threatening at least 2,000 homes
and forcing the evacuation of more than 4,500
people.84 F
85 Felter Fire 10/25/2006 10/26/2006 Burned 200 acres.

Stevens Fire 8/30/2007 9/2/2007 Burned 151 acres near Stevens Canyon Reservoir.

Lick Fire 9/3/2011 9/11/2007 Burned 47,760 acres at Henry Coe State Park, with four residences and 20 outbuildings destroyed.

Summit Fire 5/22/2008 5/30/2008 FEMA-2766-FM-CA. Burned 4,270 acres along with 35 residences, 64 outbuildings at Summit Road and
Maymen Flats, south of the Town of Loma Prieta.

Whitehurst/
Hummingbird
Fires
6/21/2008 6/26/2008 Burned 794 acres at Hummingbird and 200 acres at Whitehurst.

Pacheco Fire 8/29/2009 8/30/2009 Burned 1,650 acres.

Croy Fire 9/23/2002 10/5/2002 FM-2465. Burned 13,128 acres.

McDonald Fire 7/21/2011 7/21/2011 Burned 27 acres east of the City of Morgan Hill below Anderson Lake.

Uvas Fire 7/12/2013 7/12/2013 Burned 50 acres along Uvas Road and Casa Loma Road, near Calero County Park and west of the City of
Morgan Hill.

Grant Fire 12/31/2013 12/31/2013 Burned 40 acres off Mount Hamilton Road near Grant Ranch County Park.
82 Santa Clara County Fire Department. (2016, August). Santa Clara Community Wildfire Protection Plan. https://www.sccfd.org/santa-clara-county-community-wildfire-protection-plan/ 83 County of Santa Clara. (2012). Silicon Valley 2.0. https://sustainability.sccgov.org/silicon-valley-20 84 State of California. (2023). California Department of Forestry and Fire Protection. https://www.fire.ca.gov/ 85 Los Angeles Times. (1985, July 10). Fire Imperils 2,000 Homes Near San José. https://www.latimes.com/archives/la-xpm-1985-07-10-mn-7612-story.html Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 124
Event Name
Event Period
Additional Information
From To
Curie Fire 6/30/2014 7/1/2014 Burned 125 acres off Curie Drive south of the City of San José.

Casa Fire 8/28/2014 8/31/2014 Burned 80 acres along Highway 152 at Casa De Fruta.

Highway Fire 6/30/2015 7/3/2015 Burned 42 acres off Highway 101 near Monterey Frontage Road, south of the City of Gilroy.

Pacheco Fire 9/9/2015 9/10/2015 Burned 215 acres off Highway 152 at Dinosaur Point, three miles west of San Luis Reservoir.

Sierra Fire 7/30/2016 7/31/2016 Burned 114 acres off Sierra Road and Calaveras Road.

Bailey Fire 8/17/2016 8/18/2016 Burned 100 acres off Highway 101 and Bailey Road.

Oak Fire 9/1/2016 9/2/2016 Burned 25 acres off Oak Glen Avenue, two miles west of the City of Morgan Hill.

Loma Fire 9/26/2016 10/12/2016 Burned 4,474 acres and destroyed 12 residences and 16 outbuildings off Loma Prieta Road and Loma
Chiquita Road, 10 miles northwest of the City of
Morgan Hill.

Quimby Fire 6/21/2017 6/21/2017 Burned 54 acres off Quimby Road, west of Great Ranch Park, East San José.

Ranch Fire 6/29/2017 6/29/2017 Burned 85 acres off Grant Road, Mt. Hamilton, east of the City of San José.

Felipe Fire 7/10/2017 7/10/2017 Burned 70 acres by San Felipe Road and Metcalf Road, 8 miles northeast of City of Morgan Hill.

Lariat Fire 7/11/2017 7/11/2017 Burned 101 acres along Lariat Lane and Claitor Way, six miles northeast of the City of San José.

Castro Fire 7/23/2017 7/23/2017 Burned 78 acres off Castro Valley Road & Highway 101, southwest of the City of Gilroy.

Weller Fire 7/26/2017 7/26/2017 Burned 51 acres along Weller Road and Calaveras Road, three miles east of the City of Milpitas.

Tilton Fire 8/11/2017 8/11/2017 Burned 100 acres by Hale Avenue and Tilton Avenue in the City of Morgan Hill.

Bally Fire 9/3/2017 9/3/2017 Burned 100 acres by Ballybunion Court in the City of Gilroy.

Keeler Fire 5/27/2018 5/27/2018 Burned 16 acres by Keeler Court and Santa Teresa Boulevard, south of the City of San José.

Tesla Fire 6/29/2018 6/29/2018 Burned 70 acres across Tesla Road and Reuss Road, east of the City of Livermore.

Bridle Fire 7/6/2018 7/6/2018 Burned 116 acres off Bridal Path Drive and Butch Drive, east of the City of Gilroy.

Curie Fire 7/10/2018 7/10/2018 Burned 70 acres by Curie Drive and San Ignacio Avenue, southwest of San José.

Hale Fire 7/10/2019 7/10/2019 Burned 51 acres at Hale Avenue and Monterey Street in the City of Morgan Hill.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 125
Event Name
Event Period
Additional Information
From To
Country Fire 7/22/2018 7/22/2018 Burned 320 acres along Country Club Road and North Park Victoria Road in the City of Milpitas.

Quimby Fire 9/23/2018 9/23/2018 Burned 30 acres by Quimby Road and Borden Drive, East San José.

Park Fire 10/7/2018 10/7/2018 Burned 62 acres along Monterey Road and Coyote Creek Golf Drive, north of the City of Morgan Hill.

Canyon Fire 5/30/2019 6/11/2019 Burned 144 acres off Del Puerto Canyon Road and Diablo Grande Parkway, west of the City of Patterson.

Malech Fire 6/9/2019 6/11/2019 Burned 210 acres by Malech Road & Bailey Road, South San José.

Calaveras Fire 6/10/2019 6/17/2019 Burned 35 acres by Calaveras Road and Weller Road east of the City of Milpitas.

Mines Fire 6/26/2019 6/27/2019 Burned 17 acres by Mines Road and Turner Gulch in the San Antonio Valley.

Coyote Fire 7/2/2019 7/2/2019 Burned 74 acres by Northbound US 101 at Coyote Creek Golf Drive in the City of San José.

Aborn Fire 7/15/2019 7/15/2019 Burned 47 acres off Aborn Road and Murillo Avenue, East San José.

Sweigert Fire 7/24/2019 7/24/2019 Burned 80 acres off Kahler Court and Felter Road, East of the City of Milpitas.

Bayliss Fire 8/15/2019 8/15/2019 Burned 60 acres by Santa Teresa Boulevard and Bayless Drive, South San José.

Jamieson Fire 8/25/2019 8/25/2019 Burned 35 acres at Jamieson Road and Cañada Road near the City of Gilroy.

Reservoir Fire 9/21/2019 9/24/2019 Burned 128 acres near Calaveras Road and Felter Road, 5 miles northeast of the City of Milpitas.

Point Fire 10/7/2019 10/7/2019 Burned 29 acres between Highway 152 and Dinosaur Point Road.

Santa Clara Unit
(SCU) Lightning
Complex Fire
8/16/2020 10/1/2020 Burned 396,624 acres between Santa Clara County, Alameda County, Contra Costa County, San Joaquin
County, Merced County, and Stanislaus County.

Silver Fire 6/4/2020 6/4/2020 Burned 19 acres by Dutch Flat Trail, East of the City of San José.

Colleen Fire 6/4/2020 6/7/2020 Burned 126 acres around Colleen Drive, South San José.

Park Fire 7/4/2020 7/6/2020 Burned 353 acres by East Dunne Avenue and Finley Ridge Road, east of the City of Morgan Hill.

Crews Fire 7/5/2020 7/13/2020 Burned 5,513 acres by Crews Road and Oak Spring Circle, north of the City of Gilroy.

Alum Fire 7/11/2020 7/11/2020 Burned 31 acres by Mt. Hamilton and Crothers Road, northeast of the City of San José.

Coyote Fire 8/21/2020 8/26/2020 Burned 143 acres by Monterey Road and Coyote Creek Golf Drive.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 126
Event Name
Event Period
Additional Information
From To
Silicon Valley
Fire
6/14/2021 6/14/2021 Burned 35 acres by off Silicon Valley Road and Basking Ridge, East San José.

Paseo Fire 6/25/2021 6/25/2021 Burned 37 acres by Paseo Robles Avenue and Paseo Vista Avenue, east of the City of Morgan Hill.

The 2020 fire season was the largest wildfire season recorded in California’s modern history. It was also the most devastating in recent Santa Clara County history. One fire significantly outpaced the rest. The SCU Lightning Complex fire started as a series of almost twenty fires on August 16, 2020, and burned until October 1, 2020, engulfing 396,624 acres five counties. At least 26 structures were damaged and 225 destroyed. There were 6 confirmed injuries to fire personnel and civilians and no deaths. As of this writing, it was the fourth largest fire in California’s recorded history.

8.2.2 Location
Wildfires occur in two distinct spaces: wildlands, and the Wildland Urban Interface (WUI). Wildland fires that burn in natural, undeveloped settings actually benefit the landscape through cleaning the forest floor from heavy brush, killing disease, providing food and habitat to forest animals and birds in the new vegetation that grows, and supporting new generations of plants that require intense heat for seed germination.

According to the U.S. Fire Administration,85F
86 the WUI is the zone of transition between occupied land and human development. It is the line, area, or zone where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels. The WUI possess unique wildfire risks as fire can easily move between structural and vegetative fuels. The WUI has seen exponential growth in recent years. It is vital that WUI communities continue to work to address the WUI wildfire issue.

Figure 32: Air Tanker Dropping Fire Retardant on Lick Fire in Santa Clara County86F 87 Fire-prone areas in California are divided into three categories: federal responsibility areas, state responsibility areas, and local responsibility areas. The California Department of Forestry and Fire Protection (CAL FIRE) has responsibly for fire prevention and firefighting services within the state 86 U.S. Fire Administration. (2022). What is the WUI? https://www.usfa.fema.gov/wui/what-is-the-wui.html 87 Schulz, W. (n.d.). Air tanker dropping fire retardant on Lick Fire in Santa Clara County [Photograph]. California Department of Forestry and Fire Protection, California.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 127
responsibility areas, while local agencies have local responsibility areas, and the U.S. Forest Service has fire-related responsibilities in the federal responsibility areas.

CAL FIRE’s Fire and Resource Assessment Program has modeled and mapped fire hazard risk using a science-based and field-tested model that assigns a hazard score based on factors that influence fire likelihood and fire behavior such as fire history, existing and potential fuel (natural vegetation), predicted flame length, blowing embers, terrain, and typical fire weather for an area. These factors include the following:
 Fuel: Fuel may include living and dead vegetation on the ground, along the surface as brush and small trees, and above the ground in tree canopies. Lighter fuels such as grasses, leaves and needles quickly expel moisture and burn rapidly, while heavier fuels such as tree branches, logs and trunks take longer to warm and ignite. Trees killed or defoliated by forest insects and diseases are more susceptible to wildfire.
 Weather: Relevant weather conditions include temperature, relative humidity, wind speed and direction, cloud cover, precipitation amount and duration, and the stability of the atmosphere. Of particular importance for wildfire activity are wind and thunderstorms:
▪ Strong, dry winds produce extreme fire conditions. Such winds generally reach peak velocities during the night and early morning hours. It accounts for flying ember production, which is the principal driver of the wildfire hazard in densely developed areas. ▪ The thunderstorm season typically begins in June with wet storms and turns dry with little or no precipitation reaching the ground as the season progresses into July and August. Traditionally, this “fire season” between July and November would be when the State sees the most wildfires. However, according to the 2018 Strategic Fire Plan, climate change has rendered that term obsolete, as fires now burn year-round.  Terrain: Topography includes slope and elevation. The topography of a region influences the amount and moisture of fuel; the impact of weather conditions such as temperature and wind; potential barriers to fire spread, such as highways and lakes; and elevation and slope of landforms (fire spreads more easily uphill than downhill).  Probability of Future Occurrence: The likelihood of an area burning over a 30- to 50-year time period, based on history and other factors.

Fire Hazard Severity Zones (FHSZ) are ranked into the following risk classifications: moderate, high, or very high. The model covers the State Responsibility Area (SRA), which is the land where the State of California is financially responsible for the prevention and suppression of wildfires. It does not include lands within incorporated city boundaries or in federal ownership.

Significant land-use changes need to be accounted for through periodic model updates. The Wildfire Hazard Severity Zone Map87 F
88 was updated in 2007, and since updated in 2023 to reflect all that has happened in terms of scientific data, a changing climate, and other factors. The new model incorporates local climate data and changes in burn probability based on recent trends in fire occurrence. Overall, the map shows increase fire hazard, reflecting the State’s increase in wildfire occurrence and severity. It is important CAL FIRE continues to maintain these maps in order to build more resilient, fire-adapted communities. GIS data of the 2023 update was not yet released to include in the maps for this plan. The FHSZs shown throughout use the 2007 data.

Figure 32 shows the FHSZ mapping for the Santa Clara County OA. 88 State of California. (2023). Fire Hazard Severity Zones Map. https://osfm.fire.ca.gov/divisions/community-wildfirepreparedness-and-mitigation/wildfire-preparedness/fire-hazard-severity-zones/fire-hazard-severity-zones-map/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 128
Figure 33: Fire Hazard Severity Zones (FSHZ)
Typically, wildfires will occur anywhere in the County outside of the urbanized Highway 101 corridor and Santa Clara Valley. In general, the areas with the highest fire risk hazard are found in the parts of the OA farthest from urbanized areas, including along the border with Stanislaus and Santa Cruz Counties.

However, there are also Very High FHSZs near urban areas, including south of Los Gatos, west of Saratoga, west of Morgan Hill, and west of Gilroy.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 129
Wildfires are not also limited to Very High risk areas and can occur in Moderate or High FHSZs. The Santa Clara County General Plan8F
89 suggests much of Santa Clara County is at high risk to wildfires due to:
 Climatic factors, such as rainfall, humidity, and wind patterns;  Volume of naturally occurring fuel, such as brush, dead trees, and grasses that ignite easily and burn hotly;
 Steepness of slopes; and
 Inaccessibility and lack of available water supplies for fire suppression.

Additional information on wildfire hazard and risk to structures are available in the 2020 Santa Clara, Santa Cruz, San Mateo County Wildfire Risk to Structures and Classified Wildfire Hazard Maps.89F 90 The
classified wildfire hazard was calculated by 9 weighted input data sets that contribute to the potential for wildfire. These include fire environment factors such as fuel, weather, topography and ignition sources, the probability of a fire occurring at a specific point during a specific time period, and the expected distribution of intensity. This wildfire hazard model resulted in a 20-meter raster with 6 classes of relative wildfire hazards. Because this classified hazard data was of finer resolution and completed more recently, it was the primary source used to evaluate potential exposure and risk in the OA. 89 County of Santa Clara. (1994, December 20). General Plan. https://plandev.sccgov.org/ordinances-codes/generalplan 90 Santa Cruz Mountains Stewardship Network. (2020) Santa Clara, Santa Cruz, San Mateo County Wildfire Risk to Structures and Classified Wildfire Hazard Maps for Fire Prevention Planning.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 130
Figure 34: Classified Wildfire Hazard
 This hazard classification does not account for resources or assets exposed to the hazard.

Wildfire risk is the potential for adverse consequences to valued resources or assets. The Wildfire Risk to Structures map models risk by one value: structures. This map displays 10-acre hexagons ranked for wildfire hazard and structure density. Hexagons with high structure density and high wildfire hazard indicate areas of greatest concern.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 131
Figure 35: Wildfire Risk to Structures

8.2.3 Frequency
Wildfire frequency can be assessed through review of the portion of an area burned in previous wildfire events. Table 42 includes a summary of CAL FIRE records of fires from 1950 to 2021. About 39 percent of the mapped wildfire risk zones in the Santa Clara County OA have burned in that period.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 132
Table 42: Record of Fire Affecting Operational Area
Fire Hazard
Severity Zone
(FHSZ)
Total Area in
Wildfire Severity Zone
(acres)
Area Burned, 1950-2021
Acres Percent of Total
Moderate FHSZ 33,549 2,377 7.1
High FHSZ 372,517 119,693 32.1
Very High FHSZ 148,389 93,224 62.8
Total 554,455 215,295 38.8
The National Fire Plan directs funding to be provided for projects intended to reduce fire risks to a community. To meet this object, high risk communities within the wildland-urban interface were identified and publicized in the Federal Register in 2001. Since then, states have been responsible for updating this list. According to CAL FIRE’s list of Communities at Risk,90F 91 14 out of 15 local jurisdictions within Santa
Clara County are at high risk of damage from wildfire. The City of Mountain View is not included on this list. It is surrounded by urban development and the San Francisco Bay.

It is important to consider changing conditions when assessing the future probability of wildfires in the OA.

According to CAL FIRE,91F
92 over the last 5 years, 13 out the 20 most destructive wildfires in California’s history have occurred. Thousands of homes, business, and pieces of infrastructure were damaged or destroyed. This isn’t a new trend. Since the 1970s, the number of statewide fires has steadily been increasing. NASA’s Earth Observatory92F
93 summarized the causes of this surge of large, destructive of fires as; heat waves and droughts influenced by climate changed, a century of fire suppression, and fastgrowing populations expanding the WUI.

Despite recent storm and flooding events, the U.S. Drought Monitor indicates that most of California is still experiencing moderate to severe drought conditions. Santa Clara County is in a moderate drought and experienced the 35th driest year to date over the past 128 years in 2022. Drought leads to more severe, costly fires as it contributes to high burn intensity, the rate at which fire spreads, availability of dry fuels, and fires in typically wet parts of the state. When fuel is dry, sparks from both natural sources such as lightning and human sources like power lines, are more likely to ignite. Droughts can hamper first responder’s firefighting capabilities by reducing water reserves necessary to combat the blazes, resulting in longer lasting, wider spreading events.

According to California’s Fourth Climate Change Assessment,93F 94 the frequency of extreme wildfires may
increase, and the average area burned statewide may increase by 77% if greenhouse gas emissions continue to rise. Water resources, both in terms of rainfall and the availability of fuel for fires and water for fire suppression, also may be impacted by shifting water patterns due to climate change. 91 State of California. (n.d.). Communities at Risk. California Department of Forestry and Fire Protection. https://osfm.fire.ca.gov/divisions/community-wildfire-preparedness-and-mitigation/fire-plan/communities-at-risk/#c 92 State of California. (2023). California Department of Forestry and Fire Protection. https://www.fire.ca.gov/ 93 National Aeronautics and Space Administration Earth Observatory. (2021). What’s Behind California’s Surge of Large Fires? https://earthobservatory.nasa.gov/images/148908/whats-behind-californias-surge-of-large-fires 94 State of California. (2018). California’s Fourth Climate Change Assessment. https://climateassessment.ca.gov/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 133
Figure 36: Burned Hillslopes above Pulse Canyon near San Antonio Valley, SCU Lightning Complex, Santa Clara County94F
95 Changing fire management practices also impact fire risk. Early in the 20th century, fire fighters adopted practices of fire suppression, with few prescribed burns. That meant that vegetation which would have been thinned due to naturally occurring fires was allowed to become overgrown and dense. Now, decades later, the impacts of those practices are being felt. A new consensus is developing that proactive fuel treatment is critical to wildfire management.

Human behavior will also play a large role in predicting the future probability of wildfire. Human-caused fires, both accidental and arson, are the leading cause of wildfires in California. Education and outreach campaigns are important tools for reducing the risk of human-caused fires.

Further information on the impact of climate change on the probability of wildfire is included in Section 15, Tsunami.

Probability in OA: Highly Likely

8.2.4 Severity and Impacts
Potential losses from wildfire include human life, structures and other improvements, and natural resources. There are no recorded incidents of loss of life from wildfires in the OA. There have been multiple destructive wildfires in the OA destroying residences, burning thousands of acres, and forcing people to evacuate. Given the immediate response times to reported fires, the likelihood of injuries and casualties is minimal. Economic losses may also occur given the size and location of the fire event. The 95 Spangler, E. (2020). Burned hillslopes above Pulse Canyon [Photograph]. California Department of Conservation. https://www.conservation.ca.gov/cgs/landslides/recent
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extent of a wildfire can be moderate to severe and depends on the size, rate of spread, fuel type, cause, and impact on communities. The greater the extent, the more severe the wildfire will be.

The Santa Clara County CWPP states that high fire danger conditions that can support very active fire behavior may be uncommon, but when it does occur, it can have very severe and destructive potential.

Instances such as the 1985 Lexington fire burned 37 homes, 4,200 acres, and caused $7 million in damage. The 2009 Loma Pieta fire burned 669 acres, cost $2.7 million to suppress, involved 1,742 fire fighters, destroyed 1 residence, and caused 4 injuries. It is important to know while these cases are rare, the severity can be detrimental.

8.2.5 Warning Time
Wildfires are often caused by humans, intentionally or accidentally. Approximately 94% of wildfires in California are human caused.95F
96 There is no way to predict when one of these human-caused wildfires might break out. Dry seasons and droughts are factors that greatly increase fire likelihood. Dry lightning may trigger wildfires. Inclement weather can be predicted, so special attention can be paid during weather events that may include lightning. Reliable National Weather Service lightning warnings are available on average 24 to 48 hours prior to a significant electrical storm.

The National Weather Service alerts fire departments through Red Flag Warnings & Fire Weather Watches when there is critical weather and dry conditions that could lead to the development or rapid increase of wildfire activity. A Fire Weather Watch is issued when weather conditions could exist in the next 12–72 hours. A Red Flag Warning is the highest alert. It is important that all residents and visitors take step to prevent wildfires, particularly when either of these alerts are issued.

If a fire does break out and spread rapidly, residents may need to evacuate within hours or days. Once a fire has started, fire alerting is reasonably rapid in most cases. The rapid spread of cellular phone and two-way radio communications in recent years has further contributed to a significant improvement in warning time. Recent wildfires have put these warning systems to the test. Rapidly spreading severe California wildfires has left residents with only minutes to evacuate in some cases.

8.3 Cascading Impacts
Wildfires can have a range of cascading impacts, which in some cases may cause more widespread and prolonged damage than the fire itself. They strip slopes of vegetation, exposing them to greater amounts of runoff. This in turn can weaken soils and cause failures on slopes. Major landslides can occur several years after a wildfire. The following figure depicts the areas of the OA most at risk for landslides post wildfire:
96 State of California. (2023). California Department of Forestry and Fire Protection. https://www.fire.ca.gov/.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 135
Figure 37: Post Fire Soil Erosion Potential
Wildfires cause the contamination of reservoirs, destroy transmission lines, and contribute to flooding.

Most wildfires burn hot and for long durations which can bake soils, especially those high in clay content, thus increasing the imperviousness of the ground. This increases the runoff generated by storm events, thereby increasing the chance of flooding. Flash floods are particularly common after a wildfire. Even areas that are not traditional at high-risk to flooding can flood due to changes in the landscape post-fire.96F 97 Flooding and flood damage after fire is often more severe, as debris and ash left from the fire can form mudflows. As rainwater moves across charred and barren ground, it can also pick up soil and sediment and carry it in a stream of floodwaters. Impacts to the watershed can be felt for years after a wildfire. 97 Federal Emergency Management Agency. (2020, November). FEMA Fact Sheet Flood after Fire: Flood Risks Increase after Fires. https://www.fema.gov/sites/default/files/documents/fema_flood-after-fire_factsheet_nov20.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 136
Fires can cause direct economic losses in the reduction of harvestable timber and indirect economic losses in reduced tourism. Cultural and historic resources, scenic vista, and recreational areas may burn.

Fire and smoke can reduce employee’s ability to go to work, decrease productivity, and delay outdoor projects. Adapting to these conditions will cost businesses, consumers, and governments.97F 98 Wildfires can
also affect personal and household economics through loss of income, increased medical costs, and property damage that may not be covered by insurance.

Wildlife can also be impacted by wildfires. After the historic wildfire seasons California has seen recently, there were increased sighting of animals such as mountain lions, raccoons, and coyotes in urban neighborhoods. Wildfires may be one reason why they are encroaching on urban areas, both putting urban populations at risk from these animals and exposing these animals to the risk humans present to them.

8.3.1 Smoke and Air Quality
Smoke exposure is one of the most concerning secondary impacts of wildfires. Smoke generated by wildfire consists of visible and invisible emissions that contain particulate matter (soot, tar, water vapor, and minerals), gases (carbon monoxide, carbon dioxide, nitrogen oxides), and toxics (formaldehyde, benzene). Emissions from wildfires depend on the type of fuel, the moisture content of the fuel, the efficiency (or temperature) of combustion, and the weather. The biggest threat from smoke is fine particles. Fine particles in smoke can get into eyes and respiratory systems, cause burning eyes, runny noses, and illness like bronchitis, as well as aggravate chronic heart and lung disease potentially resulting in premature death for people with these conditions.98F 99 The inhalation of wildfire smoke can harm many
and become fatal. Wildfire smoke is known to be even more dangerous than wildfire flames and burns.

Wildfire smoke is rolling back decades of investments in improving air quality in the U.S. Over the last decade, the estimated amount of each individual’s exposure to light, medium, and heavy wildfire smoke has gone up.9F
100 The rapid acceleration of poor air quality days and number of people exposed is particularly concerning. One study found a 27% increase in people annually exposed to a particle pollution known as PM2.5 – an increase from less than half a million people only a decade ago to over eight million exposed on at least one day a year ago now10F 101. Smoke does not recognize jurisdictional
boundaries. The impact of this hazard can be felt far from its source. Wildfires started outside of the OA, from northern California to Oregon, have brought smoke to the Bay Area in recent years.

Severe smoke events are expected to only get worse as climate change increases the frequency and severity of wildfires. This poses a chance to exasperate already challenging air quality issues. According to the American Lung Association’s 2023 State of the Air report, Santa Clara County received a grade of “F”. An estimated almost 1.9 million people within the OA are considered to be at risk from poor air quality. While wildfires are certainly not the only source of air pollution, the increase in wildfire smoke in recent years has still demonstrated the serious impact of poor air quality across sectors. 98 Lappe, B. & Vargo, J. (2022, November). Disruptions from Wildfire Smoke: Vulnerabilities in Local Economies and Disadvantaged Communities in the U.S. Federal Reserve Bank of San Francisco. https://www.frbsf.org/communitydevelopment/publications/community-development-research-briefs/2022/november/disruptions-from-wildfire-smoke/ 99 Environmental Protection Agency. (2021, June 16). Wildfires and Indoor Air Quality (IAQ). https://www.epa.gov/indoor-air-quality-iaq/wildfires-and-indoor-air-quality-iaq 100 Lappe, B. & Vargo, J. (2022, November). Disruptions from Wildfire Smoke: Vulnerabilities in Local Economies and Disadvantaged Communities in the U.S. Federal Reserve Bank of San Francisco. https://www.frbsf.org/communitydevelopment/publications/community-development-research-briefs/2022/november/disruptions-from-wildfire-smoke/ 101 Garthwaite, J. (2022, September). Stanford researchers find wildfire smoke is unraveling decades of air quality gains, exposing millions of Americans to extreme pollution levels. Wildfire smoke is unraveling decades of air quality gains | Stanford News
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Smoke and poor air quality disproportionately impacts vulnerable populations and frontline workers (those in outdoor occupations typically without air filtration). The most vulnerable to smoke’s impacts include the elderly, children, people with pre-existing conditions including respiratory and cardiovascular diseases, communities of color, and low-income populations. One of the most common pieces of advice to people during a severe smoke event is to stay indoors. However, particularly in inadequate housing situations or when people do not have the means to evacuate, simply staying indoors is not sufficient considering how smoke can infiltrates buildings through windows and doors, vents, air conditioning, and small cracks or other openings. Additional measures such as clean air centers, masks, and air purifiers may be required.

Smoke is as disruptive as it is deadly. Exposure to air pollution by children can reduce lung growth, inhibit brain development, and increase the risk of health conditions like asthma.10F 102 Children’s education can
also be disrupted, resulting in decreased test scores and educational attainment. Although these impacts may be hard to quantify now, it is likely those exposed will be experiencing them for years to come. The economy is also impacted through decrease labor income, employment, and labor force participation.

Wildfire smoke reduced earnings across the country by an estimated $125 billion a year between 2007 and 2019.102F
103

8.4 Exposure

8.4.1 Population
Population could not be examined by wildfire hazard classification because the boundaries of census block groups do not coincide with the zone boundaries. However, population was estimated using the residential building count in the areas of moderate to high hazard and multiplying by the 2017-2021 US Census Bureau average population per household for Santa Clara County. Table 43 presents the results.

Hazus 6.0 demographic data indicates that 260,705 persons or 13.5 percent of the population in the OA are over 64 years old, and 422,719 persons or 21.8 percent of the population within the OA under 18 years of age. These ages groups may experience worse affects from poor air quality resulting from a wildfire. They may also have a greater dependency on assistance from others in the event of an evacuation.
102 United Nations Environment Programme. (October 2018). Young and old, air pollution affects the most vulnerable.

Young and old, air pollution affects the most vulnerable (unep.org) 103 Stanford Institute for Economic Policy Research. (December 2022). Wildfires reveal the large toll of air pollution on labor market outcomes. Wildfires reveal the large toll of air pollution on labor market outcomes | Stanford Institute for Economic Policy Research (SIEPR)
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Table 43: Population Within Wildfire Hazard Areas
Jurisdiction
Number of Buildings in Wildfire Hazard Area Population in Wildfire Hazard Area Residential Public Industrial Commercial
Total
Number of
Buildings
Population % of Total
Population
Campbell 83 1 1 0 85 247 0.57
Cupertino 2,116 4 5 42 2,167 6,306 10.40
Gilroy 4,426 7 40 109 4,582 13,189 22.18
Los Altos 1,019 7 10 31 1,067 3,037 9.55
Los Altos Hills 2,305 5 20 65 2,395 6,869 81.27
Los Gatos 2,789 9 23 87 2,908 8,311 24.79
Milpitas 1,401 2 17 36 1,456 4,175 5.20
Monte Sereno 535 0 2 13 550 1,594 46.21
Morgan Hill 5,237 17 56 167 5,477 15,606 34.65
Mountain View 318 1 1 30 350 948 1.15
Palo Alto 574 3 4 23 604 1,711 2.50
San José 15,507 44 118 453 16,122 46,211 4.56
Santa Clara (city) 109 0 0 4 113 325 0.25
Saratoga 2,823 7 33 96 2,959 8,413 27.10
Sunnyvale 348 2 6 10 366 1,037 0.67
Unincorporated
County 10,913 66 242 664 11,885 32,521 36.03
Total 50,503 175 578 1830 53,086 150,499 7.78
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 139

8.4.2 Property
Property damage from wildfires can significantly alter entire communities. The number of structures in each FHSZ within the OA and their values are summarized in Table 44. Table 45 shows the general land use of parcels exposed to the wildfire hazard in unincorporated areas of the OA. According to the Santa Clara County CWPP, there are 107 properties and districts listed on the National Register of Historic Places in Santa Clara County. Many of these sites are urban, but some are within the WUI. The Lick Observatory is one such place of historic and cultural significant which was almost burned due to a recent wildfire.

Table 44: Exposure and Value of Structures in Moderate to High Wildfire Hazard Areas Jurisdiction Buildings
Exposed
Value Exposed % of Total
Replacement
Structure Contents Vehicle Value
Campbell 85 $26,018,757.17 $13,518,215 $2,718,000 0.37
Cupertino 2,167 $851,005,863 $433,722,243 $66,474,000 8.17 Gilroy 4,582 $1,915,907,959 $1,063,212,359 $137,916,000 22.02 Los Altos 1,067 $443,693,069 $241,831,582 $30,906,000 8.56 Los Altos Hills 2,395 $1,234,211,033 $654,595,360 $67,059,000 71.11 Los Gatos 2,908 $1,310,513,983 $712,187,966 $93,780,000 19.75 Milpitas 1,456 $513,489,424 $279,091,477 $44,361,000 4.02 Monte Sereno 550 $269,260,704 $137,202,957 $15,273,000 43.58 Morgan Hill 5,477 $2,273,625,913 $1,266,973,143 $179,847,000 29.65 Mountain View 350 $114,334,578 $63,331,824 $14,103,000 0.88 Palo Alto 604 $319,419,553 $166,253,134 $25,092,000 2.26 San José 16,122 $6,080,110,863 $3,333,308,139 $487,431,000 4.77 Santa Clara
(city) 113 $34,986,342 $17,821,587 $3,978,000 0.16
Saratoga 2,959 $1,347,146,278 $736,302,667 $86,508,000 26.01 Sunnyvale 366 $116,046,797 $65,337,581 $15,030,000 0.53 Unincorporated
County 11,885 $5,720,386,230 $3,403,867,991 $444,906,000 44.35 Total 53,086 $22,570,157,353 $12,588,558,231 $1,715,382,000 8.14 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 140
Table 45: Land Within the Wildfire Hazard Classification Areas Type of Land Use
Moderate
Hazard Zone
High
Hazard Zone
Very High
Hazard Zone
Area
(acres) % of total Area (acres) % of total Area (acres) % of total Campbell 7.8 0.2% 5.33 0.1% 0.69 0.0%
Cupertino 415.13 5.8% 262.34 3.6% 62.11 0.9%
Gilroy 1249.51 11.8% 1080.12 10.2% 117.51 1.1%
Los Altos 115.63 2.8% 44.83 1.1% 2.2 0.1%
Los Altos Hills 1491.83 25.7% 697.59 12.0% 38.52 0.7%
Los Gatos 929.39 12.5% 667.03 8.9% 139.32 1.9%
Milpitas 322.51 3.7% 303.12 3.5% 127.1 1.5%
Monte Sereno 142.96 13.8% 66.92 6.4% 3.56 0.3%
Morgan Hill 1131.79 13.7% 876.38 10.6% 249.36 3.0%
Mountain View 65.66 0.8% 49.97 0.6% 13.29 0.2%
Palo Alto 1246.27 7.5% 1180.12 7.1% 735.18 4.4%
San Jose 6722.21 5.8% 5036.3 4.4% 1951.14 1.7%
Santa Clara 40.39 0.3% 5.15 0.0% 0 0.0%
Saratoga 1269.79 15.5% 723.72 8.8% 71.02 0.9%
Sunnyvale 44.85 0.3% 30.79 0.2% 2.48 0.0%
Unincorporated 111,878.48 18.5% 144,629.2 24.0% 129,146.5 21.4% Total 127,074.2 15.2% 155,658.9 18.6% 132,660 15.9%

8.4.3 Critical Facilities and Infrastructure
Table 46 and Table 47 identify critical facilities exposed to the wildfire hazard in the OA. In the event of wildfire, there would likely be little damage to the majority of infrastructure. Most road and railroads would be without damage except in the worst scenarios. Power lines are the most at risk to wildfire because most are made of wood and susceptible to burning. In the event of a wildfire, pipelines could provide a source of fuel and lead to a catastrophic explosion.

The Santa Clara County Community Wildfire Protection Plan notes that there are many arterial roads and highways that are critical to transportation in the WUI. The transportation networks exposed to the WUI include Skyline/Highway 35, Summit Road, Junipero Serra Blvd/Foothill Expressway, Blossom Hill Road, Almaden Road, Old Monterey Highway, Page Mill Road, Stevens Canyon Road, Highway 9, Highway 17, Old Santa Cruz Highway, Watsonville Road, Hecker Pass/Highway 152 West, Pacheco Pass/Highway 152 East, and Mt. Hamilton Road/Highway 130.

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Table 46: Critical Facilities within Moderate to High Wildfire Hazard Areas Jurisdiction Essential
Facilities Transportation Utilities Hazardous Materials Community
Assets
Campbell 0 0 0 0 0
Cupertino 0 7 0 0 1
Gilroy 1 7 0 0 4
Los Altos 0 0 0 0 0
Los Altos Hills 0 8 0 0 1
Los Gatos 0 1 0 0 3
Milpitas 0 2 0 0 0
Monte Sereno 0 0 0 0 1
Morgan Hill 0 5 0 3 6
Mountain View 0 3 0 0 1
Palo Alto 0 1 0 0 6
San Jose 2 26 2 2 19
Santa Clara 0 1 0 0 2
Saratoga 1 9 0 0 2
Sunnyvale 0 0 0 0 0
Unincorporated 3 100 14 1 29
Total 7 170 16 6 75
Table 47: Critical Facilities Within 100 Meters of Moderate to High Wildfire Hazard Areas Jurisdiction Essential
Facilities Transportation Utilities Hazardous Materials Community
Assets
Campbell 1 7 0 0 2
Cupertino 2 11 0 0 8
Gilroy 12 29 2 2 7
Los Altos 7 6 0 0 6
Los Altos Hills 6 21 0 0 2
Los Gatos 11 25 0 0 7
Milpitas 4 24 0 0 13
Monte Sereno 0 1 0 0 1
Morgan Hill 16 14 1 5 10
Mountain View 2 26 0 2 7
Palo Alto 4 4 1 3 16
San Jose 62 207 8 19 91
Santa Clara 7 13 1 2 5
Saratoga 9 31 0 0 10
Sunnyvale 3 17 2 2 8
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 142
Jurisdiction Essential
Facilities Transportation Utilities Hazardous Materials Community
Assets
Unincorporated 28 177 16 2 37
Total 174 610 31 37 230
There are registered hazardous material containment sites in wildfire risk zones in the OA. During a wildfire, containers for these materials could rupture due to excessive heat and act as fuel for the fire, causing rapid spreading and escalating the fire to unmanageable levels. In addition, they could leak into surrounding areas, saturating soils and seeping into surface waters, and have a disastrous effect on the environment.

Although the risk assessment did not include any modeling to determine specific damage estimates for these facilities, it does indicate a large number of assets are exposed to wildfire hazard. There are a large number of essential facilities, transportation features, and other community assets within close proximity to high wildfire hazard classification areas. Structures may be exposed to damage directly from fire.

Additionally, utility services may be disrupted, particularly areas with above ground utility systems, some of which have been identified in the 2023 CWPP. Further evaluation may be needed to consider building construction materials, landscape conditions, road access, and defensible space to further determine their susceptibility to wildfire and where specific priority mitigation actions are needed.

8.4.4 Environment
Fire is a natural and critical ecosystem process in most terrestrial ecosystems, dictating in part the types, structure, and spatial extent of native vegetation. However, wildfires can cause severe environmental impacts:
 Soil Erosion: The protective covering provided by foliage and dead organic matter is removed, leaving the soil fully exposed to wind and water erosion. Accelerated soil erosion occurs, causing landslides and threatening aquatic habitats.
 Spread of Invasive Plant Species: Non-native woody plant species frequently invade burned areas. When weeds become established, they can dominate the plant cover over broad landscapes, and become difficult and costly to control.  Disease and Insect Infestations: Unless diseased or insect-infested trees are swiftly removed, infestations and disease can spread to healthy forests and private lands. Timely active management actions are needed to remove diseased or infested trees.  Destroyed Endangered Species Habitat: Catastrophic fires can have devastating consequences for endangered species.
 Soil Sterilization: Topsoil exposed to extreme heat can become water repellant, and soil nutrients may be lost. It can take decades or even centuries for ecosystems to recover from a fire.

Some fires burn so hot that they can sterilize the soil.  Damaged Fisheries: Critical fisheries can suffer from increased water temperatures, sedimentation, and changes in water quality.

Many ecosystems are adapted to historical patterns of fire occurrence. These patterns, called “fire regimes,” include temporal attributes (e.g., frequency and seasonality), spatial attributes (e.g., size and spatial complexity), and magnitude attributes (e.g., intensity and severity), each of which have ranges of natural variability. Ecosystem stability is threatened when any of the attributes for a given fire regime diverge from its range of natural variability.

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8.5 Vulnerability
There are significant assets, including structures, systems, populations, and community lifelines, vulnerable to wildfire in the OA. In particular, the communities of Gilroy, Los Altos Hills, Los Gatos, Monte Sereno, Morgan Hill, Saratoga, and the unincorporated county have substantial percentages of their area, population, and structural value within high risk areas.

Changes in conditions: Increase in Vulnerability
• Recent drought has impacted vegetation, tree mortality and other • CMRA data indicates an increase in the annual number of days without precipitation, an increase in the number of consecutive days without precipitation, and the number of days with high temperatures. These conditions can all contribute to greater wildfire risk. • Large wildfires occur throughout California, and poor air quality from smoke from wildfire in other portions of the state contribute to poor air quality in the OA. • These climate trends are ongoing and projected to continue. • Management of fire risk requires repetitive action to manage fuels and maintain defensible space.

Vulnerability will increase without ongoing management. • Many areas throughout the OA reside in foothill areas where roads may be narrow, be located on dead end spurs, or have long drive-times to fire response facilities, which may increase the difficulty of fire suppression near these structures. Residents bear some of the burden in maintaining vegetation near their homes to try and reduce the risk of fire. • Wildfire leads to an increased risk of debris flow in burned areas, with increases vulnerability to homes and roadways in foothills following a wildfire.

8.5.1 Population
There are no recorded incidents of loss of life from wildfires within the OA. Given the immediate response times to reported fires, the likelihood of injuries and casualties is minimal; therefore, injuries and casualties were not estimated for the wildfire hazard.

That is not to say that wildfires would not impact the OA population. If any OA residents were to be injured or killed by a wildfire, besides fire responders, it would most likely be a member of a vulnerable population. This includes people with limited mobility that required assistive devices like wheelchairs or medical oxygen, people with respiratory or other illnesses, people over 60, people with a communication barrier, migrant populations, people from low-income communities, and people without regular access to a vehicle they could use to evacuate. Wildfire may threaten the health and safety of those fighting the fires too. First responders are exposed to the dangers from the initial incident and after-effects from smoke inhalation and heat stroke.

Gilroy, Los Altos hills, Los Gatos, Monte Sereno, Morgan Hill, Saratoga all have a significant percentage of their population within or close to high wildfire risk areas. People residing in these areas are at higher risk to possible injury and also from being displaced from their homes if an evacuation is required.

The public is also exposed to the negative impacts of smoke. Public health impacts associated with wildfire include difficulty in breathing, odor, and reduction in visibility. Smoke and air pollution from wildfires can be a severe health hazard, especially for vulnerable populations, including children, the elderly, outdoor workers, and those with respiratory and cardiovascular diseases. The 2018 wildfires alone were estimated to have health costs in Santa Clara County over $1.5 billion.103F 104
104 Bay Area Council Economic institute. (November 2021). The True Cost of Wildfires Analyzing the Impact of Wildfires on the California Economy. BACEI_WildfireImpacts_Nov2021.pdf (bayareaeconomy.org) Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 144
Commuters may also be impacted. Wildfires around the Bay Area may cause route/commuter delays or disruption due to closed roadways. Some drivers may have to stay home during poor air quality days, particularly if they are part of vulnerable population including people with lung diseases such as asthma and chronic obstructive pulmonary disease, adults over 65, people with cardiovascular disaster, people who smoke, and people in poverty who lack access to healthcare.

Additionally, the California Department of Public Health104F 105 recognizes the potential negative impact of
wildfires on mental health. The stress of coping with the loss of a home, personal items, pets, livestock, and other traumatic events can trigger mood swings, sleep disruption, and cause extreme nervous tension and/or depression. Children may find it particularly challenging to cope with losses caused by wildfire and present symptoms adults may not initially recognize as a sign of this stress. A comprehensive review of mental health and fire literature found that there was increased cases of PTSD, depression, anxiety, and substance use post-fire both in short-term and long-term studies. The impacts to the populations’ mental health should be considered when evaluating the benefits and costs of alternative mitigation actions.

8.5.2 Property
Loss estimations for the wildfire hazard are not based on damage functions, because no such damage functions are currently available. Instead, loss estimates were developed representing 10 percent, 30 percent, and 50 percent of the replacement value of exposed structures. This allows emergency managers to select a range of economic impact based on an estimate of the percent of damage to the general building stock. Damage in excess of 50 percent is considered to be substantial by most building codes and typically requires total reconstruction of the structure. Table 48 lists the loss estimates for the general building stock for jurisdictions that have an exposure to a fire hazard severity zone (the aggregate of the 3 zones assessed).
105 California Department of Public Health. (2022, December 29). Wildfires & Mental Health. https://www.cdph.ca.gov/Programs/EPO/Pages/Wildfire%20Pages/Wildfires--Mental-Health.aspx Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 145
Table 48: Loss Estimates for Wildfire within Moderate to High Wildfire Hazard Class Jurisdiction Exposed Value
Estimated Loss Potential from Wildfire
10% Damage 30% Damage 50% Damage
Campbell $42,254,972.95 $4,225,497.30 $12,676,491.89 $21,127,486.48 Cupertino $1,351,202,106.61 $135,120,210.66 $405,360,631.98 $ 675,601,053.31 Gilroy $3,117,036,318.53 $311,703,631.85 $935,110,895.56 $1,558,518,159.27 Los Altos $716,430,652.27 $71,643,065.23 $214,929,195.68 $358,215,326.14 Los Altos Hills $1,955,865,393.65 $195,586,539.37 $586,759,618.10 $977,932,696.83 Los Gatos $2,116,481,950.18 $211,648,195.02 $634,944,585.05 $1,058,240,975.09 Milpitas $836,941,901.80 $83,694,190.18 $251,082,570.54 $418,470,950.90 Monte Sereno $421,736,661.94 $42,173,666.19 $126,520,998.58 $210,868,330.97 Morgan Hill $3,720,446,057.04 $372,044,605.70 $1,116,133,817.11 $1,860,223,028.52 Mountain View $191,769,402.82 $19,176,940.28 $57,530,820.85 $95,884,701.41 Palo Alto $510,764,687.23 $51,076,468.72 $153,229,406.17 $255,382,343.62 San José $9,900,850,002.92 $990,085,000.29 $2,970,255,000.88 $4,950,425,001.46 Santa Clara (city) $56,785,930.11 $5,678,593.01 $17,035,779.03 $28,392,965.06 Saratoga $2,169,956,945.61 $216,995,694.56 $650,987,083.68 $1,084,978,472.81 Sunnyvale $196,414,379.07 $19,641,437.91 $58,924,313.72 $98,207,189.54 Unincorporated
County $9,569,160,222.23 $956,916,022.22 $2,870,748,066.67 $4,784,580,111.12 Total $36,874,097,584.96 $3,687,409,758.50 $11,062,229,275.49 $18,437,048,792.48 It should be noted that of the 53,086 structures in the OA determined to be at risk to wildfire, 50,503 are residences. This places a high burden of loss directly on individual homeowners. It may also coincide with a large number of people displaced, both for short-term evacuations, or possibly long-term if homes are lost to wildfire.

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8.5.3 Critical Facilities and Infrastructure
As shown in Table 47, many essential facilities and infrastructure are in close proximity to areas at high risk to wildfire. Individual facility and structure types within the hazard areas were not counted. Essential facilities at risk could include schools, fire or police stations, or hospitals that are near the high wildfire risk classification zones. It is expected that most of the transportation facilities potentially include railway, light rail, or highway bridges. Air and rail facilities are predominantly in more developed urban areas with less direct risk to wildfire. Several electric power facilities are located near high hazard areas.

Critical facilities of wood frame construction are especially vulnerable during wildfire events. Roads and railroads could be damaged by fallen trees, slides, debris flows, cracking, heavy fire fighting vehicles, and loss of signs and road delineators. Narrow one-lands roads are common in communities throughout the county. Fires can create conditions that block or prevent access and can isolate residents and emergency service providers. Wildfire typically does not have a major direct impact on bridges, but it can create conditions in which bridges are obstructed. Many bridges in areas of high to moderate fire risk are important because they provide the only ingress and egress to large areas and in some cases to isolated neighborhoods.

Communications and power and gas distribution infrastructure may also be threatened. Power lines are the most at risk from wildfire because most poles are made of wood and susceptible to burning. In 2018, Pacific Gas & Electric, the primary gas and electricity supplier to the northern half of California, declared bankruptcy following the 2017 and 2018 northern California wildfire. This bankruptcy has been called the first climate change bankruptcy (Center on Global Energy Policy).105F 106 It serves as an important case study
for how to understand risk to critical infrastructure and the many stakeholders impacted.

The function of critical facilities and infrastructure may also be impacted by fire mitigation measures, such as public safety power shutoffs. Electrical transmission and distribution lines may ignite fires if they are downed by winds and/or trees. To reduce this risk, electrical grids or blocks of an area may be deenergized during heightened risk conditions. This is important for critical facilities to be aware of and prepare for in order to reduce disruptions.

8.5.4 Wildlife and Livestock
The Santa Clara County CWPP Plan notes that horses, livestock, and animals may be especially vulnerable if a wildfire occurs. Many rural homes in the OA have horses, other large animals, and livestock. Farm animals and pets are common in homes of the OA. It can be difficult to evacuate large animals during a wildfire, and they can be harmed by smoke and other wildfire impacts. The loading of horses during a fire, and transportation of stock vehicles down narrow roads under stressful situations can be difficult. Other wildlife, like birds, are highly vulnerable during wildfires due to habitat destruction, smoke inhalation, loss of food sources, and even adverse effects on rare and specialized species.

8.6 Future Trends in Development
The population of Santa Clara County increase 8.7% between 2010 and 2020. However, the population has begun to decline in recent years any future growth is expected at a slow rate. The highly urbanized portions of the OA have little or no wildfire risk exposure. Development in the wildland urban interface can be managed with strong fire-resilient land use and building codes. Santa Clara County has been a leader 106 Center on Global Energy Policy. (2020, January 28). Out of Control: The Impact of Wildfires on our Power Sector and the Environment. https://www.energypolicy.columbia.edu/publications/out-control-impact-wildfires-our-powersector-and-environment Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 147
in urban planning for decades. Planning partners have taken steps to reduce geographic spread into wildland areas and promote “smart growth,” which includes focusing on moderate to higher density development near existing infrastructure.106F
107 These efforts have been fairly effective in accommodating residential growth without significant urban encroachment. However, despite these efforts, as population grows, it is likely the development of wildland will continue, and the WUI will grow. In some cases, parcels may be developed without a planning permit. New development is also occurring in areas that have limited water supply, putting residents at risk. The technology industry is a major employer in the county.

Many employees of tech-based industries are choosing to build property in the Santa Clara foothills, creating additional concerns around the value of property in the WUI, proper fire-resident landscaping, and gated communities.

Overall though, this plan has assessed capabilities with regards to the tools necessary to encourage fireresilient future development and found the OA was equipped with sufficient resources. In fact, the OA was actively involved in expanding planning capabilities at the time of this plan update. The Santa Clara County General Plan and individual city General Plans also address wildfire and can reduce risk through developing land use policies for hazard prone areas (e.g., proper community design, open space land use, and reducing population in areas prone to wildfire). The Safety Element of the Santa Clara County General Plan is currently being updated. Updating the Safety Element will ensure safety considerations are identified and included during the decision-making and planning processes as they relate to future developments within the county. The Safety Element addresses Wildland/Urban Fire risk.

The Santa Clara County Community Wildfire Protection Plan (CWPP)107F 108 is also currently being updated
and will outline a mitigation and preparedness plan to reduce wildfire risk. The CWPP advocates for wildfire risk reduction measures including updating applicable policies, codes, and ordinances, prioritizing fuel reduction, improving available water supply networks, and engaging in outreach and education. It emphasizes property’s owners’ responsibility to reduce structure ignitability and mitigate risk.

8.7 Scenario
A major wildfire in the OA might begin with a water shortage causing tinder-like wildlands and “Red Flag” conditions occurring, indicating a combination of higher-than-normal temperatures, low humidity and winds blowing from the east across California to the ocean. Lightning strikes or human carelessness with combustible materials could trigger a multitude of small, isolated fires.

The embers from these smaller fires could be carried miles by hot, dry winds. Fires that start in flat areas move slower, but wind still pushes them. It is not unusual for a wildfire pushed by wind to burn the ground fuel and later climb into the crown and reverse its track. This is one of many ways that fires can escape containment, typically during periods when response capabilities are overwhelmed. These small new fires would most likely merge. Suppression resources would be redirected from protecting the natural resources to saving more remote subdivisions.

The worst-case scenario would include an active fire season throughout the American west, spreading resources thin. Firefighting teams would be exhausted or unavailable. Many federal assets would be responding to other fires that started earlier in the season. Multiple fires burn in the State or OA at one time would limit State and local capabilities to respond.

If fire management capabilities are stretched too thin, and weather conditions remained favorable for wildfires, the fire could encroach upon the WUI. Losses in the WUI could be devastating. Residents would need to evacuate, residential and commercial properties would be damaged or destroyed, lives could be 107 Santa Clara County Fire Department. (2016, August). Santa Clara Community Wildfire Protection Plan. https://www.sccfd.org/santa-clara-county-community-wildfire-protection-plan/ 108 Santa Clara County FireSafe Council (2019). https://sccfiresafe.org/cwpp/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 8: Wildfire 148
lost, and infrastructure and utilities including communication towers, power grids, water utilities, transportation corridors and community watersheds could be impacted.

To further complicate the problem after the fire has been contained, heavy rains could follow, causing flooding and landslides and releasing tons of sediment into rivers, and damaging sensitive habitat and riparian areas. Such a fire followed by rain could release millions of cubic yards of sediment into streams, creating new floodplains and changing existing ones. With the vegetation removed from the watershed, stream flows could easily double. Floods that could be expected every 50 years may occur every couple of years. With the streambeds unable to carry the increased discharge because of increased sediment, the floodplains and floodplain elevations would increase. Floodplain management capabilities would find it challenging to adapt to changed conditions and new flood map studies would be warranted.

8.8 Issues
Important issues associated with wildfires in the OA include the following:
 Public education and outreach to people living in or near the fire hazard zones should include information about and assistance with mitigation activities such as defensible space, and advance identification of evacuation routes and safe zones.
 Wildfires could cause landslides as a secondary natural hazard.  Climate change could affect the wildfire hazard.
 Future growth into interface areas should continue to be managed.  Area fire districts need to continue to train on wildland-urban interface events.  Vegetation management activities. This would include enhancement through expansion of the target areas as well as additional resources.
 Regional consistency of higher building code standards such as residential sprinkler requirements and prohibitive combustible roof standards.
 Fire department water supply in high-risk wildfire areas.  Expand certifications and qualifications for fire department personnel. Ensure that all firefighters are trained in basic wildfire behavior, basic fire weather, and that all company officers and chief level officers are trained in the wildland command and strike team leader level.

Table 49: EMAP Consequence Analysis: Wildfire
Subject Ranking Impacts/Wildfire
Public Minimal to
Severe
Residents in the high wildfire risk zones are most likely to be impacted. Impacts include injuries related to burns, smoke inhalation, and loss of property and homes. Residents outside of the immediate wildfire area may still be impacted by a wildfire event due to smoke, disruption of services, or inaccessible roads.

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Subject Ranking Impacts/Wildfire
Responders Minimal Responders will be called upon to manage the overall incident including potentially supporting evacuations, closing roads, assisting injured members of the public, and more. Climate conditions also need to be considered. Fire management
agencies face more uncertainty in planning, change in
suppression and fire management techniques, and the need for more agency coordination considering compounding hazards like drought. With proper training, data, equipment, and time for responders with pre-existing conditions to take precautionary steps to protect themselves prior to exposure, it is anticipated the impact to responders will be minimal.

Continuity of
Operations (including
continued delivery of
services)
Minimal to
Moderate
The impacts on continuity of operations depends largely on the location of the fire and whether any facility or critical infrastructure component would be impacted. Each fire will present unique risks.

Communication systems could be damaged or destroyed. Power connectivity could be disrupted. Other community lifelines could be disrupted or destroyed. Delivery of services may be slowed or stopped in impacted areas.

Property, Facilities,
and Infrastructure
Minimal to
severe
The localized impact to properties, facilities, and infrastructure could be severe. The impact to critical infrastructure depends in part on the preparation taken prior to a fire during high-risk warning levels (e.g., raising water levels and fueling generators).

Fire conditions and the ability of responder’s to quickly suppress the fire will also play a large role in determining the impact.

Environment Minimal to
severe
Fire plays an important role in California’s ecosystem. A wildfire does not necessarily have a negative impact on the environment.

However, fires can also have severe negative impact in terms of habitat destruction, soil erosion, soil sterilization, spread of invasive species, and disease and insect infestation.

Economic
Conditions
Minimal to
severe
Impacts on the economy will depend greatly on the size and location of the wildfire event. A major wildfire event could impact the local economy through the destruction of property,
businesses, and infrastructure; delays or halts in supply chains; and impacts to health and air quality, which may decrease worker productivity or prevent workers from going to work.

Public Confidence in
the Government
Minimal to
severe
The public’s confidence will vary, depending on the perception of how well the event was managed, the warning time, and the time it takes for response and recovery. Timely and accurate public information and notification during these events will impact public trust.

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9 Inclement Weather
Definitions
• Atmospheric River: A long, narrow region in the atmosphere that transports most of the water vapor outside of the tropics. These columns of vapor move with the weather, carrying large amounts of water vapor and strong winds. When atmospheric rivers make landfall, they release this vapor in the form of rain or snow, causing flooding and mudslide events.
• Damaging Winds: Winds exceeding 50–60 mph. NOAA identifies eight types of damaging winds. • Extreme Heat: A period of high heat and humidity with temperatures above 90 degrees for at least two to three days.
• Extreme Temperatures: Unexpected, unusual, or unseasonal temperatures—cold or hot—that can create dangerous situations.
• Heat Index: The temperature the body feels when heat and humidity are combined. • Heavy Precipitation: Also known as heavy rain, refers to instances where the amount of rain or snow experienced in one area exceeds what is normal.
• Space Weather: Variations in the space environment between the sun and earth. It can influence the performance of technology used on Earth.
• Thunderstorm: A rain event that includes thunder, lightning and occasionally strong gusty winds and hail.

9.1 General Background
Inclement weather refers to any dangerous meteorological phenomena with the potential to cause damage, serious social disruption, or loss of human life. Inclement weather can be categorized into two groups: systems that form over wide geographic areas are classified as general severe weather; those with a more limited geographic area are classified as localized severe weather. In this plan, we refer to this hazard by the broad “inclement weather” term. Inclement weather, technically, is not the same as extreme weather, which refers to unusual weather events at the extremes of the historical distribution for a given area.

The most common inclement weather events that impact the Santa Clara County OA are heavy rains/atmospheric rivers/, extreme weather (hot and cold), high wind, and space weather. These types of inclement weather are described in the following sections. Flooding issues associated with inclement weather are discussed in Section 13.

Inclement weather episodes account for the majority of OEM EOC activations since 2017. Each year since the last plan update, Santa Clara County has experienced an average of 10 inclement weather episodes (cold and hot). The Office of Emergency Management has a robust system for coordinating response across multiple jurisdictions during inclement weather episodes. The process is described in the Inclement Weather Annex to the Emergency Operations Plan. This annex was developed in cooperation with over 40 area stakeholders representing more than 20 different agencies.

9.1.1 Heavy Precipitation/Atmospheric River
Most severe storms in the Santa Clara County OA consist of atmospheric rivers, heavy rains, hail, and thunderstorms.

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Heavy precipitation, or heavy rain, refers to instances where the amount of rain or snow experienced in one area exceeds what is normal.108F
109 The amount of precipitation needed to qualify as heavy rain varies with each location and season. Heavy rain is distinct from climate change analyses on increasing precipitation. It does not mean that the total amount of precipitation at a location has increased, just that the rain is occurring in a more intense event. More frequent heavy rain events, however, can serve as indicators of changing precipitation levels. Heavy precipitation is measured by tracking the event frequency, analyzing the mean return period, and by measuring the amount of precipitation within a specific timeframe, such as the inches of rain within a 24-hour period.

Rainfall intensity is based on the amount of rainfall per unit of time. Light rain is typically less than 0.1 inch per hour, moderate rain is .1 to .3 inches of rain per hour, heavy rain is .3 to 2 inches per hour, and violent rain can be used to characterize rates greater than 2 inches per hour.109 F 110
Figure 38: NOAA Atlas Intensity - Santa Clara, California According to the NOAA, about 30 to 50 percent of annual precipitation in the west coast states, such as California, are due to atmospheric river events. Atmospheric Rivers are long, concentrated regions in the atmosphere that transport moist air away from the tropics and into higher latitudes. When combined with high wind, they produce large amounts of heavy rain and snow which can lead to flash floods, mudslides and significant damage to life and property.10F 111
109 United States Environmental Protection Agency. (2021 April). Climate Change Indicators: Heavy Participation. https://www.epa.gov/climate-indicators/climate-change-indicators-heavyprecipitation#:~:text=%22Heavy%20precipitation%22%20refers%20to%20instances%20during%20which%20the,can %20affect%20the%20intensity%20and%20frequency%20of%20precipitation. 110 Rain rate intensity classification. Manual of Surface Weather Observations. https://www.baranidesign.com/faqarticles/2020/1/19/rain-rate-intensity-classification 111 National Oceanic and Atmospheric Administration Research News. (2023, January 11). Atmospheric Rivers: What are they and how does NOAA study them? https://research.noaa.gov/article/ArtMID/587/ArticleID/2926/AtmosphericRivers-What-are-they-and-how-does-NOAA-studythem#:~:text=Infographic%3A%20The%20science%20behind%20atmospheric%20rivers%20%28NOAA%29%20Atm ospheric,and%20snow%20upon%20landfall%2C%20especially%20over%20mountainous%20terrain.

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A thunderstorm is a rain event that includes thunder, lightning and occasionally strong gusty winds and hail.1F
112 A thunderstorm is classified as “severe” when it contains one or more of the following: hail one inch or greater, winds gusting in excess of 50 knots (57.5 mph), or tornado. Thunderstorms are usually short in duration (seldom more than two hours). Heavy rains associated with thunderstorms can lead to flash flooding during the wet or dry season. According to the American Meteorological Society Glossary of Meteorology, thunderstorms are reported as light, medium, or heavy according to the following characteristics:12F
113
 Nature of the lightning and thunder
 Type and intensity of the precipitation, if any
 Speed and gustiness of the wind
 Appearance of the clouds
 Effect on surface temperature
Three factors cause thunderstorms to form: moisture, rising unstable air (air that keeps rising when disturbed), and a lifting mechanism to provide the disturbance. The sun heats the surface of the earth, which warms the air above it. If this warm surface air is forced to rise (hills or mountains can cause rising motion, as can the interaction of warm air and cold air or wet air and dry air) it will continue to rise as long as it weighs less and stays warmer than the air around it. As the air rises, it transfers heat from the surface of the earth to the upper levels of the atmosphere (the process of convection). The water vapor it contains begins to cool and it condenses into a cloud.

The cloud eventually grows upward into areas where the temperature is below freezing. Some of the water vapor turns to ice and some of it turns into water droplets. Both have electrical charges. Ice particles usually have positive charges, and rain droplets usually have negative charges. When the charges build up enough, they are discharged in a bolt of lightning, which causes the sound waves we hear as thunder.

Thunderstorms have three stages (see Figure 38):
 Developing Stage: The developing stage of a thunderstorm is marked by a cumulus cloud that is being pushed upward by a rising column of air (updraft). The cumulus cloud soon looks like a tower (called towering cumulus) as the updraft continues to develop. There is little to no rain during this stage but occasional lightning. The developing stage lasts about 10 minutes.  Mature Stage: The thunderstorm enters the mature stage when the updraft continues to feed the storm, but precipitation begins to fall out of the storm, and a downdraft begins (a column of air pushing downward). When the downdraft and rain-cooled air spread out along the ground, they form a gust front, or a line of gusty winds. The mature stage is the most likely time for hail, heavy rain, frequent lightning, strong winds, and tornadoes. The storm occasionally has a black or dark green appearance.
 Dissipating Stage: Eventually, a large amount of precipitation is produced, and the updraft is overcome by the downdraft beginning the dissipating stage. At the ground, the gust front moves out a long distance from the storm and cuts off the warm moist air that was feeding the thunderstorm. Rainfall decreases in intensity, but lightning remains a danger. 112 National Oceanic and Atmospheric Administration National Severe Storms Laboratory. (n.d.). Severe Weather 101-Thunderstorm Basics. https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/ 113 American Meteorological Society Glossary of Meteorology. (2022). Thunderstorm. https://glossary.ametsoc.org/wiki/Thunderstorm#:~:text=(Sometimes%20called%20electrical%20storm.),rain%2C%20 and%20sometimes%20with%20hail.

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Figure 39: Thunderstorm Life Cycle13F
114
There are different types of thunderstorms identified by the NOAA and some are listed below14F 115:
 Single-Cell Thunderstorms: Single-cell thunderstorms are small and brief. They usually grow and die within an hour and may produce brief heavy rain and lightning.  Multi-Cell Storm: A multi-cell storm is the most common type of thunderstorm in which new updrafts form along the leading edge of cool air. Single cells usually last 30 to 60 minutes while multi-cell storm systems may last for many hours. They may produce hail, strong winds, brief tornadoes, and flooding.
 Squall Line: A squall line is a group of storms arranged into a line, often accompanied by squalls or gusty winds and heavy rains. They tend to pass quickly and are less likely to produce tornadoes. They are usually 10 or 20 miles wide but can be up to hundreds of miles long.  Supercell: A supercell is a long-lived (usually greater than 1 hour) and highly organized storm that feeds off an updraft (a rise of current air) that is tilted and rotating. This rotating updraft can be as large as 10 miles in diameter and up to 50,000 feet tall and can be present as much as 20 to 60 minutes before a tornado forms. This rotation is called a mesocyclone when it is detected by a Doppler radar. The tornado is a small extension of this larger rotation. Most large and violent tornadoes come from supercells.

A thunderstorm is a storm with lightning and thunder produced by cumulonimbus clouds, usually producing gusty winds, heavy rain, and sometimes hail. Thunderstorms are usually short in duration (seldom more than two hours). Heavy rains associated with thunderstorms can lead to flash flooding during the wet or dry season. According to the American Meteorological Society Glossary of Meteorology, thunderstorms are reported as light, medium, or heavy according to the following characteristics:
• Nature of the lightning and thunder
• Type and intensity of the precipitation, if any
• Speed and gustiness of the wind
114 National Oceanic and Atmospheric Administration National Severe Storms Laboratory. (n.d.). Severe Weather 101-Thunderstorms. https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/ 115 National Oceanic and Atmospheric Administration National Severe Storms Laboratory. (n.d.). Severe Weather 101-Thunderstorm Types. https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/types/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 154
• Appearance of the clouds
• Effect on surface temperature

9.1.2 Extreme Temperatures
Extreme temperatures are unexpected, unusual, or unseasonal temperatures—cold or hot—that can create dangerous situations.

Extreme cold temperatures are below normal temperatures that may lead to serious health problems.

Exposure to the extreme cold can lead to hypothermia and frostbite in people exposed to the weather without adequate clothing protection. It may result in death if it exacerbates preexisting chronic conditions. The NWS provides a Wind Chill Chart to calculate the dangers from winter winds and freezing temperatures. Wind chill is represented by the actual air temperature factored in by wind speed. Figure 39 displays the extent and intensity by the time it takes to develop frostbite.

Figure 40: National Weather Service Wind Chill Chart
The NOAA Weather Prediction Center also has a Winter Storm Severity Index (WSSI) tool. This tool communicates the general level of severe winter weather and can be viewed in the figure below. The levels range from “minor” to “extreme.”
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Figure 41: Winter Storm Severity Index
According to FEMA, extreme heat is defined as a period of high heat and humidity with temperatures above 90 degrees for at least two to three days.15F
116 Heat is the primary cause of weather-related death in the United States and can be very taxing on the human body. Vulnerable populations such as young children, infants, people with chronic medical conditions, and pregnant women are at higher risk of heat related illness. The heat index is the temperature the body feels when heat and humidity are combined.16F
117 The direct relationship between humidity and heat can affect the severity of extreme heat events. The graphic from the NWS below classifies the level of severity in relation to the heat index. 116 U.S. Department of Homeland Security. (2022, August 1). Extreme Heat. https://www.ready.gov/heat 117 National Oceanic and Atmospheric Administration National Weather Service. (n.d.). Heat Forecast Tools. https://www.weather.gov/safety/heat-index
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Figure 42: National Weather Service Heat Index Chart17F 118
Figure 43: National Weather Service Heat Index Classifications and Corresponding Effects on the Body18F
119

9.1.3 High Winds
High Winds can occur during severe thunderstorms, with strong weather systems, or can flow down a mountain. High winds are defined as winds of 40 mph or greater lasting for an hour or more, and gusts to 58 mph or greater (NOAA). Windstorms are especially dangerous in areas with significant tree stands and areas with exposed property, poorly constructed buildings, mobile homes (manufactured housing units), major infrastructure, and above-ground utility lines. A windstorm can topple trees and power lines, cause damage to residential, commercial, and critical facilities, and leave tons of debris in its wake. 118 National Oceanic and Atmospheric Administration National Weather Service. (n.d.). What is the heat index? https://www.weather.gov/ama/heatindex
119 National Oceanic and Atmospheric Administration National Weather Service. (n.d.). What is the heat index? https://www.weather.gov/ama/heatindex
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Damaging winds are classified as those exceeding 50–60 mph.19 F 120 Damage from such winds accounts
for half of all severe weather reports in the lower 48 states and is more common than damage from tornadoes. Wind speeds can reach up to 100 mph and can produce a damage path extending for hundreds of miles.

NOAA identifies eight types of damaging winds120F
121:
 Straight-line Wind: Any thunderstorm wind that is not associated with rotation; this term is used mainly to differentiate from tornado winds.
 Downdraft: A small-scale column of air that rapidly sinks toward the ground.  Downburst: Downburst is the general term for all localized strong wind events that are caused by a strong downdraft within a thunderstorm.
 Macroburst: An outward burst of strong winds near the surface with horizontal dimensions larger than 4 km (2.5 mi) and occurs when a strong downdraft reaches the surface. Macroburst winds may begin over a smaller area and then spread out over a wider area, sometimes producing damage similar to a tornado. Although usually associated with thunderstorms, macrobursts can occur with weak showers.
 Microburst: A small, concentrated downburst that produces an outward burst of damaging winds at the surface. Microbursts are small, usually less than 4 km across, and short-lived, lasting only 5 to 10 minutes, with maximum wind speeds sometimes exceeding 100 mph. There are two kinds of microbursts: wet and dry. A wet microburst is accompanied by heavy precipitation at the surface. Dry microbursts, common in places like the high plains and the intermountain west, occur with little or no precipitation reaching the ground.  Gust Front: A gust front is the leading edge of rain-cooled air that clashes with warmer thunderstorm inflow. Gust fronts are characterized by a wind shift, temperature drop, and gusty winds out ahead of a thunderstorm. Sometimes the winds push up air above them, forming a shelf cloud or detached roll cloud.
 Derecho: A widespread, long-lived windstorm that is associated with a band of rapidly moving showers or thunderstorms. It consists of numerous microbursts, downbursts, and downburst clusters. By definition, if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length, then the event may be classified as a derecho.
 Haboob: A wall of dust that is pushed out along the ground from a thunderstorm downdraft at high speeds.

The Beaufort Scale is a classification system that relates wind speed to observed conditions. As shown in Figure 9-6, this scale indicates likely conditions that can be observed at increasing wind speed levels. 120 National Oceanic and Atmospheric Administration National Severe Storms Laboratory. (n.d.). Severe Weather 101-Damaging Winds Basics. https://www.nssl.noaa.gov/education/svrwx101/wind/ 121 National Oceanic and Atmospheric Administration National Severe Storms Laboratory. (n.d.). Severe Weather 101-Types of Damaging Winds. https://www.nssl.noaa.gov/education/svrwx101/wind/types/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 158
Figure 44: The Beaufort Wind Scale12F
122
122 National Weather Service. Beaufort Scale. Estimating Wind Speed and Sea State. https://www.weather.gov/pqr/beaufort
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9.1.4 Space Weather
Space weather refers to conditions resulting from solar activity that can potentially affect Earth, our atmosphere, and the near-Earth environment.12F
123 Our planet’s atmosphere helps protect us from solar radiation, but occasional eruptions of radiation and matter can disrupt our power grids and communications systems, as well as impact satellite operations and GPS navigation capabilities.

In severe cases, it produces solar energetic particles, which can damage satellites used for commercial communications, global positioning, intelligence gathering, and weather forecasting.

NOAA’s Space Weather Prediction Center has developed space weather scales. The scales describe the environmental disturbances for three event types: geomagnetic storms, solar radiation storms, and radio blackouts. The scales have numbered levels to convey severity, similar to hurricanes, tornadoes, and earthquakes. They list possible effects at each level, show the frequency of such events, and help measure of the possible intensity of the physical causes.

The NOAA space weather scales are included in Table 50, Table 51, and Table 52. NOAA studies have determined that different types of space weather may occur separately. 123 National Oceanic and Atmospheric Administration National Environmental Satellite, Data, and Information Service. (n.d.). Space Weather. https://www.nesdis.noaa.gov/next-generation/space-weather Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 160
Table 50: NOAA Geomagnetic Storms Space Weather Scale and Potential Effects123F 124
124 National Oceanic and Atmospheric Administration. (2011, April 7). Space Weather Scales. https://swpc-drupal.woc.noaa.gov/noaa-scalesexplanation#:~:text=The%20NOAA%20Space%20Weather%20Scales%20were%20introduced%20as,and%20their%20possible%20effects%20on%20people%20 and%20systems.

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Table 51: NOAA Solar Radiation Storms Space Weather Scale and Potential Effects124F 125
125 National Oceanic and Atmospheric Administration. (2011, April 7). Space Weather Scales. https://swpc-drupal.woc.noaa.gov/noaa-scalesexplanation#:~:text=The%20NOAA%20Space%20Weather%20Scales%20were%20introduced%20as,and%20their%20possible%20effects%20on%20people%20 and%20systems.

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Table 52: NOAA Radio Blackouts Space Weather Scale and Potential Effects125F 126
126 National Oceanic and Atmospheric Administration. (2011, April 7). Space Weather Scales. https://swpc-drupal.woc.noaa.gov/noaa-scalesexplanation#:~:text=The%20NOAA%20Space%20Weather%20Scales%20were%20introduced%20as,and%20their%20possible%20effects%20on%20people%20 and%20systems.

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9.2 Hazard Profile

9.2.1 Past Events
The National Centers for Environmental Information (NCEI) receives storm data from the National Weather Service (NWS) that is then compiled into a Storm Events Database. NWS receives their information from a variety of sources, which include but are not limited to, county, City, and federal emergency management officials; local law enforcement officials; SkyWarn spotters; NWS damage surveys; newspaper clipping services; the insurance industry; and the general public, among others.

Please note that the NWS does not guarantee the accuracy, validity, or completeness of the event data in the Storm Events Database.

The Storm Events Database has a record of inclement weather events that occurred in the OA during the last twenty-one years (see Table 53). These events include heavy rain/precipitation, excessive heat or cold, and high winds. In total, inclement weather has caused an estimated $24,152,120 in property damage in the OA. $10,025,020 was from Heavy Precipitation Events Heavy Precipitation
11/30/2012 A series of storms brough strong winds, heavy rainfall and flooding to the region and reported of 13,800 power outages in the Bay Area.
12/3/2014 Rain, wind, some flooding issues and downed trees and power lines were reported. 12/11/2014 An atmospheric river brought heavy rain and gusty winds. Rainfall rates of 1.5 – 2 inches/hour were reported. Many locations around the Bay Area had urban flooding of streets and highways and flooding of creeks.
2/9/2015 Heavy rain, gusty winds, and damage to trees and power lines along with some minor flooding of urban areas occurred.
1/8/2017 Potent atmospheric river brought heavy rain, strong southerly winds, and storm surge issues.

Dec 27, 2022 – Jan. 31, 2023. A series of heavy rainstorms affected multiple counties, prompting emergency declarations. Road closures occurred in Gilroy, including closer of southbound Hwy 101.

Other road closures occurred in San Jose and other parts of the valley due to flooding. Heavy rain contributed to a landslide that temporarily blocked Hwy 17 at Glenwood Drive in Los Gatos. On January 13, 2023, Santa Clara County issued evacuation warnings for watershed areas of the Uvas Reservoir, Pacheo Pass River bases, and Highway 101 and Bolsa Road due to continued weather and flooding concerns.

Additional examples of heavy rain contributing to landslides can be found in Section 14.2.1.

Table 53: 2001–2022 Heavy Rain and Hail Events
Dates of Event Event Type Location
12/15/2002 Heavy Rain Santa Clara County/Los Gatos
12/15/2002 Heavy Rain Santa Clara County/Saratoga
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 164
Dates of Event Event Type Location
11/30/2012 Heavy Rain Santa Clara County
11/30/2012 Heavy Rain Santa Clara County
10/10/2012 Hail Santa Clara County/Gilroy
10/10/2012 Hail Santa Clara County/Gilroy
2/9/2014 Heavy Rain Santa Clara County
12/3/2014 Heavy Rain Santa Clara County/Saratoga
12/11/2014 Heavy Rain Santa Clara County
2/9/2015 Heavy Rain Santa Clara County
2/9/2015 Heavy Rain Santa Clara County
1/8/2017 Heavy Rain Santa Clara County/Morgan
Hill
1/19/2017 Hail Santa Clara County/Los Gatos
1/19/2017 Hail Santa Clara County
1/20/2017 Hail Santa Clara County/Los Gatos
2/17/2017 Heavy Rain Santa Clara County
3/5/2017 Hail Santa Clara County/Los Gatos
1/19/2018 Hail Santa Clara County
1/25/2018 Hail Santa Clara County/San Jose
1/25/2018 Hail Santa Clara County/Gilroy
1/25/2018 Hail Santa Clara County/Gilroy
1/25/2018 Hail Santa Clara County/Morgan
Hill
2/26/2018 Hail Santa Clara County/Gilroy
3/2/2018 Hail Santa Clara County/San Jose
3/17/2018 Hail Santa Clara County/Sunnyvale
4/16/2018 Hail Santa Clara County/San Jose
4/16/2018 Hail Santa Clara County
2/15/2019 Hail Santa Clara County
3/10/2019 Hail Santa Clara County/San Jose
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 165
Dates of Event Event Type Location
3/10/2019 Hail Santa Clara County/San Jose
3/10/2019 Hail Santa Clara County
1/16/2020 Hail Santa Clara County
1/16/2020 Hail Santa Clara County
3/17/2020 Hail Santa Clara County
3/25/2020 Hail Santa Clara County/Los Gatos
3/25/2020 Hail Santa Clara County/Palo Alto
3/25/2020 Hail Santa Clara County/Mountain
View
3/25/2020 Hail Santa Clara County/Mountain
View
3/25/2020 Hail Santa Clara County/Gilroy
3/25/2020 Hail Santa Clara County/Sunnyvale
3/25/2020 Hail Santa Clara County/Gilroy
3/25/2020 Hail Santa Clara County/Santa
Clara
4/6/2020 Hail Santa Clara County
3/10/2021 Hail Santa Clara County/San Jose
Extreme Heat or Cold
The NCEI reports 14 deaths in Santa Clara County since 2002 as a direct result of cold and wind chill.

Seven deaths and 61 injuries have been directly attributed to heat. • NCEI reports that excessive heat led to rolling blackouts in the Bay Area on 8/14/2020 • On 8/16/2020, extreme heat contributed to 464 EMS calls across Santa Clara County. • NCEI documents the use of cooling centers to counter the effects of extreme heat in Santa Clara on 5/17/2009 and 9/4/2022.
• On 1/6/2007, the NCEI records that freezing temperatures in Santa Clara Valley fell into the lower 20s, causing $50,000 in crop damage.
• On 12/8/2009, Light rail trains were delayed and Highway 101 to Interstate 280 in San Jose were closed due to severe ice on the roadway. Flights from San Jose International Airport were delayed because some airlines do not have de-icing equipment. Ice also contributed to a vehicle accident.

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Table 54: 2001–2022 Extreme Temperature Events
Dates of Event Event Type Location
7/20/2006 Heat Santa Clara Valley Including
San Jose
7/21/2006 Heat East Bay Hills and the Diablo
Range (Zone)
7/22/2006 Heat San Francisco Bay Shoreline
(Zone)
7/22/2006 Heat Santa Cruz Mountains (Zone)
5/17/2009 Heat Santa Clara Valley Including
San Jose
5/17/2009 Heat San Francisco Bay Shoreline
(Zone)
5/17/2009 Heat East Bay Hills and the Diablo
Range (Zone)
5/17/2009 Heat Santa Cruz Mountains (Zone)
6/19/2017 Heat Santa Clara Valley Including
San Jose
12/25/2018 Cold/Wind Chill Santa Clara Valley including San Jose
1/1/2019 Cold/Wind Chill Santa Clara Valley including
San Jose
11/27/2019 Cold/Wind Chill Santa Clara Valley including San Jose
11/28/2019 Cold/Wind Chill Santa Clara Valley including San Jose
11/29/2019 Cold/Wind Chill Santa Clara Valley including San Jose
6/10/2019 Heat Santa Clara Valley Including
San Jose
6/10/2019 Excessive Heat San Francisco Bay Shoreline
(Zone)
8/14/2020 Excessive Heat San Francisco Bay Shoreline
(Zone)
8/16/2020 Excessive Heat Santa Clara Valley Including
San Jose
9/6/2020 Excessive Heat Santa Clara Valley Including
San Jose
9/7/2020 Excessive Heat San Francisco Bay Shoreline
(Zone)
6/17/2021 Heat Santa Clara Valley Including
San Jose
6/17/2021 Heat Santa Clara Valley Including
San Jose
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 167
Dates of Event Event Type Location
7/11/2021 Excessive Heat East Bay Hills and the Diablo
Range (Zone)
6/10/2022 Heat Santa Clara Valley Including
San Jose
6/21/2022 Heat San Francisco Bay Shoreline
(Zone)
6/21/2022 Heat San Francisco Bay Shoreline
(Zone)
6/21/2022 Heat Santa Clara Valley Including
San Jose
9/4/2022 Heat Santa Clara Valley Including
San Jose
9/4/2022 Heat San Francisco Bay Shoreline
(Zone)
9/4/2022 Heat Santa Clara Valley Including
San Jose
9/4/2022 Heat Santa Clara Valley Including
San Jose
9/5/2022 Heat San Francisco Bay Shoreline
(Zone)
9/5/2022 Heat Santa Clara Valley Including
San Jose
9/6/2022 Heat San Francisco Bay Shoreline
(Zone)
9/6/2022 Heat Santa Clara Valley Including
San Jose
9/8/2022 Heat Santa Clara Valley Including
San Jose
High Wind
• In addition, the NOAA/NCEI database reports 494 high wind events that have occurred in the OA since 2005. This is the most common inclement weather hazard type to affect the OA, and these events have caused an estimated $7,406,100 in property damage since the first recorded incident in 2005.
• On 1/19/2010-1/22/2000, the NCEI records strong winds that affected the Bay Area. Winds knocked two trees down along East Santa Clara Street in San Jose and around 10,000 customers lost power in the San Jose area. Additional incidents of trees and limbs falling and causing damage were reported. These reports include damage to utilities such as telephone poles and power transformers, damage caused to vehicles, partially blocked roadways, or injured people. Specific impacts were recorded in San Jose, Los Gatos, and Milpitas.

Table 55:2002-2022 High Wind Events
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 168
Years Number of Wind Events
2005 6
2006 11
2008 16
2009 18
2010 21
2011 15
2012 14
2013 23
2014 32
2015 15
2016 3
2017 51
2018 26
2019 92
2020 52
2021 61
2022 9
Although rare, Santa Clara County has also experienced tornados, which have caused a total of $6,721,000 in damage.

Table 56: 1951–2022 Tornado Events
Date Event Type Location
1/11/1951 F2 Tornado Santa Clara County
12/8/1997 F0 Tornado San Jose
2/6/1998 F0 Tornado Sunnyvale
5/5/1998 F1 Tornado Los Altos
5/5/1998 F2 Tornado Sunnyvale
4/14/2007 EF0 Tornado Gilroy
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 169
Space Weather
Space weather monitoring is relatively new, and there is limited data available regarding historical occurrences. However, we know that space weather has impacted the OA and is likely to impact the OA in the future.

9.2.2 Location
Heavy precipitation/Rain, extreme heat or extreme cold, high winds, and even space weather can occur anywhere within the OA. The extent is highly variable. Given their widespread nature, these events have the potential to impact large areas simultaneously. Historical records show that these events can happen in one isolated part of the OA, or in the entirety of the planning area. Therefore, inclement weather events are not confined to any geographical barrier and may impact all parts of the OA.

9.2.3 Frequency
Several types of inclement weather have shown an increasing number of events in recent years. This represents a trend that due to factors such as climate change it is likely that inclement weather events will become more frequent over time. Based on the frequency of historic events, inclement weather events can be expected to occur multiple times annually.

Heavy Precipitation: According to the historical events reported by the NCEI database, 44 heavy precipitation events have occurred in the last twenty-one years. Of these 44 events, 33 incidents have occurred in the last five years alone.

Probability in OA: Highly Likely
Extreme Temperature: 33 extreme temperature events were recorded in the NCEI database since 2002. 24 of those have occurred since 2017.

Probability in OA: Highly Likely
High Wind: 470 high wind events have occurred in the OA since 2005. Wind speeds in these events have ranged from 9 to 96 knots.

Probability in OA: Highly Likely
Space Weather: Data was not available to estimate the frequency of space weather events.

Probability in OA: Likely

9.2.4 Severity
Severity will depend on the extent of each event and can range from mild to severe. Inclement weather can cause disruption to critical facilities and extensive damage to property and infrastructure. The NCEI database reports a total of $24,152,120 in property damage from these events in some of the most severe cases, not including space weather.

The levels of severity related to space weather are best described in Table 50, Table 51, and Table 52.

The level of severity can range from minor to extreme and will mostly impact the OA’s technological, communication, and power grid systems.

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9.2.5 Warning Time
The National Weather Service provides forecasting and prediction services for a variety of inclement weather events and maintains an established process for issuing advisories, watches and warnings for each. The amount of warning time varies on the type of weather event. 126 F 127
Heavy Precipitation: warning times for significant weather events may vary widely. Initial storm advisories can have a lead time of 36-48 hours. More extreme events like thunderstorms, hail, or other severe weather may have warning of an hour or less.

Extreme Temperature: Advisories regarding extremes in heat or cold can be issued with 0-36 hours of lead time.

High Wind: Wind advisories can have a lead time of 12 to 36 hours.

Space Weather: Space weather prediction services are provided by NOAA’s Space Weather Prediction Center. The SWPC draws on various data sources to provide forecasts, watches, warning and alerts with a possible lead time of hours to days of possible space weather activity.127F 128 Lead time varies from hours to
days.

9.3 Cascading Impacts
While inclement weather is the most common hazard to occur in the OA, it is important to note the potential cascading impacts of these events.

Heavy precipitation can lead to significant flooding, also contributing to landslides and mudslides, posing serious threats to human lives, property, infrastructure and ecosystems. Flooding and other cascading impacts of heavy rain can interrupt transportation, utility services, or other emergency services.

Extreme temperatures, whether excessively hot or cold, will have impacts on human health, potentially leading to heatstroke, dehydration, and cold-related illnesses. Additionally, extreme temperatures can strain energy resources and infrastructure, increasing the risk of blackouts and disruption of critical services and infrastructure.

High winds have historically caused damage across the OA. They can damage or disrupt essential functions and interrupt service from energy and communication systems.

Space weather events, such as solar flares and geomagnetic storms can be significant and pose substantial risks to modern technological systems and critical infrastructure. Space weather can disrupt satellite communications, GPS, and aviation systems, affecting various sectors, including telecommunications, transportation, and emergency services.

9.4 Exposure

9.4.1 Population
Because of the unconfined and variable nature of inclement weather, the entire population is considered to be exposed. Heavy rain, hail, lightning, high winds, and extreme temperatures all have the potential to harm the health of or injure people within the OA.
127 https://www.weather.gov/safety/
128 Space Weather Watc https://www.weather.gov/safety/space-wwhes, Warnings and Alerts Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 171
Table 57: Population by Jurisdiction
Jurisdiction 2022
City of Campbell 42,833
City of Cupertino 59,610
City of Gilroy 59,269
City of Los Altos 31,526
Town of Los Altos Hills 8,400
Town of Los Gatos 33,062
City of Milpitas 80,839
City of Monte Sereno 3,488
City of Morgan Hill 46,451
City of Mountain View 83,864
City of Palo Alto 67,473
City of San José 976,482
City of Santa Clara 130,127
City of Saratoga 30,667
City of Sunnyvale 156,234
Unincorporated County 84,458
Total 1,894,783

9.4.2 Property
There are 535,391 buildings in the OA, with a total replacement value of $381 billion. All of these buildings exist in an area susceptible to inclement weather; however, dollar loss estimates for specific building occupancy types or geographic areas are not available. Although inclement weather events are the most frequent hazard in the OA, historic dollar losses have been comparatively moderate.

9.4.3 Critical Facilities and Infrastructure
All critical facilities in the OA are potential exposed to inclement weather. Facilities may be damaged directly by high winds, hail, or by flooding that results from heavy rain. Water, electric, fuel, transportation, and communication services could be disrupted by damage caused by heavy precipitation, high winds, or space weather. Extreme temperature may also disrupt services or strain energy systems.

9.5 Vulnerability
Changes in conditions: Increase in vulnerability
 A review of past events indicates that an increasing number of inclement weather events per year for heavy rain, extreme heat, and high winds.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 172
 CMRA indicates a trend in increasing number of extreme heat days each year and the number of consecutive hot days. Climate change will continue to increase the amount of very hot days and impacts to residents will increase as a result.
 Climate change affects the frequency and intensity of storms, which contributes to the potential of damaging inclement weather events such as heavy rain, hail, and high wind across the OA.  Overall population and building growth are slow in the OA, and are not expected to be a significant factor in increased vulnerability. Currently the increase in vulnerability appears to be driven more by an increased number of events than changes in development. However, continued monitoring of demographic shifts, new insights regarding the effects of climate change, economic changes that may impact building and other development, and aging of building stock and infrastructure should continue to receive consideration on potential weather impacts.

Individual jurisdictional annexes may note localized growth at a smaller scale.

9.5.1 Population
Because of the unpredictable nature of when and where significant weather events can occur, and variable intensity of these events, all of the OAs population of 1,894,783 residents are potentially vulnerable to impacts of inclement weather. The OA has a population of nearly 10,000 people that are homeless, according to the 2023 Santa Clara Point-In-Time report. This population is especially vulnerable to the impacts of inclement weather, especially with extreme heat and cold events, which can be detrimental to human health. Only 25% of individuals experiencing homelessness are sheltered, and the other 75% may be exposed to the elements and inclement weather events. NCEI has documented cases of illness or death in Santa Clara County related to extreme heat or cold.

All other vulnerable populations such as those in poverty, the elderly, and children can be negatively impacted by inclement weather events. Hazus 6.0 demographic data indicates that 260,705 persons or

13.5 percent of the population in the OA are over 64 years old. Older persons are particularly at risk to health problems caused by extreme heat. 422,719 persons or 21.8 percent of the population within the OA under 18 years of age. It is estimated that 2.45 percent of the people within the OA are economically disadvantaged, defined as having household incomes of $20,000 or less.

People with disabilities, communities of color, persons with limited English proficiency, housing condition, health care access and education are additional factors that affect vulnerability to severe weather hazards identified in the Silicon Valley 2.0 hazard fact sheet for extreme heat. Outdoor workers and unhoused residents are among the population most at risk. According to the Silicon Valley 2.0 report, 62% of the total County population is currently exposed to extreme heat conditions and 42% of those exposed have moderate to high social vulnerability. Approximately 60,000 people within moderate socially vulnerable communities in South County jurisdictions, such as Morgan Hill and Gilroy, could be exposed to frequent extreme heat events.

All business, schools, and government systems reliant on technology are vulnerable to the impacts of space weather. As space weather has the potential to disrupt the OA’s power and communication systems, any entity reliant on technology may experience more severe impacts.

9.5.2 Property, Critical Facilities, Infrastructure
Hazus modeling is not available to quantify potential damage to property, critical facilities, or infrastructure in the OA. Physical damage and service disruption are variable depending on the size and severity of the weather event.

Although the exact location and intensity of weather events makes it difficult to project exactly what physical assets may be at risk, possible impacts might include:

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 173
Heavy Rain
• Localized pooling of water on roadways has occurred during or following past heavy rain events.

Flooding in early 2023 lead to closures of major transportation routes, including Hwy 101 in Gilroy. Vehicles may lose traction or may be unable to safely traverse some roadways. Impacts to roadways may cause delays to emergency responders.
• Heavy rain has contributed to landslides and other slope failures that have blocked or damaged roadways.
• Pedestrian travel is particularly difficult during a severe weather event. Those who rely on public transportation may have difficulty reaching transit points or difficulty finding shelter if service is interrupted
• Heavy rain has caused localized flooding and subsequent water damage to nearby structures.

Flooding from heavy rain can damage residences, commercial, industrial, or other building types.

High Wind
• Above ground utilities such as communication towers, telephone lines and power lines are vulnerable to damage from high winds. High winds have caused trees to fall which have damaged power lines and transformers, disrupting power service to large areas. • Critical facilities may also lose power if high winds damage power distribution systems and may need to rely on back-up power systems.
• High winds can damage roofs or windows to homes and businesses or other critical facilities.

Winds can also lead to fallen trees which may damage nearby buildings or sidewalks. • Outdoor events such as sporting activities, farmers markets, and community festivals can be disrupted, and participants may have difficulty seeking shelter from a fast-moving storm.

Extreme Heat
• Extreme heat may lead to increased demand on energy systems which may strain their ability provide adequate cooling to facilities and increases potential for power outages. Rolling brownouts have occurred in the Bay Area during past extreme heat events. • High temperatures can cause pavement to soften and expand which can cause rutting, potholes, or other damage to streets.
• Extreme heat has had serious health consequences for people who are unhoused or for outdoor workers.

Extreme Cold
• Extreme cold is less common in the OA, but results in difficult travel if combined with precipitation that may lead to icy roadways, airport runways, and other transportation systems. • NCEI records have documented impacts to highways, airports, and mass transit systems due to icy conditions during period of extreme cold.
• Dangerous travel conditions can lead to damage from collisions, personal injury, or economic disruption.

9.5.3 Environment
Cascading effects of heavy rain could be damaging to the environment, such as erosion caused by increased runoff or flooding, or to systems damage from landslides. Hail can cause extensive damage to plants. High winds can break tree branches or cause other damage to plant life or animal habitat.

9.5.4 Economy
Inclement weather events can disrupt the economy of the OA. Economic impact will largely be associated with the disruption of transportation, power, gas, and telecommunication services caused by high winds, or associated with flooding caused by heavy precipitation. Events severe enough to cause structural damage can also cause business interruptions. The economic sectors affected may vary significantly depending on the extent and severity of the event.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 174

9.6 Future Trends in Development, Scenario, Issues
Impacts from inclement weather pose a real threat to physical, social and economic well-being in the OA.

Multiple events can be expected to affect the OA every year, with variable severity. OA residents can use weather advisories to prepare themselves for inclement weather events, but sometimes severe events have limited warning time. Inclement weather has the potential to cause cascading impacts and can damage multiple systems in both limited and widespread areas. Although there have been small decreases in population in recent years, Santa Clara County has experienced significant growth in the past. New development may affect drainage patterns and change impacts from heavy rain. An increase in population coincides with an increased number of people at risk to weather events. As discussed further in Section 11: Climate Change, impacts of severe weather are projected to intensify due to climate change.

9.7 Issues
 Inclement weather is inherently uncertain. Conditions can change rapidly, and the severity and exact locations of an event are highly variable.
 The variable nature of inclement weather makes it difficult to identify specific locations, structures, or systems that might be more likely to be damaged in an event. This makes it difficult to identify priorities or areas for risk reduction projects.
 People may not heed weather warnings.
 Heavy rain events may result in ponding or localized flooding in low-lying areas.  Heavy rain may result in inland stormwater flooding after stormwater management systems are overwhelmed.
 Inclement weather can cause secondary hazards such as flooding, landslides, mudslides, and disruption of systems or infrastructure.
 Inclement weather events are directly related to climate change; however, climate change impacts still are poorly understood. Average temperatures are expected to increase and changes in precipitation patterns are anticipated, but it is not yet known how that will impact local weather patterns. Impacts of inclement weather events are anticipated to become more severe.

9.8 Consequence Analysis
Inclement weather events occur frequently, and these events are likely to increase in frequency over time.

They may cause a wide range of impacts, which vary greatly depending on the level of severity and extent for each event. The information in Table 58 provides the consequence analysis of the potential for detrimental impacts of inclement weather done for accreditation with the Emergency Management Accreditation Program (EMAP).

Table 58: EMAP Consequence Analysis Inclement Weather
Subject Ranking Impacts/Inclement Weather
Health and Safety of
Public in the Area of the
Incident
Severe Impact of the immediate area could be severe for affected areas and moderate to light for other less
affected areas.

Responders Moderate Impact to responders could be severe for unprotected personnel and moderate to light for prepared personnel.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 9: Inclement Weather 175
Subject Ranking Impacts/Inclement Weather
Continuity of Operations
(including continued
delivery of services)
Moderate There is a moderate expectation to execute the COOP, though a severe level of impact can be expected for the full extent of an inclement weather event.

Property, Facilities, and
Infrastructure
Minimal to
Severe
There is potential for localized impact to facilities and infrastructure in the incident area, which can range from minimal to severe depending on the extent of the
incident.

Delivery of Services Minimal to
Severe
Delivery of services could be affected if there is any
disruption to the roads and/or utilities due to damages sustained.

Environment Moderate to
Severe
Greatest impact will be to trees, bushes, foliage, crops, and wildlife, which could be severe.

Economic Conditions Minimal to
Severe
Impacts to the economy will greatly depend on the
severity of the inclement weather event, longevity of the storm, and any damages sustained such as utilities and
roads. Public Confidence in the
Government
Minimal to
Severe
Response and recovery will be in question if not timely and effective.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 176
10 Drought
Definitions
 Meteorological Drought: Occurs when rainfall has been deficient for an extended period.  Hydrological Drought: Occurs when rainfall deficits impact the water supply available from streams, reservoirs, lakes, and groundwater.
 Agricultural Drought: Occurs when factors such as rainfall deficits, soil water deficits, reduced groundwater, or low reservoir levels for irrigation result in impacts on agriculture.  Socioeconomic Drought: Occurs when diminished water supply reduces the supply of economic goods such as fruits, vegetables, grains, or meat.
 Ecological Drought: Occurs when a prolonged and widespread deficit in naturally available water supplies—including changes in natural and managed hydrology—creates multiple stresses across ecosystems.

10.1 General Background
Drought is a significant decrease in water supply relative to what is “normal” in a given location. A normal phase in the climate cycle of most geographical regions, drought originates from a deficiency of precipitation over an extended period, usually a season or more. This leads to a water shortage for some activity, group, or environmental sector.

Determination of when drought begins is based on impacts on water users and assessments of the available water supply, including water stored in surface reservoirs or groundwater basins. Different water agencies have different criteria for defining drought. Some issue drought watch or drought warning announcements. The California Water Code does not include a statutory definition of drought; however, analysis of the code indicates that legal matters most frequently focus on drought conditions during times of water shortages.

10.1.1 Monitoring and Categorizing Drought
Drought monitoring at the national, regional, and local levels is an integral part of drought early warning, planning, and mitigation.128 F
129 Nationally, agencies involved in this effort include the National Oceanic and Atmospheric Administration, National Integrated Drought Information System which produces the U.S.

Drought Monitor, and the National Drought Mitigation Center at the University of Nebraska-Lincoln.

In California, drought is addressed by the California Department of Water Resources (DWR).

The National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration (NOAA) has developed several indices to measure drought impacts and severity and to map their extent and locations:
 The Palmer Crop Moisture Index measures short-term drought weekly to quantify drought’s impacts on agriculture during the growing season.
129 National Oceanic and Atmospheric Administration. (n.d.). Monitoring Drought. https://www.drought.gov/what-isdrought/monitoring-drought Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 177
 The Palmer Drought Severity Index is based on long-term weather patterns. Long-term drought is cumulative, so the intensity of drought during a given month depends on current weather plus the cumulative weather of previous months. The Palmer Drought Index responds rapidly as weather patterns change quickly.
 The Palmer Z Index measures short-term drought on a monthly scale.  The hydrological impacts of drought (e.g., reservoir levels, groundwater levels, etc.) take longer to develop and it takes longer to recover from them. The Palmer Hydrological Drought Index is a long-term index to quantify hydrology effects. The Palmer Hydrological Drought Index responds more slowly to changing conditions than the Palmer Drought Index.  The Standardized Precipitation Index considers only precipitation. In the Standardized Precipitation Index, an index of zero indicates the median precipitation amount; the index is negative for drought and positive for wet conditions. The Standardized Precipitation Index is computed for time scales ranging from one month to 24 months.

The following graphics show the Palmer Drought Index and Palmer Hydrological Drought Index for California Climate Division 4, of which Santa Clara County is a part, from January 1, 2005, to May 20, 2023. Near normal conditions are indicated by -1.9 to +1.9. Drought conditions are indicated by -2.0 to -

4.0 or less and wet conditions are indicated by +2.0 to +4.0 or above.

Figure 45: Palmer Drought Index from January 1, 2005, to May 20, 2023129F 130
Figure 46: Palmer Hydrological Drought Index from January 1, 2005, to May 20, 2023130F 131
130 National Centers for Environmental Information. (2023, May). Weekly Palmer Drought Indices Divisional Time Series. https://www.ncei.noaa.gov/access/monitoring/weekly-palmers/time-series/0404 131 National Centers for Environmental Information. (2023, February). North American Drought Monitor. https://www.ncei.noaa.gov/access/monitoring/nadm/indices/spi/div Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 178
U.S. Drought Monitor
The U.S. Drought Monitor (USDM) is a map that is updated weekly to show the location and intensity of drought across the country. The USDM uses a five-category system.13F 132
 D0: Abnormally Dry
▪ Short-term dryness slowing planting and growth of crops ▪ Some lingering water deficits
▪ Pastures or crops not fully recovered
 D1: Moderate Drought
▪ Some damage to crops and pastures
▪ Some water shortages are developing
▪ Voluntary water-use restrictions requested
 D2: Severe Drought
▪ Crop or pasture loss likely
▪ Water shortages are common
▪ Water restrictions imposed
 D3: Extreme Drought
▪ Major crop/pasture losses
▪ Widespread water shortages or restrictions
 D4: Exceptional Drought
▪ Exceptional and widespread crop/pasture losses
▪ Shortages of water creating water emergencies

10.1.2 Normal Precipitation in California
Most of California’s precipitation comes from storms moving across the Pacific Ocean. Extremely dry and extremely wet years have become more common in California.132F 133 On average, 75 percent of California’s
annual precipitation occurs between November and March, with 50 percent occurring between December and February. A persistent Pacific high-pressure zone over California in mid-winter signals a tendency for a dry water year. A typical water year produces about 100 inches of rainfall over the North Coast, 50 inches of precipitation (combination of rain and snow) over the Northern Sierra, and 15 inches in Santa Clara County. In extremely dry years, these annual totals can fall to as little as one half, or even one third of these amounts.
132 National Integrated Drought Information System. (n.d.). U.S. Drought Monitor (USDM). https://www.drought.gov/data-maps-tools/us-droughtmonitor#:~:text=Thepercent20U.S.percent20Droughtpercent20Monitorpercent20percent28USDMpercent29percent20 ispercent20apercent20map,Severepercent20percent28D2percent29percent2Cpercent20Extremepercent20percent28 D3percent29percent20andpercent20Exceptionalpercent20percent28D4percent29percent20Drought. 133 Office of Environmental Health Hazard Assessment. (2018). Precipitation. https://oehha.ca.gov/media/epic/downloads/09precipitation_19dec2018.pdf#:~:text=Extremelypercent20drypercent20 andpercent20extremelypercent20wetpercent20yearspercent20havepercent20become,thatpercent20providepercent2 0mostpercent20ofpercent20thepercent20statepercentE2percent80percent99spercent20waterpercent20supplies.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 179
As the winter months have become warmer in recent years, more precipitation has been falling as rain instead of snow over the watersheds that provide most of the state’s water supplies. With climate change, more intense dry periods under warmer conditions are anticipated, leading to extended, more frequent drought in California. A higher proportion of precipitation falling as rain instead of snow and an increase in the duration, frequency, and intensity of warm, wet storms are also projected. This can result in greater flooding, and force reservoirs to release more water early in the spring, which means less water will be available for agriculture and municipal uses in the summer and fall.13F 134
The Sierra Nevada snowpack serves as the primary agent for replenishing water in the San Francisco Bay area, including Santa Clara County, and for much of the State of California. A reduction in spring snowpack runoff, whether due to drier winters or to increasing temperatures leading to more rain than snow, can increase the risk of summer or fall water shortages throughout the region.

Increases in temperature are already causing decreases in snowpack. The mountain snowpack provides as much as a third of California’s water supply by accumulating snow during our wet winters and releasing it slowly during our dry springs and summers. Warmer temperatures will melt the snow faster and earlier, making it more difficult to store and use throughout the dry season. The DWR Climate Change Team expects that by the end of this century, California’s Sierra Nevada snowpack is projected to experience a 48–65 percent loss from the historical April 1 average of 66.5 inches.134F 135

10.1.3 Water Supply Strategy
The Bay Area Water Supply Conservation Agency (BAWSCA) is the main water provider for much of the Bay Area, allowing Santa Clara Valley Water District (SCVWD) to manage the continual water supply necessary to maintain health, safety, and economic wellbeing of residents, businesses, and community organizations. BAWSCA developed a two-phase, long-term water supply strategy for customers throughout the Bay Area, as outlined in the 2015 Long-Term Reliable Water Supply Strategy Phase II Final Report.135 F
136 Purposes of its strategy are as follows:
 Quantifying water supply reliability needs of BAWSCA member agencies through 2040.  Identifying water supply management programs or programs that can be developed to meet those regional water reliability needs.
 Developing an implementation plan for the water supply strategy.

This strategy recognized that drought-year shortfalls could be significant but determined that normalyear water supply would be adequate through at least 2040. Dry years could result in system-wide cutbacks of up to 20 percent, but 10 to 15 percent is the more consistent standard. BAWSCA noted that the impacts of water shortages would be regional and could lead to secondary detrimental economic effects. To address this concern, the strategy focused on identifying options for filling all or part of the drought-year supply shortfall and investigating and potentially implementing actions that seem most beneficial.136F
137
134 Office of Environmental Health Hazard Assessment. (2018). Precipitation. https://oehha.ca.gov/media/epic/downloads/09precipitation_19dec2018.pdf#:~:text=Extremelypercent20drypercent20 andpercent20extremelypercent20wetpercent20yearspercent20havepercent20become,thatpercent20providepercent2 0mostpercent20ofpercent20thepercent20statepercentE2percent80percent99spercent20waterpercent20supplies. 135 California Department of Water Resources. (n.d.). Climate Change and Water. https://water.ca.gov/Programs/AllPrograms/Climate-Change-Program/Climate-Change-and-Water 136 Bay Area Water Supply Conservation Agency. (2015 February). Long-Term Reliable Water Supply Strategy. https://bawsca.org/water/reliability/strategy
137 Bay Area Water Supply & Conservation Agency. (n.d.). Water Supply & System. https://bawsca.org/water/supply Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 180
BAWSCA also developed a Water Conservation Implementation Plan,137F 138 focusing on the following
objectives:
 Help BAWSCA member agencies evaluate potential water savings and cost-effectiveness associated with implementing additional water conservation measures beyond their commitments of 2004.
 Determine potential water savings in 2018 and 2030 based on a selected range of new conservation measures and the 2004 water conservation commitments.  Determine BAWSCA’s role in helping member agencies achieve individual water conservation goals.
 Develop a coordinated regional plan for water conservation implementation measures to serve as a guideline for member agencies.

In the Santa Clara County OA, the following districts and cities are members of BAWSCA: SCVWD, Milpitas, Mountain View, Palo Alto, San José, City of Santa Clara, Sunnyvale, Purissma Hills Water District, and Stanford University.138F
139
The SCVWD is the wholesale water and groundwater management agency throughout Santa Clara County, relying on local retailers (municipalities and private companies) to deliver water throughout the County.139F
140 The following are the retailer water providers for each municipal planning partner:
 Campbell: San José Water Company
 Cupertino: San José Water Company and California Water Service Company  Gilroy: Gilroy Public Works Department
 Los Altos: California Water Service Company
 Los Altos Hills: Purissima Hills Water District and California Water Service Company  Los Gatos: San José Water Company
 Milpitas: City of Milpitas Community Services
 Monte Sereno: San José Water Company
 Morgan Hill: City of Morgan Hill
 Mountain View: City of Mountain View Public Works
 Palo Alto: City of Palo Alto Utilities Department
 San José: San José Water Company, Great Oaks Water Company, and San José Municipal Water System
 Santa Clara City: City of Santa Clara Water Department  Saratoga: San José Water Company
138 Bay Area Water Supply & Conservation Agency. (n.d.). Conservation Implementation Plan. https://bawsca.org/conserve/reports/plan#:~:text=Thepercent20specificpercent20objectivespercent20ofpercent20thep ercent20WCIPpercent20arepercent20as,beyondpercent20whatpercent20theypercent20hadpercent20committedperc ent20topercent20inpercent202004.
139 Bay Area Water Supply & Conservation Agency. (2020). Member Agency Map. https://bawsca.org/members/map 140 Santa Clara Valley Water District. (2021). Groundwater Management Plan. https://s3.us-west2.amazonaws.com/assets.valleywater.org/2021_GWMP_web_version.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 181
 Sunnyvale: City of Sunnyvale Public Works Department and California Water Service Company
The SCVWD has its own water supply strategy outlined in the SCVWD Water Supply Master Plan 2040.140F 141
The Water Master Plan 2040 outlines a water supply strategy with three key elements:
 Secure existing supplies and facilities.
 Optimize the use of existing supplies and facilities.  Expand water use efficiency efforts.

Some County residents have domestic wells on their property. The North Central Regional Office of California DWR monitors wells for Santa Clara County to help protect groundwater quality.14F 142 Under
Ordinance 90-1, as of July 1, 2013, a person must obtain a permit from SCVWD to perform any well activities. In response to extreme and expanding drought conditions, as those existing on March 28, 2022, the state can prohibit Valley Water and other well permitting agencies from issuing a construction permit for a new groundwater well.142F
143

10.1.4 Water Supply Infrastructure
Figure 46 shows the SCVWD water supply system. Santa Clara County receives 50 percent of its water supply from the San Francisco Bay-Delta watershed. Of this water, 40 percent comes directly through the Delta watershed or water conveyance systems and 10 percent is from the Hetch-Hetchy System. Another 30 percent of the County’s supply is local, from natural groundwater, reservoirs to groundwater, and reservoirs to drinking water treatment plans. Five percent is recycled water, primarily used for irrigation, industry, and agriculture. A 15 percent water-use reduction by the community is required to reach the needed water supply total.143F
144
141 Santa Clara Valley Water District. (2019, November). Water Supply Master Plan 2040. https://www.valleywater.org/sites/default/files/Waterpercent20Supplypercent20Masterpercent20Planpercent202040_

11.01.2019_v2.pdf
142 California Department of Water Resources. (n.d.). Technical Assistance. https://water.ca.gov/Programs/Integrated-Regional-Water-Management/Technical-Assistance 143 Santa Clara Valley Water District. (n.d.). Well Permits and Inspections. https://www.valleywater.org/contractors/doing-businesses-with-the-district/wells-well-owners/well-permits-andinspections 144 Santa Clara Valley Water District. (n.d.). Where Your Water Comes From. https://www.valleywater.org/yourwater/where-your-water-comes Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 182
Figure 47: Santa Clara Valley Water District System Water Supply14F 145
The Hetch-Hetchy Water System was approved in 1913 under the Raker Act, which allowed use of federal lands to build that water system. The water system was constructed by San Francisco over the next 20 years, with first delivery of water in 1934. Although the system is owned by San Francisco, it was designed from the beginning to serve as a regional water supply system.145 F 146 Figure 47 shows the HetchHetchy Water System.
145 Santa Clara Valley Water District. (n.d.). Where Your Water Comes From. https://www.valleywater.org/yourwater/where-your-water-comes 146 Bay Area Water Supply and Conservation Agency. (n.d.). Hetch Hetchy System. https://bawsca.org/water/supply/hetchhetchy
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 183
Figure 48: Hetch Hetchy Water System146F
147

10.2 Hazard Profile
Droughts originate from a deficiency of precipitation resulting from an unusual weather pattern. Such patterns can be short-term, lasting for a few weeks or months, or long-term, lasting for many months or for years. It is possible for a region to experience a long-term circulation pattern that produces drought, and to have short-term changes in this long-term pattern that result in short-term wet spells. Likewise, it is possible for a long-term wet circulation pattern to be interrupted by short-term weather spells that result in short-term drought. Droughts typically occur after 2 or 3 years of below-average rainfall during the period from November to March, when about 75 percent of California’s average annual precipitation falls.

10.2.1 Past Events
California is no stranger to drought; it is a recurring feature of our climate.147F 148 The DWR has state
hydrologic data from as far back as the early 1900s which indicate occurrences of multi-year droughts from 1912 to 1913, 1918 to 1920, and 1922 to 1924. Between 1954 and 2016, California experienced one FEMA-declared emergency (EM) classified as a drought: FEMA Declaration EM-3023 in 1977, which applied to 58 California counties, including Santa Clara County.148F 149 Santa Clara’s drought history includes
years of drought followed by years with little drought.  1976 to 1977: California had one of its most severe droughts during the winters of 1976 and 1977. 1977 was the driest period on record in California, with the previous winter recorded as the fourth driest in California’s hydrological history. The cumulative impact led to widespread water shortages and severe water conservation measures across the state. Only 37 percent of normal Sacramento Valley runoff was received.
147 Bay Area Water Supply and Conservation Agency. (n.d.). Hetch Hetchy System. https://bawsca.org/water/supply/hetchhetchy
148 California Department of Water Resources. (n.d.). Drought. https://water.ca.gov/drought/ 149 Federal Emergency Management Agency. (n.d.). California Drought EM-3023-CA. https://www.fema.gov/disaster/3023
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 184
 Over $2.6 billion in crop damage was recorded in 31 counties. Santa Clara County was included in FEMA-3023-EM-CA declaration on January 20, 1977.
 1987 to 1992: California’s received precipitation was well below average levels for four consecutive years. While the Central Coast was most affected, the Sierra Nevada mountains in Northern California and the San Joaquin Valley (Central Valley) were also affected. Water suppliers did not experience shortages until the third or fourth year of the drought. Reservoir storage provided a buffer against drought impacts during the initial years of the drought. In 1991, the State Water Project sharply decreased deliveries to water suppliers, including the San Francisco Bay Area. The SCVWD implemented drought contingency measures such as rationing and mandatory conservation to reach its 25 percent reduction goal. By February 1991, all 58 counties in California were suffering under drought conditions that affected urban, rural, and agricultural areas. Some counties had declared a local drought emergency, but Santa Clara County was not included.
 1993 to 2006: Rainfall in this period reached previous highs, but severe drought conditions returned in 2007.
 2007 to 2009: A governor’s executive order proclaimed a statewide drought emergency on June 4, 2008, after spring 2008 was the driest spring on record, with low snowmelt runoff. On February 27, 2009, after the largest court-ordered water restriction in state history up to that time, a state of emergency was proclaimed for the entire state as the severe drought conditions continued. Santa Clara County received about half of its water through the Sacramento-San Joaquin River Delta, which was already significantly limited that year because of pumping restrictions mandated under the Endangered Species Act.149F 150 Water deliveries through the Delta
were cut by about 20 to 30 percent. The SCVWD had mandatory water conservation and rationing measures in effect to reduce usage by 15 percent.
 2012 to 2017: California’s drought has set several records. From 2012 to 2014, it ranked as the driest three consecutive years for statewide precipitation. New climate records were set in 2014 for statewide average temperatures and for record-low water allocations from State Water Project and Central Valley Project contractors. A statewide drought emergency was declared in January 2014. Minimum annual precipitation records were set for many communities in 2013. Executive orders and regulations called for water conservation and management. A new law requires retail urban water suppliers with more than 3,000 customers to establish rules defining “excessive water use” and impose those rules during drought emergencies. On its website, DWR refers to “the five-year drought that ended in 2016.150 F
151 On April 2, 2017, Governor Brown lifted the drought emergency imposed in 2014 but declared that California must continue water conservation efforts USGS).15F
152
 2017 to Present: The National Drought Mitigation Center developed the Drought Impact Reporter152 F
153 as a national drought impact database for the United States. Information comes from a variety of sources: on-line, drought- related news stories and scientific publications, members of the public who visit the website and submit a drought-related impact for their region, members of the media, and members of relevant government agencies. The database is being populated beginning with the most recent impacts and working backward in time. 150 U.S. Fish and Wildlife Service. (n.d.). Endangered Species Act. https://www.fws.gov/media/endangered-speciesact 151 California Department of Water Resources. (n.d.). Countywide Drought and Water Shortage Contingency Plans. https://water.ca.gov/Programs/Water-Use-And-Efficiency/2018-Water-Conservation-Legislation/County-DroughtPlanning 152 USGS. (n.d.). 2012-2016 California Drought: Historical Perspective. (https://ca.water.usgs.gov/californiadrought/california-drought-comparisons.html 153 National Drought Mitigation Center. (n.d.). Drought Impact Reporter. https://www.drought.gov/data-mapstools/drought-impact-reporter-dir Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 185
Between January 2017 and January 2023, the Drought Impact Reporter153F 154 described more than
fifty incidents of drought-related events in the Santa Clara OA. Highlights of that list are presented below.
▪ Feb. 8, 2017: The State Water Resources Control Board opted to keep the water restrictions until spring to see how the rest of winter plays out, in terms of precipitation, before making any changes to the restrictions.
▪ March 22, 2017: Farmers south of the Sacramento-San Joaquin Delta learned that they would receive 65 percent of full allocations from the U.S. Bureau of Reclamation, despite the heavy rainfall the state has received, leading to flooding, full reservoirs, and deep snowpack. ▪ April 11, 2017: The U.S. Bureau of Reclamation announced that South of Delta water contractors would receive a 100 percent allocation from the Central Valley Project. ▪ Jan. 30, 2018: The California Department of Water Resources announced that customers of the State Water Project would receive 20 percent of their requests. ▪ Feb. 22, 2018: Eastside water service contractors will receive 100 percent of their contracts. ▪ 2019: No relevant reports on drought.
▪ Feb. 25, 2020: North-of-Delta agriculture contractors will receive 50 percent of their contracted supply, while South-of-Delta agriculture contractors will receive 15 percent. ▪ Feb. 27, 2020: Northern California ranchers with unirrigated pastures were already giving their cattle supplemental feed as grasses have dried out months earlier than usual. ▪ May 26, 2020: After a dry winter, the State Water Project increased its allocation to 20 percent following above normal precipitation in May.
▪ Feb. 23, 2021: The upcoming March snowpack survey and a planned airborne snow survey will provide more information on the amount of water available for growers. The Tuolumne snowpack measured just 55.6 percent of the historical average for the date. ▪ March 17, 2021: Customers of the Santa Clara Valley Water District were urged to increase their conservation efforts, but no water restrictions were mandated just yet. ▪ March 23, 2021: The California Department of Water Resources updated its initial water allocation for the 2021 water year to 5 percent of requested supplies, down from 10 percent as announced in December 2020.
▪ March 23, 2021: The State Water Board sent notices to California’s 40,000 water users, including small farms and big cities, to alert them to prepare for cuts in water deliveries. ▪ April 28, 2021: The board also voted unanimously to double the price it pays homeowners to use drought-tolerant landscaping from $1 per square foot to $2. The district serves nearly two million people in Santa Clara County.
▪ May 5, 2021: Farmers north of the Sacramento-San Joaquin Delta learned that they will not receive even 5 percent of contracted water from the Central Valley Project. Water deliveries were suspended, due to limited supply, according to the Bureau of Reclamation. ▪ May 26, 2021: The U.S. Bureau of Reclamation announced that municipal water agencies that get water from the Central Valley Project would receive just 25 percent of their allocation. 154 National Integrated Drought Information System. (n.d.). Drought Impact Reporter Dashboard. https://unldroughtcenter.maps.arcgis.com/apps/dashboards/46afe627bb60422f85944d70069c09cf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 186
▪ May 27, 2021: The federal government announced water cuts to urban areas of more than half, which will lead the Santa Clara Valley Water District. ▪ June 10, 2021: Mandatory water restrictions were issued for Santa Clara County, due to the low water supply.
▪ June 25, 2021: A local emergency was declared in Santa Clara County, due to extreme drought.
▪ July 4, 2021: Farmers were not getting any water from the state or federal projects. ▪ July 8, 2021: California Gov. Gavin Newsom requested that people and businesses curb their water use by 15 percent as intense drought persisted.
▪ Aug 2, 2021: Santa Clara Valley Water District does not have enough water to release to support the fish.
▪ Nov 23, 2021: The San Francisco Public Utilities Commission urged almost 3 million water customers in the Bay Area to curb water use by 10 percent and declared a water shortage emergency.
▪ Dec 2, 2021: The State Water Resources Control Board proposed new emergency drought regulations to discourage water waste as water supplies were low after continued drought. ▪ March 15, 2022: Despite the record dry January and February, Californians are falling short on voluntary water conservation.
▪ May 23, 2022: Urban water use increased 18.9 percent in March. ▪ May 25, 2022: Water users in Santa Clara County could be fined $500, or even up to $10,000, as the Santa Clara Valley Water District enacted new drought rules. ▪ June 7, 2022: Public systems, like the City of San Francisco, will have to have to turn to groundwater or other sources.
▪ Oct 19, 2022: Many trees in California’s forests were turning rust colored as another year of drought and bark beetles or other insects.
▪ Nov 28, 2022: Water storage was near historic lows, with Shasta Reservoir, the largest reservoir in the Central Valley Project, at 31 percent of capacity. ▪ Nov 30, 2022: A survey of California urban water agencies representing about 90 percent of the state’s population showed that about 18 percent, or 73 of the 414 water suppliers, indicated that they will soon face potential shortages. ▪ Dec 1, 2022: The Department of Water Resources announced an initial State Water Project allocation of 5 percent of requested supplies for 2023. ▪ Jan 26, 2023: The series of storms that brought heavy rain and snow to California have partially filled reservoirs, allowing the State Water Project to offer 30 percent of requested water supplies to 29 public water agencies that serve 27 million Californians. The initial allocation in December was just 5 percent.

U.S. Department of Agriculture Disaster Declarations
The U.S. Department of Agriculture (USDA) Farm Service Agency provides assistance for natural disaster losses resulting from drought, flood, fire, freeze, tornadoes, pest infestation, and other natural disasters.

The USDA Secretary of Agriculture is authorized to designate counties as disaster areas to make emergency loans to producers suffering losses in those counties and in contiguous counties.

For drought-related data between 2017 and 2022, the period for which data was available, California has been included in 55 State and County Level Records of Disaster Designation Information made by the US Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 187
Secretary of Agriculture. Santa Clara County was included in seven of these declarations in relation to drought. 154F
155
Table 59: U.S. Department of Agriculture Disaster Declarations Including Santa Clara County, 2017–2022
Year Declaration Number(s)
2017 S4144 and S4163
2018 None
2019 None
2020 S4697
2021 S4916, S4969, and S4958
2022 S5146

10.2.2 Location
Drought is a regional phenomenon. A drought that affects the Santa Clara County OA would affect all aspects of the environment and the community simultaneously and has the potential to impact every person directly or indirectly in the county as well as adversely affect the local economy. “The norm for California’s climate is to move back and forth frequently between wet and dry conditions, and water conservation must be a way of life for all who enjoy living in or visiting our state.”
Karla Nemeth, Director of California Department of Water Resources March 12, 2018

10.2.3 Frequency
Historical drought data regarding Santa Clara County indicate four significant droughts over the last 40 years, with drought occurring in 12 of those 40 years.15F 156 Based on risk factors and this history, droughts
likely will continue to occur cyclically in the Santa Clara County OA.

Further information on the impact of climate change on the probability of drought is included in Section

11. Probability in OA: Likely
155 U.S. Department of Agriculture. (n.d.). Disaster Designation Information. https://www.fsa.usda.gov/programs-andservices/disaster-assistance-program/disaster-designation-information/index 156 National Integrated Drought Information System. (n.d.). Drought Conditions for Santa Clara County. https://www.drought.gov/states/california/county/santapercent20clara Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 188

10.2.4 Warning Time
Empirical studies conducted over the past century have shown that meteorological drought is never the result of a single cause. It is the result of many causes, often synergistic in nature; these include global weather patterns that produce persistent, upper-level high-pressure systems along the West Coast with warm, dry air resulting in less precipitation.

Scientists at this time do not know how to predict drought more than a month in advance for most locations. Predicting drought depends on the ability to forecast precipitation and temperature. Anomalies of precipitation and temperature may last from several months to several decades; California is currently finishing a several-year-long drought, while other areas in the United States may undergo droughts as short as 1 or 2 months. How long droughts last depends on interactions between the atmosphere and the oceans, soil moisture and land surface processes, topography, internal dynamics, and the accumulated influence of weather systems on the global scale.

10.2.5 Extent
Figure 48 displays data from the U.S. Drought Monitor for the State of California from 2000 through 2023.

Several periods of moderate to extreme drought have occurred during this time. D0 Abnormally Dry represents the least severe drought conditions and D4 Exceptional Drought represents the most severe.

As noted in 10.2.1 Past Events, significant droughts have occurred from 2007-2009, 2012-2017 and 2000-2023. During these events, significant portions of the entire state were impacted. The OA has experienced conditions from D0 to D4 at different times within this time frame. Figure 49 displays a snapshot of conditions during the most recent drought. During the fall of 2022, the entire OA was experiencing Severe Drought conditions, with the easternmost part of the county experiencing Extreme Drought. As noted in 10.1.4, a significant portion of the OA water supply originates outside of the area which may experience different drought severity.

Figure 49: U.S. Drought Monitor Time Series California 2000-2023 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 189
Figure 50: U.S. Drought Monitory Map of California

10.2.6 Severity and Impacts
The severity of a drought depends on the degree of moisture deficiency, the duration, and the size and location of the affected area. The longer the duration of the drought and the larger the area impacted, the more severe the potential impacts. Drought can have a widespread impact on the environment and the economy, although it typically does not result in loss of life or damage to property, as do other natural disasters. Drought affects agriculture, business and industry, energy, fire, plants, tourism and recreation, and water supply and quality.

The Drought Impact Reporter contains information on 154 impacts from droughts that affected Santa Clara County from January 2017 through January 18, 2023. The following are the categories and reported number of impacts. Note that some impacts have been assigned to more than one category.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 190
Figure 51: Reported Number of Drought Impacts by Category156F 157
The National Drought Mitigation Center uses three categories to describe drought impacts:
 Economic Impacts: These impacts of drought cost people or businesses money. They include farmers’ loss of crops, costs for irrigation or drilling new wells to address low water supply, lost business for companies that sell boats or fishing equipment, and water companies’ costs for additional water supplies.
 Environmental Impacts: Plants and animals depend on water. When a drought occurs, their food supply can shrink, and their habitat can be damaged.
 Social Impacts: Social impacts include public safety, health, conflicts between people when there is not enough water to go around, and changes in lifestyle.

Drought generally does not affect groundwater sources as quickly as surface water supplies, but groundwater supplies generally take longer to recover. Reduced precipitation during a drought means that groundwater supplies are not replenished at a normal rate. This can lead to a reduction in groundwater levels and problems such as reduced pumping capacity or wells going dry. Shallow wells are more susceptible than deep wells. Reduced replenishment of groundwater affects streams. Much of the flow in streams comes from groundwater, especially during the summer when there is less precipitation and after snowmelt ends. Reduced groundwater levels mean that even less water will enter streams when steam flows are lowest.
157 National Drought Mitigation Center. (n.d.). Drought Impact Reporter. https://www.drought.gov/data-mapstools/drought-impact-reporter-dir Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 191

10.2.7 Responses to Recent Drought
Table 60: Recent Federal and State Drought Responses
Date Federal and State Drought Response
April 2021 Drought emergency proclamation for parts of the state.

May 2021 Drought emergency proclamation issued in April 2021 expanded to include Santa Clara County and $5.1 billion package to:
 Address immediate emergency needs.
 Build regional capacity to endure drought.
 Safeguard water supplies for communities, the economy, and the environment.

July 2021 Voluntary 15 percent water use reduction.

October 2021 State Water Board empowered to prohibit wasteful uses of potable water such as washing sidewalks or driveways.

January 2022 State Water Board prohibited using drinking water for activities such as filling decorative fountains/ponds, washing sidewalks and driveways, watering lawns during and right after rain, and using hoses without automatic shutoff nozzles.

March 2022 Local water suppliers called to move to Level 2 of their Water Shortage Contingency Plans. U.S Department of Agriculture Livestock Forage Disaster Program activated.

August 2022 California’s Water Supply Strategy, which includes creating additional water storage space, recycling and reusing water, increasing efficient water use and conservation, and diversifying water supplies, was released.

September 2022 California Legislature provides additional funds to state residents to replace their lawns with drought-resistant plants and landscaping.

November 2022 The California Department of Water Resources Control Board adopted new performance standards that require urban retail water suppliers to monitor and reduce leakage in their distribution systems. The California Legislature authorized over a billion dollars in funding to the California Department of Water Resources for drought relief in 2021 and 2022.

December 2022 The California Department of Water Resources Control Board extends its emergency regulation to January 2024.

Urban Water Suppliers’ Responses to Defined Drought Stages The California Water Code, Sec. 10632 was amended in 2016 to provide guidance on stages of action to be undertaken by urban water suppliers. It requires them to develop a plan that incorporates an urban water shortage contingency analysis that includes each of the following elements that are within the authority of the urban water supplies. Stages of action to be undertaken by the urban water supplier in response to water supply shortages, including up to a 50 percent reduction in water supply.

The extreme drought and water shortage emergency condition in summer 2022 called for water use restrictions. In responding to the drought condition, the SCVWD declared a water shortage emergency condition in June 2021 that called for 15 percent water use reduction to minimize water shortage risk. The call for water conservation has been instrumental in reducing county-wide water use and helps alleviate the negative consequence of the ongoing drought.

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Since the call, county-wide water use has been reduced by 6 percent cumulatively against a 2019 baseline.157F
158 In winter 2023 when this plan is being written, conditions continue to improve; but the county is still in a “D-1 Moderate Drought”. Participating municipality retail water providers’ drought contingency measures are described in the annexes in Volume 2 of this hazard mitigation plan, as applicable.

10.3 Cascading Hazards
When natural hazard events overlap or occur in quick succession, the events can compound and cause detrimental effects. Drought is particularly likely to be part of a cascading hazard because it can cover a large area and go on for a long time.158F
159

10.3.1 Drought and Wildfire
The hazard most associated with drought is wildfire (see Section 8). A prolonged lack of precipitation dries out vegetation, which becomes increasingly susceptible to ignition as the duration of the drought extends. Reduced ponds, streams, and reservoir levels can also limit withdrawal sources for fighting wildfires. The extreme conditions can also increase the likelihood of shrub and tree mortality by wildfire in previously fire-adapted ecosystems, Millions of board feet of timber have been lost, and in many cases, erosion occurred, which caused considerable damage to aquatic life, irrigation, and power production by heavy silting of streams, reservoirs, and rivers in addition to habitat and infrastructure losses and threats to animal and human life.

10.3.2 Drought and Extreme Heat
Drought is often accompanied by extreme heat, exposing people to the risk of sunstroke, heat cramps and heat exhaustion. Periods of extreme heat increase evaporation, leading to reduced water availability in soils and surface water supplies. Periods of drought can cause extreme heat due to lack of water in the atmosphere, soils, and rivers, where decreased water availability in the system reduces the amount of evaporation happening at the surface, quickly increasing temperatures. Extreme heat can also increase water demands, in which human activities can reduce water supplies, leading to human-caused drought.

These hazards occurring together can compound health impacts, reduce energy production, cause loss of aquatic life due to reduced stream and reservoir levels and increased water temperatures, kill vegetation, and create dangerous air quality issues.

10.3.3 Drought and Flooding
Drought, along with wildfires that can stem from drought, increases flood risk. Extended drought and wildfire can stress and reduce the amount of vegetation. When it does rain, the reduction of vegetation can increase flooding due to faster runoff rates, compared to normal conditions when abundant vegetation slows runoff and increases water absorption into the ground. Drought or wildfire conditions prior to flooding can also cause water quality deterioration from the increased soil and ash particles in the runoff. On farmlands, drought conditions prior to flooding may also cause a surge of farm chemicals applied to crops to enter streams through runoff. These factors can affect the water quality for aquatic life, animals, and humans, who are all dependent on the water source. Increased instances of flash flooding may also occur.
158 Santa Clara Valley Water District. (2022, November 22). Board of Directors Meeting Agenda. https://scvwd.legistar.com/Calendar.aspx
159 American Planning Association. (2019). Falling Dominoes: A Planner’s Guide to Drought and Cascading Impacts. https://abag.ca.gov/sites/default/files/falling-dominoes-planners-guide-to-drought-and-cascading-impacts.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 193

10.3.4 Drought and Landslides
Droughts can indirectly cause landslides through a cascade of natural hazards. For example, drought can cause dry conditions and increased fuel loads for wildfires that, in turn, can increase the likelihood of flooding. The ash-infused topsoil, which is water repellent, and loss of vegetation can increase runoff and take large amounts of earthen material with them, causing devastating impacts to populations in the path of the landslide event. Such events could cause the loss of infrastructure and life. From an environmental standpoint, they may also affect the water quality of downstream rivers and streams and the habitat for animals, flora, and fauna. Landslides can also alter the topography of the landscape, which can modify surface and groundwater flow patterns.

10.4 Vulnerability
Changes in conditions: increase in vulnerability
 The CMRA tool in Figure 51 shows an increasing number of days without precipitation and an increase in the consecutive number of days without precipitation.  Extended periods of drought have the potential to impact the water supply in the OA.  Drought results in dryer vegetation and increased tree mortality, which compounds conditions that contribute to wildfire risk.
 Loss of vegetation due to drought may increase vulnerability to landslides.  Ongoing drought may contribute to land subsidence if groundwater is not recharged.  SCVWD is implementing recycled and purified water programs to provide access to droughtresistant water supply.  The National Risk Index reports and Expected Annual Loss of $1,771,981 for drought based on crop impacts.
 Santa Clara has adopted the Water Efficient Landscape Ordinance to promote water use efficiency and sustainable landscape design practices.

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Figure 52: CMRA Drought Hazard: Days without Precipitation Indicator for Santa Clara County

10.4.1 Population
The entire population of the Santa Clara County OA is vulnerable to drought events. Drought can affect people’s health and safety, including health problems related to low water flows, insect infestation, poor water quality, or dust. Droughts can also lead to loss of human life.159F 160 The Centers for Disease Control
and Prevention (CDC) has identified the indirect role of drought in people’s deaths through disruptions of agriculture and water systems, poor air quality, and increased heat-related and respiratory illnesses. In a recent study, they have also addressed the increased occupational psychosocial stress among U.S. farmers.160F
161 Other possible impacts include recreational risks; effects on air quality; diminished living conditions related to energy, air quality, and hygiene; compromised food and nutrition.

These negative health effects are more likely to impact populations that already have higher health risks, such as the old or young. Hazus 6.0 demographic data indicates that 260,705 persons or 13.5 percent of the population in the OA are over 64 years old and 422,719 persons or 21.8 percent of the population within the OA under 18 years of age. These people may experience worse effects from poor air quality or reduced nutrition resulting from agricultural production loss. It is also estimated that 2.45 percent of the people within the OA are economically disadvantaged, defined as having household incomes of $20,000 or less. Those with fewer financial resources are often less resilient to hazard impacts.

The SCVWD, BAWSCA, regional water purveyors, and other regional stakeholders have devoted considerable time and effort to protect life, safety, and health during times of consecutive dry years, such as the current drought. Provisions and measures have been taken to analyze and account for anticipated 160 National Oceanic and Atmospheric Administration. (2016, June 15). Drought in America: Slow Moving, Far Reaching. https://www.noaa.gov/explainers/drought-in-america-slow-moving-far-reaching 161 National Integrated Drought Information Systems. (2021, July 24). The Association Between Drought Conditions and Increased Occupational Psychosocial Stress Among U.S. Farmers. https://www.drought.gov/documents/association-between-drought-conditions-and-increased-occupationalpsychosocial-stress Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 195
water shortages. With coordination from its cities, the SCVWD has the ability to minimize and reduce impacts on residents and water consumers in the Santa Clara County OA.

10.4.2 Property
Significant depletion of groundwater supplies—from drought, excessive groundwater pumping or both— can lead to subsidence, which is the downward collapse of the land surface when groundwater aquifers lack the water to support the weight of the ground. Compaction of aquifer systems is the greatest cause of subsidence in California. Although this is typically due to groundwater pumping rather than drought, drought creates a need for greater groundwater pumping as freshwater sources disappear. Droughtinduced subsidence is not as common as wildfire or extreme heat, but it can significantly impact the local environment, floodplain/wetlands, and water supply, and it typically is irreversible. It may cause wetlands to change size and shape, migrate to lower elevations, or disappear entirely. Rivers may change course, and patterns of erosion and deposition may change.16F
162
No structures will be directly affected by drought conditions, though droughts often lead to reduced local fire suppression capabilities which could threaten structures. Some structures may become vulnerable to wildfires, which are more likely following years of drought.

Drought conditions may also be the cause of serious foundation problems and have significant impacts on landscapes, which could cause a financial burden to property owners. However, these impacts are not considered critical in planning for impacts from the drought hazard.

Drought is detrimental to agricultural assets and other natural resources. Although the agricultural sector is relatively small in the OA, a significant area in the southeast area of the county near Gilroy is involved in agricultural production. Extended drought may diminish the productivity of agricultural lands and impact their value. The National Risk Index reports and Expected Annual Loss of $1,771,981 to crops due to drought in Santa Clara County. This area would likely feel more significant impact of drought due to crop losses caused by drought or impacts to water supplies.

10.4.3 Critical Facilities
Critical facilities as defined for this plan will continue to be operational during a drought. Critical facility elements such as landscaping may not be maintained due to limited resources, but the risk to the Santa Clara County OA’s critical facilities functions is low.

10.4.4 Environmental Impact
Environmental losses from drought are associated with damage to plants, animals, wildlife habitat, and air and water quality; forest and range fires; degradation of landscape quality; loss of biodiversity; and soil erosion. Some of the effects are short-term and conditions quickly return to normal following the end of the drought. Other environmental effects linger for some time or may even become permanent.

Wildlife habitat, for example, may be degraded through the loss of wetlands, lakes, and vegetation.

However, many species will eventually recover from this temporary aberration. The degradation of landscape quality, including increased soil erosion, may lead to a more permanent loss of biological productivity. Although environmental losses are difficult to quantify, growing public awareness and 162 United States Geological Survey. (2000, December). Land Subsidence in the United States. https://water.usgs.gov/ogw/pubs/fs00165/#:~:text=Thepercent20sitepercent20ispercent20inpercent20thepercent20Sa npercent20Joaquinpercent20Valley,resultedpercent20inpercent20permanentpercent20subsidencepercent20andperc ent20relatedpercent20groundpercent20failures.

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concern for environmental quality has forced public officials to focus greater attention and resources on these effects.

Santa Clara County Tree Mortality Exposure
Large numbers of trees have died in California since the beginning of the 2012-2016 drought. Most of these trees were stressed from higher temperatures and a shortage of water, making them more vulnerable to insects and diseases. California’s pattern of tree mortality corresponds with global trends that are linked to increasingly dry and hot climatic conditions. Prolonged periods of drought, combined with the increased infestation of native bark beetles, have contributed to the death of millions of trees on federal, state, and private lands across the state. Removal of these dead trees can be costly and challenging, which can add to the financial impacts of drought. “Many trees in California’s forests were turning rust colored as another year of drought and bark beetles or other insects led to higher tree mortality. Trees were stressed from inadequate water and could not produce enough sap or pitch to defend themselves against insects.” Drought Impact Reporter Dashboard
October 19, 2022
The following figures show the areas where the state is focused for removal of dead trees. The Tier 1 Tree Mortality High Hazard Zones (see Figure 52) represent areas of tree mortality in direct proximity to assets determined to be important to life and property (including communications, transportation, recreation, communities, and utilities). These areas were designated by state and local governments as being in greatest need of dead tree removal, pursuant to the California Governor’s Emergency proclamation on October 30, 2015.

The Tier 2 Tree Mortality High Hazard Zones, shown in Figure 53, are defined by watersheds that have elevated tree mortality as well as significant community and natural resource assets.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 197
Figure 53: Tier 1 Tree Mortality High Hazard Zones162 F 163
Figure 54: Tier 2 Tree Mortality High Hazard Zones163 F 164
163 California State Geoportal. (2022 June 2). California High Hazard Zones (Tier 1). https://gis.data.ca.gov/maps/a71a85136b0b414ea734fdfbe3d7674a/explore?layer=0&location=37.231739%2C121.694821%2C9.99 164 California State Geoportal. (2022 June 2). California High Hazard Zones (Tier 2). https://hub.arcgis.com/maps/e50b7577426c4367a518b80b38e9b5d8/explore?location=37.371146%2C121.549960%2C10.88 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 198

10.4.5 Economic Impact
Drought causes the most significant economic impacts on industries that use water or depend on water for their business, most notably, agriculture and related sectors (forestry, fisheries, and waterborne activities). In addition to losses in yields in crop and livestock production, drought is associated with increased insect infestations, plant diseases, and wind erosion. Water- and lake-related recreational activities including, but not limited to, fishing, swimming, rafting, and canoeing are valuable for the local and regional economy, particularly when the lake/reservoir is located in a rural area with limited other recreational/tourism opportunities. Drought can lead to other losses because so many sectors are affected losses that include reduced income for farmers and reduced business for retailers and others who provide goods and services to farmers.

This leads to unemployment, increased credit risk for financial institutions, capital shortfalls, and loss of tax revenue. Prices for food, energy, and other products may also increase as supplies decrease. When a drought occurs, the agricultural industry faces risk of economic impact and damage. During droughts, crops do not mature, resulting in smaller crop yields, undernourishment of wildlife and livestock, decreases in land values, and ultimately financial losses to farmers.164F 165 Agriculture production has been a
significant and growing factor in Santa Clara County, especially as agricultural effects on the economy start to normalize (after a period of decline).

Evaluation of direct effects (i.e., excluding indirect and induced spending benefits) can occur based on information conveyed in USDA reports. According to the 2017 Census of Agriculture, 890 farms were present in Santa Clara County, encompassing 288,084 acres of total farmland. The average farm size was 324 acres.

Santa Clara County farms had a total market value of products sold of $310.2 million ($293.7 million in vegetable crops including nursery and greenhouse; and $18.4 million in cattle, layers, and horses, and related products), averaging $348,524 per farm.

A prolonged drought can affect a community’s economy significantly. Increased demand for water and electricity may result in shortages and higher costs of these resources. Industries that rely on water for business may be impacted the most (e.g., landscaping businesses). Although most businesses will still be operational, they may be affected aesthetically—especially the recreation and tourism industry. Moreover, droughts within another area could affect food supply/price of food for residents within the Santa Clara County OA.

10.5 Future Trends in Development
Land use planning is also directed by general plans adopted under California’s General Planning Law.

Municipal planning partners are encouraged to establish General Plans with policies directing land use and dealing with issues of water supply and protection of water resources. These plans increase capability at the local municipal level to protect future development from impacts of drought. All planning partners reviewed their general plans under the capability assessments undertaken for this effort.

Deficiencies revealed by these reviews can be identified as mitigation actions to increase capability to deal with future trends in development.

To confront the challenges of increasing drought vulnerability, several efforts are underway to address water needs in the OA. Santa Clara Valley Water District is investing in locally reliable, sustainable and efficient water supplies such as recycled and purified water. Santa Clara County has adopted a modified Water Efficient Landscape Ordinance to guide future landscape and water management practices to promote long-term water efficiency.
165 National Integrated Drought Information System. (n.d.). Agriculture. https://www.drought.gov/sectors/agriculture Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 199

10.6 Scenario
Drought is a cyclic part of the climate of California. Continuation or exacerbation of the current situation across the State (i.e., an extreme, multiyear drought associated with record-breaking rates of low precipitation and high temperatures) is the worst-case scenario for Santa Clara County. Low precipitation and high temperatures increase possibility of wildfires throughout the County, increasing need for water when water is already in limited supply. Surrounding counties, also under drought conditions, could increase their demand for the water supplies on which Santa Clara County also relies, triggering social and political conflicts. The higher density population of the Bay Area increases the likelihood of such conflicts. Additionally, the longer drought conditions last in or near the Santa Clara OA, the greater the effect on the local economy; water-dependent industries especially will undergo setbacks. According to the USGS, “Climate change exacerbates droughts by making them more frequent, longer, and more severe.”165F
166

10.7 Issues
Important issues associated with drought in the OA include the following:
 Identification and development of alternative water supplies.  Utilization of groundwater recharge techniques to stabilize the groundwater supply.  The probability of increased drought frequencies and durations due to climate change.  The promotion of active water conservation even during non-drought periods.  Monitoring of implementation and benefits of the Long-Term Reliable Water Supply Strategy projects, Water Conservation Implementation Plan projects, and water system capital improvement upgrades.
 Application of alternative techniques (groundwater recharge, water recycle, local capture and reuse, desalination, and transfer) to stabilize and offset Sierra Nevada snowpack water supply shortfalls.
 Regular occurrence of drought or multiyear droughts that may limit the Operational Area’s ability to successfully recover from or prepare for more occurrences-particularly noteworthy due to longevity of the current ongoing drought.

Table 61: EMAP Consequence Analysis: Drought
Subject Ranking Impacts/Drought
Health and Safety of
Persons in the Area of the
Incident
Minimal to
moderate
Drought impact tends to be agricultural; however,
because of the lack of precipitation that leads to drought, water supply disruptions can occur, which can affect
people. The impact is expected to be minimal.

Responders Minimal With proper preparedness and protection, the impact on the responders is expected to be minimal.

Continuity of Operations Minimal There is minimal expectation for utilization of the COOP. 166 U.S. Geological Survey. (n.d.). Droughts and Climate Change. https://www.usgs.gov/science/scienceexplorer/climate/droughts-and-climate-change Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 10: Drought 200
Subject Ranking Impacts/Drought
Property, Facilities, and
Infrastructure
Minimal to
severe
Impact on property, facilities, and infrastructure could be minimal to severe, depending on the length and intensity of the drought. The structural integrity of buildings and buckling of roads could be affected.

Delivery of Services Minimal The impact on the delivery of services should be nonexistent or minimal.

Environment Minimal to
severe
The impact on the environment could be severe. Drought
can severely affect farming, ranching, wildlife, and plants due to the lack of precipitation.

Economic Conditions Minimal to
moderate
Impacts on the economy will be dependent on how
extreme the drought is and how long it lasts.

Communities that depend on water recreation could be
tested, as well as agricultural.

Public Confidence in
Jurisdiction’s Governance
Minimal Confidence could be an issue during periods of extreme drought if planning is not in place to address intake needs and the loss of agricultural crops.

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11 Climate Change

11.1 General Background
Definitions
 Climate Change: changes in average weather conditions that persist over multiple decades or longer1.
 Climate Mitigation: action taken to curb climate change by reducing or preventing the emission of greenhouse gases.
 Climate Adaptation: action taken to protect the community from the impacts of a changing climate.  Adaptative Capacity: an estimate of the community’s current ability to deal with the projected impacts of climate change.

Climate, consisting of patterns of temperature, precipitation, humidity, wind and seasons, plays a fundamental role in shaping natural ecosystems and the human economies and cultures that depend on them. Climate change is defined as “changes in average weather conditions that persist over multiple decades or longer. Climate change encompasses both increases and decreases in temperature, as well as shifts in precipitation, changing risk of certain types of inclement weather events, and changes to other features in the climate system.”16F
167 A key indicator of climate change is the increase of global temperatures.

Multiple temperature records from all over the world have shown a warming trend. The Intergovernmental Panel on Climate Change (IPCC) has stated that the warming of the climate system is unequivocal.167F 168
The 2022 global average surface temperature was 1.55 °F warmer than the 20th-century average of 57.0 °F and about 1.90 ˚F warmer than the pre-industrial period (1880-1900). In fact, the ten warmest years on record have all occurred since 2010, with the last nine years of 2014-2022 among the ten warmest years.168F
169 2022 ranked as the sixth-warmest year on record since 1880.169F170 Although this temperature change may seem small, it means a significant increase in accumulated heat worldwide which is driving regional and seasonal temperature extremes, reducing snow cover and sea ice, intensifying heavy rainfall, and changing habitat ranges for plants and animals—expanding some and shrinking others.170F 171
167 Globalchange.gov. (No Date). Glossary. https://www.globalchange.gov/climate-change/glossary 168 The Intergovernmental Panel on Climate Change. (n.d.). Summary for Policymakers. https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_SummaryForPolicymakers.pdf 169 https://www.noaa.gov/news/2022-was-worlds-6th-warmest-year-on-record 170 National Oceanic and Atmospheric Administration. (2023, January 12). 2022 Was World’s 6th -Warmest Year on
Record. https://www.noaa.gov/news/2022-was-worlds-6th-warmest-year-on-record 171 National Oceanic and Atmospheric Administration. (2023, January 18). Climate Change: Global Temperature. https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature#SnippetTab Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 202
Figure 55: Global Temperature 1880-202217 F
172
The global warming temperature trend and its related impacts are caused by an exponential increase of greenhouse gas emissions including carbon dioxide, methane, nitrous oxide, and fluorinated gases.

Emissions of these gases come from a variety of sources, such as the combustion of fossil fuels for energy and transportation, agricultural production, changes in land use and volcanic eruptions. According to the U.S. Environmental Protection Agency (EPA), carbon dioxide concentrations measured about 280 parts per million before the industrial era began in the late 1700s and reached 414 parts per million in 2021, a 48% increase.172F
173 See Figure 54. In addition, the concentration of methane has more than doubled since pre-industrial times, and nitrous oxide is being measured at a record high of 334 parts per billion.173F 174
172 NASA. (n.d.). World of Change: Global Temperatures. https://earthobservatory.nasa.gov/world-of-change/globaltemperatures 173 Environmental Protection Agency. (n.d.) Climate Change Indicators: Atmospheric Concentrations of Greenhouse Gases. https://www.epa.gov/climate-indicators/climate-change-indicators-atmospheric-concentrations-greenhousegases#:~:text=Carbon%20dioxide%20concentrations%20have%20increased,is%20due%20to%20human%20activitie s
174 Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock, eds. (2017). Climate science special report: Fourth National Climate Assessment, volume I. U.S. Global Change Research Program. https://science2017.globalchange.gov/.

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Figure 56: Global Carbon Dioxide Concentrations Over Time174F 175
Scientists can place this rise in carbon dioxide in a longer historical context through the measurement of carbon dioxide in ice cores. According to these records and illustrated in Figure 55, carbon dioxide concentrations in the atmosphere are the highest that they have been in 650,000 years.175F 176
The major scientific agencies of the United States and the world—including NASA, NOAA, and the Intergovernmental Panel on Climate Change (IPCC)—agree that long-term climate change is occurring.

There is broad scientific consensus (97 percent of scientists) that the current, unprecedented climatewarming trends are very likely due to human activities.176 F 177 Unless emissions of greenhouse gases are
substantially reduced, this warming trend is expected to continue.

11.1.1 Climate Change Indicators
Climate change will affect the people, property, economy, and ecosystems of the Santa Clara County Operational Area (OA) in a variety of ways. Some of these impacts are already being felt. Widespread, pervasive impacts to ecosystems, people, settlements, and infrastructure have resulted from observed increases in the frequency and intensity of climate and weather extremes, including temperature extremes on land and in the ocean, heavy precipitation, drought, and fire weather.17F 178 Rising global
temperatures have also been accompanied by other more localized changes in weather and climate. 2022 serves as a good example of this.
175 Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock, eds. (2017). Climate science special report: Fourth National Climate Assessment, volume I. U.S. Global Change Research Program. https://science2017.globalchange.gov/.
176 NASA. (2023). Carbon Dioxide. https://climate.nasa.gov/vital-signs/carbon-dioxide/ 177 NASA. (n.d.). Scientific Consensus: Earth’s Climate is Warming. https://climate.nasa.gov/scientific-consensus/ 178 The Intergovernmental Panel on Climate Change. (n.d.). Summary for Policymakers. https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_SummaryForPolicymakers.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 204
The OA started the year in the drought, experienced record high temperatures in the summer that reached as high as 109 degrees Fahrenheit in San José and ended with the start of multiple atmospheric rivers which brought record rainfall and flooding.

California’s number of extreme heat events (including both days and nights) has increased. In particular, there has been an increase in nighttime temperatures. Scientists have demonstrated that nighttime temperatures are more sensitive to the greenhouse gases which cause climate change178 F 179. This example
helps demonstrate the consequence of climate change that are already being felt throughout the region.

The planet’s oceans and glaciers have also experienced changes: oceans are warming and becoming more acidic, ice caps are melting, and sea levels are rising.179F 180,
180F
181 Sea level along the U.S. coastline is
projected to rise, on average, 10 to 12 inches in the next 30 years (2020–2050), which will be as much as the rise measured over the last 100 years (1920–2020). This has already put some coastal homes, beaches, roads, bridges, and wildlife at risk. As a coastal county, sea-level rise is one of the most concerning impacts of climate change facing the OA. At the time of the development of this plan, NASA reports the following trends18F
182:
 Carbon Dioxide: Increasing trend, currently at 419 parts per million as of February 2023.  Global Temperature: Increasing trend, increase of 1.6 ºF since 1880.  Arctic Ice Minimum: Decreasing trend, 12.6% per decade.  Land Ice: Decreasing trend, Antarctica is losing approximately 150 billion tons a year and Greenland is losing about 270 billion tons per a year.
 Sea Level: Increasing trend, 3.8 inches per year.

Climate change impacts are most frequently associated with negative consequences, for example, warmer average temperatures could increase air conditioning costs and affect the spread of diseases like Lyme disease but could also improve conditions for growing some crops. More extreme variations in weather are also a threat to society. More frequent and intense extreme heat events can increase illnesses and deaths, especially among vulnerable populations, and damage some crops. While increased precipitation can replenish water supplies and support agriculture, intense storms can damage property, cause loss of life and population displacement, and temporarily disrupt essential services such as transportation, telecommunications, energy, and water supplies.182F
183 The most important effect for the development of this plan is that climate change will have a measurable impact on the occurrence and severity of natural hazards.

11.1.2 Projected Future Impacts
The Fourth National Climate Assessment Report for the United States183F 184 indicates that impacts resulting
from climate change will continue through the 21st century and beyond. Evidence of human-caused climate change is overwhelming and continues to strengthen. 179 California Office of Environmental Health Hazard Assessment. (2019, February 11). Extreme Heat Events. https://oehha.ca.gov/epic/changes-climate/extreme-heat-events 180 National Oceanic and Atmospheric Administration. (2023, January 12). 2022 Was World’s 6th -Warmest Year on
Record. https://www.noaa.gov/news/2022-was-worlds-6th-warmest-year-on-record 181 U.S. Geological Survey. (2022, March 1). Global and Regional Sea Level Rise Scenarios for the United States. https://www.usgs.gov/publications/global-and-regional-sea-level-rise-scenarios-united-states 182 NASA. (n.d.). Ice Sheets. https://climate.nasa.gov/vital-signs/ice-sheets/ 183 Environmental Protection Agency. (n.d.). Climate Change Indicators: Weather and Climate. https://www.epa.gov/climate-indicators/weather-climate
184 U.S. Global Change Research Program. (n.d.). Fourth National Climate Assessment. https://nca2018.globalchange.gov/
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 205
The impacts of climate change are intensifying across the country and represent a real threat to Americans’ physical, social, and economic well-being are rising. These impacts are projected to intensify, however how much they intensify will depend on actions taken to reduce global greenhouse gas emissions and to adapt to the risks from climate change now and in the coming decades.184F 185
The California Climate Adaptation Planning Guide (APG) outlines the following climate change impact concerns for the Bay Area Region communities185F
186:
 Increased temperature
 Reduced precipitation
 Sea level rise – coastal inundation and erosion
 Public health – heat and air pollution
 Reduced agricultural productivity
 Inland flooding
 Reduced tourism
According to the Fourth U.S. National Climate Change Assessment, after the third climate assessment where there were more than twice as many high temperature records as low temperature records broken between 2001 and 2012, global high temperature records continued to be broken in 2014, 2015, and 2016. Heavy rainfall events and large forest fire incidents are becoming more frequent and more severe.

Long-term impacts, like a continued decline in arctic ice and increase chronic drought, are expected.

Cal-Adapt,186F
187 a resource for public information on how climate change might impact local communities, based on the most current data available, has projected increases in temperature within the OA in particular. Table 62 shows the expected increases in average maximum temperatures and Table 63 addresses the number of extreme heat days per year. The increase in average surface temperatures can also lead to more intense heat waves that can be exacerbated in urbanized areas by what is known as the urban heat island effect.

Table 62: Average Maximum Temperature – Santa Clara County187F 188
Baseline (1961–1990)
Medium Emissions (RCP 4.5) High Emissions (RCP 8.5)
Mid-Century End-Century Mid-Century Mid-Century
30-year
average

68.6 oF 72.0 oF 73.1 oF 72.8 oF 76.0 oF
30-year range 68.4–68.8 oF 70.5–73.5 oF 71.0–75.7 oF 70.9–75.0 oF 73.2–80.5 oF 185 U.S. Global Change Research Program. (n.d.). Fourth National Climate Assessment, Chapter 1: Overview. https://nca2018.globalchange.gov/chapter/1/
186 Cal OES. (June 2020). Climate Adaptation Planning Guide. https://www.caloes.ca.gov/wpcontent/uploads/Hazard-Mitigation/Documents/CA-Adaptation-Planning-Guide-FINAL-June-2020-Accessible.pdf 187 Cal-Adapt. (n.d.). Explore and analyze climate data from California’s Climate Change Assessment. https://caladapt.org/ 188 Cal-Adapt. (n.d.). Annual Averages. https://cal-adapt.org/tools/annual-averages Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 206
Table 63: Number of Extreme Heat Days Per Year
(Heat Is above 92.7 oF) Santa Clara County18F
189
Baseline (1961-1990)
Medium Emissions (RCP 4.5) High Emissions (RCP 8.5)
Mid-Century End-Century Mid-Century End-Century
30-year
average
4 days/yr. 12 days/yr. 17 days/yr. 17 days/yr. 31 days/yr. 30-year range 0–16 days/yr. 0–32 days/yr. 2–44 days/yr. 1–61 days/yr. 0–101 days/yr.

Although the California Climate Adaptation Planning Guide projected reduced precipitation in the region, recent Cal-Adapt projections show significant increases in Santa Clara County’s average annual precipitation levels (see Table 64).

Table 64: Average Annual Precipitation – Santa Clara County189F 190
Baseline (1961-1990)
Medium Emissions
(RCP 4.5)
High Emissions
(RCP 8.5)
Mid-Century End-Century Mid-Century End-Century
30-year
average

23.8 inches 26.0 inches 26.0 inches 26.3 inches 9.1–68.6 inches
30-year range

8.2–51.5
inches

9.2–54.5
inches

9.0–51.3
inches 29.2 inches 8.6–63.6 inches
Climate change projections contain inherent uncertainty, largely derived from the fact that they depend on future greenhouse gas emission scenarios. Generally, the uncertainty in greenhouse gas emissions is addressed by the presentation of differing scenarios: low-emissions to high-emissions scenarios. In lowemissions scenarios, there is an effort to limit greenhouse gas emissions leading to emissions starting to decline close to mid-century. In high-emissions scenarios, greenhouse gas emissions continue to increase at current rates through the end of the century. Different climate scenarios can also be described in terms of likelihood and confidence. Likelihood refers to the statistical probability of the effect described occurring. Confidence refers to how valid that result is likely to be, based on available data and its consistency with current literature. There will always be some level of uncertainty when estimating future conditions. Uncertainty in outcomes is addressed by averaging a variety of climate change model outcomes or providing a range of outcomes. Despite this general uncertainty, climate change projections present valuable information to help guide decision-making. 189 Cal-Adapt. (n.d.). Extreme Heat Days & Warm Nights. https://cal-adapt.org/tools/extreme-heat 190 Cal-Adapt. (n.d.). Annual Averages. https://cal-adapt.org/tools/annual-averages Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 207
Figure 57: Impacts of Climate Change on Human Health190F 191

11.1.3 How Climate Change Impacts Hazard Mitigation
An essential aspect of hazard mitigation is estimating the likelihood of hazard events. Traditionally, the probability of a hazard event occurring has been expressed as a statistical projection based on records of past events. This approach assumes that the likelihood of hazard events occurring remains essentially unchanged over time. Thus, averages based on the past frequencies of floods, for example, are used to estimate future flooding frequencies: if a river has flooded an average of once every five years for the past 100 years, then it can be expected to continue to flood an average of once every five years.

For hazards that are affected by climate conditions, the assumption that future behavior will be equivalent to past behavior may not be valid given that climate conditions are changing. As flooding is generally associated with precipitation frequency and quantity, for example, the frequency of flooding will not remain constant if broad precipitation patterns change over time. 191 California Department of Public Health. (February 2017). Climate Change and Health Profile Report – Santa Clara County.
https://www.cdph.ca.gov/Programs/OHE/CDPH%20Document%20Library/CHPRs/CHPR085SantaClara_County2- 23-17.pdf
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 208
Specifically, as hydrology changes, storms currently considered to be a one percent annual chance flood event (100-year flood) might strike more often, leaving communities at greater risk of flooding. The risks of landslide, severe storms, extreme heat events and wildfire are all affected by climate patterns as well.

For this reason, an understanding of climate change is pertinent to efforts to mitigate natural hazards.

Information about how climate patterns are changing provides insight on the reliability of future hazard projections used in mitigation analysis. This section summarizes current understandings about climate change in order to provide a context for the recommendation and implementation of hazard mitigation measures.

Table 65: Potential Direct and Related Climate Change Impacts in the Operational Area Direct Impacts Related Impacts
Rising temperatures  Heat wave
 Changes in wind patterns19F
192
 Drought
 Reduced snowpack
 Increased extreme events, including severe storms and wildfires  Shifting human health and disease patterns.
 Sea Level Rise
 Permanent inundation of previously dry land
 Larger area impacted by extreme high tide
 Increased coastal erosion
 Saltwater intrusion into freshwater systems
Changes in precipitation192F
193  Changed seasonal patterns
 Flooding
 Saturated earth
 Reduced snowpack
 Drought
The links between these climate change indicators and most of the natural and other hazards of concern profiled in this MJHMP are direct but less clear for other hazards as illustrated in Table 66 and discussed later in this section.
192 Columbia Climate School. (2021, January 6). Will Global Warming Bring a Change in the Winds? https://news.climate.columbia.edu/2021/01/06/westerly-winds-climate-change/ 193 Columbia Climate School. (2021, January 6). Will Global Warming Bring a Change in the Winds? https://news.climate.columbia.edu/2021/01/06/westerly-winds-climate-change/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 209
Table 66: Climate Change Impacts on Natural and Other Hazards Negative Impact on Natural and Other Hazards
Climate Change
Indicator
Natural Hazards Other
Dam and Levee
Failure
Drought
Earthquake
Flood
Landslide
Inclement
Weather
Tsunami
Wildfire
Sea Level Rise
Terrorism
Technological
Incidents
Power Outages
Epidemic/Pandemic
Fog
Rising temperatures X X X X X X X X X
Heat wave X X X X X X X
Changes in wind
patterns193F
194

X X X X X X X
Drought N/A X X X
Reduced snowpack X X X
Increased extreme events,
including severe storms
and wildfires

X X X N/A X
Shifting human health and
disease patterns
X
Sea Level Rise X X X X X N/A X X
Changes in precipitation194F
195 X X X X X X X X X
Changes in seasonal
patterns

X X X X X X X X X
Flooding X N/A X X X X
Saturated earth X X X X X
194 Columbia Climate School. (2021, January 6). Will Global Warming Bring a Change in the Winds? https://news.climate.columbia.edu/2021/01/06/westerly-windsclimate-change/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 210

11.2 Responses to Climate Change
Communities and governments worldwide are working to address, evaluate and prepare for climate changes that are likely to impact communities in coming decades. Climate change discussions encompass two separate but inter-related considerations: mitigation and adaptation. The term “mitigation” can be confusing because its meaning changes across disciplines:
 Mitigation in restoration ecology and related fields generally refers to policies, programs or actions that are intended to reduce or to offset the negative impacts of human activities on natural systems. Mitigation can be understood as avoiding, minimizing, rectifying, reducing, or eliminating, or compensating for known impacts.195F
196
 Mitigation in climate change discussions is defined as “reducing emissions of and stabilizing the levels of heat-trapping greenhouse gases in the atmosphere.”196F 197 The goal is to stabilize the
climate and avoid significant human interference.
 Mitigation in emergency management is typically defined as the effort to reduce loss of life and property by lessening the impact of disasters.197F
198
In this section, mitigation is used as defined by the climate change community. In the other sections of this plan, mitigation is primarily used in an emergency management context. The IPCC defines adaptation as “the process of adjustment to actual or expected climate and its effects.” Mitigation and adaptation are related, as the world’s ability to reduce greenhouse gas emissions will affect the degree of adaptation that will be necessary. Moreover, some initiatives and actions can both reduce greenhouse gas emissions and support adaptation to likely future conditions. The ability to adapt to changing conditions is often referred to as adaptive capacity, which is “the ability of systems, institutions, humans and other organisms to adjust to potential damage, to take advantage of opportunities, or to respond to consequences.”198F 199
Societies across the world are facing the need to adapt to changing conditions and to identify ways to increase their adaptive capacity. Some efforts are already underway. Farmers are altering crops and agricultural methods to deal with changing rainfall and rising temperature; architects and engineers are redesigning buildings; planners are looking at managing water supplies to deal with droughts or flooding.

Adaptive capacity goes beyond human systems, as some ecosystems show a remarkable ability to adapt to change and to buffer surrounding areas from the impacts of change. Forests can bind soils and hold large volumes of water during times of plenty, releasing it through the year; floodplains can absorb vast volumes of water during peak flows; coastal ecosystems can hold out against storms, attenuating waves and reducing erosion. Other ecosystem services—such as food provision, timber, materials, medicines, and recreation—can provide a buffer to societies in the face of changing conditions. Ecosystem-based adaptation is the use of biodiversity and ecosystem services as part of an overall strategy to help people adapt to the adverse effects of climate change. This includes the sustainable management, conservation and restoration of specific ecosystems that provide key services. 196 Environmental Protection Agency. (n.d.). Types of Mitigation Under CWA Section 404. https://www.epa.gov/cwa404/types-mitigation-under-cwa-section-404-avoidance-minimization-and-compensatorymitigation#:~:text=The%20White%20House%20Council%20on%20Environmental%20Quality%20%28CEQ%29,rectif ying%2C%20reducing%20over%20time%2C%20and%20compensating%20for%20impacts. 197 NASA. (N.D.). Responding to Climate Change. https://climate.nasa.gov/solutions/adaptation-mitigation/ 198 Federal Emergency Management Agency. (2017, November). Fact Sheet, Planning for a Resilient Community. https://www.fema.gov/sites/default/files/documents/fema_planning-resilient-communities_fact-sheet.pdf 199 Intergovernmental Panel on Climate Change. (n.d.). Annex II, Glossary. https://www.ipcc.ch/site/assets/uploads/2018/02/WGIIAR5-AnnexII_FINAL.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 211
One type of mitigation measure that is also important to acknowledge is nature-based solutions (NBS).

FEMA defines NBS as sustainable planning, design, environmental management, and engineering practices that weave natural features or processes into the built environment to promote adaptation and resilience19F
200. These actions usually have multiple benefits such as reducing flood risk, reducing urban heat, adding recreation space, protecting nature spaces like shorelines and wetlands, and improving water quality in addition to fighting climate change. They may be more cost-effective than traditional grey infrastructure projects and are often more palatable by the public due to their hard to quantify benefits like additional recreation space, community beautification, increased property values, and better public health.

The immediacy of some of these benefits can also increase public support for NBS when compared to less clear, long-term benefits of other climate adaptation measures. Many communities within the OA have taken an interest in NBS, also known as green infrastructure, and actively engage in and encourage implementation of NBS separately or in conjunction with traditional infrastructure projects. Further information is included in Volume 2.

A coordinated response to climate change is necessary to implement effective risk reduction measures across the OA. Initiatives including the Silicon Valley 2.0 Climate Change Preparedness Tool, the Santa Clara County Climate Collaborative and Climate Resilience Tool, and local climate action and adaptation plans reflect the OA’s commitment to assessing and implementing climate mitigation and adaptation actions. Assessment of the current efforts and adaptive capacity of the planning partners participating in this hazard mitigation plan are included in the jurisdiction-specific Annexes in Volume 2.

11.3 Vulnerability Assessment – Hazards of Concern
The following sections provide information on how each identified hazard of concern for this planning process may be impacted by climate change and how these impacts may alter current exposure and vulnerability to these hazards for the people, property, critical facilities, and the environment in the OA.

11.3.1 Earthquake
Climate Change Impacts on Earthquake
Currently, the impact, if any, of climate change on earthquakes is not well understood. “Climate-related stress changes might or might not promote an earthquake to occur, but we have no way of knowing by how much.”20F
201 Some scientists say that melting glaciers could induce tectonic activity. As ice melts and water runs off, tremendous amounts of weight are shifted on the earth’s crust. As newly freed crust returns to its original, pre-glacier shape, it could cause seismic plates to slip and stimulate volcanic activity, according to research into prehistoric earthquakes and volcanic activity. NASA and USGS scientists found that retreating glaciers in southern Alaska may be opening the way for future earthquakes.201F
202 Other researchers are studying whether the stress of alternating periods of drought and heavy precipitation in the Sierra Nevada could potentially be felt on faults in or near the range and whether the increased pumping of groundwater in the Central Valley during times of drought could have an effect on the seismicity on the adjacent San Andreas Fault.20F 203
200 FEMA. (May 2023). Nature-Based Solutions. https://www.fema.gov/emergency-managers/riskmanagement/nature-based-solutions 201 NASA. (2019, October 29). Can Climate Affect Earthquakes, Or Are the Connections Shaky? https://climate.nasa.gov/news/2926/can-climate-affect-earthquakes-or-are-the-connections-shaky/ 202 NASA. (2004, August 2). Retreating Glaciers Spur Alaskan Earthquakes. https://www.nasa.gov/home/hqnews/2004/jul/HQ_04252_glaciers.html 203 NASA. (2019, October 29). Can Climate Affect Earthquakes, Or Are the Connections Shaky? https://climate.nasa.gov/news/2926/can-climate-affect-earthquakes-or-are-the-connections-shaky/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 212
Secondary impacts of earthquakes could be magnified by climate change. Soils saturated by repetitive storms or heavy precipitation could experience liquefaction or an increased propensity for slides during seismic activity due to the increased saturation. Dams storing increased volumes of water due to changes in the hydrograph could fail during seismic events.

Exposure, Sensitivity, and Vulnerability
Because impacts on the earthquake hazard are not well understood, increases in exposure and vulnerability of the local resources are not able to be determined. In general, everywhere that is susceptible to earthquake-induced liquefaction may be more susceptible if saturated with water due to climate change conditions when an earthquake occurs.

11.3.2 Wildfire
Climate Change Impacts on Wildfire
Wildfire risk is determined by climate variability, local topography, and human intervention. Climate change has the potential to affect multiple elements of the wildfire system: fire behavior, ignitions, fire management, and vegetation fuels. The frequency of extreme wildfires which burn over 25,000 acres is also expected to increase by nearly 50 percent across the state by 2100 according to the state’s Fourth Climate Change Assessment. Under both high- and medium-emissions scenarios, the change in acres burned in Santa Clara County is likely to increase until 2050 and then decrease by the end of the century.

Fire season for the OA is also expected to begin earlier in the year and last longer203F 204. The Cal-Adopt
projections204F
205 demonstrating how wildfire risk in the areas surrounding the OA is expected to increase over the next century is shown in Table 67.

Hot, dry spells create the highest fire risk. Increased temperatures may intensify wildfire risk by warming and drying out vegetation. Changes in climate patterns may impact the distribution and perseverance of insect outbreaks that create dead trees and vegetation, increasing the amount of available fire fuel. Wetter periods followed by a drought can result in increased dry vegetative ready to be burned. When climate alters fuel loads and fuel moisture, forest susceptibility to wildfires changes. Climate change also may increase winds that spread fires.

Table 67: Wildfire – Projected Santa Clara County Acres Burned 204 County of Santa Clara Office of Sustainability. (n.d.). Climate Change Projections in Santa Clara County. https://siliconvalleytwopointzero.org/climateprojections/wildfire 205 https://cal-adapt.org/tools/wildfire
Baseline (1961–1990)
Medium Emissions (RCP 4.5) High Emissions (RCP 8.5)
Mid-Century End-Century Mid-Century End-Century
30-year
average
6212.0 acres 6848.3 acres 6897.2 acres 6957.8 acres 6613.5 acres 30-year range
6143.0–
6366.3 acres
6512–7295.2
acres
6459.2–7388.5
acres
6570.1–7599.1
acres
6158.9–7378.2
acres
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 213
Exposure, Sensitivity, and Vulnerability
Population and Property
While previous Cal-Adapt projections showed wildfire risk in the areas surrounding the OA decreasing over the next century, current projections show increased risk to wildfire, with increases in annual acres burned. Table 68 indicates the population and buildings at risk in the moderate, high, and very high FHSZs. Should the risk increase as Cal-Adapt projects, these totals are likely to increase also. WUI fires are an increased concern of the OA. While not all OA residents may experience increased risk to wildfire directly, secondary impacts, such as smoke and poor air quality will impact many more. These impacts are likely to be felt disproportionally. Vulnerable populations, including the elderly, low-income populations, and people with disabilities, will face some of the greatest negative impacts. Long-term impacts to public health, including mental health, will also be important to consider as the frequency and severity of wildfires increase.

Table 68: Population and Buildings at Risk – Santa Clara County Moderate FHSZ High FHSZ Very High FHSZ
Buildings Population Buildings Population Buildings Population 995 3,714 2,599 9,622 9,547 33,167
Critical Facilities
The risk to critical facilities would increase with the overall increased risk of wildfires. Key infrastructure including utilities, water, gas, electric, and communications infrastructure can be damaged during a wildfire. Secondary impacts, like increased power outages, transportation delays or disruptions, and smoke, are also likely to impact the operations of critical facilities.

Environment
It is possible that the exposure and vulnerability of the environment will be impacted by changes in wildfire risk due to climate change. Natural fire regimes may change, resulting in more frequent or higher intensity burns. While the California ecosystem is adapted to some fire, these types of events and fuel conditions represent risk beyond the norm for the local environment. These changes may alter the composition of the ecosystems in areas in and surrounding the OA including destroying vulnerable fish and wildlife habitats.

Economy
Recent fires destroyed residences, burned thousands of acres, forced people to evacuate. Costs involved included personal and business losses, lost economic activity, and the cost of containing a wildfire.

Seasonal agricultural workers and workers outside on poor air quality days are most likely to experience increased negative impacts or disruptions to their work due to increase wildfire events. Transportation infrastructure could also be impacted.

11.3.3 Inclement Weather
Climate Change Impacts on Inclement Weather
Climate change presents a challenge for risk management associated with inclement weather. While only slight changes in annual rainfall is expected in the OA, there is an increased risk that this rainfall will occur during an extreme precipitation event. These severe storms will be an essential to replenish fresh water supplies particularly during times of drought however, they may result in increased flooding. The number of weather-related disasters during the 1990s was four times that of the 1950s and led to 14 times as much in economic losses.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 214
Historically, the County has experienced just two extreme precipitation events per year. Depending on the emissions scenario, the OA is predicted to experience 3-5 events per year by the end of the century.205F 206
The type of inclement weather event may also change. Fewer snow events and additional rain events are predicted.

Climate projections such as found in the CMRA tool show an increasing number of days over 95 and over 100 degrees through mid to late century, in both lower and high emission scenarios. Projections also anticipate higher maximum temperatures averaged over a 5 day period, which indicates there may also be extended periods of extreme heat.

Extreme cold events are less common in the OA. The Temperature Minimum explorer as part of the ClimRR climate tool, shows the minimum temperature increasing through mid- to end-century. Current projections suggest that climate change may reduce vulnerability to extreme cold in the OA.

It is not fully understood how climate change may impact high wind events. Climate change is expected to contribute to more severe weather in the future. However, the Wind Explorer in the ClimRR tool shows little difference in wind miles per hour between mid-and end-century. Further investigation may be needed to fully understand how climate change may impact high winds in the OA.

Exposure, Sensitivity, and Vulnerability
Population and Property
Population and property exposure and vulnerability would be unlikely to increase as a direct result of climate change impacts on the inclement weather hazard. Inclement weather events may occur more frequently, but exposure and vulnerability will remain the same. Secondary impacts, such as the extent of localized flooding, may increase, impacting greater numbers of people and structures.

Critical Facilities
Critical facility exposure and vulnerability would be unlikely to increase as a result of climate change impacts on the inclement weather hazard; however, critical facility owners and operators may experience more frequent disruption to service provision. For example, more frequent and intense storms may cause more frequent disruptions in power service.

Environment
Exposure and vulnerability of the environment would be unlikely to increase; however, more frequent storms and heat events and more intense rainfall may place additional stressors on already stressed systems.

Economy
Climate change impacts on the inclement weather hazard may impact the local economy through more frequent disruption to services, such as power outages.

11.3.4 Drought
Climate Change Impacts on Drought
Due to a warmer climate, droughts could become more frequent, more severe, and longer lasting. As stated in the National Climate Resilience Toolkit, “higher surface temperatures brought about by global warming increase the potential for drought. Evaporation and the higher rate at which plants lose moisture 206 Santa Clara County. (February 2023) Draft Unincorporated Santa Clara County Climate Vulnerability Assessment.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 215
through their leaves both increase with temperature. Unless higher evapotranspiration rates are matched by increases in precipitation, environments will tend to dry, promoting drought conditions.206F 207
Drought is one of the most expensive hazards due to its impacts across sectors, particularly the agricultural industry. Valley Water indicates that it poses a severe threat to their normal operations due to the region’s dependency on imported water and increased demand for water across the region. The OA could likely experience what stresses other regions globally have started to experience:
 Growing populations
 Increased competition for available water
 Poor water quality
 Environmental claims
 Uncertain reserved water rights
 Groundwater overdraft
 Aging urban water infrastructure
California is particularly well-aware of the potential negative impacts of prolonged drought. Until storms in early 2023, the entire state, including the entire OA, was in severe to extreme drought. DWR has noted impacts of climate change on statewide water resources by charting changes in snowpack, sea level, and river flow. As temperatures rise and more precipitation comes in the form of rain instead of snow, these changes will likely continue or grow even more significant.

Cal-Adapt indicated in early 2023 that Santa Clara County should expect future April snowpack levels to be reduced by up to 25 inches from the baseline (1961-1990) by 2099.207F 208 These future projections may or
may not be adjusted following the area’s recent record-breaking snowpack levels. In addition to snowpack resources, the OA’s water supply is derived from groundwater and surface water resources. Increased incidence of drought may cause a drawdown in groundwater resources without allowing for the opportunity for aquifer recharge. Under the HadGEM-ES simulation, a high-emissions scenario, an extended drought is predicted for California from 2025–2075.208F 209
Exposure, Sensitivity and Vulnerability
Population and Property
Population exposure and vulnerability to drought are unlikely to change as a result of climate change given that the entire OA is already exposed to this hazard. Greater numbers of people may need to engage in behavior change, such as water saving efforts, significant life or health impacts are unlikely so long as water supplies can be managed to account for the additional strain. Property exposure and vulnerability may increase as a result of increased drought resulting from climate change, although this would most likely occur in non-structural property such as crops and landscaping. It is unlikely that structure exposure and vulnerability would increase as a direct result of drought, although secondary impacts of drought, such as wildfire, may increase and threatenstructures. 207 U.S. Climate Resilience Toolkit. (n.d.). Drought.
https://toolkit.climate.gov/topics/water/drought#:~:text=Higher%20surface%20temperatures%20brought%20about%2 0by%20global%20warming,environments%20will%20tend%20to%20dry%2C%20promoting%20drought%20condition s.
208 Cal-Adapt. (n.d.). Snowpack. https://cal-adapt.org/tools/snowpack/ 209 Santa Clara County. (February 2023) Draft Unincorporated Santa Clara County Climate Vulnerability Assessment.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 216
Critical Facilities
Critical facility exposure and vulnerability are unlikely to increase as a result of increased drought resulting from climate change; however, critical facility operators may be sensitive to changes and need to alter standard management practices and actively manage resources, particularly in water-related service sectors. Water-related infrastructure may experience disruptions.

Environment
The vulnerability of the environment may increase as a result of increased drought resulting from climate change. Ecosystems and biodiversity in the Bay Area are already under stress from development and water diversion activities. Prolonged or more frequent drought resulting from climate change may further stress the ecosystems in the region, which include many special status species.

Economy
Increased incidence of drought could increase the potential for impacts on the local economy including the agricultural and recreational sectors, the wine industry, and related tourism activities. Crop-related losses would be expected to be particularly high given a severe drought.

11.3.5 Dam and Levee Failure
Climate Change Impacts on Dam and Levee Failure
Dams and levees are engineered barriers designed to retain surface water based on assumptions including information on a river’s flow behavior (depicted on a hydrograph). Safeguards are built into these structures but there is increased risk associated with hazard events that surpass what the impacted dam or levee was designed to withstand. Substantial increases in rainfall or/or snowmelt in an area can have significant effects on the hydrograph used for the design of a dam or levee. If the hydrograph changes, it is conceivable that the dam or levee can lose some or all of its designed margin of safety, also known as freeboard.

In the case of dams, if freeboard is reduced, dam operators may be forced to release increased volumes early in a storm cycle in order to maintain the required margins of safety. Such early releases of increased volumes can increase flood potential downstream. According to the California Department of Water Resources (DWR), flood flows on many California rivers have been record-setting since the 1950s. This means that water infrastructure, such as dams and levees, have been forced to manage flows for which they were not designed. The California Division of Dam Safety (DSOD) has indicated that climate change may result in the need for increased safety precautions to address higher winter runoff, frequent fluctuations of water levels, and increased potential for sedimentation and debris accumulation from changing erosion patterns and increases in wildfire events. According to the DSOD, climate change also will impact the ability of dam operators to estimate extreme flood events.209F 210
Dams are constructed with safety features known as “spillways.” Spillways are put in place on dams as a safety measure in the event of the reservoir filling too quickly. Spillway overflow events, often referred to as “design failures,” result in increased discharges downstream and increased flooding potential.

Although climate change will not increase the probability of catastrophic dam failure, it may increase the probability of design failure.

In the case of levees, a reduction in freeboard caused by a changing hydrograph means that a levee may no longer protect an area against the design-storm standard for which it was originally built. This means that risk to the area that a levee is protecting from inundation will increase. 210 California Department of Water Resources. (n.d.). Climate Change Basics. https://water.ca.gov/WaterBasics/Climate-Change-Basics Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 217
Exposure, Sensitivity and Vulnerability
Population and Property
While the exposure and vulnerability of population and property are unlikely to change significantly as result of climate change alone, the likelihood of failure of water infrastructure (dams and levees) is generally expected to increase because of more frequent exposure to extreme events.210F 211 Dam failures
may experience increase overtopping or breaches due to extreme precipitation events, even if the overall precipitation in the OA is expected to decrease.

This problem is exacerbated because of the age of many of the dams in the OA and the increasing population living in potential inundation areas. It should be noted that dams, and those levees in the OA that are accredited, are mapped in a FEMA special flood hazard area where flood insurance applies. If a levee loses its accreditation, additional people and property can be considered exposed to increased flood risk. There are a number of ongoing projects in the OA which would impact the existing FEMA flood layers including the Lower Berryessa Flood Protection Project, Permanente Creek Flood Protection Project, Upper Berryessa Creek Flood Protection Project, and Sunnyvale East and West Channels.21F 212
These projects may reduce the local risk to riverine flooding.

Critical Facilities
Dam owners and operators are sensitive to the risk and may need to alter maintenance and operations to account for changes in the hydrograph and increased sedimentation. Critical facility owners and operators in levee failure inundation areas should always be aware of residual risk from flood events that may overtop the levee system.

Environment
The exposure and vulnerability of the environment to dam and levee failure may change as a result of climate change. Cascading hazards, as discussed throughout this plan, could have a notable impact on the environment. For example, if there is a long period of drought caused by climate change prior to a dam failure, it could reduce the land’s ability to hold water resulting in increased runoff and damage.

Such a scenario could result in additional disaster events, such as landslides and mudslides.

Ecosystem services may be used to mitigate some factors that could increase the risk of design failures, such as increasing the natural water storage capacity in watersheds above dams. The use of nature-based solutions or green stormwater infrastructure systems could also help with stormwater collection around the dam.

Economy
Changes in the dam failure hazard related to climate change may affect the local economy. More frequent flooding events due to dam failure would negatively impact the local economy. Economic impacts may also result from changes to the levee failure hazard if accreditation is lost.

11.3.6 Flood
Climate Change Impacts on Flood
Climate change is expected to impact both precipitation-driven riverine and surface flooding as well as coastal flooding in the OA. High frequency flood events (e.g., 10-year floods) in particular will likely 211 Mallakpour, I., AghaKouchak, A., & Sadegh, M. (2019). Climate‐induced changes in the risk of hydrological failure of major dams in California. Geophysical Research Letters. https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2018GL081888 212 Silicon Valley 2.0. Memorandum SV2.0 Tool Update – Flood Hazar Layer Map Updates. (June 2021). https://siliconvalleytwopointzero.org/downloads/SiliconValley2.0_Flood-Hazard-Layer-Map-Update-Memo.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 218
increase with a changing climate. What is currently considered a 1-percent-annual-chance (100-year flood) also may strike more often, leaving many communities at greater risk.

Climate change is already impacting water resources, and resource managers have observed the following:
 Historical hydrologic patterns can no longer be solely relied upon to forecast the water future.  Precipitation and runoff patterns are changing, increasing the uncertainty for water supply and quality, flood management and ecosystem functions.
 Extreme climatic events will become more frequent, necessitating improvement in flood protection, drought preparedness and emergency response.

The amount of snow is critical for water supply and environmental needs, but so too is the timing of snowmelt runoff into rivers and streams. Rising snowlines caused by climate change will allow more mountain areas, such as the Sierra Nevada watersheds, to contribute to peak storm runoff. Changes in watershed vegetation and soil moisture conditions will likewise change runoff and recharge patterns. As stream flows and velocities change, erosion patterns will also change, altering channel shapes and depths, possibly increasing sedimentation behind dams, and affecting habitat and water quality. Intense dry periods followed by wet periods will result in additional flooding. With potential increases in the frequency and intensity of wildfires due to climate change, there is potential for more floods following fire, which increase sediment loads and water quality impacts.

Use of historical hydrologic data has long been the standard of practice for designing and operating water supply and flood protection projects. For example, historical data are used for flood forecasting models and to forecast snowmelt runoff for water supply. This method of forecasting assumes that the climate of the future will be similar to that of the period of historical record. However, the hydrologic record cannot be used to predict changes in frequency and severity of extreme climate events such as floods. Scientists project greater storm intensity with climate change, resulting in more direct runoff and flooding. Going forward, model calibration must happen more frequently, new forecast-based tools must be developed, and a standard of practice that explicitly considers climate change must be adopted.

Exposure, Sensitivity, and Vulnerability
Population and Property
Population and property exposure and vulnerability may increase as a result of climate change impacts on the flood hazard. Runoff patterns may change, resulting in flooding in areas where it has not previously occurred. People experiencing homelessness are particularly susceptible to the impacts of climate change, including flooding.

Critical Facilities
Critical facility exposure and vulnerability may increase as a result of climate change impacts on the flood hazard. Runoff patterns may change, resulting in risk to facilities that have not historically been at risk from flooding. Additionally, changes in the management and design of flood protection for critical facilities may be needed as additional stress is placed on these systems. Planners will need to factor a new level of safety into the design, operation, and regulation of flood protection facilities such as dams, bypass channels and levees, as well as the design of local sewers and storm drains.

Environment
The exposure and vulnerability of the environment may increase as a result of climate change impacts on the flood hazard. Changes in the timing and frequency of flood events may have broader ecosystem impacts that alter the ability of already stressed species to survive. The destruction due to fire or sea level rise of habitats with important flood protection ability may impact the vulnerability of the OA.

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Economy
If flooding becomes more frequent, there may be impacts on the local economy. More resources may need to be directed to response and recovery efforts, and businesses may need to close more frequently due to loss of service or access during flood events. Flood damage to essential utilities will also present a major concern for the local economy.

11.3.7 Landslide
Climate Change Impacts on Landslide
Climate change may impact storm patterns, increasing the probability of more frequent, intense storms with varying duration. Increase in global temperature is likely to affect the snowpack and its ability to hold and store water. Warming temperatures also could increase the occurrence and duration of droughts, which would increase the probability of wildfire, reducing the vegetation that helps to support steep slopes.

All of these factors would increase the probability for landslide and/or mudslide occurrences.

Exposure, Sensitivity, and Vulnerability
Population and Property
Population and property exposure and vulnerability would be unlikely to increase as a result of climate change impacts on the landslide hazard. Landslide events may occur more frequently, but the extent and location should be contained within mapped hazard areas or recently burned areas.

Critical Facilities
Critical facility exposure and vulnerability would be unlikely to increase as a result of climate change impacts on the landslide hazard; however, critical facility owners and operators may experience more frequent disruption to service provision as a result of landslide hazards. For example, transportation systems may experience more frequent delays if slides blocking these systems occur more frequently.

Towers supporting power lines and bridges could also collapse during a landslide event. In addition, increased sedimentation resulting from landslides may negatively impact flood control facilities, such as dams and levees.

Environment
Exposure and vulnerability of the environment would be unlikely to increase as a result of climate change, but more frequent slides in river systems may impact water quality and have negative impacts on stressed species.

Economy
Changes to the landslide hazard resulting from climate change are unlikely to result in significant impacts on the local economy. The economy of the OA is considered to be highly adaptive to landslide risk.

11.3.8 Tsunami
Climate Change Impacts on Tsunami
The impacts of global climate change on tsunami probability are unknown. Some scientists say that melting glaciers could induce tectonic activity, inducing earthquakes, which could result in tsunamis. Other scientists have indicated that underwater avalanches (also caused by melting glaciers), may also result in additional tsunamis. Even if climate change does not increase the frequency with which tsunamis occur, it may result in more destructive waves. As sea levels continue to rise, tsunami inundation areas would likely reach further into communities than current mapping indicates.

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Exposure, Sensitivity, and Vulnerability
As land area likely to be inundated by tsunami waves increases, exposure and vulnerability to the tsunami hazard may increase for population, property, critical facilities, and the environment. Changes to the tsunami hazard from climate change may result in more direct economic impacts on a greater number of businesses and economic centers, as well as the infrastructure systems that support those businesses.

Population and Property
The population and property identified in the tsunami inundation areas are mostly likely to experience the most detrimental impacts of a tsunami event. This area is described in Figure 61. While most of the OA is unlikely to experience these impacts, vulnerable populations are at the highest risk of these impacts, including the homeless, elderly, children, and even the historically underserved communities.

Based on the National Structure Inventory, 14 commercial buildings and 2 industrial buildings are potentially vulnerable to tsunami. A tsunami has the potential to cause over $6 million in damages to these buildings.

If sea level rise increases the tsunami inundation area, then the population and property at risk will increase.

Critical Facilities
The risk to critical facilities would be similar to that of the flood risk. Key infrastructure including utilities, water, gas, electric, and communications infrastructure can be damaged during a tsunami. Destructive waves can damage buildings, homes, and businesses. Severe flooding, and other impacts, like power outages, transportation disruptions, are also likely to impact the operations of critical facilities.

Environment
A tsunami has the potential to cause detrimental impacts on the OA’s environment. This may include uprooted trees and plants and destroyed animal habitats such as nesting sites for birds. Tsunami’s may result in the disappearance or abrupt erosion of beaches. During a tsunami event hazardous material infrastructure and pipelines may become damaged, causing the contamination of the environment with oil, raw sewage, and poisonous pollutants.

Economy
The cost of repair after a tsunami can impacts the economy. The tourism industry may be impacted as historic coastal properties and popular coastal businesses are damaged. Critical facilities and other important assets may be damaged by temporary inundation, resulting in loss of services such as power or wastewater treatment. Local tax revenue may decline as areas that were previously occupied by houses and businesses that may permanently close or have difficulty repairing.

11.3.9 Extreme Temperatures
Climate Change Impacts on Extreme Temperatures
Extreme temperatures are a serious consequence of climate change. Extreme heat is of particular concern to the OA. Climate change is expected to bring longer, more frequent, and more severe extreme heat events to the region.21F
213 By 2100, the area can expect 6 to 10 heat waves a year. Also, by the end of the century according to a medium emissions model, there will also be an estimated 2-44 days per year 213 County of Santa Clara Office of Sustainability. (N.D.). Climate Change Projections in Santa Clara County – Extreme Heat. https://siliconvalleytwopointzero.org/climateprojections/extremeheat Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 221
defined as extreme heat days – or days where the maximum temperature is above 92.7 °F.213F 214 Extreme
heat days followed by warm nights are dangerous because they don’t allow time for the population, landscapes, and the built environment to cool off. This can result in increased mortality, health issues, and wildfire risk.

Exposure, Sensitivity and Vulnerability
Population and Property
Extreme temperature days can directly harm human health. While flooding is the most common natural disaster, extreme temperatures are the deadliest. Extreme heat can result in a variety of heat-related illness from mild heat stress to fatal heat stroke. Mental health stress and other illnesses can also increase. Vulnerable populations, including the elderly, children, and people with pre-existing conditions will be disproportionally impacted by extreme heat. Societally inequities, such as the distribution of minority populations in areas more exposed to the urban heat island effect, can be exasperated by extreme heat conditions.

Critical Facilities
The impacts to critical facilities from extreme heat can range from barely noticeable to profound. More and more the value of using building materials that can reduce or withstand the impacts of extreme temperatures is being acknowledged. When building materials are pushed beyond their temperature thresholds, they are at risk of failure. Transportation infrastructure may also be damaged or destroyed, including asphalt, rail tracks, and cars. There is increased demand on energy utilities as the need for air conditioning rises. Back-up generators or alternative cooling methods such as community resilience hubs may be necessary if power supplies are insufficient to cool the community.

Environment
Extreme temperatures, especially hotter temperatures, can wreak havoc on unprepared ecosystems.

They are responsible for reducing biodiversity, resulting in numerous species death. Water supplies are also strained during extreme temperature events. Climate change also alters the range, biogeography, and growth of microbes which could result in additional foodborne and waterborne illnesses.214F 215
Economy
The economy will be impacted by the increase in extreme heat days. Extreme heat is associated with loss of productivity, increased chances of mortality, and increased of a workplace accident. A study from UCLA found that workers comp claims occurred more frequently on hotter days for both indoor and outdoor workers. An estimated 15,000 injuries occur per year in California and the financial cost may be between $750 million to $1.25 billion per year.215F
216 It also costs power more to maintain normal operations, such as keep the air conditioning running in an office. Some industries, such as construction, simply may not be able to function in too hot an environment. Research indicates that overall, economic growth declines and crop yields drop during periods of extreme heat. 214 Cal-Adapt. (N.D.) Extreme Heat Days & Warm Nights. https://cal-adapt.org/tools/extreme-heat/ 215 California Department of Public Health. (February 2017). Climate Change and Health Profile Report Santa Clara County.
https://www.cdph.ca.gov/Programs/OHE/CDPH%20Document%20Library/CHPRs/CHPR085SantaClara_County2- 23-17.pdf
216 UCLA Luskin. (June 2021). High Temperatures Increase Workers’ Injury Risk Whether They’re Outdoors or Inside. https://luskin.ucla.edu/high-temperatures-increase-workers-injury-risk-whether-theyre-outdoors-orinside#:~:text=A%20UCLA%20study%20published%20today%20shows%20that%20hot,from%20California%E2%80 %99s%20workers%E2%80%99%20compensation%20system%2C%20the%20nation%E2%80%99s%20largest.

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11.3.10 Sea Level Rise
Climate Change Impacts on Sea Level Rise
In addition to impacts on the identified hazards of concern, climate change presents risks related to sea level rise. Sea level rise will cause currently dry areas to be permanently inundated. The scope of temporary inundation from extreme tide events and storm surge also will also expand. Within the OA, the cities of Palo Alto, Mountain View, Sunnyvale, Milpitas, and San José are expected to experience the most impacts from sea level rise.216 F
217 Multiple possible sea level rise scenarios are presented in Table 69. Although the exact extent and timing of sea level rise is still uncertain, assessing potential areas at risk provides important information appropriate for planning purposes.

Table 69: Silicon Valley 2.0 Santa Clara County Sea Level Rise Projections and Inundation Layers SV 2.0 Tool Scenarios OPC 2018 Projections Permanent Sea Level Rise 100-year Storm Surge (+47”) Timeframe Scenario Risk
Tolerance
Projection
(in)
Inundation Layer Used in
Tool (in)
Projection
(in)
Inundation Layer Used in
Tool (in)
Baseline Current n/a 0 none 47 48
Mid-Century
Medium Top of likely
range

13.2 12 60.2 66
High 1 in 200 22.8 24 69.8 66
Late-Century
Medium Top of likely
range

40.8 36 87.8 84
Medium-High 1 in 20 52.8 52 99.8 96
High 1 in 200 82.8 84 129.8 131
217 County of Santa Clara Office of Sustainability. (n.d.). Climate Change Projections in Santa Clara County. https://siliconvalleytwopointzero.org/climateprojections/slr Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 223
Exposure, Sensitivity, and Vulnerability
The following assessment was conducted using data provided by the San Francisco Bay Conservation and Development Commission. A sea level rise of 48 inches above current mean higher high water was assumed.

Population
Sea level rise will increase the population exposed to both permanent and temporary inundation.

Currently, approximately 0.94 percent of the OA population is estimated to reside in areas subject to sea level rise impacts. The vast majority of these individuals reside in Palo Alto. Table 70 shows exposed population by jurisdiction.

Table 70: Estimated Population Residing in Sea Level Rise Inundation Areas Jurisdiction Estimated
Population
Estimated Population
Exposed
% of Population
Exposed
Campbell 43,442 0 0.0%
Cupertino 60,646 0 0.0%
Gilroy 59,472 0 0.0%
Los Altos 31,809 0 0.0%
Los Altos Hills 8,452 0 0.0%
Los Gatos 33,526 0 0.0%
Milpitas 80,248 0 0.0%
Monte Sereno 3,450 0 0.0%
Morgan Hill 45,037 0 0.0%
Mountain View 82,097 60 0.07%
Palo Alto 68,523 9,373 13.68%
San José 1,014,125 6,275 0.62%
Santa Clara (city) 127,608 0 0.0%
Saratoga 31,039 0 0.0%
Sunnyvale 154,808 2,421 1.56%
Unincorporated
County 90,253 36 0.04%
Total 1,934,535 18,165 0.94%
Property
The majority of losses from sea level rise are related to residential structures, closely followed by commercial and industrial. The majority of these assets are in Sunnyvale, San José, and Palo Alto.

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Table 71: Structure Type in Sea Level Rise Inundation Areas Jurisdiction Residential Commercial Industrial Agricultural Religious Government Education Total Campbell $0 $0 $0 $0 $0 $0 $0 $0
Cupertino $0 $0 $0 $0 $0 $0 $0 $0
Gilroy $0 $0 $0 $0 $0 $0 $0 $0
Los Altos $0 $0 $0 $0 $0 $0 $0 $0
Los Altos Hills $0 $0 $0 $0 $0 $0 $0 $0
Los Gatos $0 $0 $0 $0 $0 $0 $0 $0
Milpitas $0 $0 $0 $0 $0 $0 $0 $0
Monte Sereno $0 $0 $0 $0 $0 $0 $0 $0
Morgan Hill $0 $0 $0 $0 $0 $0 $0 $0
Mountain View $0 $128,886,000 $83,412,000 $1,034,000 $836,000 $6,966,000 $18,923,000 $240,057,000 Palo Alto $1,415,492,000 $525,812,000 $209,418,000 $4,075,000 $21,582,000 $15,911,000 $206,524,000 $2,398,814,000 San José $489,324,000 $562,847,000 $634,429,000 $4,243,000 $47,844,000 $13,429,000 $16,031,000 $1,768,147,000 Santa Clara
(city) $0 $0 $0 $0 $0 $0 $0 $0
Saratoga $0 $0 $0 $0 $0 $0 $0 $0
Sunnyvale $314,344,000 $755,253,000 $774,439,000 $377,000 $238,000 $5,129,000 $0 $1,849,780,000 Unincorporated
County $0 $998,000 $0 $0 $0 $0 $0 $998,000.00
Total $2,219,160,000 $1,973,796,000 $1,701,698,000 $9,729,000 $70,500,000 $41,435,000 $241,478,000 $6,257,796,000 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 11: Climate Change 225
Table 72: Structure and Contents Value in Sea Level Rise Inundation Areas Jurisdiction Structures
Exposed
Estimated
Value of
Exposed
Structures
Estimated
Value of
Exposed
Contents
Estimated
Total Value
% of Total
Replacement
Value
Campbell 0 $0 $0 $0 0.0%
Cupertino 0 $0 $0 $0 0.0%
Gilroy 0 $0 $0 $0 0.0%
Los Altos 0 $0 $0 $0 0.0%
Los Altos
Hills 0 $0 $0 $0 0.0%
Los Gatos 0 $0 $0 $0 0.0%
Milpitas 635 $468,554,661 $386,407,648 $854,962,309 4.5% Monte
Sereno 0 $0 $0 $0 0.0%
Morgan Hill 0 $0 $0 $0 0.0%
Mountain
View 102 $1,012,240,021 $1,110,560,396 $2,122,800,417 8.5% Palo Alto 4,014 $2,069,879,805 $1,642,022,511 $3,711,902,316 14.4% San José 912 $2,573,152,965 $2,275,265,284 $4,848,418,248 2.3% Santa Clara
(city) 450 $1,273,778,027 $1,228,024,465 $2,501,802,492 5.8% Saratoga 0 $0 $0 $0 0.0%
Sunnyvale 355 $2,632,745,163 $3,074,816,827 $5,707,561,990 13.3% Table 73: Structure and Contents Value in Sea Level Rise Inundation Areas, Unincorporated Santa Clara County
Jurisdiction Structures
Exposed
Estimated Value of
Exposed Structures
Estimated Value of
Exposed Contents
Estimated Total
Value
Unincorporated
County 1 $262,260 $131,130 $393,390
County + All
Cities 6,469 $10,030,612,900 $9,717,228,260 $19,747,841,162 Critical Facilities
There are 72 critical facilities located in OA areas subject to impacts from sea level rise.

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Table 74: Critical Facilities in Sea Level Rise Inundation Areas Jurisdiction Essential
Facilities Transportation Utilities Community Assets
Hazardous
Materials Total
Campbell 0 0 0 0 0 0
Cupertino 0 0 0 0 0 0
Gilroy 0 0 0 0 0 0
Los Altos 0 0 0 0 0 0
Los Altos Hills 0 0 0 0 0 0
Los Gatos 0 0 0 0 0 0
Milpitas 0 0 0 0 0 0
Monte Sereno 0 0 0 0 0 0
Morgan Hill 0 0 0 0 0 0
Mountain View 1 0 0 1 2 3
Palo Alto 9 12 3 5 9 29
San José 2 7 1 5 7 20
Santa Clara (city) 0 1 0 0 0 1
Saratoga 0 0 0 0 0 0
Sunnyvale 1 2 0 1 11 14
Unincorporated
County 0 0 0 1 0 1
Total 13 26 4 13 29 72
Environment
All sea level rise inundation areas are exposed and vulnerable to impacts. Important coastal habitat may be lost as sea level rise permanently inundates areas, or it may be damaged due to extreme tide and storm surge events. Saltwater intrusion into freshwater resources may occur, further altering habitat and ecosystems and threatening the water supply. Protective ecosystem services may be lost as land area and wetlands are permanently inundated.

Economy
Sea level rise will impact the local economy. The tourism industry may be impacted as historic coastal properties are inundated. Critical facilities and other important assets may be damaged by temporary inundation, resulting in loss of services such as power or wastewater treatment. Coastal businesses may relocate to other areas rather than face high costs from increased risk of storm surge and costs associated with managed retreat. Local tax revenue may decline as areas that were previously occupied by houses and businesses are permanently inundated.

Future Development
The land area of the OA will be reduced as sea level rise permanently inundates areas. This will have significant impacts on land use and planning in local communities. Local General Plans in the OA will guide this future development.

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11.4 Issues
This assessment of climate change led to identification of the following issues throughout the Santa Clara County OA:
 Planning for climate change related impacts can be difficult due to inherent uncertainties in projection methodologies.
 Average temperatures are expected to continue to increase in the OA, which may lead to a host of primary and secondary impacts, such as an increased incidence of heat waves.  Expected changes in precipitation patterns are still poorly understood and could have significant impacts on the water supply and flooding in the OA.
 Some impacts of climate change are poorly understood such as potential impacts on the frequency and severity of earthquakes, thunderstorms, and tsunamis.  Heavy rain events may result in inland stormwater flooding after stormwater management systems are overwhelmed.
 Permanent and temporary inundation resulting from sea level rise has the potential to impact significant portions of the population and assets in the OA.

Table 75: EMAP Consequence Analysis: Climate Change
Subject Ranking Impacts/Climate Change
Public Minimal to
Severe
Residents across the OA will be impacted by climate change.

Noticeable impacts will include changes in temperature, increased frequency and severity of natural hazards, and the permanent inundation of part of the community due to sea level rise. Even residents outside of areas immediately impacted by hazard events will experience secondary effects such as smoke, a reduction in air quality, disruption of services, and transportation delays or disruptions.

Responders Minimal to
moderate
Responders will be relied upon when a disaster event occurs. They may need to consider climate change and the changing likelihood of future events when allocating resources towards certain hazards.

However, overall, since climate change is a long-term challenge with occurs over many years, there is unlikely to be significant changes needed to responder’s immediate response and recovery efforts.

Continuity of
Operations
(including
continued
delivery of
services)
Minimal to
Severe
The impacts on continuity of operations depends largely on facility and critical infrastructure location, hazard location, frequency, and severity, and human interference. Certain types of infrastructure, such as wastewater treatment plants which could be inundated by sea level rise or power utilities in high-risk wildfire areas, are more likely to be disrupted or destroyed. Delivery of services may also be slowed or stopped in impacted areas. Since climate change occurs over time, there is the opportunity for at-risk facilities and organizations to develop continuity of operations plans which address the increased risks associated with climate change.

Property,
Facilities, and
Infrastructure
Minimal to
Severe
The localized impact to properties, facilities, and infrastructure could be severe. Sea level rise impact estimates are one of the best examples of how climate change could directly relate to the complete loss of property, facilities, and infrastructure. Increased frequency and severity of other hazard events will likely result in damage, destruction, or disturbances to other structures and infrastructure across the OA.

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Subject Ranking Impacts/Climate Change
Environment Minimal to
Severe
California’s ecosystem has adapted to some of the impacts of climate change including wildfires. However, the increased frequency and severity of hazard events could strain the adaptative capacity of an ecosystem already stressed by increased human development.

Climate change could result in changes to the watershed, water supply, destroy or damage fish and wildlife habitats, destroy crucial flood protective habitats near the ocean, and increase the spread of invasive spices and the death of trees and vegetation.

Economic
Conditions
Minimal to
Severe
Climate change may impact the local economy in multiple different ways. Increased severe hazards events will test the financial resilience of the OA. Certain sectors, including agriculture and tourism, are likely to experience the worse impacts of climate change. Disturbances to transportation, communication, power, and water infrastructure due to climate change can also have a significant impact on the economy.

Impacts largely depend on how effectively the population and built environment can respond to changing climate conditions.

Public
Confidence in
the Government
Minimal to
Severe
Climate change is at the forefront of the national discussion on natural disasters. The public often has intense opinions on the subject. In general, climate change adaptation measures are widely supported in the OA. Solutions which consider short-term benefits, such as planting trees which increase shade and enhance the community’s curb appeal while at the same time reducing the urban heat island effect, are likely to be the most supported. Consistent messaging, accurate and timely public information, and clear reasoning for climate change adaptation measures will increase public’s confidence in the government.

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12 Dam and Levee Failure
Definitions
 Dam: Any artificial barrier, together with appurtenant works, which does or may impound or divert water, and which is or will be either 25 feet or more in height from the natural bed of the stream or watercourse at the downstream toe of the barrier, as determined by the department, or from the lowest elevation of the outside limit of the barrier, as determined by the department, if it is not across a stream channel or watercourse, to the maximum possible water storage elevation or has or will have an impounding capacity of 50 acre-feet or more.40  Levee: A man-made structure, usually an earthen embankment, designed and constructed to prevent inland flooding from major storm events and extreme waterlevels.  Emergency Action Plan: A formal document that identifies potential emergency conditions at a dam and specifies actions to be followed to minimize property damage and loss of life. It contains procedures and information to help the dam owner issue early warning and notification messages and inundation maps to show emergency management authorities the critical areas for action in case of an emergency.
 High Hazard Dam: Dams where failure or improper operation will probably cause loss of at least one human life.
 Extremely High Hazard Dam: California’s Division of Safety of Dams (DSOD) has classified some High Hazard Dams as Extremely High Dams. These are expected to cause considerable loss of human life or would result in an inundation area with a population of 1,000 ormore.

12.1 General Background
Dams and levees are designed to mitigate flood events but sometimes floods larger than the estimated risk occur which can cause a partial or total failure. Other causes of dam and levee failure vary.

12.2 Causes of Dam and Levee Failure
A dam failure occurs when the barrier constructed does not obstruct or restrain water as designed, which can rapidly result in a large area of completely inundated land. Levees, though similar, are embankments built to prevent the overflow of a river or stream.

12.2.1 Causes of Dam Failure
Dam failures can be catastrophic to human life and property downstream. Dam failures in the United States typically occur in one of four ways:
 Overtopping of the primary dam structure, which accounts for 34 percent of all dam failures, can occur due to inadequate spillway design, settlement of the dam crest, blockage of spillways, and other factors.
 Foundation defects due to differential settlement, slides, slope instability, uplift pressures, and foundation seepage can also cause dam failure. These account for 30 percent of all dam failures.  Failure due to piping and seepage accounts for 20 percent of all failures. These are caused by internal erosion due to piping and seepage, erosion along hydraulic structures such as spillways, erosion due to animal burrows, and cracks in the dam structure.

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 Failure due to problems with conduits and valves, typically caused by the piping of embankment material into conduits through joints or cracks, constitutes 10 percent of all failures.

The remaining six percent of U.S. dam failures are due to miscellaneous causes. Many dam failures in the United States have been secondary results of other disasters. The prominent causes are earthquakes, landslides, extreme storms, massive snowmelt, equipment malfunction, structural damage, foundation failures, and sabotage.

The most likely disaster-related causes of dam failure in the OA are earthquakes, excessive rainfall, and landslides. Poor construction, lack of maintenance and repair, and deficient operational procedures are preventable or correctable by a program of regular inspections. Terrorism and vandalism are serious concerns that all operators of public facilities must plan for; these threats are under continuous review by public safety agencies.

12.2.2 Causes of Levee Failure
A levee breach occurs when part of a levee gives way, creating an opening through which floodwaters may pass. A breach may occur gradually or suddenly. The most dangerous breaches happen quickly during periods of high water. The resulting torrent can quickly swamp a large area behind the failed levee with little or no warning. When a levee system fails or is overtopped, severe flood damage can occur.

Earthen levees can be damaged in several ways. Strong river currents and waves can erode the surface.

Trees growing on a levee can blow over, leaving a hole where the root wad and soil used to be.

Burrowing animals, such as the California ground squirrel, the salt marsh harvest mouse, or the western burrowing owl can create holes that enable water to pass through a levee. If severe enough, any of these situations can lead to a zone of weakness that could cause a levee breach. In seismically active areas, earthquakes and ground shaking can cause a loss of soil strength, weakening a levee and possibly resulting in failure. Seismic activity can also cause levees to slide or slump, both of which can lead to failure.

No levee provides protection from events for which it was not designed, and levees require maintenance to continue to provide the level of protection they were designed and built to offer. Maintenance responsibility belongs to a variety of entities including local, state, and federal government and private landowners.

12.3 Hazard Profiles
Levees and dams serve different purposes. Though both can be made with the same materials, their relationship to water is different. Levees run parallel to water while dams lie across. A levee’s primary focus is to reduce flood risk and protect life and property. Dams also serve risk management functions but deliver other infrastructure benefits for communities and industry. The aging dam infrastructure in the OA is notable. Table 76 shows that the Lake Ranch Dam was built in 1877 and ten dams were built in the 1930s.

12.3.1 Past Dam Failure Events
According to the 2018 State of California Multi-Hazard Mitigation Plan, there have been ten dam failures in the state since 1950. The most recent dam emergency occurred in February 2017 at Oroville Dam in northern California’s Butte County when it was on the verge of overflow. The concrete spillway was damaged by erosion and a massive hole developed. The auxiliary spillway was used to prevent overtopping of the dam and it experiences erosion problems also. Evacuation orders were issued out of concern about a potential large uncontrolled release of water from Lake Oroville. Such a release was ultimately prevented, and evacuees returned to their homes.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 231
Table 76: Dams Classified as a High Hazard or an Extremely High Hazard Risk 217F 218,
218F
219
Name National
ID #
Hazard
Class Owner Dam Type
Dam
Height
(feet)
Crest
Length
(feet)
Reservoir
Capacity
(acrefeet)
Year
Built
Inundation
Map
Closest
City
Almaden CA00289 Extremely
High SCVWD Earth 110 500 2,000 1936 Yes San José
Almaden Valley CA00661 High San José
Water Co. Earth 38 1,100 27 1955 Yes San José
Austrian 622.013 Extremely
High
San José
Water Co. Earth 185 700 6,200 1950 Yes Los Gatos
Calero 72.003 Extremely
High SCVWD Earth 90 840 9,850 1935 Yes San José
Cherry Flat CA00158 Extremely
High
City of San
José Earth 60 230 500 1936 Yes San José
Coyote CA00287 Extremely
High SCVWD Earth and Rock 140 980 22,541 1936 Yes Gilroy Coyote Percolation
(Steel flashboard dam
being replaced with
an inflatable rubber
dam)
CA00286 High SCVWD Steel
Flashboard 24 204 72 1934 Yes San José
DeBell CA00686 High City of Gilroy Earth 53 580 120 1952 Yes Gilroy Ed R. Levin CA00890 Extremely
High
County of
Santa Clara Earth 38 470 150 1968 Yes Milpitas
Elmer J. Chesbro CA00806 Extremely
High SCVWD Earth and Rock 95 690 8,086 1955 Yes Morgan Hill 218 National Inventory of Dams. (n.d.). Dams of the Nation. https://nid.sec.usace.army.mil/#/ 219 California Department of Water Resources. (n.d.). California Dam Breach Inundation Maps. https://fmds.water.ca.gov/maps/damim/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 232
Name National
ID #
Hazard
Class Owner Dam Type
Dam
Height
(feet)
Crest
Length
(feet)
Reservoir
Capacity
(acrefeet)
Year
Built
Inundation
Map
Closest
City
Felt Lake CA00670 Extremely
High
Stanford
University
Board of
Trustees
Earth 67 590 900 1930 Yes Palo Alto
Foothill Park CA00868 High City of Palo
Alto
Earth 86 600 67 1988 Yes Palo Alto
Guadalupe CA00290 Extremely
High
SCVWD Earth 142 695 3,460 1935 Yes San José
Higuera CA00687 Extremely
High
Wells Fargo
Bank
Earth 44 525 65 1953 Yes Milpitas
James J. Lenihan,
“Lexington Reservoir”
CA00293 Extremely
High
SCVWD Earth 208 810 21,430 1953 Yes Los
Gatos
Kuhn CA00683 Extremely
High
Private Entity Earth 67 312 85 1947 Yes San José
Lake Ranch CA00676 High San José
Water Co.

Earth 38 160 215 1877 Yes San José
Leroy Anderson
(inactive)
CA00294 Extremely
High
SCVWD Earth 235 1,430 91,300 1950 Yes Morgan
Hill
North Fork CA00299 Extremely
High
Pacheco
Pass Water
District
Earth 100 600 6,150 1939 No Hollister
Rinconada Reservoir CA00295 High SCVWD Earth 40 240 46 1969 Yes Campbell Stevens Creek CA00292 Extremely
High
SCVWD Earth 132 1,080 3,074 1935 Yes Cupertino
Uvas CA00807 Extremely
High
SCVWD Earth 118 1,100 10,000 1957 Yes Morgan
Hill
Vasona Percolating CA01516 Extremely
High
SCVWD Earth 34 1,00 410 1935 Yes Los
Gatos
San Mateo County Dam with an Inundation Area extending into the OA.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 233
Name National
ID #
Hazard
Class Owner Dam Type
Dam
Height
(feet)
Crest
Length
(feet)
Reservoir
Capacity
(acrefeet)
Year
Built
Inundation
Map
Closest
City
Searsville CA00669 Extremely
High
Stanford
Board of
Trustees
Masonry 68 260 1,840 1890 Yes Palo Alto
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 234
Historically, overtopping caused two of the state’s nine dam failures; the others were caused by seepage or leaks. One failure, the 1963 Baldwin Hills Dam Failure in Los Angeles County, resulted in three deaths because the leak turned into a washout. The historical record indicates that California has had about 45 failures of non-federal dams. The failures occurred for a variety of reasons, the most common being overtopping. Other reasons include shortcomings in the dams or an inadequate assessment of surrounding geomorphologic characteristics.

One dam failure event was recorded in the OA in 2017. After a series of slow-moving storms fronts, despite attempts to release water through at outlet at the bottom of the dam, the man-made Anderson Reservoir in Morgan Hill reached its peak capacity and water overtopped Anderson Dam, resulting in flooding downstream along Coyote Creek. The flooding was estimated to have cause $100 million in damages and displaced 14,00 residents219 F
220
.

12.3.2 Dam Location and Extent
According to the USACE National Inventory of Dams (NID), there are 44 regulated dams in the OA (Figure 57). Extremely high hazard dams are indicated in red, high hazard dams are indicated in orange, and dams with a significant hazard are shown in green. Low hazard dams are not mapped.

The DSOD has certified all these dams and has designated all of them with a Condition Assessment of “Satisfactory.” In addition, these dams all have the emergency action plan (EAP) required for all dams that do not have a low downstream hazard potential designation20F 221
. The EAP requirements include an
early warning system and operational procedures that may be used, such as reducing reservoir levels and reducing downstream flows, as well as procedures for notifying affected residents and agencies responsible for emergency management. The Searsville Dam, an Extremely High Hazard Dam located in San Mateo County, has an inundation area that could impact parts of the City of Palo Alto. This dam has been added to Table 76.

The Anderson Dam, located three miles east of U.S. 101 in Morgan Hill, was discussed in the 2019 MJHMP but on February 24, 2020, the Federal Energy Regulatory Commission ordered that Anderson Lake should be drained due to earthquake risk. At the time of writing this update, work on the $576-million Anderson Dam Seismic Retrofit Project continues. The project is expected to be complete by 2031.

Dam Inundation Mapping
The most significant issue associated with dam failure involves the potential impact on properties and populations in the inundation zones. As listed in Table 76, all but two of the dams have an approved inundation map. Flooding because of a dam failure would significantly impact these areas. Figure 58 shows dam inundation depth grids within the County.
220 San José Spotlight. (2022, June 1). Valley Water settles with San José residents over 2017 flood. San José flood victims get multimillion-dollar settlement - San José Spotlight (sanjosespotlight.com) 221 California Legislative Information. (n.d.). Water Code, Division 3, Dams and Reservoirs. Chapter 8. https://leginfo.legislature.ca.gov/faces/codes_displayexpandedbranch.xhtml?tocCode=WAT&division=3.&title=&part= &chapter=&article=&nodetreepath=4
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 235
Figure 58: Location of Dams Impacting Santa Clara County21F 222
222 California Department of Water Resources, Division of Safety of Dams. (n.d.). Dam Breach Inundation Map Web Publisher. https://fmds.water.ca.gov/webgis/?appid=dam_prototype_v2 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 236
Figure 59: Dam Inundation Depth Grids

12.3.3 Levee Location
Currently, there are 89 levees listed by the United States Army Corps of Engineers (USACE) in Santa Clara County,2F
223 a significant increase from the seven levees listed in 2017. As shown in Figure 59, most of these structures are located in the South San Francisco Bay area. 223 National Levee Database. (n.d.). Levees of the Nation. https://levees.sec.usace.army.mil/#/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 237
Figure 60: Levees in Santa Clara County23F
224
The Santa Clara Valley Water District (SCVWD) owns and maintains most of these levees. It manages approximately 100 miles of levees in Santa Clara County. About 50 miles provide 100-year flood protection and nearly 18 miles were constructed in partnership with the Corps. Other levee sponsors include U.S. Fish and Wildlife Service (USFWS) (12), the City of Palo Alto (2) Caltrans District 4, and the Alameda County Flood Control District with Santa Clara County (1). Table 77 provides information about levees in the County.

Most of the levees have not been screened by the USACE for risk. Of the seven that have been screened, three are considered to be low risk, three are considered moderate risk and one review is labeled “No Verdict.” Of the 89 levees, a total of 14 have been accredited by FEMA and recognized on a Flood Insurance Rate Map (FIRM). One levee is designated as a Provisionally Accredited Levee (PAL).

This designation may be used for a levee system that FEMA has previously accredited as providing base flood hazard reduction on an effective FIRM, and for which FEMA is awaiting data and/or documentation that will show the levee system is compliant with 44 CFR 65.10. 224 National Levee Database. (n.d.). Levees of the Nation. https://levees.sec.usace.army.mil/#/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 238
Table 77: Levees in Santa Clara County 24F
225

FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Coyote Creek, Santa
Clara – LB
Santa Clara SCVWD 6.72 9,477 1,879 $1.59B Low A A
Coyote Creek, Santa
Clara – RB
Santa Clara SCVWD 4.9 26,188 4,721 $3.47B Moderate A A
Coyote Creek, Santa
Clara – RB Bypass
Alameda,
Santa Clara
SCVWD 1.67 1,247 21 $219M No Verdict N A
Cunningham Flood
Detention Facility
Certification Project
Santa Clara SCVWD 4.32 20,689 3,588 $3.08B Not Screened A N Cunningham Flood
Detention Facility
Certification Project 2
Santa Clara State 4.5 32,882 6,174 $3.64B Not Screened A N Guadalupe River - LB Santa Clara SCVWD 8.48 30,391 3,364 $3.85B Moderate A A Guadalupe River - RB Santa Clara SCVWD 6.9 24,361 2,335 $3.21B Moderate A A King & Lyons Alameda and
Santa Clara
Alameda
County
Flood
Control

3.5 3,497 62 $449M Low PAL A
Los Gatos Creek Santa Clara Caltrans
District 4
.41 92 27 $29.9M Not Screened A N
Santa Clara County
Levee 1
Alameda,
Santa Clara
Local 1.33 0 0 0 Not Screened N N
225 National Levee Database. (n.d.). Levees of the Nation. https://levees.sec.usace.army.mil/#/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 239

FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 10
Santa Clara USFWS 0.68 0 1 0 Not Screened N N
Santa Clara County
Levee 11
Santa Clara USFWS 2.28 0 0 0 Not Screened N N
Santa Clara County
Levee 12
Santa Clara SCVWD 0 0 4 $212M Not Screened N N
Santa Clara County
Levee 13
Santa Clara City of Palo
Alto

0.62 0 0 0 Not Screened N N
Santa Clara County
Levee 14
Santa Clara Local 1.06 0 0 0 Not Screened N N
Santa Clara County
Levee 15
Santa Clara SCVWD 1.13 1,632 298 $436M Not Screened N N Santa Clara County
Levee 16
Santa Clara USFWS 8.66 0 0 0 Not Screened N N
Santa Clara County
Levee 17
Santa Clara SCVWD 1.39 140 21 $248M Not Screened N N
Santa Clara County
Levee 18
Santa Clara USFWS 1.67 0 0 0 Not Screened N N
Santa Clara County
Levee 19
Santa Clara SCVWD 1.42 2,181 727 $450M Not Screened N N Santa Clara County
Levee 20
Santa Clara SCVWD 0.19 269 89 $134M Not Screened N N
Santa Clara County
Levee 21
Santa Clara SCVWD 1.97 1,512 420 $364M Not Screened N N Santa Clara County
Levee 22
Santa Clara USFWS 3.24 0 0 0 Not Screened N N
Santa Clara County
Levee 23
Santa Clara SCVWD 1.56 1,722 628 $401M Not Screened N N Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 240

FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 24
Santa Clara USFWS 1.24 0 0 0 Not Screened N N
Santa Clara County
Levee 25
Santa Clara USFWS 0.43 0 0 0 Not Screened N N
Santa Clara County
Levee 26
Santa Clara SCVWD 2.86 0 0 0 Not Screened N N
Santa Clara County
Levee 27
Santa Clara USFWS 0.66 0 0 0 Not Screened N N
Santa Clara County
Levee 28
Santa Clara SCVWD 4.01 0 0 0 Not Screened N N
Santa Clara County
Levee 29
Santa Clara SCVWD 3.05 5,409 1,719 $1.08B Not Screened N N Santa Clara County
Levee 3
San Mateo,
Santa Clara
SCVWD 7.56 17,748 6,351 $4.45B Not Screened N N
Santa Clara County
Levee 30
Santa Clara SCVWD 1.31 3,389 750 $628M Not Screened A N Santa Clara County
Levee 30.2
Santa Clara - 1.21 4,107 1,315 $777M Not Screened N N
Santa Clara County
Levee 31
Santa Clara USFWS 1.01 0 0 0 Not Screened N N
Santa Clara County
Levee 32
Santa Clara - 0.66 0 0 0 Not Screened N N
Santa Clara County
Levee 33
Santa Clara - 0.11 0 2 $1.09 Not Screened N N
Santa Clara County
Levee 34
Santa Clara USFWS 1.8 0 0 0 Not Screened N N
Santa Clara County
Levee 35
Santa Clara SCVWD 5.7 21,352 715 $6.03B Not Screened A N Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 241

FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 36
Santa Clara SCVWD 5.19 0 0 0 Not Screened N N
Santa Clara County
Levee 37
Santa Clara SCVWD 2.76 32,113 5,873 $10.6B Not Screened A N Santa Clara County
Levee 37 North
Santa Clara - 8.89 0 0 0 Not Screened N N
Santa Clara County
Levee 38
Santa Clara SCVWD 3.78 0 0 0 Not Screened N N
Santa Clara County
Levee 4
Santa Clara - 0.08 0 0 0 Not Screened N N
Santa Clara County
Levee 40
Santa Clara SCVWD 1.26 8,031 43 $169M Not Screened N N
Santa Clara County
Levee 41
Santa Clara SCVWD 3.7 2,454 208 $951M Not Screened A N
Santa Clara County
Levee 42
Santa Clara SCVWD 3.52 11,654 4,092 $2.99B Not Screened N N Santa Clara County
Levee 43
Santa Clara SCVWD 0.02 0 0 0 Not Screened N N
Santa Clara County
Levee 44
Santa Clara - 0.26 0 0 0 Not Screened N N
Santa Clara County
Levee 45
Santa Clara SCVWD 3.56 0 0 0 Not Screened N N
Santa Clara County
Levee 46
Santa Clara SCVWD 1.11 5,616 53 $641M Not Screened N N
Santa Clara County
Levee 47
Santa Clara - 0.54 0 0 0 Not Screened N N
Santa Clara County
Levee 48
Santa Clara City of Palo
Alto

0.29 865 33 $82M Not Screened N N
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 242

FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 49
Santa Clara USFWS 0.41 0 0 0 Not Screened N N
Santa Clara County
Levee 5
Santa Clara - 0.21 0 0 0 Not Screened N N
Santa Clara County
Levee 50
Santa Clara - 1.44 0 0 0 Not Screened N N
Santa Clara County
Levee 52
Santa Clara USFWS 2.5 0 0 0 Not Screened N N
Santa Clara County
Levee 53
Santa Clara - 0.03 0 0 0 Not Screened N N
Santa Clara County
Levee 54
Santa Clara SCVWD 1.83 8,645 688 $1.54B Not Screened A N Santa Clara County
Levee 55
Santa Clara City of Palo
Alto

0.33 2 2 $3.93M Not Screened N N
Santa Clara County
Levee 56
Santa Clara - 0.72 0 0 0 Not Screened N N
Santa Clara County
Levee 57
Santa Clara - 0.36 0 0 0 Not Screened N N
Santa Clara County
Levee 58
Santa Clara - 1.78 0 0 0 Not Screened N N
Santa Clara County
Levee 6
Santa Clara SCVWD 1.51 6,548 1,840 $1.2B Not Screened N N Santa Clara County
Levee 61
Santa Clara SCVWD 1.58 2,370 382 $247M Not Screened N N Santa Clara County
Levee 62
San Benito,
Santa Clara
SCVWD 2.41 41 14 $24.4M Not Screened N N
Santa Clara County
Levee 64
Santa Clara SCVWD 1.06 50,774 1,610 $10.2B Not Screened N N Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 243

FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 65
Santa Clara - 1.39 12,714 2,494 $2.6B Not Screened N N
Santa Clara County
Levee 67
Santa Clara - 0.88 180 48 $82.7M Not Screened N N
Santa Clara County
Levee 7
Santa Clara - 0.2 0 0 0 Not Screened N N
Santa Clara County
Levee 72
Santa Clara SCVWD 0.86 0 5 $2.27M Not Screened N N
Santa Clara County
Levee 73
Santa Clara SCVWD 0.94 475 186 $97.6M Not Screened N N
Santa Clara County
Levee 74
Santa Clara - 0.62 413 128 $63.7M Not Screened N N
Santa Clara County
Levee 75
Santa Clara SCVWD 1.09 181 21 $100M Not Screened N N
Santa Clara County
Levee 79
Santa Clara - 0.87 6,131 1,840 $917M Not Screened N N
Santa Clara County
Levee 8
Santa Clara - 0.56 0 0 0 Not Screened N N
Santa Clara County
Levee 80
Santa Clara - 0.72 47 7 $1.87M Not Screened N N
Santa Clara County
Levee 81
Santa Clara SCVWD 0 0 0 Not Screened N N
Santa Clara County
Levee 82
Santa Clara SCVWD 0 0 0 Not Screened N N
Santa Clara County
Levee 83
San Benito,
Santa Clara
SCVWD 2.65 149 19 $22.5M Not Screened N N
Santa Clara County
Levee 84
Santa Clara SCVWD 0.54 1,647 759 $253M Not Screened N N Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 244

FEMA - NFIP/FIRM
Information Only
listing active levees County Sponsor Total
Miles
What is Behind the Levee
Risk
Accredited
Levee*
USACE Rehab**
Levee Name Population Buildings Property
Value
Santa Clara County
Levee 85
Santa Clara - 0.87 1,767 551 $246M Not Screened N N
Santa Clara County
Levee 86
Santa Clara SCVWD 1.88 0 0 0 Not Screened N N
Santa Clara County
Levee 88
Santa Clara SCVWD 0.75 1,517 244 $633M Not Screened N N Santa Clara County
Levee 89
Santa Clara SCVWD 1.04 9,275 2,261 $1.97B Not Screened A N Santa Clara County
Levee 9
Santa Clara SCVWD 3.41 12,080 1,617 $2.79B Not Screened N N Santa Clara County
Levee 90
Santa Clara SCVWD 0.81 2,052 344 $191M Not Screened N N Santa Clara County
Levee 92
Santa Clara SCVWD 0.21 5,982 295 $4224M Not Screened N N Santa Clara County
Levee 93
Santa Clara - 1.3 13 5 $238M Not Screened N N
Santa Clara County
Levee 96
Santa Clara - 0.5 273 5 $27.7M Not Screened N N
Uvas Creek - LB Santa Clara SCVWD 2.19 14,505 4,377 $1.72B Low A A *Accredited Levee column abbreviations: accredited (A), not accredited (N), and Provisionally Accredited Levee (PAL). **USACE Rehab column abbreviations: active (A) and not active (N).

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 245

12.3.4 Frequency of Dam and Levee Failure
Dam and levee failure events are infrequent and usually coincide with events that cause them, such as earthquakes, landslides and excessive rainfall and snowmelt. There is a “residual risk” associated with dams that remains after safeguards have been implemented. The residual risk is associated with events beyond those that the facility was designed to withstand. However, the probability of occurrence of any type of dam failure event is low in today’s regulatory and safety oversight environment.

Further information on the impact of climate change on the probability of dam failure is included in Section 11.

Probability in OA: Unlikely

12.3.5 Severity
FEMA categorizes the downstream hazard potential of a dam into three categories in increasing severity:

Low, Significant, and High. The state’s Division of Safety of Dams (DSOD) adds a fourth category of "Extremely High." The OA has dams in all four categories; this plan focuses on the Extremely High Hazard and High Hazard dams.

Table 78: Potential Downstream Hazard from Dams25F
226
Hazard
Potential Potential Downstream Impacts to Life and Property Number of Dams in the OA Low No probable loss of human life and low economic and environmental losses. Losses are expected to be principally limited to the owner’s property.
13 Significant No probable loss of human life but can cause economic loss, environmental damage, impacts to critical facilities, or other significant impacts.
4 High Expected to cause loss of at least one human life. 6 Extremely High Expected to cause considerable loss of human life or would result in an inundation area with a population of 1,000 or more. 18 12.3.6 Warning Time for Dam Failure
EAPs are critical in identifying areas downstream from dams requiring warning and evacuation in the event of dam failure. Warning and evacuation time can dramatically influence the number of persons at risk and the number of fatalities per dam failure.
226 California Department of Water Resources. (2021, September). Downstream Hazard. https://water.ca.gov/- /media/DWR-Website/Web-Pages/Programs/All-Programs/Division-of-Safety-of-Dams/Files/Publications/Division-ofSafety-of-Dams-Definitions-for-Downstream-Hazard-and-Condition-Assessment.pdf Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 246
Advance Warning of Failure
Warning time for dam failure varies depending on the cause of the failure. In events of extreme precipitation or massive snowmelt, evacuations can be planned with sufficient time. In the event of a structural failure due to earthquake, there may be no warning time.

Time for the Failure to Occur
A dam’s structural type also affects warning time. Earthen dams do not tend to fail completely or instantaneously. Once a breach is initiated, discharging water erodes the breach until either the reservoir water is depleted, or the breach resists further erosion. Concrete gravity dams also tend to have a partial breach as one or more monolith sections are forced apart by escaping water. The time of breach formation ranges from a few minutes to a few hours.26F
227
Time after Failure for Notification
Time available to notify those in the impacted area will depend on the dam’s distance from it and the river flow. The warning and protective action process is divided into the following three time periods:
 Warning delay time is the period between when a threat is first detected, or when an emergency manager is first notified of the threat and when an emergency manager issues a first alert/warning.
 Warning diffusion time is the period after the first alert/warning is issued and the time that people receive that alert/ warning.
 Protective action initiation time is the period after people receive the first alert/ warning and when they initiate protective action. In this time period, most people take a range of actions to prepare to implement a protective action and may receive subsequent warning messages.27F 228
Santa Clara County and its planning partners have established protocols for emergency warning and response through the County’s adopted emergency operations plan28F 229. The SCVWD Dam Safety
Program maintains the operation of its dams and works with Santa Clara County Emergency Management to provide copies of the most recent dam EAPs and inundation maps and uses this information to plan notification needs for downstream areas in the event of a failure.

12.3.7 Warning Time for Levee Failure
As with dam failure, warning time for levee failure depends on the cause of the failure. A levee failure caused by structural failure can be sudden and occur with little to no warning. If heavy rains are impacting a levee system, communities located in the immediate danger zone can be evacuated before a failure occurs. If the levee failure is caused by overtopping, the community may or may not be able to recognize the impending failure and evacuate. If a levee failure occurs suddenly, evacuation may not be possible. 227 Starosolszky, O. and Melder, O.M. (2014, April 23) Hydrology of Disasters: Proceedings of the World Meteorological Organization Technical Conference Held in Geneva, November 1988. https://books.google.com/books?id=DSFpAwAAQBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=o nepage&q&f=false
228 U.S. Army Corps of Engineers. (2019 April 30). A Guide to Public Alerts and Warnings for Dam and Levee Emergencies. https://www.publications.usace.army.mil/Portals/76/Users/182/86/2486/EP%201110-2-

17.pdf?ver=2019-06-20-152050-550
229 Santa Clara County. (2017, January). County of Santa Clara Emergency Operations Plan. Emergency Operations Plan (EOP) - Office of Emergency Management - County of Santa Clara (sccgov.org) Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 247

12.4 Exposure
Exposure to the dam failure hazard was assessed by use of GIS spatial analysis, overlaying the inundation areas with data from the underlying population, buildings, and critical facilities. The consistency of the data available to support this risk assessment varied greatly within the OA. The level of analyses varied based on available data.

12.4.1 Population
The estimated total population living in the inundation area of an Extremely High Hazard, or a High Hazard dam is 32.17% of the total county population.

12.4.2 Property
Table 79 summarizes the estimated property exposure in the inundation area of an Extremely High Hazard or a High Hazard dam. These estimates were determined using a combination of Hazus and GIS data.

Table 79: Estimated Exposure and Value of Structures in the Dam Failure Inundation Area Exposure County Total
Inundation Area 162.90 square miles
Number of Buildings Exposed 168,271
Percentage of Exposed Buildings in the County 31.43%
Exposed Value in the County $131,358,283,000
Total Percentage of Exposed Value in the County 34.48%

12.4.3 Environment
The environment would be exposed to a number of risks in the event of dam failure. The inundation could introduce many foreign elements into local waterways. This could result in destruction of downstream habitat and could have detrimental effects on many species.

12.5 Vulnerability
The vulnerability of people, property, critical facilities, and the environment was evaluated for the combined dam failure inundation area. Countywide summaries are provided below.

Change in conditions: no change in vulnerability
 Growth in population and building is slow and not concentrated in areas at particular risk to dam failure.
 No new dams have been constructed in the OA.
 Dams with significant or high hazard potential are required to have an EAP.  Dam safety programs include inspection, maintenance, and ongoing monitoring of dams to ensure stability and proper functioning of dams.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 248
 DSOD and dam owners such as SCVWD periodically undertake special engineering studies to ensure that its dams are compliant with the latest design guidelines and regulations to minimize seismic risks to its dams.
• Although vulnerability to dams is not increasing, risk to people and structures in dam inundation remains high. In the unlikely even of a failure, the high volume and velocity of resulting flood waters can have devastating impacts downstream.

12.5.1 Population
All populations downstream from dam failures that are incapable of escaping the area within the allowable time period are vulnerable. Those that particularly vulnerable includes the elderly and children, people with medical conditions, people who are visually impaired and/or have vision loss, people with public transportation needs, people with non-visible disabilities, people with limited English proficiency. The vulnerable population also includes those who would not have adequate warning from a television or radio emergency warning system or cell phone alert or people who may unable to get themselves out of the inundation area. The potential for loss of life is affected by the capacity and number of evacuation routes available to populations living in areas of potential inundation. Those who are located closest to the dam would have the least warning time.

Table 80 shows the number of households and population within potential dam inundation areas in each city in the OA. These values were obtained using Hazus 6.0 dasymetric census blocks that were within a dam inundation boundary.

Table 80: Population in Dam Inundation Area
Jurisdiction Population Households
Campbell 32,482 13,326
Cupertino 840 284
Gilroy 27,185 7,752
Los Altos 3,242 1,097
Los Altos Hills 0 0
Los Gatos 5,721 2,523
Milpitas 14,242 4,315
Morgan Hill 25,469 8,296
Monte Sereno 0 0
Mountain View 17,931 7,215
Palo Alto 8,200 3,318
San Jose 396,703 137,686
Santa Clara 51,519 18,932
Saratoga 350 111
Sunnyvale 30,143 11,832
Unincorporated 8,955 2,629
Total 622,982 219,316
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 249

12.5.2 Property
Vulnerable properties are those closest to the dam inundation area. These properties would experience the largest, most destructive surge of water. Low-lying areas are also vulnerable since they are where the dam waters would collect. Dam inundation areas can be extensive depending on the volume of water contained by the dam. Table 81 shows the value of buildings exposed to potential dam inundation within the OA. This does not take into account any damage functions based on depth of flooding, it is only a summary of building values within the potential inundation zone.

12.5.3 Critical Facilities
Typical vulnerabilities of critical facilities impacted by dam failure include road failure with road segments and bridges washed out creating isolation issues., This includes all roads, railroads, and bridges in the path of the dam inundation. Those that are most vulnerable are those that are already in poor condition and would not be able to withstand a large water surge. Utilities such as overhead power lines, cable and phone lines could also be damaged from the rushing water. Other critical facilities buildings can become flooded and inoperable. Loss of these utilities could create additional isolation issues for the inundation areas. Emergency response could also be delayed. The analysis in Santa Clara County shows the following facilities could be impacted by dam failure:
 Highway bridges: 352
 Rail bridges: 67
 Light rail bridges: 6
 Light rail facilities: 36
 Wastewater treatment facilities: 1
 Schools: 158
 Fire stations: 24
 Hospitals: 7
 Communication Facilities: 6
 Electric Power Facilities: 7

12.5.4 Environment
The environment would be vulnerable to multiple risks in the event of dam failure. The inundation could introduce foreign elements into local waterways, resulting in destruction of downstream habitat and detrimental effects on many species of animals, especially endangered species such as coho salmon. The extent of the vulnerability of the environment is the same as the exposure of the environment.

Reservoirs held behind dams affect many ecological aspects of a river. River topography and dynamics depend on a wide range of flows, but rivers below dams often experience long periods of very stable flow conditions or saw-tooth flow patterns caused by releases followed by no releases. Water releases from dams usually contain very little suspended sediment; this can lead to scouring of riverbeds and banks.

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Table 81: Value of Exposed Structures in the Dam Inundation Area by Jurisdiction Jurisdiction Residential Commercial Industrial Agricultural Religious Government Educational Total Campbell $4,338,205,000 $1,534,627,000 $418,973,000 $13,221,000 $90,790,000 $14,829,000 $216,448,000 $6,627,093,000 Cupertino $160,643,000 $6,496,000 $2,027,000 $0 $675,000 $1,054,000 $5,339,000 $176,234,000 Gilroy $2,768,627,000 $1,566,395,000 $507,771,000 $19,205,000 $24,057,000 $66,266,000 $204,184,000 $5,156,505,000 Los Altos $687,482,000 $6,339,000 $12,817,000 $0 $4,831,000 $0 $19,788,000 $731,257,000 Los Altos Hills $0 $0 $0 $0 $0 $0 $0 $0
Los Gatos $758,943,000 $615,193,000 $67,764,000 $251,000 $32,366,000 $28,170,000 $107,868,000 $1,610,555,000 Milpitas $1,497,684,000 $626,566,000 $811,058,000 $156,000 $23,605,000 $1,175,000 $31,025,000 $2,991,269,000 Monte Sereno $0 $0 $0 $0 $0 $0 $0 $0
Morgan Hill $4,114,421,000 $1,308,828,000 $773,853,000 $17,254,000 $96,415,000 $46,581,000 $161,812,000 $6,519,164,000 Mountain View $2,615,045,000 $1,500,804,000 $562,361,000 $3,282,000 $67,756,000 $19,574,000 $57,915,000 $4,826,737,000 Palo Alto $1,478,921,000 $420,664,000 $27,422,000 $464,000 $5,489,000 $0 $157,677,000 $2,090,637,000 San José $46,073,871,000 $17,490,269,000 $7,035,829,000 $96,030,000 $748,644,000 $925,107,000 $4,665,413,000 $77,035,163,000 Santa Clara
(city) $6,161,892,000 $3,784,586,000 $2,203,267,000 $22,795,000 $175,731,000 $44,789,000 $123,534,000 $12,516,594,000 Saratoga $66,875,000 $202,000 $5,927,000 $0 $0 $0 $0 $73,004,000 Sunnyvale $4,084,357,000 $1,325,027,000 $745,125,000 $303,000 $36,082,000 $15,642,000 $110,192,000 $6,316,728,000 Unincorporated
County $2,183,239,000 $1,458,486,000 $315,766,000 $406,032,000 $40,527,000 $83,070,000 $200,223,000 $4,687,343,000 Total $76,990,205,000 $31,644,482,000 $13,489,960,000 $578,993,000 $1,346,968,000 $1,246,257,000 $6,061,418,000 $131,358,283,000 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 251

12.6 Cascading Hazards
Dam and levee failures can lead to cascading hazards including landslides, bank erosion, and destruction of downstream habitat. It could also impact future drought events by releasing stored water resources.

12.7 Regulatory Oversight for Dams
Responsibility for dam safety in the OA is distributed among federal agencies, state agencies, the SCVWD and private dam owners.

12.7.1 National Dam Safety Act
Potential for catastrophic flooding due to dam failures led to passage of the National Dam Safety Act (Public Law 92-367). The goal of this FEMA-monitored effort is to identify and mitigate the risk of dam failure so as to protect the lives and property of the public. The National Dam Safety Program is a partnership among the states, federal agencies, and other stakeholders that encourages individual and community responsibility for dam safety. Under FEMA’s leadership, state assistance funds have allowed all participating states to improve their programs through increased inspections, emergency action planning, and purchases of needed equipment. FEMA has also expanded existing and initiated new training programs. Grant assistance from FEMA provides support for improvement of dam safety programs that regulate most of the dams in the United States.29F 230

12.7.2 U.S. Army Corps of Engineers Dam Safety Program
The USACE is responsible for safety inspections of some federal and non-federal dams in the United States that meet size and storage limitations specified in the National Dam Safety Act. The USACE has inventoried dams; surveyed each state and federal agency’s capabilities, practices, and regulations regarding design, construction, operation, and maintenance of dams; and developed guidelines for inspection and evaluation of dam safety.230F
231

12.7.3 Federal Energy Regulatory Commission Dam Safety Program The Federal Energy Regulatory Commission (FERC) cooperates with a large number of federal and state agencies to ensure and promote dam safety. More than 3,000 dams are part of regulated hydroelectric projects in the FERC program. Two-thirds of these are more than 50 years old. As dams age, concern about their safety and integrity grows, so oversight and regular inspection are important.

FERC inspects hydroelectric projects on an unscheduled basis to investigate the following:
 Potential dam safety problems
 Complaints about constructing and operating a project  Safety concerns related to natural disasters
 Issues concerning compliance with the terms and conditions of a license 230 Federal Emergency Management Agency. (n.d.). Dam Safety. https://www.fema.gov/emergency-managers/riskmanagement/dam-safety 231 U.S. Army Corps of Engineers. (n.d.). Dam Safety Program. https://www.usace.army.mil/Missions/CivilWorks/Dam-Safety-Program/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 252
Every five years, an independent consulting engineer, approved by the FERC, must inspect and evaluate projects with dams higher than 32.8 feet (10 meters), or with a total storage capacity of more than 2,000 acre-feet.

FERC monitors and evaluates seismic research in geographic areas such as California where there are concerns about possibly seismic activity. This information is applied in investigating and performing structural analyses of hydroelectric projects. FERC also evaluates the effects of potential and actual large floods on the safety of dams. During and following floods, FERC visits dams and licensed projects, determines the extent of damage, if any, and directs any necessary studies or remedial measures the licensee must undertake. The FERC publication Engineering Guidelines for the Evaluation of Hydropower Projects (2021) guides the FERC engineering staff and licensees in evaluating dam safety. The publication is frequently revised to reflect current information and methodologies.

FERC requires dam licensees to prepare EAPs and conducts training sessions on how to develop and test these plans. The EAPs outline an early warning system if there is an actual or potential sudden release of water from a dam due to failure. The plans include operational procedures that may be used, such as reducing reservoir levels and reducing downstream flows, as well as procedures for notifying affected residents and agencies responsible for emergency management. These plans are frequently updated and evaluated to ensure that everyone knows what to do in emergency situations.231F 232

12.7.4 State of California
One of the earliest state regulatory programs was enacted in California in the 1920s. California’s Division of Safety of Dams (DSOD) monitors dam maintenance and safety at the state level. When a new dam is proposed, DSOD engineers and geologists inspect the site and the subsurface. Upon submittal of an application, DSOD reviews the plans and specifications prepared by the owner to ensure that the dam is designed to meet minimum requirements and that the design is appropriate for the known geologic conditions. After approval of the application, DSOD inspects all aspects of the construction to ensure that the work accords with the approved plans and specifications. After construction, DSOD inspects each dam annually to ensure performance as intended and to identify developing problems. DSOD periodically reviews stability of dams and their major appurtenances in light of improved design approaches, requirements, and new findings regarding earthquake hazards and hydrologic estimates in California.23 F 233
Finally, on June 27, 2017, SB 92 required an EAP for all dams that do not have a low downstream hazard potential designation.23F
234
An EAP is a dam owner’s formal plan that identifies potential emergency conditions at a dam and specifies actions to be followed to minimize loss of life and property damage. It includes information that dam owners use to notify local emergency management officials and state and federal dam safety regulators. The EAPs must do all of the following:
 Be based upon an inundation map approved by DWR pursuant to Section 6161 of the state’s Water Code.
 Be developed by the dam’s owner in consultation with any local public safety agency that may be impacted by an incident involving the dam, to the extent a local public safety agency wishes to consult.
232 Federal Energy Regulatory Commission. (2015, July). Chapter VI, Emergency Action Plans. https://cmsstage.ferc.gov/sites/default/files/2020-04/chap6.pdf 233 California Department of Water Resources. (2021, June 1). Dam Safety and the Importance of the Division of Safety of Dams with Andy Mangney. https://water.ca.gov/News/Blog/2020/June/DSOD-Andy-MangneyQA#:~:text=DSOD%20also%20conducts%20independent%20reviews%20of%20applications%20for,in%20light%20of %20improved%20design%20approaches%20and%20requirements. 234 California Legislative Information. (2021). Government Code Title 2, Division 1, Chapter 7. https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?sectionNum=8589.5&lawCode=GOV Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 253
 Adhere to FEMA guidelines, and include, at a minimum, all of the following:
▪ Notification flowcharts and contact information
▪ The response process
▪ The roles and responsibilities of the dam owner and impacted jurisdictions following an incident involving the dam
▪ Preparedness activities and exercise schedules
▪ Inundation maps approved by the Department of Water Resources pursuant to Section 6161 of the Water Code
▪ Any additional information that may impact life or property

12.7.5 Santa Clara Valley Water District
The SCVWD Dam Safety Program includes four main components234F 235:
 Periodic Special Engineering Studies
The SCVWD periodically undertakes special engineering studies to ensure that its dams are compliant with the latest design guidelines and regulations to keep pace with the growing body of knowledge surrounding earthquakes. In addition to seismic studies, the SCVWD periodically conducts other special engineering studies to minimize the risks to its dams. Though not required by the regulatory agencies, the water district has proactively expanded this potential failure mode analysis approach to the remainder of our dams.
 Surveillance and Monitoring
Instrumentation placed in and on the dam furnishes data for water district engineers to determine if the structure is functioning as intended. SCVWD continuously monitors the conditions of its dams and uses automated instrumentation at five dams. The equipment can collect, check, record, and archive the collected data and alert staff when parameters exceed set threshold limits.
 Dam Inspections and Maintenance
SCVWD routinely inspects and monitors the condition of each dam and provides an annual surveillance report to the DSOD and each year they also jointly inspect each of its dams with DSOD.
 Emergency Response and Preparedness
At the core of the Dam Safety Program’s emergency response and preparedness is its postearthquake dam evaluation program team. After significant earthquakes, trained personnel inspect the dams for any signs of damage or potential for failure. SCVWD works with various agencies on emergency action planning and training exercises each year. Under the Dam Safety Program, SCVWD is developing updated maps which estimate what areas could flood in the highly unlikely event of a dam failure.
235 Santa Clara Valley Water District. (n.d.). Dam Safety Program. https://www.valleywater.org/flooding-safety/damsafety-program Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 12: Dam and Levee Failure 254

12.7.6 Regulatory Oversight for Levees
Regulatory oversight depends on whether the levee is accredited or not. The USACE has recently updated its guidance for evaluating, designing, and constructing levees. Engineer Manual (EM) 1110-2- 1913. The document has been available for review and publication was expected at the end of December 2022.

Federal Emergency Management Agency (FEMA)
FEMA does not evaluate the performance of a levee system—this is the responsibility of the levee owner.

FEMA is responsible for establishing levee system evaluation and mapping standards for an accredited levee, determining flood insurance risk zones, and reflecting these determinations on FIRMs.

State of California
The Department of Water Resources (DWR), Division of Flood Management inspects the levees annually and prepares a report which addresses vegetation, animal control, slope stability, erosion, and vehicle traffic.

12.8 Future Trends in Development
Land use in the OA is directed by general plans adopted under state law and local regulations. The safety elements of the general plans establish standards and plans for the protection of the community from hazards. Dam and levee failure are currently not addressed as stand-alone hazards in the safety elements, but flooding is. Municipalities participating in this MJHMP have established comprehensive policies regarding sound land use in identified flood hazard areas. Most of the areas vulnerable to the more severe impacts from dam and levee failure intersect the mapped flood hazard areas. Flood-related policies in the general plans will help to reduce the risk associated with dam and levee failure hazard for all future development in the OA.

12.9 Scenario
An earthquake in the region could lead to liquefaction of soil around a dam. This could occur without warning during any time of the day. A terrorist or other intentional attack also could cause a catastrophic failure of a dam that impacts the OA. While the probability of dam failure is very low, the probability of flooding associated with changes to dam operational parameters in response to climate change is higher.

Dam designs and operations are developed based on hydrographs with historical record. If these hydrographs experience significant changes over time due to the impacts of climate change, the design and operations may no longer be valid for the changed condition. This could have significant impacts on dams that provide flood control. Specified release rates and impound thresholds may have to be changed.

This would result in increased discharges downstream of these facilities, thus increasing the probability and severity of flooding.

12.10 Issues
There is often limited warning time for dam failure. These events are frequently associated with other natural hazard events such as earthquakes, landslides, or inclement weather, which limits their predictability and compounds the hazard. Important issues associated with dam failure hazards include the following:
 Federally regulated dams have an adequate level of oversight and sophistication in the development of an EAP for public notification in the unlikely event of failure. However, the protocol for notification of downstream citizens of imminent failure needs to be tied to local emergency response planning.

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 Mapping for federally regulated dams is required and available; however, mapping for nonfederal-regulated dams that estimates inundation depths is needed to better assess the risk associated with dam failure from these facilities. Moreover, although mapping is required for federally regulated dams, development downstream of dams and upgrades to older dams may have altered inundation areas; however, these inundation maps may not have been updated for significant periods of time. Encouraging property owners of dams to update EAPs and inundation maps will ensure availability of the most accurate data to assist emergency planners and local officials.
 Most dam failure mapping required at federal levels requires determination of the probable maximum flood. While the probable maximum flood represents a worst-case scenario, it is generally the event with the lowest probability of occurrence. For non-federal-regulated dams, mapping of dam failure scenarios that are less extreme than the probable maximum flood but have a higher probability of occurrence can be valuable to emergency managers and community officials downstream of these facilities. This type of mapping can illustrate areas potentially impacted by more frequent events to support emergency response and preparedness.  The concept of residual risk associated with structural flood control projects should be considered in the design of capital projects and the application of land use regulations.  Addressing security concerns and the need to inform the public of the risk associated with dam failure is a challenge for public officials.
 Limited financial resources for dam maintenance during economic downturns result in decreased attention to dam structure operational integrity because available funding is often directed to more urgent needs. This could increase potential for maintenance failures. Dam failure inundation areas are often not considered special flood hazard areas under the NFIP, so flood insurance coverage in these areas is not common.

12.11 Consequence Analysis
When a dam fails, the stored water can be suddenly released and have catastrophic effects on life and property downstream. The amount of warning time depends largely on the nature of the failure. Homes, bridges, and roads may be demolished in minutes. The impact of the event may be felt for an extended period of time. Residents near a significant or high-hazard dam should become familiar with the dam’s emergency action plans if one is available. EAPs written for dams include procedures for notification and coordination with law enforcement and other governmental agencies; information on the potential inundation area; plans for warning and evacuation; and procedures for making emergency repairs.

The information in Table 82 provides the consequence analysis of the potential for detrimental impacts of dam failure done for accreditation with the Emergency Management Accreditation Program (EMAP).

Table 82: EMAP Consequence Analysis: Dam Failure
Subject Ranking Impacts/Dam Failure
Health and Safety of
Public in the Area of
the Incident
Severe The localized impact is expected to be severe for the inundation area and moderate to minimal for other affected areas.

Responders Minimal The impact on responders is expected to be minimal with proper training. The impact could be severe if there is a lack of training.

Continuity of
Operations (including
continued delivery of
services)
Minimal Temporary relocation may be necessary if inundation affects government facilities.

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Subject Ranking Impacts/Dam Failure
Property, Facilities,
and Infrastructure
Minimal to
severe
The localized impact could be severe for facilities and infrastructure in the inundation area of the incident. The farther away from the incident area, the more likely the damage will lessen, from moderate to minimal.

Delivery of Services Minimal to
severe
Delivery of services could be affected if there is any disruption to the roads and/or utilities due to the inundation. Minimal to severe, depending on area size and location affected.

Environment Severe The impact will be severe for the immediate area. The impact will lessen as distance increases from the immediate incident area.

Economic Conditions Minimal to
severe
Impacts on the economy will greatly depend on the scope of the inundation and the amount of time it takes for the water to recede.

Public Confidence in
the Government
Minimal to
severe
The public’s confidence will vary, depending on the perception of whether the failure could have been prevented, the warning time, and the time it takes for response and recovery.

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13 Flood
Definitions
 Flood: The inundation of normally dry land.
 Floodplain: The land area along the sides of a river that becomes inundated with water during a flood.
 1-Percent-Annual-Chance (100-Year) Floodplain: The area flooded by the flood that has a 1- percent chance of being equaled or exceeded in a given year. The 1-percent-annual-chance flood is the standard used by most federal and state agencies.  0.2-Percent-Annual-Chance (500-Year) Floodplain: The area flooded by the flood that has a 0.2- percent chance of being equaled or exceeded in a given year.  Regulatory Floodway: Channel of a river or other water course and adjacent land areas that must be reserved for discharge of the base flood without cumulatively increasing water surface elevation more than a designated height. Communities must regulate development in these floodways to ensure no increases in upstream flood elevations.
 Return Period: The average number of years between occurrences of a hazard (equal to the inverse of the annual likelihood of occurrence).
 Riparian Zone: The area along the banks of a natural watercourse.

13.1 General Background
Flooding is a temporary condition in which normally dry land is partially or completely inundated. There are number of ways in which flooding can happen. The water levels in bodies such as streams, rivers, lakes, and reservoirs can exceed the water body’s banks, causing water to overflow into nearby areas.

Heavy precipitation can overwhelm the ability of soil to absorb water or local storm drains to carry it away, causing water to build up on the surface. Water from oceans and bays can inundate shoreline areas during exceptionally high tides or be pushed ashore by the winds of an intense storm during coastal floods. Flooding may also occur from infrastructure failure, such as a burst water tank or pipe. Dam inundation, a specific type of infrastructure failure flood that occurs when a dam partially or completely fails, is discussed separately under Dam Failure. Flooding is California’s second most frequent disaster after wildfire.

A floodplain is the area adjacent to a river, creek, or lake that becomes inundated during a flood.

Floodplains may be broad, as when a river crosses an extensive flat landscape, or narrow, as when a river is confined in a canyon.

When floodwaters recede after a flood event, they leave behind layers of rock and mud. These gradually build up to create a new floor of the floodplain. Floodplains generally contain unconsolidated sediments (accumulations of sand, gravel, loam, silt, and/or clay), often extending below the bed of the stream.

These sediments provide a natural filtering system, with water percolating back into the ground and replenishing groundwater. These are often important aquifers, the water drawn from them being filtered compared to the water in the stream. Fertile, flat reclaimed floodplain lands are commonly used for agriculture, commerce, and residential development.

Connections between a river and its floodplain are most apparent during and after major flood events.

These areas form a complex physical and biological system that not only supports a variety of natural resources but also provides natural flood and erosion control. When a river is separated from its Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 258
floodplain with levees and other flood control facilities, natural, built-in benefits can be lost, altered, or significantly reduced.

Coastal communities face additional unique flooding hazards. This includes storm surge, waves, and erosion. Coastal flooding can be especially dangerous when high waters combine with the power of waves. Storm surge refers to the abnormal rise in seawater level during a storm. It can cause major coastal and inland flooding. Waves are generated by wind blowing across water. During a storm, wind speeds tend to be higher and last longer, creating larger, more powerful waves. These waves can cause significant damage to anything they impact along the coast. In this case, erosion refers to the wearing away of beaches, dunes, or bluffs by the forces of waves, flowing water, and/or winds. This process can quickly change the appearance of a coastline.

13.1.1 Measuring Floods and Floodplains
Flood frequency and severity are calculated using a number of variables. Flood studies determine the likelihood that a certain river discharge (flow) level will occur in a given year. For example, the 100-year flood has a 1-percent chance of being equaled or exceeded in any given year. For many years, federal agencies referred to the flood frequency statistics in terms of reoccurrence internals (i.e., the “100-year” or “500-year” flood). However, these measurements reflect statistical averages only; it is possible for two or more floods with a 100-year or higher recurrence interval to occur in a short time. The same flood can have different recurrence intervals at different points on a river. In recent years, the terminology has changed to the annual exceedance probability (i.e., 1%, 0.2% chance of occurring) to clear up this confusion.235F
236 The “annual flood” is the greatest flood event expected to occur in a typical year.

The extent of flooding associated with a 1-percent annual probability of occurrence (the base flood or 100-year flood) is the standard regulatory boundary for many organizations. Also referred to as the special flood hazard area (SFHA), this boundary is a convenient tool for assessing vulnerability and risk in flood-prone communities. Many communities have maps that show the extent and likely depth of flooding for the base flood. Corresponding water-surface elevations describe the elevation of water that will result from a given discharge level which is important to understand for floodplain management and community development in order to mitigate risk to new and existing structures.

13.1.2 Floodplain Ecosystems
Floodplains can support ecosystems that are rich in plant and animal species. A floodplain can contain 100 or even 1,000 times as many species as a river. Wetting of the floodplain soil releases an immediate surge of nutrients: those left over from the last flood, and those that result from the rapid decomposition of organic matter that has accumulated since then. Microscopic organisms thrive and larger species enter a rapid breeding cycle. Opportunistic feeders (particularly birds) move in to take advantage. The production of nutrients peaks and falls away quickly, but the surge of new growth endures for some time. This makes floodplains valuable for agriculture. Species growing in floodplains are markedly different from those that grow outside floodplains. For instance, riparian trees (trees that grow in floodplains) tend to be very tolerant of root disturbance and very quick growing compared to non-riparian trees.236F 237
236 U.S. Geological Survey. (2018, June 7). The 100-Year Flood. https://www.usgs.gov/special-topics/water-scienceschool/science/100-yearflood#:~:text=The%20USGS%20and%20other%20agencies%20often%20refer%20to,and%20this%20corresponds% 20to%20a%205-year%20recurrence-interval%20flood.
237 International Union of Forest Research Organizations. (n.d.). Riparian and Coastal Ecosystems. https://www.iufro.org/science/divisions/division-8/80000/80100/80105/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 259

13.1.3 Effects of Human Activities
Because they border water bodies, floodplains have historically been popular sites to establish settlements. Human activities tend to concentrate in floodplains for a number of reasons: water is readily available; land is fertile and suitable for farming; transportation by water is easily accessible; and land is flatter and easier to develop. But human development in floodplains frequently interferes with the natural function of floodplains. It can affect the distribution and timing of drainage, thereby increasing flood problems. Urbanization can create local flooding problems by altering or confining drainage channels.

This increases flood potential in two ways: it reduces the stream’s capacity to contain flows, and it increases flow rates or velocities downstream during all stages of a flood event. River debris, such as the dumping of waste and rubbish, can decrease the conveyance of the river channels. Mining and other industries can change water patterns. Sometimes, humans intentionally make changes, through structural flood control measures such as dams, levees, and embankments.

13.1.4 Federal Flood Programs
FEMA Regulatory Flood Zones
FEMA Flood Zones are geographic areas FEMA has defined according to their levels of flood risk. These areas are determined via statistical analyses of records of river flow, storm tides, and rainfall; information obtained through consultation with the community; floodplain topographic surveys; and hydrologic and hydraulic analysis. These zones are described in terms of high-, moderate-, and low-risk. The “low-risk” area does not mean “no-risk.” Anywhere it rains, it can flood. About 25-percent of NFIP claims come from properties in a low-risk flood zone. Everyone is in a flood zone, but not everyone is in a Special Flood Hazard Area (SFHA). The SFHA is the high-risk area, or the land area covered by floodwaters during the base flood where communities that participate in the NFIP must enforce floodplain management regulations and where mandatory purchase of flood insurance applies for federally backed mortgages. A structure within a 1-percent annual chance floodplain (the SFHA) has a 26-percent chance of undergoing flood damage during the term of a 30-year mortgage.

FEMA Flood Zones are further defined as follows:
 Zones A1-30 and AE: SFHAs that are subject to inundation by the base flood, determined using detailed hydraulic analysis. Base Flood Elevations are shown within these zones.  Zone A (Also known as Unnumbered A-zones): SFHAs where no Base Flood Elevations or depths are shown because detailed hydraulic analyses have not been performed.  Zone AO: SFHAs subject to inundation by types of shallow flooding where average depths are between 1 and 3 feet. These are normally areas prone to shallow sheet flow flooding on sloping terrain.
 Zone VE, V1-30: SFHAs along coasts that are subject to inundation by the base flood with additional hazards due to waves with heights of 3 feet or greater. Base Flood Elevations derived from detailed hydraulic analysis are shown within these zones.  Zone B and X (shaded): Moderates flood hazard areas between the limits of the base flood and the 0.2-percent-annual-chance (or 500-year) flood.
 Zones C and X (unshaded): Areas of minimal flood hazards outside the SFHA with an elevation higher than the 0.2-percent-annual-chance flood.

Modern visualizations can help residents understand their flood risk. DFIRMS identify locations of specific properties in relation to SFHAs; base flood elevations (1-percent annual chance) at specific sites; magnitudes of flood within specific areas; undeveloped coastal barriers where flood insurance is not available; and regulatory floodways and floodplain boundaries (1-percent and 0.2-percent annual chance floodplain boundaries). FEMA’s National Flood Hazard Layer is a compilation of GIS data including a Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 260
nationwide digital Flood Insurance Rate Map and updated data, like a LOMA (Letter of Map Amendment) or LOMR (Letters of Map Revision) which amend the FIRM.

Risk changes over time. These flood maps are not designed to incorporate future conditions including climate change, sea-level rise, and changes in development. Additional studies are necessary when significant changes occur in order to keep up with changing conditions.

Risk Mapping, Assessment, and Planning
FEMA’s Risk Mapping, Assessment and Planning (Risk MAP) program develops non-regulatory guidance documents. Risk MAP supports community resilience by providing data, building partnerships, and supporting long-term hazard mitigation planning.237F
238 Each Risk Map product is tailored to the needs of the individual community and may involve different steps, processes, and end results. A “whole community” approach is used throughout the development of these products and the public is provided multiple opportunities to participate. The resulting products are intended to help property owners, community planners, emergency management officials, and others make risk-informed planning and development decisions. Additionally, at the end these products should help local officials identify mitigation opportunities that will work for their communities.

There are currently no Risk MAP products available for the Operational Area (OA). However, through Risk MAP FEMA is looking to conduct flood hazard studies for all the populated coastlines in order to update their FIRMs and Flood Insurance Studies (FISs) so communities have access to the best available data on their coastal flood risk.238F
239
National Flood Insurance Program
The NFIP makes federally backed flood insurance available to homeowners, renters, and business owners in participating communities. A federal disaster declaration is not necessary for an NFIP payout.

Insurance can also cover significantly more than FEMA’s Individuals and Household Program, which is sometimes available post-disaster. The average NFIP Claims Payment for California between 1996 and 2019 was $18,400.239 F
240 Most homeowner’s insurance does not cover flood insurance. Flood insurance is an important measure of a community’s resiliency to the flood hazard.

For most participating communities, FEMA has prepared a detailed Flood Insurance Study (FIS). The study presents water surface elevations for floods of various magnitudes, including the 1-percent annual chance (100-year) flood and the 0.2-percent annual chance (500-year) flood. Base flood elevations and the boundaries of the 100- and 500-year floodplains are shown on Flood Insurance Rate Maps (FIRMs), which are the principal tools for identifying the extent and location of the flood hazard. FIRMs are the most detailed and consistent data source available, and for many communities they represent the minimum area of oversight under their floodplain management program. Santa Clara County also has DFIRMs. This means the FIRM data is accessible to residents, local governments, and stakeholders online at FEMA’s Map Service Center and National Flood Hazard Layer websites. 238 Federal Emergency Management Association. (2021, November 4). Risk Mapping, Assessment and Planning (Risk MAP). https://www.fema.gov/flood-maps/tools-resources/risk-map 239 Federal Emergency Management Association. (2021, November 4). Risk Mapping, Assessment and Planning (Risk MAP). https://www.fema.gov/flood-maps/tools-resources/risk-map 240 Federal Emergency Management Association. (2022). Historical Flood Risks and Costs. https://www.fema.gov/data-visualization/historical-flood-risk-and-costs Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 261
Participants in the NFIP must, at a minimum, regulate development in the SFHA in accordance with NFIP criteria. The minimum criteria for NFIP participation include, but are not limited to240 F 241:
 Require permits for all proposed construction or other development in the community to determine whether such construction or development will be place in flood-prone areas.  Review proposed development to assure that all necessary permits have been received.  Require the elevation of new and substantially improved residential structures to above the base flood level.
 Require the elevation or dry floodproofing (making watertight) new or substantially improved nonresidential structures in Zone A.  With limited exception, prohibit encroachments, including fill, new construction, substantial improvements, and other development within the adopted regulatory floodway.  Adhere to additional requirements to protect buildings in coastal areas from the impacts of waves, high velocity, and storm surge.

Table 83 lists each participating municipal jurisdiction’s date of entrance into the NFIP and the effective date for its current FIRM.

Table 83: NFIP Status in the Operational Area
Community NFIP Community # NFIP Entry Date Current Effective FIRM
City of Campbell 060338 06/30/1976 02/19/2014
City of Cupertino 060339 05/01/1980 05/18/2009
City of Gilroy 060340 08/01/1980 05/18/2009
City of Los Altos 060341 07/16/1980 05/18/2009
Los Altos Hills 060342 01/02/1980 05/18/2009
Los Gatos 060343 01/17/1979 02/19/2014
City of Milpitas 060344 07/16/1980 02/19/2014
City of Monte Sereno 060345 05/18/2009 02/19/2014
City of Morgan Hill 060346 06/18/1980 05/18/2009
City of Mountain View 060347 08/15/1980 05/18/2009
City of Palo Alto 060348 09/19/1984 10/16/2012
City of San José 060349 08/02/1982 02/19/2014
City of Santa Clara 060350 07/16/1980 02/19/2014
City of Saratoga 060351 01/17/1979 02/19/2014
City of Sunnyvale 060352 05/15/1978 05/18/2009
Unincorporated County 060337 08/02/1982 02/19/2014
241 Federal Register. (2021). Request for Information on the National Flood Insurance Program’s Floodplain Management Standards. https://www.federalregister.gov/documents/2021/10/12/2021-22152/request-for-informationon-the-national-flood-insurance-programs-floodplain-management-standardsfor#:~:text=The%20minimum%20NFIP%20requirements%20for%20participating%20communities%20include%2C,im pacts%20of%20waves%2C%20high%20velocity%2C%20and%20storm%20surge.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 262
Building codes are an important part of developing resilient communities. All community’s that participate in the NFIP must adhere to the NFIP floodplain management criteria, including adopting a flood damage prevention ordinance. The California Department of Water Resources (DWR) has developed a 2020 model ordinance which reflects NFIP requirements and California Building Standards Code (CCR Title 24). Communities that did not use this ordinance may make amendments to their existing regulations.

This ordinance reflects the fact that the flood provisions of CCR Title 24 meet or exceed the minimum requirements for buildings and structures.241F
242
“Substantial improvement” refers to any reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds 50 percent (or less, if defined as so in the jurisdiction’s floodplain management ordinance) of the market value of the structure before the start of construction of the improvement. “Substantial damage” means any damage of any origin sustained by a structure that would cause the cost of restoring the structure to its before damage condition to equal or exceed 50 percent of the market value of the structure before the damage occurred. The repairs to a substantially damaged structure are considered a substantial improvement and that structure would be required to meet current NFIP standards in order to protect it from future flood losses. These kind of post-disaster policies and procedures are further described in Volume 2, as applicable.

All participating planning partners are currently in good standing with the provisions of the NFIP. In California, the DWR is the coordinating agency for floodplain management. The DWR works with FEMA and local governments by providing grants and technical assistance, evaluating community floodplain management programs, reviewing local floodplain ordinances, participating in statewide flood hazard mitigation planning, and facilitating annual statewide workshops. Compliance is monitored by FEMA regional staff and by the DWR. Maintaining compliance under the NFIP is an important component of flood risk reduction. All planning partners that participate in the NFIP have identified actions to maintain compliance and good standing. Details about participation in the NFIP are further described the individual annexes in Volume 2 of this plan.

Risk Rating 2.0
FEMA recently updated the pricing methodology for the NFIP through Risk Rating 2.0. This new methodology builds on years of investment in flood hazard information by leveraging new technology and best practices such as private sector data sets, catastrophe models, and evolving actuarial science to develop rates that are actuarily sound, equitable, easier to understand, and better reflective of risk.24F 243
Previously, rates were based on relatively static measurements, emphasizing a property’s zone on the FIRM. Now, FEMA is able to incorporate additional flood risk variables into their rating calculations. This includes flood frequency, multiple flood types – river overflow, storm surge, coastal erosion, and heavy rainfall – and distance to water source, along with such property characteristics as elevation, numbers of floors, and the cost to rebuild. This reflects a significant change to their rating system. It is intended to make flood insurance more equitable. Before, policyholders were lower-valued homes were paying more than their share of the risk while policy holders with higher-valued homes were paying less than their share. With Risk Rating 2.0, FEMA is able to distribute premiums across all policyholders based on home value and a property’s unique flood risk.243F
244
Risk Rating 2.0 rates went into effect for new policies in October 2021. All remaining policies renewed on or after April 1, 2022, utilize the new rating methodology as well. The FEMA estimated first-year premium changes for existing NFIP policies in Santa Clara County is displayed in Figure 60: Risk Rating 2.0:

Project Premium Changes for Santa Clara County.
242 California Department of Water Resources. (n.d.). National Flood Insurance Program. https://water.ca.gov/nfip/ 243 Federal Emergency Management Association. (2022, April 18). Risk Rating 2.0: Equity in Action. https://www.fema.gov/flood-insurance/risk-rating
244 Federal Emergency Management Association. (2022, April 18). Risk Rating 2.0: Equity in Action. https://www.fema.gov/flood-insurance/risk-rating
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 263
Figure 61: Risk Rating 2.0: Project Premium Changes for Santa Clara County24F 245
The Community Rating System
The community rating system (CRS) is a voluntary program within the NFIP that encourages floodplain management activities that exceed the minimum NFIP requirements. Flood insurance premiums are discounted to reflect the reduced flood risk resulting from community actions meeting the following three goals of the CRS:
 Reduce flood damage to insurable property.
 Strengthen and support the insurance aspects of the NFIP.  Encourage a comprehensive approach to floodplain management.

For participating communities, flood insurance premium rates are discounted in increments of 5 percent.

For example, a Class 1 community would receive a 45 percent premium discount, and a Class 9 community would receive a 5 percent discount. (Class 10 communities are those that do not participate in the CRS; they receive no discount.) Previously, properties outside of the SFHA received smaller discounts: a 10-percent discount if the community is at Class 1 to 6 and a 5-percent discount if the community is at Class 7 to 9. Now, under Risk Rating 2.0, the discount is applied uniformly to all policies throughout the participating community regardless of whether the structure is located in the SFHA.

The CRS classes for local communities are based on 19 creditable activities in the following categories:
 Public information
 Mapping and regulations
245 Association of State Floodplain Managers. (2021, September). Data Visualization Dashboards for FEMA’s Risk Rating 2.0 Projected Premium Change Analysis. https://floodsciencecenter.org/projects/data-visualizationdashboards-for-fema-risk-rating-2-0-projected-premium-change-analysis/ Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 264
 Flood damage reduction
 Warning and response
Figure 61 shows the nationwide number of CRS communities by class as of October 2022, when there were 1,353 communities receiving flood insurance premium discounts under the CRS program.

Figure 62: CRS Communities by Class Nationwide as of October 2022245F 246
CRS activities can help to save lives and reduce property damage. Communities participating in the CRS represent a significant portion of the nation’s flood risk; over 70 percent of the NFIP’s policy base is located in these communities. Communities receiving premium discounts through the CRS range from small to large and represent a broad mixture of flood risks, including both coastal and riverine flood risks.

Table 84: CRS Community Status in the Operational Area246F 247
Community NFIP
Community #
CRS Entry
Date
Current CRS
Classification
% Premium
Discount,
SFHA/non-SFHA
Cupertino 060339 10/01/2005 7 15/5
Gilroy* 060340 05/01/2007 8 10/5
Los Altos 060341 10/01/1991 8 10/5
Milpitas 060344 10/01/1991 7 15/5
Morgan Hill 060346 05/01/2003 7 15/5
246 Federal Emergency Management Association. (2022, October). Community Rating System. https://www.fema.gov/floodplain-management/community-rating-system 247 FEMA. (2023). Community Rating System. https://www.fema.gov/floodplain-management/community-ratingsystem Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 265
Community NFIP
Community #
CRS Entry
Date
Current CRS
Classification
% Premium
Discount,
SFHA/non-SFHA
Mountain View 060347 05/01/2002 8 10/5
Palo Alto 060348 10/01/1991 6 20/10
San José 060349 10/01/1991 7 15/5
Santa Clara (city) 060350 05/01/2002 7 15/5
Sunnyvale 060352 10/01/1998 7 15/5
*Gilroy CRS rating is 8 as of 5/1/2007. Starting 10/1/2023, the rating will be a 7 with a percentage premium discount of 15% of SFHA and 5% for non-SFHA.

Santa Clara Valley Water will lead the development of a separate Floodplain Management Plan specifically dedicated to meeting the CRS planning requirements, allowing planning partners that participate in the CRS program to maintain or enhance their CRS classifications. Relevant information from this Hazard Mitigation Plan will be incorporated into the Floodplain Management Plan.

13.2 Hazard Profile
The following information is extracted from the Santa Clara County Flood Insurance Study247F 248:
 The mountains and foothills in northern Santa Clara County are the sources of the watercourses that flow through the north portion of the OA. Near San José, the major waterways include Los Gatos, Guadalupe, and Alamitos Creeks flowing out of the Santa Cruz Mountains; Coyote Creek and a host of tributaries, including Upper Penitencia and Silver Creeks, flowing out of the Diablo Range; and Fisher Creek with headwaters on the western side of the Coyote Creek Valley. The 75-mile-long Coyote Creek is the primary natural drainage facility for the eastern side of the Santa Clara Valley.
 Permanente and Stevens Creeks, which flow north through the OA near Mountain View, are the primary runoff drainage channels in that area. In addition to providing flood control, these creek beds provide gravel lenses that penetrate the impervious underground clay layers. These lenses allow rain runoff to percolate down to replenish the underground water supply.  The principal watercourses in the south portion of the OA are Llagas, Uvas, and Coyote Creeks.

Edmundson (Little Llagas), Church, Center, Tennant, Maple, and Foothill Creeks also flow through the area. The area is unusual in that creeks originate in both the Diablo Range, to the east, and the Santa Cruz Mountains, to the west. Waters originating in the area are conveyed to Monterey Bay via the Pajaro River.
 Drainage-ways in the OA are a combination of natural channels (creek beds) and channels altered by human activity.
 Drainage patterns in the OA have been altered by urbanization, and the runoff, which has increased, is a greater flood threat than in previous years. The construction of water-conservation flood retention facilities has also altered the drainage pattern.  A variety of conditions cause flooding in the Santa Clara County OA. In smaller drainage basins, flooding is usually the result of intense storms. In larger basins, flooding results from storms of long duration. Shallow overland flooding often occurs due to the small capacity of the creeks. 248 Federal Emergency Management Association. (2014, February 19). Flood Insurance Study Santa Clara County. https://www.milpitas.gov/_pdfs/FISReport.pdf
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 266

13.2.1 Types of Flood-Related Hazards
Flooding in the Santa Clara County OA typically occurs during the rainy winter season. Four types of flooding primarily affect the County: stormwater runoff, riverine, flash floods, and tidal floods.

Stormwater Runoff Floods
Stormwater runoff is generated from rain and snowmelt events that flows over land or impervious surfaces, such as parking lots and roads, without being absorbed.248F 249 Stormwater flooding is a result of
local drainage issues and high groundwater levels. Locally, heavy precipitation, especially during high lunar tide events, may induce flooding within areas other than delineated floodplains or along recognizable channels. If local conditions cannot accommodate intense precipitation through a combination of infiltration and surface runoff, water may accumulate and cause flooding problems.

Flooding issues of this nature generally occur within areas with flat gradients, and generally increase with urbanization, which speeds accumulation of floodwaters because of impervious areas249F 250. Pump stations
may be unable to pump stormwater during a large precipitation event due to insufficient channel capacity or submergence of the pump station, rendering it inoperable. Shallow street flooding can occur unless channels have been improved to account for increased flows. Numerous areas within the County undergo stormwater flooding that contributes to street and structure inundation.

Urban flooding is by increased water runoff due to urban development and drainage systems. Drainage systems are designed to remove surface water from developed areas as quickly as possible to prevent localized flooding on streets and within other urban areas. These systems utilize a closed conveyance system that channels water away from an urban area to surrounding streams, and bypasses natural processes of water filtration through the ground, containment, and evaporation of excess water. Because drainage systems reduce the amount of time surface water takes to reach surrounding streams, flooding in those streams can occur more quickly and reach greater depths than prior to development within that area.250F
251
Riverine Floods
Riverine flooding is overbank flooding of rivers and streams. Natural processes of riverine flooding add sediment and nutrients to fertile floodplain areas. Flooding in large river systems typically results from large-scale weather systems that generate prolonged rainfall over a wide geographic area, causing flooding in hundreds of smaller streams, which then drain into the major rivers. Shallow area flooding is a special type of riverine flooding. FEMA defines shallow flood hazards as areas inundated by the 100-year flood with flood depths of only 1 to 3 feet. These areas are generally flooded by low-velocity sheet flows of water. Two types of flood hazards are generally associated with riverine flooding:
 Inundation: Inundation occurs when floodwater is present, and debris flows through an area not normally covered by water. These events cause minor to severe damage, depending on velocity and depth of flows, duration of the flood event, quantity of logs and other debris carried by the flows, and amount and type of development and personal property along the floodwater’s path.  Channel Migration: Erosion of banks and soils worn away by flowing water, combined with sediment deposition, causes migration or lateral movement of a river channel across a floodplain.

A channel can also abruptly change location (termed “avulsion”); a shift in channel location over a large distance can occur within as short a time as one flood event. 249 Environmental Protection Agency. (2023, February 2). National Pollutant Discharge Elimination System (NPDES) Stormwater Program. https://www.epa.gov/npdes/npdes-stormwater-program 250 FEMA. (1997, January). Multi Hazard Identification and Risk Assessment: The Cornerstone of the National Mitigation Strategy. https://babel.hathitrust.org/cgi/pt?id=pst.000032338492&view=1up&seq=5 251 Environmental Protection Agency. (n.d.). Flow Alteration. https://www.epa.gov/caddis-vol2/flow-alteration Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 267
Natural stream channels in rural parts of the Santa Clara County OA typically can accommodate average rainfall amounts and mild storm systems; however, severe floods occur in years of abnormally high rainfall or unusually severe storms. During those periods of severe floods, high-velocity floodwaters carry debris over long distances, block stream channels, and create severe localized flooding.

Flash Floods
The National Weather Service defines a flash flood as a rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level. Such floods generally begin within 6 hours of the rain event that causes them. Ongoing flooding can intensify to flash flooding in cases where intense rainfall results in a rapid surge of rising flood waters.251F 252
Flash floods can tear out trees, undermine buildings and bridges, and scour new channels. In urban areas, flash flooding is an increasingly serious problem due to removal of vegetation and replacement of ground cover with impermeable surfaces such as roads, driveways, and parking lots. The greatest risk from flash floods is occurrence with little to no warning. Major factors in predicting potential damage are intensity and duration of rainfall, and steepness of watershed and streams.

Coastal Floods
Coastal flooding of normally dry land by the coastline is caused by abnormally high tides, storm surge, and persistent onshore winds and waves. Rising and falling water levels, breaking waves, and shifting sands are common sights along the shore. Typically, they are a normal part of life on the coast, however when they strengthen intensity they can threaten life, property, and livelihoods of coastal populations.

Coastal floods come with a unique range of concerns including storm, waves, and erosion. All of these can contribute to extensive damage to homes, businesses, and infrastructure. The flooding of bay adjacent SFHAs is likely in the Santa Clara County OA, particularly where land is at or slightly above sea level. Areas mapped as Zone V and Zone VE are considered at high-risk from coastal flooding and are subject to stricter building requirements because of the likelihood of damage from strong waves.

High Tide Floods
It no longer takes a strong storm or hurricane to flood coastal areas. Tidal floods are characterized by inundation of normally dry lands by the coast, often caused by extreme high tide events that result in shallow flooding of low-lying coastal areas. Colloquially known as “King Tides,” these tides exceed the highest water level reached at high tide on an average day and normally occur once or twice per year.

King Tide events are the leading cause of flooding by bay waters.

Tidal flooding is becoming increasingly exacerbated by sea level rise as a result of climate change or tectonic activity.25F
253 Average daily water levels are rising along with the oceans. As a result, high tides are reaching higher and extending further inland than in the past. Additional information regarding the impacts and exposure of the OA to sea level rise is presented in Section 11, Climate Change. 252 National Weather Service. (n.d.). Flood Related Hazards. https://www.weather.gov/safety/flood-hazards 253 National Oceanic and Atmospheric Administration. (n.d.). Flooding on a Sunny Day? Here’s How. https://oceantoday.noaa.gov/flooding-sunny-day/
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 268

13.2.2 Principal Flooding Sources
FEMA’s Flood Insurance Study for Santa Clara County assessed over 50 creeks, channels, and water bodies, including the following principal flooding sources253F 254:
 Adobe Creek
 Alamitos Creek
 Alviso Slough
 Arastradero Creek
 Arroyo Calero
 Barron Creek
 Berryessa Creek
 Calabazas Creek
 Canoas Creek
 Concepcion Drain
 Coyote Creek
 Daves Creek
 East Little Llagas Creek
 East Penitencia Creek
 Evergreen Creek
 Fisher Creek
 Fisher Creek Overbank
 Flint Creek
 Fowler Creek
 Guadalupe River
 Guadalupe Slough
 Hale Creek
 Lions Creek
 Llagas Creek
 Llagas Overbank
 Los Gatos Creek
 Lower Penitencia Creek
 Matadero Creek
 Miguelita Creek
 Miller Slough
 North Morey Creek
 Permanente Creek
 Permanente Diversion
 Purissima Creek
 Quimby Creek
 Ronan Channel
 Ross Creek
 Ruby Creek
 San Francisco Bay
 San Francisquito Creek
 San Joaquin River
 Santa Teresa Creek
 San Tomas Aquino Creek
 San Tomas Aquino Creek
Reach 2
 Saratoga Creek
 Silver Creek
 Smith Creek
 South Babb Creek
 South Morey Creek
 Stevens Creek
 Sunnyvale East Channel
 Sunnyvale West Channel
 Thompson Creek
 Upper Penitencia Creek
 Upper Penitencia Creek Reach 2
 Upper Penitencia Creek Reach 2
Overflow
 Uvas Creek
 West Branch Llagas Creek
 West Little Llagas Creek
 Wildcat Creek
Understanding watershed conditions can help clarify the OA’s vulnerability to flooding. A watershed is the area of land that drains to a common waterway. Every watershed has unique qualities that affect its response to rainfall. Stormwater discharge is influenced by the watershed’s soil type, geology, typography, vegetation, shape, and land use.254F
255 The Santa Clara County OA contains five watersheds25F256:
 Coyote Watershed is the OA’s largest watershed, with 322 square miles. It contains Coyote Creek, which is the longest creek in the county.
 Guadalupe Watershed drains the Guadalupe River and its tributaries through downtown San José.
 Lower Peninsula Watershed is a small-creek watershed that feeds tidal wetlands along the San Francisco Bay’s southwest shoreline.
 Uvas-Llagas Watershed is mainly agricultural land and natural areas. This is the only watershed in the county in which waterways flow southward.
254 Federal Emergency Management Association. (2014, February 19). Flood Insurance Study Santa Clara County. https://www.milpitas.gov/_pdfs/FISReport.pdf
255 USGS. (2019, June 8). Surface Runoff and the Water Cycle. https://www.usgs.gov/special-topics/water-scienceschool/science/surface-runoff-and-water-cycle 256 Santa Clara Valley Water District. (n.d.). Watersheds of Santa Clara Valley. https://www.valleywater.org/learningcenter/watersheds-santa-clara-valley Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 269
 West Valley Watershed is the smallest watershed in the county, covering 85 square miles of numerous small creeks.

Figure 63: Watersheds in the Operational Area256F
257

13.2.3 Past Events
Based on NOAA’s National Centers for Environmental Information, 141 flood events in the OA were recorded between 1950 and 2022, as summarized in Table 85: History of Flood Events, . These events include flash floods, lakeshore floods, coastal floods, and flooding from heavy multi-day rain events.

Since 1954, 10 presidential-declared flood events in the OA have caused in excess of $4.468 billion in property damage throughout the region.

According to the USDA’s Risk Management Agency, Santa Clara County received $13,131,222 in payments for insured crop losses on 5,031 affected acres as a result of excessive moisture and flood events between 2003 and 2022. Table 86: Crop Insurance Claims Paid from Excessive Moisture and Flood, 2003-2022 summarizes these payments. The highest damaging year was 2016. Additionally, 39 flood-related federally declared disasters or emergencies have occurred in California since 1953. This equates to a major flood event impacting the state around once every 2 years. 257 Santa Clara Valley Water District. (2023). Watersheds of Santa Clara Valley. https://www.valleywater.org/learningcenter/watersheds-santa-clara-valley Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 270
Table 85: History of Flood Events257 F
258,
258F
259
Date Declaration # Type of Event Estimated Damage
2/5/1954 15 Flood & Erosion Not available
12/23/1955 47 Flood Coyote Creek, Stevens Creek, Matadero Creek, San Francisquito Creek, and
Guadalupe River flooded
4/4/1958 82 Heavy Rainstorms and
Flood
Penitencia Creek, Guadalupe River, San
Tomas Aquinas Creek, Stevens Creek,
Permanente Creek, Matadero Creek, and
San Francisquito Creek flooded. $20 million,
plus $4 million agricultural damage
3/6/1962 122 Floods Not available
10/24/1962 138 Severe Storms and
Flooding
$4 million in regional flooding
2/25/1963 145 Severe Storms, Heavy
Rains and Flooding
Not available
1/16/1973 None Severe Storms and
Flooding
$86,207 in damage
1/7/1982 651 Severe Storms, Flood,
Mudslides and High
Tide
$273 million, 256 homes and 41 businesses
destroyed; 6,259 homes and 1,276
businesses damaged.
2/9/1983 677 Coastal Storms,
Floods, Slides and
Tornadoes
$523 million
2/21/1986 758 Severe Storms and
Flooding
$407 million; 1,382 homes and 185
businesses destroyed; 12,447 homes and
967 businesses damaged.
2/11/1992–
2/14/1992
None Severe Storms and
Flooding
$20,000 in damage
1/13/1993 None Severe Storms and
Flooding
$112,000 in damage
1/10/1995 1044 Severe Winter Storms,
Flooding, Landslides,
Mud Flows
$741 million total; 11 deaths
3/12/1995 1046 Severe Winter Storms,
Flooding Landslides,
Mud Flow
Approx. $1.1 billion total; damage to homes:
major 1,322; minor 2,299; destroyed 267.
12/10/1996 None Flood Not available
1/01/1997 None Flash Floods Not available
258 National Oceanic and Atmospheric Administration. (2017). Storm Events Database. https://www.ncdc.noaa.gov/stormevents/
259 Association of Bay Area Governments. (2010). Data and Research. https://abag.ca.gov/our-work/resilience/dataresearch Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 271
Date Declaration # Type of Event Estimated Damage
1/4/1997 1155 Severe Storms,
Flooding, Mud and
Landslides
$1.8 billion total; 23,000 homes; 2,000
businesses damaged or destroyed.
1/25/1997 None Flash Flood Not available
2/3/1998 None Flash Flood Not available
2/7/1998 None Flash Flood Not available
2/8/1998 None Flash Flood Not available
2/9/1998 1203 Severe Winter Storms
and Flooding
$550 million; 17 deaths
2/13/2000 None Flash Flood Mainly on Coyote Creek
10/13/2009 None Heavy Rain and
Flooding
$400,000
1/18/2010–
1/20/2010
None Heavy Rain and
Flooding
Localized flooding, roads closed, damage
estimate not available.
12/23/2012 None Heavy Rain and
Tornado
Localized flooding, levee overtopped in East
Palo Alto.
2/28/2014 None Heavy Rain and
Flooding
Flooding of urban areas, small streams and
creeks, and a few localized mud and
rockslides.
12/2/2014 None Flood Not available
12/3/2014 None Flood Not available
12/11/2014 None Heavy Rain and
Flooding
Flooding and mudslides
2/06/2015 None Heavy Rain and
Flooding
Multiple off ramps from I-280 flooded.
10/28/2016 None Flood Not available
12/10/2016 None Flood Not available
2/7/2017 None Flash Flood Not available
2/9/2017 None Flood Not available
2/14/2017 4301 Severe Winter Storms,
Flooding, and
Mudslides
34 of 57 CA Counties declared for flooding
events that occurred from January 3 to
January 12, 2017
2/20/2017 None Flood, Flash Flood Not available
2/21/2017 None Flood Not available
1/8/2018 None Flood Not available
1/9/2018 None Flood Not available
1/25/2018 None Flood Not available
3/1/2018 None Flood Not available
4/6/2018 None Flood Not available
11/22/2018 None Flood Not available
11/23/2018 None Flood Not available
11/29/2018 None Flood Not available
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 272
Date Declaration # Type of Event Estimated Damage
12/17/2018 None Flood Not available
1/6/2019 None Flood Not available
1/16/2019 None Flood Not available
1/17/2019 None Flood Not available
2/4/2019 None Flood Not available
2/13/2019 None Flood Not available
2/14/2019 None Flood Not available
2/27/2019 None Flood Not available
5/15/2019 None Flood Not available
11/26/2019 None Flood Not available
12/1/2019 None Flood Not available
12/2/2019 None Flood Not available
1/16/2020 None Flood Not available
1/27/2021 None Flood Not available
3/10/2021 None Flood Not available
12/27/2022–
1/31/2023
4683 Severe Winter Storms,
Flooding, Landslides,
and Mudslides
Damage estimates are ongoing at the time of
this writing. Damage was sufficient for a
Presidential Disaster Declaration.

Note: N/A = Not Applicable.

Table 86: Crop Insurance Claims Paid from Excessive Moisture and Flood, 2003-2022259F 260
Crop Year Commodity Acres
Affected Indemnity Amount
2003 None None None
2004 None None None
2005 All Other Crops 79 $13,144
2006 All Other Crops 83 $6,937
2007 None None None
2008 None None None
2009 None None None
2010 None None None
2011 Walnuts, Cherries, Processing Apricots 910 2,706,413 2012 Cherries 239 $113,052
2013 None None None
2014 Cherries 18 $29,015
260 United States Department of Agriculture. (n.d.). Cause of Loss Historical Data Files. https://www.rma.usda.gov/Information-Tools/Summary-of-Business/Cause-of-Loss Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 273
Crop Year Commodity Acres
Affected Indemnity Amount
2015 Cherries, Processing Apricots, All Other Crops 322 $1,053,095 2016 Cherries, Processing Apricots 1,059 $4,279,020
2017 Cherries, Processing Apricots 119 $69,405
2018 None None None
2019 Cherries, Cultivated Wild Rice, All Other Crops 1,725 $3,975,874 2020 Cherries, Processing Apricots, All Other Crops 245 $337,118 2021 Cherries, Grapes 80 $122,467
2022 Cherries 152 $425,682
Total 5,031 $13,131,222

13.2.4 Location
Flooding that has occurred in portions of the OA has been extensively documented by gage records, high water marks, damage surveys, and personal accounts. This documentation was the basis for the 2014 FIRMs generated by FEMA for the Santa Clara County OA. The 2014 current effective Flood Insurance Study is the sole source of data used in this risk assessment to map the extent and location of the flood hazard, as shown in Figure 63: Mapped Flood Hazard Areas in the Operational Area.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 274
Figure 64: Mapped Flood Hazard Areas in the Operational Area

13.2.5 Frequency
Recurrence intervals and average annual numbers of events in the Santa Clara County OA were calculated based on data from 1996 to 2022 in NOAA’s Storm Events Database. Santa Clara County has experienced one hundred fourteen significant events since 1996 classified as “flood” in the database.

Smaller floods may occur more frequently and be categorized as a different event type, typically “flash flood” or “winter storm.” Based on these data, floods have a 158 percent chance of occurring in any given year, flash floods have a 33 percent chance, and coastal floods have a 4 percent chance. The total estimated percent chance of occurrence for any type of flood in a given year is 100 percent, meaning that flooding will likely continue to be an annual hazard.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 275
The frequency and magnitude of floods will likely be influenced by climate change. Climate change may cause an increase in the number of intense rainfall events, resulting in increased flood risk. Sea level rise, which may exacerbate the risk of flooding in shore areas, is also of concern.

Further information on the impact of climate change on the probability of flooding is included in Section 11.

Probability in OA: Occasional

13.2.6 Severity
The principal factors affecting flood damage are flood depth and velocity. The deeper and faster flood flows become, the more damage they can cause. Shallow flooding with high velocities can cause as much damage as deep flooding with slow velocity. This is especially true when a channel migrates over a broad floodplain, redirecting high velocity flows and transporting debris and sediment. Another element that characterizes the community’s flood threat is length of time floodwaters remain above flood stage.

Although jurisdictions can implement mitigation and take preventative actions to significantly reduce severity and threat of flood events, some type of residual risk will always exist (i.e., risk of a hazard event occurring despite technical and scientific measures applied to reduce/prevent it). Threats associated with residual risk could include failure of a reservoir, a dam breach, or other infrastructure failure, or a severe flood event that exceeds flood design standards or drainage capacity.

Flood severity is often evaluated by examining peak discharges. Table 87 lists peak flows used by FEMA to map the floodplains of the OA as found in the effective Santa Clara County Flood Insurance Study.

Table 87: Summary of Peak Discharges Within the Operational Area260F 261
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
Adobe Creek
 Above Railroad (At El Camino Real) 1,350 2,500 2,700a 2,700a  At East Charleston Road 1,400a 1,400a 1,400a 1,400a
 At East Meadow Drive 1,350 1,350 1,350 1,350
 At Edith Road 1,000 1,830 2,140 2,700
 At El Monte Avenue 690 1,340 1,700 2,370
 At corporate limits 890 1,650 1,920 2,400
 At Foothill Expressway 1,070 2,120 2,320 2,690
 At Middlefield Road 1,020a 1,020a 1,020a 1,020a
 At Moody Road 590 1,150 1,430 1,930
 At Old Altos Road 960 1,760 2,050 2,490
 At Pine Lane 1,110 2,150 2,360 2,730
261 Federal Emergency Management Agency. (2014, February 19). Flood Insurance Study. https://map1.msc.fema.gov/data/06/S/PDF/06085CV002B.pdf?LOC=65c0f78954006b048e415150264ffe4b Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 276
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 At Railroad 1,350 1,450a 1,450a 1,450a
 At U.S. Highway 101 1,660 1,780 1,780 1,780
 At Van Buren Road 1,060 1,890 2,220 2,810
 Below Alma Street 1,450 1,700 1,700 1,750
 Below Purissima Creek 1,040 1,980 2,200 2,510
Alamitos Creek
 Downstream of confluence with
Arroyo Calero
2,150 5,180 6,750 11,000
 Downstream of confluence with Golf
Creek
3,530 7,020 8,680 12,700
 Downstream of confluence with
Greystone Creek
2,940 6,200 7,800 11,800
 Downstream of confluence with
Randol Creek
2,660 5,800 7,380 11,400
 Upstream of confluence with Arroyo
Calero
1,430 3,580 4,750 7,900
 Upstream of confluence with
Guadalupe River
3,630 7,180 8,860 12,900
Alamitos Creek By-Pass Channel b B 3,250 b
Alamitos Creek Overflow Area b B 140 b
Arastradero Creek
At Page Mill Road 140 300 360 460
Arroyo Calero
 Downstream of confluence with Santa
Teresa Creek
1,020 1,820 2,180 3,010
 Upstream of confluence with Alamitos
Creek
1,180 1,980 2,330 3,110
 Upstream of confluence with Santa
Teresa Creek
660 1,120 1,320 1,770
Arroyo De Los Coches
 At confluence with Berryessa Creek b B 1,420 b
Barron Creek
 At El Camino Real 270 270 270 270
 At Foothill Expressway 176 364 453 640
 At Foothill Expressway 320 630 760 1,100
 At Laguna Avenue 180b 180b 180b 180b
 At Lower Fremont Road 96 208 268 390
 At mouth 320 430 430 430
 At Ramona Street 320 430a 430a 430a
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 277
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 At Railroad 320 675 675 675
 At Upper Fremont Road 32 77 98 143
 Downstream of El Camino Real 270 270 270 270
 Upstream of Barron Creek Diversion b B 740 b
 Upstream of Fabian Way b B 250 b
 Upstream of Laguna Avenue b B 1,603 b
 Upstream of Railroad 320 820 920 1,080
Berryessa Creek
 At confluence with Calera Creek b B 3,600a b
 At confluence with Sierra Creek 1,230 2,250 2,580 1,230  At confluence with Tularcitos Creek b B 2,500a b
 At confluence with Wrigley Ditch b B 2,000a b
 At Morrill Avenue 1,230 1,7001 1,750a 1,230
 At Piedmont Road b B 1,600 b
 Downstream of confluence with
Arroyo De Los Coches
b B 2,000a b
 Downstream of Montague
Expressway
800a 800a 800a 800a
Calabazas Creek
 Above Prospect Road b B 1,800 b
 Above Railroad and Prospect Creek b B 1,140 b
 At Coffin Road 3,000 4,100 4,600 5,800
 At El Camino Real 2,090d 2,290d 2,340d 2,360d
 At Grant Road 1,200 1,600 1,800 2,300
 At Interstate Highway 280 1,950 2,490 2,700 3,360
 At Junipero Serra 2,000 2,700 3,100 3,900
 At Kifer Road 2,600 3,600 4,000 5,200
 At Lawrence Expressway 2,100 3,000 3,300 4,200
 At Rainbow Drive Below La Mar
Court
750 1,070 1,310 1,370
 Below Miller Avenue 1,670 2,050 2,210 2,670
 Below Tantau Avenue/Upstream of
Pruneridge Avenue
1,700a 1,900a 1,950a 2,000a
 Downstream of confluence with
Rodeo Creek
1,170 1,700 1,950 2,610
 Downstream of Prospect Road 7501 1,000e 1,180e 1,220e  Downstream of U.S. Highway 101 2,760d 3,200f 4,780f 5,510f  Through box culvert at Miller Avenue 1,400a 1,550a 1,600a 1,600a Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 278
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Upstream of Benton Street 2,100d 2,170a 2,170a 2,200a  Upstream of Kifer Road 2,550d 2,820d 3,000d 3,340d
 Upstream of Lawrence Expressway 2,050d 2,310d 2,370d 2,540d  Upstream of Pomeroy Avenue 2,190d 2,200d 2,200d 2,200d  Upstream of U.S. Highway 101 2,760d 3,020d 3,200d 3,550d  Upstream of State Highway 237 3,010d 3,420d 5,000d 5,100d Calera Creek
 At confluence with Berryessa Creek b B 920 b
 Upstream of Interstate Highway 680 b B 850 b
Canoas Creek
 At Blossom Hill Road 1,320 1,390 1,400 1,420
 At Capitol Expressway 1,850 1,910 1,960 2,000
 At confluence with Guadalupe River 1,900a 1,950a 1,970a 2,000a  At Cottle Road 480 500 510 530
 At Santa Teresa Boulevard 780 810 830 850
 Upstream of Nightingale Drive 1,990 2,250 2,350 2,500 Concepcion Drainage
 At Alto Verde Lane 22 51 68 102
Coyote Creek
 At Interstate Highway 280 3,880 10,180 12,630 14,700
 At U.S. Geological Survey gage near
Edenvale
4,050 10,940 13,670 14,700a
 At U.S. geological Survey gage near
Madrone
4,500 12,000 15,000 24,000
 Downstream of Anderson Reservoir 4,500 11,000 15,000 23,500  Downstream of confluence with
Berryessa Creek
7,300 10,500 12,800 15,000
 Downstream of confluence with Silver
Creek
6,200 10,300 12,500 15,000
 Downstream of Silver Creek
Diversion
4,000 10,680 13,330 14,700
 Upstream of confluence with Fisher
Creek
4,410 12,010 14,830 16,400a
 Upstream of confluence with Silver
Creek
3,790 9,920 11,400a 11,400a
 Upstream of Silver Creek Diversion 4,000 10,680 13,330 14,700 Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 279
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
Daves Creek
 At Los Gatos Creek 130 230 270 370
East Little Llagas Creek
 Approx. 1,500 ft. upstream of
Sycamore Avenue
b B 2,211 b
 At confluence of Church Creek b B 5,355 b
 At confluence of San Martin Creek b B 3,712 b
 At U.S. Highway 101 700 1,200 1,300 1,700
 At Tenant Creek confluence b B 2,881 b
 Upstream of Seymour Avenue 330 430 460 490
East Penitencia Creek
 Downtown of Trimble Road 280 340a 340a 340a
 Upstream of confluence with Lower
Penitencia Creek
480 970h 1,080h 1,280h
 Upstream of Trimble Road 280 400 450 540
Fisher Creek
 At confluence with Coyote Creek 700a 700a 700a 700a
 At Kalana Avenue 470 960 1,130 1,500
 At Miramonte Avenue 300 600 710 930
 At Richmond Avenue 450 700 700 700
 At Willow Springs Road 270 460 560 810
 Downstream of Bailey Avenue 1,000 1,810 2,160 2,950
 Upstream of Bailey Avenue 620 900 900 900
 Upstream of Railroad 1,260 2,310 2,560 3,530
Fisher Creek Overbank
 500 feet downstream of Richmond
Avenue
250 630 900 1,540
 At Bailey Avenue 220b 680 970 1,670
Guadalupe River
 At Blossom Hill Road 3,500 8,500 11,500 19,000
 At Coleman Avenue 7,000 13,500a 15,500a 15,500a
 At Hedding Street 7,500 9,800a 9,800a 9,800a
 At Hobson Avenue 7,000 11,400a 11,400a 11,400a
 At Interstate Highway 280 6,000 7,000a 7,000a 7,000a
 At Malone Road 5,600 11,500 11,900a 11,900a
 At Railroad 5,800 10,900a 10,900a 10,900a
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 280
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Downstream of confluence with
Canoas Creek
5,500 11,000 12,800 12,800
 Downstream of confluence with Los
Gatos Creek
7,000a 10,000a 10,000a 10,000a
 Downstream of confluence with Ross
Creek
4,500 9,000 12,500 20,000
 Downstream of State Highway 17 7,500 12,000a 13,000a 17,000a  Upstream of confluence with Canoas
Creek
4,500 9,500 12,000a 12,000a
Hale Creek
 At Berry Avenue 510 1,020 1,120 1,580
 At confluence with Permanente Creek 710 880 900 960
 At Cuesta Drive/North Springer Road 595 750 760 810
 At Foothill Expressway 460 970 1,060 1,490
 At Interstate Highway 280 101 218 284 440
 At Rosita Avenue 595 700a 700a 700a
 At Summer Hill Avenue 177 370 472 735
Lions Creek
 Upstream of West Branch Llagas
Creek
b b 1,840 b
Llagas Creek
 At Rucker Avenue 4,900i 9,700i 10,200i 12,700i
 At Railroad 2,200 3,900 5,300 8,500
 Downstream of Buena Vista Creek 5,200 10,400 11,000 11,500a  Downstream of Chesbro Reservoir 900 3,100 3,900 6,000  Downstream of East Little Llagas
Creek
5,000 9,800 10,400 12,900
 Downstream of Hayes Creek 1,800 3,800 4,800 7,500
 Downstream of Leavesley Road 5,200d 5,200d 5,200d 5,200d  Downstream of Live Oak Creek 5,500 9,700 9,800 10,300  Downstream of Machado Creek 1,400 3,600 4,500 7,000
 Downstream of Panther Creek 5,300 9,700a 9,800a 10,100a  Downstream of Princevalle Drain b b 18,800 b
 Downstream of West Branch Llagas
Creek
b b 17,800 b
 Upstream of East Little Llagas Creek 2,500 4,300 5,400 8,600  Upstream of Jones Creek b b 18,800 b
 Upstream of Panther Creek 5,200 9,400a 9,400a 9,400a
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 281
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
Los Gatos Creek
 At Leigh Avenue 1,680 6,510 7,440 11,340
 At Meridian Avenue 1,770 6,620 7,570 11,500
 At Park Road 1,580 6,140 6,990 10,630
 At State Highway 17 1,540k 6,370 7,300 11,200
 Below Lexington Dam 1,610 5,850 6,650 9,630
 Below Vasona Dam 1,550 6,100 6,950 10,600
 Upstream of confluence with
Guadalupe River
2,130 7,000 7,980 11,900
Lower Penitencia Creek
 At Capitol Avenue 740 1,200 1,210 1,220
 At confluence with Berryessa Creek 2,550 3,700 3,700 3,700  At Nimitz Freeway 1,750a 3,500a 3,500a 3,500a
 At Redwood Avenue 850 1,150j 1,150j 1,150j
 At South Main Street 7003 1,120j 1,120j 1,120j
 Downstream of confluence with
Berryessa Creek
2,550 2,600a 2,600a 2,600a
 Downstream of confluence with East
Penitencia Creek
800 1,670 2,150 2,840
 Downstream of Trimble Road 320 1,060h 1,510h 1,620h
Madrone Channel
 At East Dunne Avenue b b 600 b
 Upstream of East Little Llagas Creek b b 1,200 b
Matadero Creek
 Above confluence with Arastradero
Creek
194 392 506 690
 Approximately 270 feet upstream of
U.S. Highway 101
b b 2,800 b
 At Alma Street 1,380 2,000a 2,000a 2,000a
 At corporate limits 402 795 970 1,300
 At El Camino Real 1,100 2,100 2,280 2,690
 At Louis Road 1,380 1,500b 1,500b 1,500b
 At Middlefield Road 1,380 1,900b 1,500b 1,900b
 At Railroad b b 2,435 b
 At U.S. Highway 101 1,660 1,775 1,775 1,775
 Below confluence with Arastradero
Creek
325 660 790 1,030
 Downstream of Foothill Expressway b b 1,900 b
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 282
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Downstream of Park Boulevard b b 2,700 b
 Downstream of U.S. Highway 101 b b 3,100 b
 Upstream of Railroad 1,220 2,170 2,520 2,810
Mayfield Slough
At Embarcadero Road 10.00 b 10.5 10.8
Miller Slough
 At U.S. Highway 101 b b 760 b
Middle Road Overflow Area
 At convergence with Llagas Creek b b 39 b
 At divergence from West Little Llagas
Creek
b b 658 b
North Morey Creek
 Upstream of Lions Creek b b 485 b
Pajaro River
 At U.S. Highway 101 b b 30,500 b
Permanente Creek
 At confluence with Hale Creek 780l 1,650l 1,780l 1,980l  At El Camino Real 1,150 1,310 1,310 1,310
 At Railroad 1,270 1,470 1,600 1,600
 Downstream of confluence with Hale
Creek
1,000a 1,000a 1,000a 1,000a
 Downstream of East Charleston Road 1,390n 1,400a 1,400a 1,400a  Downstream of Miramonte Avenue 370 760 890 1,030
 Downstream of Permanente Road 760 1,260 1,480 1,960
 Downstream of Portland Avenue 1,340 2,050 2,050 2,050  Downstream of U.S. Highway 101 1,350 1,400a 1,400a 1,400a  Upstream of confluence with Hale
Creek
440l 840l 980l 1,110l
 Upstream of Interstate Highway 280 1,250 2,160 2,570 3,480  Upstream of Portland Avenue 1,340 2,220 2,700 3,440
 Upstream of Tributary, 700 feet
upstream of Highway 280
860 1,460 1,720 2,310
 Upstream of U.S. Highway 101 1,350 2,250f 4,000f 7,100f Permanente Diversion
 At confluence with Stevens Creek 1,230 1,280 1,390 1,550  At Grant Road 1,200 1,240a 1,340a 1,490a
 Downstream of Carmel Terrace 1,075a 1,075a 1,075a 1,075a Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 283
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Downstream of Diversion Structure 1,190 1,610 1,610 1,610 Prospect Creek
 Upstream of confluence with
Calabazas Creek
b b 635 b
Purissima Creek
 At corporate limits 147 320 402 588
 At Interstate Highway 280 37 82 104 153
 At Viscaino Road 88 182 227 320
San Francisco Bay
At confluence of Guadalupe Slough
and Coyote Creek
b b 10.8 b
At crossing of Railroad and Alviso
Slough
b b 11.3 B
At Milpitas b b 11.4 B
At Mountain View 10.2 b 10.7 11.0
At Palo Alto 9.9 b 10.5 10.8
At Sunnyvale 3.7 b 10.7 B
San Francisquito Creek
 At Alma Street 4,350 7,050 8,280 9,850a
 At U.S. Geological Survey gage 4,050 6,700 7,860 10,500  Downstream of Chaucer Road 4,350 6,000a 6,000a 6,200a  Downstream of Middlefield Road 4,350 6,350a 6,690a 7,410a  Near Pasteur Drive 4,200 6,850 8,070 10,400
 Upstream of Middlefield Road 4,350 7,100 8,330 9,850a San Francisquito Creek – Overflow
 At Chaucer Street b b 563 B
 At Middlefield Road b b 752 B
 Combined Middlefield/Chaucer
Overflows
b b 1,080 B
San Thomas Aquino Creek
 At Cabrillo Avenue 2,560f 2,920f 2,920f 2,920f
 At confluence with Saratoga Creek 5,900 8,300 9,100 11,000  At El Camino Real 3,570 3,610 3,610 3,610
 At Homestead Road 3,450f 3,450f 3,450f 3,450f
 At Pruneridge Avenue 3,460 3,820f 3,820f 3,820f
 At Saratoga and Los Gatos Roads 620 990 1,140 1,480
 At Stevens Creek Boulevard 3,300 3,820f 3,820f 3,820f Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 284
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 At U.S. Highway 101 5,900 8,300 9,100 11,000
 At U.S. Highway 237 5,900 8,300 9,100 11,000
 Downstream of Railroad 5,900 8,300 9,100 11,000
 Upstream of Westmont Avenue 2,000 2,900 3,200 4,077o
 Near Bicknell and Quito Roads 670 1,050 1,230 1,580
 Near Old Adobe and Quito Roads 730 1,150 1,350 1,720
Saratoga Creek
 At confluence with San Tomas
Aquino Creek
2,700 3,750 4,100 4,800
 At El Camino Road 2,700 3,750 4,100 4,800
 At Herriman Avenue 1,550 3,020 3,750 4,630
 At Homestead Road 2,700 3,750 4,100 4,800
 At Kiely Boulevard 2,700 3,750 4,100 4,800
 At Stevens Creek Boulevard 2,500 3,500 3,900 4,600
 At U.S. Geological Survey gage at
Springer
1,350 2,750 3,490 4,450
 At Railroad 1,760 3,230 3,950 4,800
 Downstream of Benton Street 2,700 3,750 4,100 4,800
 Downstream of Kiely Boulevard 2,700 3,750 4,100 4,800  Downstream of Warburton Avenue 2,700 3,750 4,100 4,800 Silver Creek
 At confluence with Coyote Creek 2,550 2,650 2,670 2,750  At intersection of King and McKee
Roads
2,000a 2,000a 2,000a 2,000a
 At Interstate Highway 680 2,210 2,400 2,400 2,400
 At Ocala Avenue 1,530 2,000p 2,000p 2,000p
 Downstream of confluence with
Thompson Creek
2,080 3,200 3,600 4,300
 Downstream of Cunningham Avenue 1,420p 2,150p 2,580p 2,600p  Downstream of confluence with
Miguelita Creek
2,300 2,300 2,300 2,300
 Downstream of confluence with North
Babb Creek
1,500a 1,500a 1,500a 1,500a
 Downstream of confluence with South
Babb Creek
1,940 2,600 2,700 2,700
Smith Creek
 At Railroad 200 370 440 610
 At Wedgewood Avenue 160 300 350 480
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 285
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 Below Smith Creek Drive 125 230 280 390
South Babb Creek
 At Clayton Road 390 760 890 1,150
 At confluence with Silver Creek 200a 200a 200a 200a
 Downstream of White Road 390a 390a 390a 390a
 Upstream of Clayton Road B b 890 B
 Upstream of Lochner Drive 400 550a 550a 550a
 Upstream of White Road 400 570a 570a 570a
South Morey Creek
 Upstream of Lions Creek B b 420 B
Stevens Creek
 At Crittenden Lane 2,350g 2,350g 2,350g 2,350g
 At Homestead Road 1,110m 4,530 5,570 7,470
 At Interstate Highway 280 1,110m 4,460 5,460 7,310
 At Stevens Creek Boulevard 1,110m 4,430m 5,430 7,240
 At U.S. Geological Survey gaging
station No. 262
1,200 2,800 5,400 7,000
 At U.S. Highway 101 3,030 5,550 5,750 5,950
 Downstream of Interstate Highway
280
1,110 4,460 5,460 7,310
 Downstream of Junipero Serra 1,550 3,200 5,580 7,650
 Downstream of Stevens Creek Dam 1,140 4,440 5,280 6,940  Downstream of Railroad 2,750 5,350g 5,350g 5,350g
 Upstream of Junipero Serra 1,500 3,150 5,500 7,500
 Upstream of Permanente Diversion 1,750 3,600 6,000 8,200  Upstream of Railroad 2,750 6,110 7,360 9,610
Sunnyvale East Channel
 Downstream of Caribbean Drive B b 1,100 B
Sunnyvale West Channel
 Downstream of Highway 237 B b 360 B
Tennant Creek
 Approximately 1,250 feet upstream of
Hill Avenue
B b 420 B
 Downstream of Maple Avenue B b 650 B
 Upstream of confluence with East
Little Llagas Creek
B b 2,015 B
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 286
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
Thompson Creek
 2,000 feet downstream of Aborn
Road
1,440 2,550 3,000 3,700
 At Aborn Road 1,440 2,350 2,700 3,250
 At Quimby Road 1,480 1,900a 1,900a 1,900a
 Downstream of Yerba Buena Creek 1,060 1,750 1,950 2,400 Upper Penitencia Creek
 At Capitol Avenue 1,350a 1,350a 1,350a 1,350a
 At confluence with Coyote Creek 1,110 1,110 1,110 1,110  At Gridley Street 1,460 3,050 3,600 4,950
 Upstream of North Jackson Avenue 1,350a 1,350a 1,350a 1,350a  At King Road 960a 960a 960a 960b
 At Mabury Avenue 1,050a 1,050a 1,050a 1,050a
 At Upper Penitencia Road 1,460 2,810a 2,950a 2,950a
 At U.S. Geological survey gage at
Dorel Road
1,400 2,940 3,600 5,170
Uvas Creek
 At confluence with Bodfish Creek B b 10,910 B
 At confluence with Little Arthur Creek B b 8,500 B
 At downstream face of Watsonville
Road Bridge
B b 10,360 B
 At Thomas Road B b 14,000 B
 At Railroad B b 5,2003 B
 At U.S. Highway 101 B b 8,0003 B
 At Uvas Road B b 7,800 B
 Downstream of Hecker Pass Road B b 13,550 B
 Downstream of Santa Teresa
Boulevard
B b 14,000 B
Uvas Creek – East Overbank Above Highway 101
 Approximately 1,200 feet above U.S.

Highway 101
Q b 2,200 B
 At U.S. Highway 101 Q b 1,100 B
Uvas Creek – East Overbank Above Railroad
 At downstream limit of flooding Q b 3,200 B
 At upstream limit of flooding Q b 2,100 B
Watson Road Overflow Area
 At convergence with Llagas Creek B b 447 B
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 287
Flooding Source and Location
Discharge (Cubic Feet/Second)
10-
Year
50-
Year
100-
Year
500-
Year
 At divergence from West Little Llagas
Creek
B b 97 B
West Branch Llagas Creek
 Downstream of divergence from West
Branch Llagas Creek – East Split
B b 160 B
 Upstream of divergence from West
Branch Llagas Creek – East Split
B b 1,400 B
West Branch Llagas Creek – Lower Split
 At Day Road Interceptor (NRCS
PL566)
Q b 1,200 B
West Branch Llagas Creek – Middle Split
 Downstream of Highland Avenue Q q 80 Q
West Branch Llagas Creek – Upper Split
 Upstream of Highland Avenue Q q 200 Q
West Little Llagas Creek
 1,000 feet upstream of Wright
Avenue
A a 1882 A
 At Fourth Street A a 9002 A
 At U.S. Highway 101 A a 1,080b A
 Downstream of Edmundson Avenue A a 1,269 A
 Downstream of Monterey Highway A a 8132 A
 Downstream of Railroad A a 4602 A
 Upstream of Llagas Avenue A a 1,702b A
 Upstream of Monterey Highway A a 1,936 A
 Upstream of Seymour Avenue A a 1,770b A
Wildcat Creek
 Above Portos Drive 480 810 960 1,230
 At Saratoga and Los Gatos Roads 310 500 570 740
 Below Douglas Lane 430 710 840 1,070
a Decrease in flow rate based on capacity restrictions. b Data not available/computed.
c Discharge decrease due to Barron Creek Diversion.
d Flow rate accounts for upstream channel spills.
e Slow rate reflects upstream capacity restriction.
f Flow influenced by spill from adjoining watercourse.
g Flow reduction due to bridge or channel capacity restriction. h Increase in flow rate due to spills from neighboring subbasins. i Flow rate reduction due to attenuation in the floodplain. j Reduction in flood rate due to storage behind railroad. k Flow rate reduction due to attenuation in
reservoirs.
l High flows affected by Permanente Diversion.
m Decrease in flow rate due to storage along
channel.
n High flows diverted to Stevens Creek.
o Logarithm extrapolation.
p Flow rate reduction due to storage in Lake
Cunningham.
q Flooding due to spill—drainage area not
applicable.

Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 288

13.2.7 Warning Time
Advanced warning is essential for quick and effective response to a flood threat. Because of the sequential pattern of weather conditions needed to cause serious flooding, occurrence of a flood without warning is unusual. Warning times for floods can be between 24 and 48 hours. Flash flooding can be less predictable, but populations in potential hazard areas can be warned in advance of flash flooding danger.

NWS issues watches and warnings when forecasts indicate rivers may approach bank-full levels. Flood extent or severity categories used by NWS include minor flooding, moderate flooding, and major flooding, based on property damage and public threat261F
262:
 Minor Flooding: Minimal or no property damage, but possibly some public threat or inconvenience.
 Moderate Flooding: Some inundation of structures and roads near streams. Some necessary evacuations of people and/or transfer of property to higher elevations.  Major Flooding: Extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.

When a watch is issued, the public should prepare for the possibility of a flood. When a warning is issued, the public is advised to stay tuned to a local radio station for further information and be prepared to take quick action if needed. A warning means a flood is imminent, generally within 12 hours, or is occurring.

Local media broadcast NWS warnings. Thresholds for flood warnings have been established on some of the major rivers in Santa Clara County, based on available stream gage information. Current stream flows are gathered from the following USGS stream gauges in the county26F 263:
 USGS 11153000 Pacheco Creek, Dunneville, CA
 USGS 11153650 Llagas Creek, Gilroy, CA
 USGS 11164500 San Francisquito Creek, Stanford University  USGS 11169025 Guadalupe River along Highway 101, San José, CA  USGS 11169500 Saratoga Creek, Saratoga, CA
 USGS 11169800 Coyote Creek, Gilroy, CA
 USGS 11173200 Arroyo Hondo, San José CA

13.3 Cascading Impacts
One of the most problematic cascading impacts of flooding is bank or coastal erosion, which in some cases can be more harmful than the actual flood. This is especially true in the upper courses of rivers with steep gradients, where floodwaters may pass quickly and without much damage, but scour the banks, edging properties closer to the floodplain or causing them to fall in.

Flooding is also responsible for hazards such as landslides or mud flows when high flows over-saturate soils on steep slopes, causing them to fail. In California, there are significant ties between wildfire, floods, and subsequently landslides as one hazard cascades into the next. 262 National Weather Service. (n.d.). Severe Weather 101 – Floods. https://www.nssl.noaa.gov/education/svrwx101/floods/faq/ 263 U.S. Geological Survey. (2023). Current Conditions for California: Streamflow. https://waterdata.usgs.gov/ca/nwis/current/?type=flow
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 289
Hazardous materials spills are also a secondary hazard of flooding if storage tanks rupture and spill into streams, rivers, or storm sewers. Debris of any kind could impact water quality and change the natural flow of water. This could potentially increase the risk next time there is a storm event.

Floods could also cause dam failure, or overtopping. The risk of dam failure is described more in Section 12. This risk is of particular concern because it may create a flood substantially larger than the original flood. Depending on the topography of the area downstream of a dam failure event, the floodwaters could remain constrained in a narrow canyon area, preventing them from slowing down before the reach urbanized flatter terrain.263F
264 Furthermore, while floodwaters will travel down and absorb into the ground in flat areas, the water will also pick up sediment and debris as it travels. The sediment and debris in the water may pose additional risks.

13.4 Exposure
The Level 2 Hazus protocol was used to assess flood risk in the OA. The model used census data at the block level and FEMA floodplain data, which has a level of accuracy acceptable for planning purposes.

Where possible, the Hazus default data was enhanced using local GIS data from local, state, and federal sources.

13.4.1 Population
Population counts of those living in the floodplain within the OA were generated by estimating percent of residential buildings in each jurisdiction within the 1-percent-annual-chance flood hazard areas and multiplying this by total population within the OA. This approach yielded an estimated population in the OA of 176,882 living within the 100-year floodplain (9.14% percent of the total OA population).Table 88 lists population estimates by jurisdiction living in the 10-percent, 1-percent and 0.2-percent annual chance flood hazard areas. The City of Gilroy, City of Santa Clara, Sunnyvale, San José, Campbell, Milpitas, and Morgan hill have the highest percentage of population exposed to 1% annual flood hazard, Table 88: Population Within the 10-Percent, 1-Percent, and 0.2-Percent Annual Chance Flood Hazard Areas
Jurisdiction
10-Percent Annual
Chance Flood Hazard
Area
1-Percent Annual
Chance Flood Hazard
Area

0.2-Percent Annual
Chance Flood Hazard
Area
Population
Exposeda
% Total of
Population
Population
Exposeda
% of Total
Population
Population
Exposeda
% of Total
Population
Campbell 2446 5.63 3685 8.48 4608 10.61
Cupertino 0 0.00 1311 2.16 1740 2.87
Gilroy 5,742 9.65 10,361 17.42 13,398 22.53
Los Altos 0 0.00 0 0.00 11 0.03
Los Altos Hills 0 0.00 0 0.00 0 0.00
Los Gatos 273 0.81 1,216 3.63 1,485 4.43
264 Santa Clara Valley Water District. (2017, October). Local Hazard Mitigation Plan. https://s3.us-west1.amazonaws.com/valleywater.org.us-west-1/s3fs-public/2021- 05/R14163%20%202017%20FINAL%20LOCAL%20HAZARD%20MITIGATION%20PLAN%20v.%2004-09- 21%20(04-12-21).pdf
Santa Clara County Multijurisdictional Hazard Mitigation Plan—DRAFT Section 13: Flood 290
Jurisdiction
10-Percent Annual
Chance Flood Hazard
Area
1-Percent Annual
Chance Flood Hazard
Area

0.2-Percent Annual
Chance Flood Hazard
Area
Population
Exposeda
% Total of
Population
Population
Exposeda
% of Total
Population
Population
Exposeda
% of Total
Population
Milpitas 2,691 3.35 5,335 6.65 9,457 11.78
Monte Sereno 0 0.00 0 0.00 0 0.00
Morgan Hill 1,758 3.90 2,979 6.61 3,412 7.58
Mountain View 1,687 2.05 4,063 4.95 6,525 7.95
Palo Alto 617 0.90 629 0.92 4,534 6.62
San José 52,257 5.15 111,750 11.02 190,009 18.74
Santa Clara (city) 10,239 8.02 16,644 13.04 35,182 27.57 Saratoga 587 1.89 1,487 4.79 1,790 5.77
Sunnyvale 2,786 1.80 13,969 9.02 21,284 13.75
Unincorporated
County 2,241 2.48 3,453 3.83 4,579 5.07
Total 83,324 4.31 176,882 9.14 298,014 15.40

13.4.2 Property
Exposed Value
Table 89, Table 90, and Table 91 summarize the estimated value of exposed buildings in the OA. This methodology estimated $8.7 billion worth of exposure to the 10-percent-annual-chance flood, representing 2.3 percent of the total replacement value of the OA, $22.4 billion worth of building-andcontents exposure to the 1-percent-annual-chance flood, representing 9.1 percent of the total replacement value of the OA, and $40 billion worth of building-and-contents exposure to the 0.2-percentannual-chance flood, representing 10.56 percent of the total.