Los Altos Hills City Council
September 19, 2024

Santa Clara County Multijurisdictional Hazard Mitigation Plan 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 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..

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 7: Earthquakes 104

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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 8: Wildfire 134
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 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 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

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 8: Wildfire 137
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)

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 8: Wildfire 138
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 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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 8: Wildfire 141
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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 8: Wildfire 143

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 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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 8: Wildfire 146

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 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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 8: Wildfire 149
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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 150
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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 151
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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 152
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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 153
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 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.”

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 155
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

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 156
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

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 157
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 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

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 159

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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 161
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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 162
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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 163

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 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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 166
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 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 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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 9: Inclement Weather 170

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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 10: Drought 192
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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 10: Drought 194
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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 10: Drought 196
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 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 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 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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 11: Climate Change 201
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 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/.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 11: Climate Change 203
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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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.

Santa Clara County Multijurisdictional Hazard Mitigation Plan Section 11: Climate Change 219
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.