Agenda packet — Concord City Council, March 10, 2026 (part 3 of 5)

City of Concord Hazard Mitigation Plan Dam and Levee Failure 8-10
• Federally regulated dams have an adequate level of oversight and sophistication in the development of emergency action plans for public notification in the unlikely event of failure. However, the protocol for notification of downstream residents of imminent failure needs to be tied to local emergency response planning.
• Most dam failure mapping required at federal levels requires determination of the probable maximum flood.

While the probable maximum flood represents a worst-case scenario, it is generally the event with the lowest probability of occurrence.
• The concept of residual risk associated with structural flood control projects should be considered in the design of capital projects and the application of land use regulations. • Addressing security concerns and the need to inform the public of the risk associated with dam failure is a challenge for public officials.

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9. DROUGHT

9.1 GENERAL BACKGROUND
Drought is a significant decrease in water supply relative to what is typical in a given location. It is a normal phase in the climate cycle of most regions, originating from a deficiency of precipitation over an extended period of time, usually a season or more. This leads to a water shortage for some activity, group or environmental sector. Drought can be characterized based on the following:
• Meteorological measurements such as rainfall deficit compared to normal or expected rainfall • Agricultural impacts due to reduced rainfall and water supply (e.g., crop loss, herd culling, etc.) • Hydrological measurements of stream flows, groundwater, and reservoir levels relative to normal conditions • Direct and indirect socio-economic impacts on society and the economy (e.g., increased unemployment due to failure of an industry because of drought)
Droughts are climatic patterns that occur over long periods of time as the result of many causes. Global weather patterns that produce persistent, upper-level high-pressure systems along the West Coast result in warm, dry air and reduced precipitation. Anomalies of precipitation and temperature may last from several months to several decades.

How long they last depend on interactions between the atmosphere and the oceans, soil moisture and land surface processes, topography, internal dynamics, and the accumulated influence of global weather systems.

9.1.1 Monitoring and Rating Drought
NOAA Drought Indices
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 Drought Index is based on long-term weather patterns. The intensity of drought in a given month is dependent on current weather plus the cumulative patterns of previous months. Weather patterns can change quickly, and the Palmer Drought Severity Index can respond fairly rapidly. • The Palmer Z Index measures short-term drought on a monthly scale. • The Palmer Hydrological Drought Index quantifies hydrological effects (reservoir levels, groundwater levels, etc.), which take longer to develop and last longer. This index responds more slowly to changing conditions than the Palmer Drought Index.
• The Palmer Crop Moisture Index measures short-term drought weekly to assess impacts on agriculture.

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• The Standardized Precipitation Index considers only precipitation. A value 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.

Maps of these indices show drought conditions nationwide at a given point in time. They are not necessarily indicators of any given area’s long-term susceptibility to drought. Figure 9-1. shows recent versions of the maps at the time of this plan’s preparation (November 2022 through January 2023). Because of the frequency with which the maps are updated, the maps in this figure should not be considered current; they are provided for example only.

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 (U.S. Drought Monitor 20223):
• D0—Abnormally Dry
➢ Short-term dryness slowing planting, growth of crops
➢ Some lingering water deficits
➢ Pastures or crops not fully recovered
• D1—Moderate Drought
➢ Some damage to crops, pastures
➢ Some water shortages developing
➢ Voluntary water-use restrictions requested
• D2—Severe Drought
➢ Crop or pasture loss likely
➢ Water shortages 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
The USDM categories show experts’ assessments of conditions related to drought. These experts check variables including temperature, soil moisture, water levels in streams and lakes, snow cover, and meltwater runoff. They also check whether areas are showing drought impacts such as water shortages and business interruptions. Associated statistics show what proportion of various geographic areas are in each category of dryness or drought, and how many people are affected. U.S. Drought Monitor data go back to 2000.

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Figure 9-1. Example Drought Index Maps (November and December 2022)

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9.1.2 Drought 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 structures, as do other natural disasters. The National Drought Mitigation Center uses three categories to describe likely drought impacts:
• Economic Impacts—These impacts of drought cost people (or businesses) money. Farmers’ crops are destroyed; low water supply necessitates spending on irrigation or drilling of new wells; water-related businesses (such as sales of boats and fishing equipment) may experience reduced revenue. • 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.

The demand that society places on water systems and supplies—such as expanding populations, irrigation, and environmental protection—contributes to drought impacts. Drought can lead to difficult decisions regarding the allocation of water, as well as stringent water use restrictions, water quality problems, and inadequate water supplies for fire suppression. There are also issues such as growing conflicts between agricultural uses of surface water and in- stream uses, surface water and groundwater interrelationships, and the effects of growing water demand on uses of water.

Vulnerability of an activity to drought depends on its water demand and the water supplies available to meet the demand. The impacts of drought vary between sectors of the community in both timing and severity:
• Water supply—The water supply sector encompasses urban and rural drinking water systems that are affected when a drought depletes groundwater supplies due to reduced recharge from rainfall. • Agriculture and commerce—Impacts on the agriculture and commerce sectors include the reduction of crop yield and livestock sizes due to insufficient water supply for crop irrigation and maintenance of ground cover for grazing.
• Environment, public health, and safety—The environmental, public health, and safety sector focuses on wildfires that are both detrimental to the forest ecosystem and hazardous to the public. It also includes the impact of desiccating streams, such as the reduction of in-stream habitats for native species.

9.1.3 California Drought Response
Defined Drought Stages
During critically dry years, the California State Water Resources Control Board can mandate water entitlements on water right holders to address statewide water shortages. Table 9-1 shows the state drought management program stages mandated to water right holders.

Table 9-1. State Drought Management Program
Drought Stage State Mandated Customer Demand Reduction Rate Impacts Stage 0 or 1 <10% Normal rates
Stage 2 10 to 15% Normal rates; Drought surcharge
Stage 3 15 to 20% Normal rates; Drought surcharge
Stage 4 >20% Normal rates, Drought surcharge

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Future Water Conservation in California
California’s 2018 Water Plan Update projects that water demand in the state will increase through 2050. The Department of Water Resources predicts a modest decrease in agricultural water use and an urban water use increase of 1 to 7 million acre-feet per year (California Department of Water Resources 2018). The 2018 update explores ways to increase agricultural and urban water use efficiency. An update of the plan is currently under development.

The California governor’s, “Making Water Conservation a California Way of Life,” directs permanent changes to use water more wisely, eliminate water waste, strengthen local drought resistance, and improve agricultural water use efficiency and drought planning. With an aim to make water conservation a way of life in California, Executive Order B-37-16 requires the following:
• The State Water Resources Control Board will maintain urban water use reporting requirements and prohibitions on wasteful practices such as watering during or after rainfall, hosing off sidewalks and irrigating ornamental turf on public street medians.
• The state will continue its work to coordinate a statewide response on the bark beetle outbreak in drought- stressed forests that has killed millions of trees across California.

The Legislature enacted two bills in response to Executive Order B-37-16 to overhaul California’s approach to conserving water:
• SB 606 requires the State Water Resources and Control Board and DWR to adopt water efficiency regulations, outlines requirements for urban water suppliers, including urban drought risk assessments, and implements penalties for violations. The law contains directives on water shortage planning and water loss reporting for urban wholesale water suppliers and offers a bonus incentive for potable reuse water. • AB 1668 requires the State Water Resources Control Board, in coordination with the DWR, to adopt water efficiency standards and regulations; drought and water shortage contingency plan guidance; specified standards for per capita daily indoor residential water use; and performance measures for commercial, industrial, and institutional water use.

The bills required new long-term urban water use efficiency standards with components for indoor residential use, outdoor residential use, water losses and other uses. Regarding indoor residential use, the new laws set a standard of 55 gallons per person, per day through January 1, 2025. After that date, the amount will be incrementally reduced over time. The legislation also specifies penalties on local water suppliers for violations to these standards. Starting in 2027, local water suppliers’ failure to comply with the Water Resources Control Board’s adopted long-term standards could result in fines of $1,000 per day during non-drought years and $10,000 per day during declared drought emergencies and certain dry years.

9.1.4 Secondary Hazards
The secondary impact most commonly associated with drought is wildfire. A prolonged lack of precipitation dries out vegetation, which becomes increasingly susceptible to ignition as the duration of the drought extends. Drought is also often accompanied by extreme heat, exposing people to the risk of sunstroke, heat cramps and heat exhaustion.

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9.2 HAZARD PROFILE

9.2.1 Local Water Supply
Water service for the City of Concord is provided by the Contra Costa Water District (CCWD), which provides treated and untreated water to a population of 500,000 in central and east Contra Costa County (Contra Costa Water District n.d.). The district operates and maintains a complex system of water transmission, treatment, and storage facilities to supply both treated and untreated (raw) water to wholesale and retail customers.

CCWD diverts water from the Sacramento-San Joaquin Delta at four intake facilities. The 48-mile Contra Costa Canal conveys the water from the Delta; it starts at Rock Slough and ends at the Martinez Reservoir. Four untreated water reservoirs, Los Vaqueros, Contra Loma, Mallard, and Martinez, provide a total of 165,000 acre-feet of storage. These reservoirs are used to store water for blending and water quality purposes, dry-year and emergency use, supplying during peak demands, and flow regulation. CCWD operates three water treatment plants. The district’s treated water distribution system consists of more than 800 miles of pipelines, 40 storage reservoirs with a total capacity of 72 million gallons, and 30 pump stations (Contra Costa Water District 2021).

CCWD projects that its supply of water to retail customers, such as water users in Concord, diminishes with ongoing drought as follows (Contra Costa Water District 2021):
• Average year—100 percent of supply
• First year of multiple dry years—100 percent of supply • Second year of multiple dry years—100 percent of supply • Third year of multiple dry years—95 percent of supply • Fourth year of multiple dry years—90 percent of supply • Fifth year of multiple dry years—85 percent of supply.

9.2.2 Past Events
Drought has played an ongoing role in shaping California’s early history. The so-called Great Drought of 1863–1864 contributed to the demise of the cattle rancho system. Subsequently, a notable period of extended dry conditions was experienced during most of the 1920s and well into the 1930s, with the latter time including the Dustbowl drought that gripped much of the United States. Three 20th-century droughts were of particular importance from a water supply standpoint—the droughts of 1929–1934, 1976–1977, and 1987–1992. More recent multiyear droughts occurred in 2007–2009, 2012–2016, and 2020 to the time of this writing (National Integrated Drought Information System 2022b). The recent winter storms of 2022 – 2023 may have affected the current drought condition. Analysis on current condition is outstanding:
• 2020 to Present Drought—A new record was set during this multiyear drought, with 2022 becoming driest year in California since official drought records began in 1895 (National Integrated Drought Information System 2022). As of this writing, all 58 counties in California are under USDA disaster designations for drought (U.S. Department of Agriculture 2022). It is estimated that drought conditions were affecting all residents of Contra Costa County by October 2022, which amounts to over a million people (National Integrated Drought Information System 2022a).
• 2012 to 2016 Drought—The period from 2012 to 2014 ranked as the driest three consecutive years for statewide precipitation. Calendar year 2014 set new climate records for statewide average temperatures and

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for record-low water allocations from State Water Project and federal Central Valley Project contractors.

Calendar year 2013 set minimum annual precipitation records for many communities. • 2007 to 2009 Drought—The governor issued an executive order that 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, the governor proclaimed a state of emergency for the entire state as severe drought conditions continued. The largest court-ordered water restriction in state history (at the time) was imposed. • 1987 to 1992 Drought —California received precipitation well below average levels for four consecutive years. While the Central Coast was most affected, the Sierra Nevada in Northern California and the Central Valley counties were also affected. During this drought, only 56 percent of average runoff for the Sacramento Valley was received, totaling just 10 million acre-feet. In 1991, the State Water Project sharply decreased deliveries to water suppliers, including the San Francisco Bay area. By February 1991, all 58 counties in California were experiencing drought conditions. Urban areas as well as agricultural areas were impacted. • 1976 to 1977 Drought—California had one of its most severe droughts due to lack of rainfall during the winters of 1976 and 1977. 1977 was the driest period on record in California at that time, 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 throughout the state. Only 37 percent of the average Sacramento Valley runoff was received, with just 6.6 million acre-feet recorded. Over $2.6 billion in crop damage was recorded in 31 counties. FEMA declared a drought emergency (Declaration 3023-EM) on January 20, 1977, for all 58 California counties, including Contra Costa County.

9.2.3 Location
Drought is a regional phenomenon. A drought that affects the planning area would affect the entirety of the area simultaneously and has the potential to directly or indirectly impact every person in the county as well as adversely affect the local economy.

9.2.4 Frequency
Drought has a high probability of occurrence in the planning area. From January 2000 to December 2022, some part of Contra Costa County experienced a USDM rating of D1 or higher in 726 out of 1,196 weeks (see Figure 9-2). The planning area has also been included in USDA drought disaster declarations in nine of the last 11 years. Historical drought data for the planning area indicate there have been five significant multi-year droughts in the last 46 years (1976 to 2022), and about a 30-percent chance of a drought occurring in any given year. As temperatures increase, the probability of future droughts will likely increase. Therefore, droughts likely will occur in Concord and Contra Costa County at varied severities in the future.

Source: U.S. Drought Monitor 2023

Figure 9-2. Percent of Contra Costa County Affected by USDM Ratings, 2000 –2023

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9.2.5 Severity
The severity of any given 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. California is currently in a several-year-long drought, while other areas in the United States may undergo droughts as short as 1 or 2 months. How long they 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.

U.S. Drought Monitor Ratings
Contra Costa County and Concord have a history of severe droughts. As shown in Figure 9-2, at least part of the county has experienced extreme (D3) or exceptional (D4) droughts multiple times since 2014.

Drought Impact Reporter
The National Drought Mitigation Center developed the Drought Impact Reporter in response to the need for 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 Drought Impact Reporter contains information on 660 impacts from droughts that specifically affected Contra Costa County from 2000 through 2022 (National Drought Mitigation Center 2023a). The following are the categories and reported number of impacts (note that some impacts have been assigned to more than one category):
• General Awareness—180
• Agriculture—139
• Business and Industry—20
• Energy—15
• Fire—87
• Plants and Wildlife—132
• Relief, Response, and Restrictions—384
• Society and Public Health—131
• Tourism and Recreation—20
• Water Supply and Quality—445.

9.2.6 Warning Time
Droughts are climatic patterns that occur over long periods of time. Only generalized warning can take place due to the numerous variables that scientists have not pieced together well enough to make accurate and precise predictions.

Empirical studies conducted over the past century have shown that 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.

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At this time, scientists 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.

9.3 EXPOSURE AND VULNERABILITY
Drought can affect a wide range of economic, environmental, and social activities. Its impacts can span many sectors of the economy because water is integral to the ability to produce goods and provide services. The impacts can reach well beyond the area undergoing physical drought. Vulnerability of an activity to drought depends on its water demand and the water supplies available to meet the demand.

9.3.1 Population
Drought can affect people’s health and safety, including health problems related to low water flows, poor water quality, or dust and pollution. Drought may also lead to loss of life (National Drought Mitigation Center 2023). Other possible impacts include recreational risks; effects on air quality; diminished living conditions related to energy, air quality, and hygiene; compromised food and nutrition; and increased incidence of illness and disease (CDC 2020).

Droughts can also lead to reduced local firefighting capabilities.

9.3.2 Property
No structures will be directly affected by drought conditions. Droughts can also 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.

9.3.3 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 planning area’s critical facilities inventory will be largely aesthetic. For example, when water conservation measures are in place, landscaped areas will not be watered and may die. These aesthetic impacts are not considered significant.

9.3.4 Environment
Groundwater and Streams
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 stream flows are lowest. Where stream flows are reduced, development that relies on surface water may seek to establish new groundwater wells, which could further increase groundwater depletion.

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Other Potential Losses
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. Although environmental losses are difficult to quantify, growing public awareness and concern for environmental quality has forced public officials to focus greater attention and resources on these effects. The following are potential impacts of drought:
• Wildlife habitat may be degraded through the loss of wetlands, lakes and vegetation. The degradation of landscape quality, including increased soil erosion, may lead to a more permanent loss of biological productivity.
• Drought conditions greatly increase the likelihood of wildfires, the major threat to timber resources. • Scenic resources in the City are vulnerable to the increased likelihood of wildfires associated with droughts. • Drying up or dying off of urban forests could reduce ecological and eco-tourist values. • Any shortage of water supply can have significant economic impacts.

9.4 FUTURE TRENDS IN DEVELOPMENT
The City of Concord has a General Plan that includes policies directing land use and dealing with issues of water supply and the protection of water resources. This plan provides the capability at the local level to protect future development from the impacts of drought. The City of Concord reviewed its General Plan under the capability assessment performed for this effort. Deficiencies identified by this review can be addressed by mitigation actions to increase the capability to deal with future trends in development.

9.5 SCENARIO
An extreme, multiyear drought associated with record-breaking rates of low precipitation and high temperatures— such as the most recent drought across the State of California—is the worst-case scenario. Combinations of low precipitation and high temperatures could occur over several consecutive years. Intensified by such conditions, extreme wildfires could break out throughout the planning area, increasing the need for water. Surrounding communities, also in drought conditions, could increase their demand for water supplies relied upon by the City of Concord, causing social and political conflicts. If such conditions persisted for several years, the economy of the City could experience setbacks, especially in water dependent industries.

9.6 ISSUES
The planning team has identified the following drought-related issues:
• Identification of the availability and reliability of new water supplies • Using water transfers obtained through purchased water rights or land and short-term contracts for drought reliability
• The probability of increased drought frequencies and durations due to climate change • The promotion of active water conservation even during non-drought periods

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• 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 planning area’s ability to successfully recover from or prepare for more occurrences—particularly considering the longevity of recent droughts.

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10. EARTHQUAKE

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

10.1.1 Earthquake Location
The location of an earthquake is commonly described by its focal depth and the geographic position of its epicenter.

The focal depth of an earthquake is the depth from the Earth’s surface to the region where an earthquake’s energy originates (the focus or hypocenter). The epicenter of an earthquake is the point on the Earth’s surface directly above the hypocenter.

10.1.2 Earthquake Geology
Tectonic Plates
The Earth’s crust, which is the rigid outermost shell of the planet, is broken into seven or eight major tectonic plates (depending on how they are defined) and many minor plates. Where the plates meet, they move in one of three ways along their mutual boundary: convergent (two plates moving together), divergent (two plates moving apart), or transform (two plates moving parallel to one another). Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. Subduction is a geological process that takes place at convergent boundaries of tectonic plate, in which one plate moves under another. Regions where this process occurs are known as subduction zones, and they have the potential to generate highly damaging earthquakes.

California is seismically active because of movement of the North American Plate, east of the San Andreas Fault, and the Pacific Plate to the west, which includes the state’s coastal communities. The transform (parallel) movement of these tectonic plates against one another creates stresses that build as the rocks are gradually deformed. The rock deformation, or strain, is stored in the rocks as elastic strain energy. When the strength of the rock is exceeded, rupture occurs along a fault. The rocks on opposite sides of the fault slide past each other as they spring back into a relaxed position. The strain energy is released partly as heat and partly as elastic waves called seismic waves. The passage of these seismic waves produces the ground shaking in earthquakes.

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Faults
Geologists have found that earthquakes reoccur along faults, which are zones of weakness in the earth’s crust. When a fault experiences an earthquake, there is no guarantee that all the stress has been relieved. Another earthquake can still occur. In fact, relieving stress along one part of a fault may increase it in another part.

Faults are more likely to have future earthquakes on them if they have more rapid rates of movement, have had recent earthquakes along them, experience greater total displacements, and are aligned so that movement can relieve the accumulating tectonic stresses. Geologists classify faults by their relative hazards. “Active” faults, which represent the highest hazard, are those that have ruptured to the ground surface during the Holocene period (about the last 11,000 years). “Potentially active” faults are those that displaced layers of rock from the Quaternary period (the last 1,800,000 years) (California Department of Conservation 2022).

Determining if a fault is “active” or “potentially active” depends on geologic evidence, which may not be available for every fault. The majority of the seismic hazards are on well-known active faults. However, inactive faults, where no displacements have been recorded, also have the potential to reactivate or experience displacement along a branch sometime in the future. An example of a fault zone that has been reactivated is the Foothills Fault Zone. The zone was considered inactive until evidence of an earthquake (approximately 1.6 million years ago) was found near Spenceville, California. Then, in 1975, an earthquake occurred on another branch of the zone near Oroville, California (now known as the Cleveland Hills Fault). The State Division of Mines and Geology indicates that increased earthquake activity throughout California may cause tectonic movement along currently inactive fault systems.

10.1.3 Earthquake-Related Hazards
According to the U.S. Geological Survey (USGS) Earthquake Hazards Program, an earthquake hazard is anything associated with an earthquake that may affect people’s normal activities. This includes the following:
• Surface Faulting—Displacement that reaches the earth’s surface during slip along a fault. Commonly occurs with shallow earthquakes, those with an epicenter less than 20 kilometers. • Ground Motion (shaking)—The movement of the earth’s surface from earthquakes or explosions. Ground motion or shaking is produced by waves that are generated by sudden slip on a fault or sudden pressure at the explosive source and travel through the earth and along its surface. • Landslide—A movement of surface material down a slope. • Liquefaction—A process by which water‐saturated sediment temporarily loses strength and acts as a fluid.

Earthquake shaking can cause this effect.
• Tectonic Deformation—A change in the original shape of a material due to stress and strain. • Tsunami—A sea wave of local or distant origin that results from large‐scale seafloor displacements associated with large earthquakes, major submarine slides, or violent underwater volcanic eruptions.

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

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Magnitude
An earthquake’s magnitude is a measure of the energy released at the source of the earthquake. Magnitude is commonly expressed by ratings on the moment magnitude scale (Mw), the most common scale used today. The moment magnitude scale is a more accurate measure of earthquake size than the better-known Richter scale (ML) (U.S. Geological Survey 2021). This scale is based on the total moment release of the earthquake (the product of the distance a fault moved, and the force required to move it). The scale is as follows:
• Great—Mw > 8
• Major—Mw = 7.0 – 7.9
• Strong—Mw = 6.0 – 6.9
• Moderate—Mw = 5.0 – 5.9
• Light—Mw = 4.0 – 4.9
• Minor—Mw = 3.0 – 3.9
• Micro—Mw < 3
Intensity
The most commonly used intensity scale is the modified Mercalli intensity scale. Ratings of the scale as well as the perceived shaking and damage potential for structures are shown in Table 10-1. The modified Mercalli intensity scale is generally represented visually using a USGS product called a ShakeMap (see Section 10.1.6), which shows the expected ground shaking at any given location produced by an earthquake with a specified magnitude and epicenter.

An earthquake has only one magnitude and one epicenter, but it produces a range of ground shaking at sites throughout the region, depending on the distance from the earthquake, the rock and soil conditions at sites, and variations in the propagation of seismic waves from the earthquake due to complexities in the structure of the earth’s crust. A ShakeMap shows the variation of ground shaking in a region immediately following significant earthquakes (for technical information about ShakeMaps see (U.S. Geological Survey n.d.-a)).

Table 10-1. Mercalli Scale and Peak Ground Acceleration Comparison Modified Potential Structure Damage Estimated PGAa
Mercalli Scale Perceived Shaking Resistant Buildings Vulnerable Buildings (%g) I Not Felt None None <0.17%
II-III Weak None None 0.17% - 1.4%
IV Light None None 1.4% - 3.9%
V Moderate Very Light Light 3.9% - 9.2%
VI Strong Light Moderate 9.2% - 18%
VII Very Strong Moderate Moderate/Heavy 18% - 34%
VIII Severe Moderate/Heavy Heavy 34% - 65%
IX Violent Heavy Very Heavy 65% - 124%
X – XII Extreme Very Heavy Very Heavy >124%
a. PGA = peak ground acceleration. Measured in percent of g, where g is the acceleration of gravity Sources: (U.S. Geological Survey n.d.-b); (U.S. Geological Survey 2011)

10.1.5 Ground Motion
Earthquake hazard assessment is based on expected ground motion. During an earthquake when the ground is shaking, it also experiences acceleration. The peak acceleration is the largest increase in velocity recorded by a particular station during an earthquake. Estimates are developed of the annual probability that certain ground motion accelerations will be exceeded; the annual probabilities can then be summed over a time period of interest.

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The most commonly mapped ground motion parameters are horizontal and vertical peak ground accelerations (PGA) for a given soil type. PGA is a measure of how hard the earth shakes, or accelerates, in a given geographic area.

Instruments called accelerographs record levels of ground motion due to earthquakes at stations throughout a region.

PGA is measured in g (the acceleration due to gravity) or expressed as a percent acceleration force of gravity (%g).

These readings are recorded by state and federal agencies that monitor and predict seismic activity.

Maps of PGA values form the basis of seismic zone maps that are included in building codes such as the International Building Code. Building codes that include seismic provisions specify the horizontal force due to lateral acceleration that a building should be able to withstand during an earthquake. PGA values are directly related to these lateral forces that could damage “short period structures” (e.g., single-family dwellings). Longer period response components determine the lateral forces that damage larger structures with longer natural periods (apartment buildings, factories, high-rises, bridges). Table 10-1 lists damage potential and perceived shaking by PGA factors, compared to the Mercalli scale.

10.1.6 USGS Earthquake Mapping Programs
ShakeMaps
The USGS Earthquake Hazards Program produces maps called ShakeMaps that map ground motion and shaking intensity following significant earthquakes. ShakeMaps focus on the ground shaking caused by the earthquake, rather than on characteristics of the earthquake source, such as magnitude and epicenter. An earthquake has only one magnitude and one epicenter, but it produces a range of ground shaking at sites throughout the region, depending on the distance from the earthquake, the rock and soil conditions at sites, and variations in the propagation of seismic waves from the earthquake due to complexities in the structure of the earth’s crust.

A ShakeMap shows the extent and variation of ground shaking immediately across the surrounding region following significant earthquakes. Such mapping is derived from peak ground motion amplitudes recorded on seismic sensors, with interpolation where data are lacking based on estimated amplitudes. Color-coded instrumental intensity maps are derived from empirical relations between peak ground motions and Modified Mercalli intensity. In addition to the maps of recorded events, the USGS creates the following:
• Scenario ShakeMaps of hypothetical earthquakes of an assumed magnitude on known faults. • Probabilistic ShakeMaps, based on predicted shaking from all possible earthquakes over a 10,000-year period.

In a probabilistic map, information from millions of scenario maps are combined to make a forecast for the future. The maps indicate the ground motion at any given point that has a given probability of being exceeded in a given timeframe, such as a 100-year (1-percent-annual chance) event.

National Seismic Hazard Map
National maps of earthquake shaking hazards provide information for creating and updating seismic design requirements for building codes, insurance rate structures, earthquake loss studies, retrofit priorities and land use planning. After thorough review of the studies, professional organizations of engineers update the seismic-risk maps and seismic design requirements contained in building codes (Brown, et al. 2001). The USGS updated the National Seismic Hazard Maps in 2018. New seismic, geologic, and geodetic information on earthquake rates and associated ground shaking were incorporated into these revised maps. The 2018 map, shown in Figure 10-1., represents the best available data as determined by the USGS.

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Source: (USGS 2018)

Figure 10-1. 2018 USGS National Seismic Hazard Map

10.1.7 Liquefaction and Soil Types
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 into the ground.

A program called the National Earthquake Hazard Reduction Program (NEHRP) creates maps based on soil characteristics to help identify locations subject to liquefaction. NEHRP soil types define the locations that will be significantly impacted by an earthquake. Table 10-2 summarizes NEHRP soil classifications. NEHRP Soils B and C typically can sustain ground shaking without much effect, dependent on the earthquake magnitude. The areas that are commonly most affected by ground shaking have NEHRP Soils D, E and F. In general, these areas are also most susceptible to liquefaction.

Table 10-2. NEHRP Soil Classification System
NEHRP Soil
Type Description
Mean Shear Velocity
to 30 m (m/s)
A Hard Rock 1,500
B Firm to Hard Rock 760-1,500
C Dense Soil/Soft Rock 360-760
D Stiff Soil 180-360
E Soft Clays < 180
F Special Study Soils (liquefiable soils, sensitive clays, organic soils, soft clays >36 m thick)

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10.1.8 Secondary Hazards
Earthquakes can cause large and sometimes disastrous mudslides. Building and road foundations can lose load-bearing strength and may sink into what was previously solid ground. Earthen dams and levees are highly susceptible to seismic events, and the impacts of their failures can be considered secondary risks for earthquakes.

Unless properly secured, hazardous materials can be released, causing significant damage to the environment and people. Hazardous materials releases can occur during an earthquake from fixed facilities or transportation-related incidents. 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. Transportation corridors can be disrupted during an earthquake, leading to the release of materials to the surrounding environment.

10.2 HAZARD PROFILE

10.2.1 Past Events
Contra Costa County has been included in one FEMA declaration for earthquake: the 1989 Loma Prieta Earthquake (DR-845) Table 10-3 lists earthquakes of magnitude 5.0 or greater within a 100-mile radius of the planning area.

Table 10-3. Earthquakes Magnitude 5.0 or Larger Within 100-mile Radius of the Planning Area Date Magnitude Epicenter Location
10/25/2022 5.1 9.3 miles east-southeast of Alum Rock, CA 12/14/2016 5.0 6.2 miles west of Cobb, CA
8/24/2014 – South Napa Earthquake 6.0 South Napa
10/20/2012 – King City Earthquake 5.3 17.4 miles east-northeast of King City, CA 10/31/2007 – Alum Rock Earthquake 5.6 San Francisco Bay area, California 5/14/2002 – Gilroy Earthquake 5 Northern California
9/3/2000 – Yountville Earthquake 5 Northern California
8/12/1998 – San Juan Bautista Earthquake 5.2 Central California 4/18/1990 – Northern California 5.4 Near Aromas, Northern California 10/18/1989 – Loma Prieta Earthquake 7.2 Northern California 8/8/1989 – Santa Cruz County Earthquake 5.2 Central California 6/27/1989 5.3 Northern California
6/13/1988 5.3 San Francisco Bay area, California
2/20/1988 5.1 Central California
3/31/1986 5.6 Northern California
1/26/1986 5.4 Central California

10.2.2 Location
Fault Locations
Concord is located in a region of high seismicity with numerous local faults, as shown on Figure 10-2. The primary seismic hazard for the county is potential ground shaking from these faults, especially the Hayward, Calaveras North, Concord-Green Valley, Mount Diablo, and Greenville faults, which are further described below.

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Source: (U.S. Geological Survey 2016)

Note: Oval shows the approximate location of Concord and Contra Costa County.

Figure 10-2. Significant Known Faults in the Bay Area

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Calaveras (North Central)
The Calaveras (North Central) Fault is a major branch of the San Andreas Fault, located east of the Hayward Fault. It extends 76 miles from the San Andreas Fault near Hollister to Danville at its northern end. The Calaveras Fault is one of the most geologically active and complex faults in the Bay Area. The probability of experiencing a Magnitude 6.7 or greater earthquake along the Calaveras Fault in the next 30 years is 26 percent.

Concord-Green Valley
The Concord-Green Valley Fault, named for being located under the City of Concord, is connected to the main Green Valley Fault. The fault extends approximately 11 miles east of West Napa Fault, from Mount Diablo to the Carquinez Strait. It is considered to be under high stress and has a 16 percent probability of experiencing a Magnitude

6.7 or greater earthquake in the next 30 years.

Greenville
The Greenville Fault is in the eastern Bay Area in Contra Costa and Alameda Counties. This dextral strike-slip fault zone borders the eastern side of Livermore Valley and is considered to be part of the larger San Andreas fault system in the central Coast Ranges. The fault zone extends from northwest of Livermore Valley along the Marsh Creek and Clayton faults toward Clayton Valley.

Hayward Fault
The Hayward Fault is an approximately 45-mile-long fault that runs through densely populated areas on the East Bay, parallel to the San Andreas Fault. The Hayward Fault extends through some of the Bay Area’s most populated areas, including San Jose, Oakland, and Berkeley. The Hayward Fault is a right-lateral slip fault.

The Hayward Fault is increasingly becoming a hazard priority throughout the Bay Area because of its increased chance for activity and its intersection with highly populated areas and critical infrastructure. The probability of experiencing a Magnitude 6.7 or greater earthquake along the Hayward Fault in the next 30 years is 33 percent. An earthquake of this magnitude has regional implications for the entire Bay Area, as the Hayward Fault crosses transportation and resource infrastructure, such as multiple highways and the Hetch-Hetchy Aqueduct.

Mount Diablo
The Mount Diablo thrust fault is in the vicinity of Mount Diablo in Contra Costa County. The fault lies between the Calaveras Fault, the Greenville Fault, and the Concord Fault, all right-lateral strike slip faults, and appears to transfer movement from the Calaveras and Greenville Faults to the Concord Fault, while continuing to uplift Mount Diablo.

NEHRP Soil Type and Liquefaction Mapping
Figure 10-3 shows NEHRP soil classifications in the planning area. Figure 10-4 shows areas that have been identified as susceptible to liquefaction.

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NEHRP SOIL CLASSIFICATION
Data Sources:

CA Geologic Survey
CIty of Concord
0 1 2
Miles
4 C (Dense Soil/Soft Rock)
D (Stiff Soil)
Figure 10-3

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LIQUEFACTION SUSCEPTIBILITY
Data Sources:

CA Geologic Survey
CIty of Concord
0 1 2
Miles
4 Very Low
Low
Moderate
High
Very High
Figure 10-4

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10.2.3 Frequency
California experiences hundreds of earthquakes each year, most with minimal damage and magnitudes below 3.0 on the Richter Scale. Earthquakes that cause moderate damage to structures occur several times a year. According to the USGS, a strong earthquake measuring greater than 5.0 on the Richter Scale occurs every 2 to 3 years and major earthquakes of more than 7.0 on the Richter Scale occur once a decade.

The USGS estimated in 2016 that there is a 72 percent probability of at least one earthquake before 2043 with a magnitude of 6.7 or greater that could cause widespread damage in the San Francisco Bay area (USGS, 2016).

Table 10-4 shows the estimated probability for individual faults in the area.

Table 10-4. Earthquake Probabilities for the San Francisco Bay Area Region, 2014-2043 Fault Probability of One or More M≥6.7 Quakes Before 2043 Hunting Creek 16%
Green Valley 16%
Concord 16%
Greenville 16%
Berryessa 16%
Calaveras 26%
Maacama 8%
Rodgers Creek Fault 33%
Hayward 33%
San Andreas 22%
San Gregorio 6%
See Figure 10-2 for fault locations.

Source: (U.S. Geological Survey 2016)

10.2.4 Severity
USGS ground motion maps, based on current information about fault zones, show the PGA that has a certain probability of being exceeded in a 50-year period. The maps, last updated in 2014 with the best currently available data, show that the PGA with a 10-percent probability of exceedance in 50 years for Contra Costa County is 0.4g (see Figure 10-5).

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.

10.2.5 Warning Time
There is currently no reliable way to predict the day or month that an earthquake will occur at any given location.

Earthquake early warning systems use earthquake science and the technology of monitoring systems to alert devices and people when shaking waves generated by an earthquake are expected to arrive at their location. Strong seismic shaking from an earthquake travels at about 2 miles per second, so it is possible to detect a large earthquake near its source and broadcast a warning of imminent strong shaking to more distant areas before the shaking arrives. The seconds to minutes of advance warning can allow people and systems to take actions to protect life and property from destructive shaking.

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Figure 10-5. PGA with 2-Percent Probability of Exceedance in 50 Years

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New technology is being developed for early warnings. For example, MyShake is a global smartphone seismic network for early warning that can keep users informed about earthquakes. It monitors for earthquakes using data from smartphone sensors.

10.3 EXPOSURE
The entire planning area is exposed to the earthquake hazard, so an earthquake has the potential to affect the entire population of 125,650, all 37,556 buildings in the planning area, with a total replacement value of $35.3 billion, all of the planning area’s identified critical facilities, and the entire environment of the planning area.

10.4 VULNERABILITY
Earthquake vulnerability data for the risk assessment was generated using a Hazus Level 2 (user-defined) analysis for the scenario events listed in Table 10-5. Summary findings of the risk assessment, showing vulnerability results for the entire planning area, are provided in the sections below. Appendix D shows results broken down by Council voting district.

Table 10-5. Earthquakes Modeled for Risk Assessment
Scenario Event
Focal
Depth Epicenter Location Map Figure
100-Year Probabilistic Event N/A N/A Figure 10-6.

Concord-Green Valley Fault Scenario (M6.8) 5.6 miles 20 miles north of the City of Martinez Figure 10-7.

Hayward Fault Scenario (M7.05) 5.0 miles 3.5 miles southwest of the Town of Moraga Figure 10-8.

Mount Diablo Fault Scenario (M6.7) 8.7 miles 10.5 miles east of the City of Danville Figure 10-9.

10.4.1 Population
Impacts on Persons and Households
Impacts on persons and households in the planning area were estimated for the four scenario events through the Hazus analysis. Table 10-6 summarizes the results.

Table 10-6. Estimated Earthquake Impact on Persons and Households Earthquake Scenario
Number of Displaced
Households
Number of Persons Requiring Short-
Term Shelter
100-Year Probabilistic Event 494 344
Concord-Green Valley Fault Scenario (M6.8) 951 663
Hayward Fault Scenario (M7.05) 301 204
Mount Diablo Fault Scenario (M6.7) 1,146 757
Vulnerable Populations
The degree of vulnerability of people exposed to the earthquake hazard is dependent on many factors, including the age and construction type of the structures they live in, the soil type their homes are constructed on, their proximity to fault location, etc.

A geographic analysis of demographics using the SVI mapping described in Section 4.6.2 estimated that 52 percent of the population in Census tracts that intersect the mapped NEHRP D soil zone are in a high vulnerability area.

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EARTHQUAKE SCENARIO
100-YEAR PROBABALISTIC EVENT
Data Sources:

US Geologic Survey
CIty of Concord
0 1 2
Miles
4 Mercalli Intensity Scale described as:
(Perceived Shaking/Potential Damage)
IV (Light/None)
V (Moderate/Very Light)
VI (Strong/Light)
VII (Very Strong/Moderate)
VIII (Severe/Moderate-Heavy)
IX (Violent/Heavy)
Figure 10-6

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EARTH QUAKE SCENARIO
CONCORD-GRE EN VALL EY FAULT M6.8
Data Sources:

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Concord Blvd
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Mallard
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Concord

EARTHQUAKE SCENARIO
HAYWARD (HAYWIRED SCENARIO) M7.05
Data Sources:

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Mallard
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Concord

EARTHQUAKE SCENARIO
MOUNT DIABLO FAULT M6.7
Data Sources:

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10.4.2 Property
Building Age
Table 10-7 identifies significant milestones in building and seismic code requirements that directly affect the structural integrity of development. Using these time periods, the planning team used Hazus to identify the number of structures in the planning area by date of construction.

Table 10-7. Age of Structures in Planning Area
Time
Period
Number of Current Planning
Area Structures Built in Period Significance of Time Frame Pre-1933 167 Before 1933, there were no explicit earthquake requirements in building codes. State law did not require local governments to have building officials or issue building permits.
1933-1940 162 In 1940, the first strong motion recording was made. 1941-1960 8,145 In 1960, the Structural Engineers Association of California published guidelines on recommended earthquake provisions.
1961-1975 13,684 In 1975, significant improvements were made to lateral force requirements. 1976-1993 11,813 In 1994, the Uniform Building Code was amended to include provisions for seismic safety.
1994 –
present
3,585 Seismic code is currently enforced.

Total 37,556

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 10 percent of the planning area’s structures were constructed after the Uniform Building Code was amended in 1994 to include seismic safety provisions. Fewer than 1 percent were built before 1933 when there were no building permits, inspections, or seismic standards.

Loss Potential
Property losses were estimated through the Level 2 Hazus analysis for the five earthquake fault scenarios. The Hazus analysis also estimated the amount of earthquake-caused debris in the planning area for the five scenario events.

Table 10-8 summarizes the results.

Table 10-8. Loss Estimates for Modeled Earthquake Scenarios

100-Year
Probabilistic Event
Concord-Green Valley
Fault Scenario (M6.8)
Hayward Fault
Scenario (M7.05)
Mount Diablo Fault
Scenario (M6.7)
Estimated Loss
Structures $344,356,941 $519,037,616 $226,713,333 $450,951,632 Contents $395,596,658 $610,683,786 $253,079,463 $521,302,058 Total $739,953,599 $1,129,721,401 $479,792,796 972,253,691 % of Total Planning Area
Replacement Value

2.1% 3.2% 1.4% 2.8%
Debris to Be Removed (tons) 200,440 351,290 129,450 365,210

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10.4.3 Critical Facilities
Level of Damage
Hazus classifies the vulnerability of critical facilities to earthquake as no damage, slight damage, moderate damage, extensive damage, or complete damage. The model was used to assign a category to each critical facility in the planning area for the five earthquake fault scenarios. Figure 10-10 through Figure 10-13 summarize the results.

Time to Return to Functionality
Hazus estimates the time to restore critical facilities to fully functional use. Results are presented as probability of being functional at specified time increments: 1, 3, 7, 14, 30 and 90 days after the event. For example, Hazus may estimate that a facility has 5 percent chance of being fully functional at Day 3, and a 95-percent chance of being fully functional at Day 90. The analysis of critical facilities in the planning area was performed for the five scenario events assessed. The results are summarized in Figure 10-14 through Figure 10-17.

10.4.4 Environment
Secondary hazards associated with earthquakes will likely have damaging effects on the environment. It is possible for streams to be rerouted after an earthquake. This can change the water quality, possibly damaging habitat and feeding areas. There is a possibility of streams fed by groundwater drying up because of changes in underlying geology.

Figure 10-10. Critical Facility Damage Potential, 100-Year Probabilistic Event 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Safety and Security Food, Water and
Shelter
Medical and Health Energy Communications Transportation Probability of Experiencing Damage Level Shown,
Average of All Facilities in Category (%)
Slight Damage or Greater Moderate Damage or Greater Extensive or Complete Damage

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Figure 10-11. Critical Facility Damage Potential, Concord-Green Valley Fault Scenario (M6.8)

Figure 10-12. Critical Facility Damage Potential, Haywired Fault Scenario (M7.05) 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Safety and Security Food, Water and
Shelter
Medical and Health Energy Communications Transportation Probability of Experiencing Damage Level Shown,
Average of All Facilities in Category (%)
Slight Damage or Greater Moderate Damage or Greater Extensive or Complete Damage 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Safety and Security Food, Water and
Shelter
Medical and Health Energy Communications Transportation Probability of Experiencing Damage Level Shown,
Average of All Facilities in Category (%)
Slight Damage or Greater Moderate Damage or Greater Extensive or Complete Damage

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Figure 10-13. Critical Facility Damage Potential, Mount Diablo Fault Scenario (M6.7)

Figure 10-14. Critical Facility Functionality, 100-Year Probabilistic Event 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Safety and Security Food, Water and
Shelter
Medical and Health Energy Communications Transportation Probability of Experiencing Damage Level Shown,
Average of All Facilities in Category (%)
Slight Damage or Greater Moderate Damage or Greater Extensive or Complete Damage 0 10
20 30
40 50
60 70
80 90
100
at Day 1 at Day 3 at Day 7 at Day 14 at Day 30 at Day 90 Probability of Being Fully functional on Day Shown,
Average of All Facilities in Category (%)
Safety and Security
Food, Water and Shelter
Medical and Health
Energy
Communications
Transportation

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Figure 10-15. Critical Facility Functionality, Concord-Green Valley Fault Scenario (M6.8)

Figure 10-16. Critical Facility Functionality, Haywired Fault Scenario (M7.05) 0 10
20 30
40 50
60 70
80 90
100
at Day 1 at Day 3 at Day 7 at Day 14 at Day 30 at Day 90 Probability of Being Fully functional on Day Shown,
Average of All Facilities in Category (%)
Safety and Security
Food, Water and Shelter
Medical and Health
Energy
Communications
Transportation
0 10
20 30
40 50
60 70
80 90
100
at Day 1 at Day 3 at Day 7 at Day 14 at Day 30 at Day 90 Probability of Being Fully functional on Day Shown,
Average of All Facilities in Category (%)
Safety and Security
Food, Water and Shelter
Medical and Health
Energy
Communications
Transportation

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Figure 10-17. Critical Facility Functionality, Mount Diablo Fault Scenario (M6.7)

10.5 FUTURE TRENDS IN DEVELOPMENT
Since all of the planning area is located within earthquake hazard zones, all future development will, to some extent, be exposed to the earthquake hazard. The City of Concord will strictly enforce all seismic building codes and design standards to prevent loss of life and property from earthquakes. Public education, cooperation with the development community, and individual preparedness are essential.

The City has a General Plan with policies directing land use and dealing with issues of geologic and seismic safety.

This plan provides the capability to protect future development from the impacts of earthquakes. Deficiencies identified by development reviews can be identified as mitigation actions to increase the capability to deal with future trends in development.

10.6 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 planning area to have a significant impact on the people, property and economy of the planning area.

Any seismic activity of 6.0 or greater on faults within the planning area would have significant impacts throughout the planning area. Potential warning systems could give approximately 40 seconds notice that a major earthquake is about to occur. This would not provide adequate time for preparation. Earthquakes of this magnitude or higher would lead to massive structural failure of property on NEHRP C, D, E, and F soils. Levees and revetments built on these poor 0 10
20 30
40 50
60 70
80 90
100
at Day 1 at Day 3 at Day 7 at Day 14 at Day 30 at Day 90 Probability of Being Fully functional on Day Shown,
Average of All Facilities in Category (%)
Safety and Security
Food, Water and Shelter
Medical and Health
Energy
Communications
Transportation

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soils would likely fail, representing a loss of critical infrastructure. These events could cause secondary hazards, including landslides and mudslides that would 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.

10.7 ISSUES
Important issues associated with an earthquake include the following:
• More information is needed on the exposure and performance of soft-story construction within the planning area.
• 43 percent of the planning area’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 moderate number of facilities in the planning area are expected to have complete or extensive damage from scenario events. These facilities are prime targets for structural retrofits.
• Critical facility owner 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 take into account the probable impacts from earthquakes in the design and construction of new or enhanced facilities. • The planning area has 1,115 miles of earthen levees and revetments on soft, unstable soil. These soils are prone to liquefaction, which would severely undermine the integrity of these facilities. • 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. • Earthquakes could trigger other natural hazard events such as dam failures and landslides, which could severely impact the planning area.
• A worst-case scenario would be the occurrence of a large seismic event during a flood or high-water event.

Levee failures would happen at multiple locations, increasing the impacts of the individual events. • Residents are expected to be self-sufficient up to three days after a major earthquake without government response agencies, utilities, private-sector services, and infrastructure components. Education programs are currently in place to facilitate earthquake preparedness by individuals, families, neighborhoods, and businesses.
• After a major seismic event, Concord is likely to experience disruptions in the flow of goods and services resulting from the destruction of major transportation infrastructure across the broader region.

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11. FLOOD

11.1 GENERAL BACKGROUND
Flooding is any overflowing of water onto land that is normally dry. Floods are the most common of all weather- related natural disasters. They kill more people in the United States each year than tornados, hurricanes, or lightning (NOAA n.d.). Areas near rivers or streams are at risk from floods during heavy rain or periods of upstream snowmelt.

In urban areas, where buildings, highways, driveways, and parking lots reduce the ground’s ability to absorb rainfall, the resulting increase in runoff can overwhelm constructed storm drain systems, resulting in flooding on nearby roads and buildings.

A floodplain is the area adjacent to a river, creek or lake that becomes inundated when flooding occurs. Floodplains may be broad, as when a river crosses an extensive flat landscape, or narrow, as when a river is confined in a canyon.

These areas form a complex physical and biological system that not only supports a variety of natural resources but also provides natural flood and erosion control.

11.1.1 FEMA Regulatory Flood Zones
FEMA defines flood hazard areas through statistical analyses of records of river flow, storm tides, and rainfall; information obtained through consultation with the community; floodplain topographic surveys; and hydrologic and hydraulic analyses. Flood hazard areas are delineated on Flood Insurance Rate Maps (FIRMs), which are official maps of a community on which the Federal Insurance and Mitigation Administration has delineated special flood hazard areas (SFHAs). Digital versions of FIRMs are called DFIRMs.

The SFHA is the land area on a DFIRM covered by floodwaters of the “base flood,” which is the flood with a 1 percent chance of occurrence in any given year (also called the 1 percent annual chance flood). A structure within the SHFA (also called the 1 percent annual chance floodplain) has a 26 percent chance of undergoing flood damage during the term of a 30-year mortgage. The base flood is the regulatory standard adopted by federal agencies and most states to administer floodplain management programs. In SFHAs, National Flood Insurance Program (NFIP) floodplain management regulations must be enforced, and flood insurance is mandatory.

Common Flood Map Zones
DFIRMS show the boundaries of floodways and floodplains, as well as expected floodwater elevations at specific sites during the base flood. They define the following specific flood-related areas:
• River flood hazard zones:
➢ Zone A (also known as Unnumbered A-zones)—SFHAs where no base flood elevations or depths are shown because detailed hydraulic analyses have not been performed.

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➢ Zones A1-30 and AE—SFHAs that are subject to inundation by the base flood, determined using detailed hydraulic analysis. Base flood elevations are shown within these zones. ➢ Zone AH and AO—SFHAs subject to inundation by types of shallow flooding where average depths are between 1 and 3 feet. These are normally areas prone to ponding (Zone AH) or shallow sheet flow flooding on sloping terrain (Zone AO).
➢ Zone B and X (shaded)—Zones where the land elevation as been determined to be above the base flood elevation, but below the 500-year flood elevation. These zones are not SFHAs. ➢ Zones C and X (unshaded)—Zones where the land elevation has been determined to be above both the base flood elevation and the 500-year flood elevation. These zones are not SFHAs.

Mapping of Levee-Protected Areas
FEMA can accredit levee systems that meet federal certification requirements. Areas protected by these levees are considered to have reduced flood risk due the presence of the levee. FEMA’s mapping shows these areas as Zone X.

These are considered to be “awareness” zones that depict the “residual risk” associated with the levee systems.

Residual risk is the risk that remains after controls are accounted for. The protection level for any flood control facility is based on its design level of protection. A facility with 100-year design effectiveness loses that effectiveness for events with greater than a 100-year probability. This is residual risk.

Federal flood insurance for properties in these areas is available through the NFIP’s lower-cost Preferred Risk Policy.

While not federally required, it is strongly recommended, as there is still a risk.

11.1.2 Floodplains
Ecosystems and Beneficial Functions
Floodplains can support ecosystems that are rich in plant and animal species. Wetting of the floodplain soil releases an immediate surge of nutrients: those left over from the last flood, and those that result from the rapid decomposition of organic matter that has accumulated since then. Microscopic organisms thrive and larger species enter a rapid breeding cycle. The production of nutrients peaks and falls away quickly, but the surge of new growth endures for some time. This makes floodplains valuable for agriculture. Species growing in floodplains are markedly different from those that grow outside floodplains. For instance, riparian trees (trees that grow in floodplains) tend to be very tolerant of root disturbance and very quick growing compared to non-riparian trees.

When floodwaters recede after a flood event, they leave behind layers of rock and mud. These gradually build up to create a new floor of the floodplain. Floodplains generally contain accumulations of sand, gravel, loam, silt, and/or clay, often extending below the bed of the stream. These sediments provide a natural filtering system, with water percolating back into the ground and replenishing groundwater. These are often important aquifers, the water drawn from them being filtered compared to the water in the stream. Fertile, flat reclaimed floodplain lands are commonly used for agriculture, commerce and residential development.

Effects of Human Activities
Human activities tend to concentrate in floodplains for a number of reasons: water is readily available; land is fertile and suitable for farming; transportation by water is easily accessible; and land is flatter and easier to develop. But human activity in floodplains frequently interferes with the natural function of floodplains. When a river is separated from its floodplain with levees and other flood control facilities, natural, built-in benefits can be lost, altered, or significantly reduced. Structures can affect the distribution and timing of drainage, thereby increasing flood problems.

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Human development can create local flooding problems by altering or confining drainage channels. This increases flood potential in two ways: it reduces the stream’s capacity to contain flows, and it increases flow rates or velocities downstream during all stages of a flood event. Human activities can interface effectively with a floodplain as long as steps are taken to mitigate the activities’ adverse impacts on floodplain functions.

11.1.3 Secondary Impacts
The most problematic secondary impact for flooding is bank erosion, which in some cases can be more harmful than actual flooding. This is especially true in the upper courses of rivers with steep gradients, where floodwaters may pass quickly and without much property damage, but scour the banks, edging properties closer to the floodplain or causing them to fall in. Flooding is also responsible for hazards such as landslides when high flows over-saturate soils on steep slopes, causing them to fail. Hazardous materials spills are also a secondary impact of flooding if storage tanks rupture and spill into streams, rivers or storm drains.

Other secondary impacts of a flood include the following:
• Disruption of services:
➢ Drinking water supplies may become polluted, especially if sewage treatment plants are flooded. This may result in disease and other health effects.
➢ Gas and electrical service may be disrupted.
➢ Transportation systems may be disrupted, resulting in shortages of food and clean-up supplies. • Long-term effects (tertiary effects):
➢ Location of river channels may change as the result of flooding. New channels develop, leaving the old channels dry.
➢ Sediment deposited by flooding may destroy farm land (although silt deposited by floodwaters could also help to increase agricultural productivity).
➢ Jobs may be lost due to the disruption of services, destruction of business, etc. (although jobs may be gained in the construction industry to help rebuild or repair flood damage). ➢ Insurance rates may increase.
➢ Corruption may result from misuse of relief funds.
• Destruction of wildlife habitat.

11.2 HAZARD PROFILE

11.2.1 Types of Flooding
Flooding in Concord typically occurs during the rainy winter season. Three types of flooding primarily affect the City:
stormwater runoff, riverine, and flash floods.

Stormwater Runoff Floods
Urban drainage systems are designed to remove surface water from developed areas as quickly as possible to prevent flooding on streets and in other urban areas. These closed conveyance systems channel water away from an urban area to surrounding streams, bypassing natural processes of water filtration through the ground, containment, and evaporation of excess water. Urban drainage systems can play a role in flooding in two ways:

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• Because drainage systems reduce the amount of time surface water takes to reach surrounding streams, flooding in those streams can occur more quickly and reach greater depths than prior to development in the area (FEMA n.d.).
• If stormwater runoff exceeds the capacity of the drainage system, then stormwater runoff flooding can result throughout the system’s service area. This is especially likely when groundwater levels are high and during high tides.

Stormwater runoff flooding can occur in areas other than delineated floodplains or along recognizable channels. It generally occurs in flat areas, and generally increases with urbanization, which speeds accumulation of floodwaters because of impervious areas. Shallow street flooding can occur unless channels have been improved to account for increased flows (FEMA 2020).

Riverine Floods
Riverine flooding is overbank flooding of rivers and streams. Flooding in large river systems typically results from large-scale weather systems that generate prolonged rainfall over a wide geographic area, causing flooding in hundreds of smaller streams, which then drain into the major rivers. Two types of flood hazards are generally associated with riverine flooding:
• Inundation—Inundation occurs when floodwaters and debris flow through an area not normally covered by water. These events cause minor to severe damage, depending on velocity and depth of flows, duration of the flood event, quantity of debris carried by the flow, and amount and type of development and personal property along the floodwater’s path.
• Channel Migration—Erosion of banks and soils worn away by flowing water, combined with sediment deposition, can cause migration or lateral movement of a river channel across a floodplain. A channel can also abruptly change location (termed “avulsion”); a shift in channel location over a large distance can occur within as short a time as one flood event.

Shallow area flooding is a special type of riverine flooding. FEMA defines shallow flood hazards as areas inundated by the 100-year flood with flood depths of only 1 to 3 feet. These areas are generally flooded by low-velocity sheet flows of water.

Flash Floods
The National Weather Service defines a flash flood as a rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level. Such floods generally begin within 6 hours of the rain event that causes them. Ongoing flooding can intensify to flash flooding in cases where intense rainfall results in a rapid surge of rising floodwaters (National Weather Service 2022).

Flash floods can tear out trees, undermine buildings and bridges, and scour new channels. In urban areas, flash flooding is an increasingly serious problem due to removal of vegetation and replacement of ground cover with impermeable surfaces such as roads, driveways, and parking lots. The greatest risk from flash floods is occurrence with little to no warning. Major factors in predicting potential damage are intensity and duration of rainfall, and steepness of watershed and streams.

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11.2.2 Principal Flooding Sources
Most of Concord lies within the watersheds of Walnut Creek or Mount Diablo Creek. The following sections describe these creeks and their tributaries.

Walnut Creek Watershed (Grayson-Murderers, Concord, Pine-Galindo, San Ramon and Las Trampas Subbasins)
Walnut Creek watershed encompasses 93,556 acres in central Contra Costa County. Draining the west side of Mount Diablo and the east side of the East Bay Hills, Walnut Creek’s major tributaries include San Ramon Creek (18.89 miles), Bollinger Creek (6.72 miles), Las Trampas Creek (12.37 miles), Lafayette Creek (3.78 miles), Grayson Creek (8.87 miles), Murderer’s Creek (4.37 miles), Pine Creek (12.65 miles) and Galindo Creek (6.5 miles). Rainfall varies throughout the area in part due to the rain shadow effect of the East Bay Hills and the western slopes of Mount Diablo.

The Cities of Walnut Creek, Lafayette, Pleasant Hill and Danville lie completely within the boundaries of the watershed, and the Cities of Concord, Martinez, and small areas of Moraga and San Ramon are partly within the watershed. Rancho Monte Del Diablo, Rancho Arroyo de las Nueces y Bolbones, Rancho San Ramon, Rancho Las Juntas and Rancho Canada de Hambre all were established in the watershed in the early 1800s when agriculture and livestock played an important role. With the introduction of irrigation technologies, fruit and nut orchards started evolving in the valley. Later housing and commercial ventures along the Walnut Creek corridor resulted in an increased need for flood control. An extensive stormwater drainage system reroutes surface waters that once meandered across the valley.

Mount Diablo Creek Watershed
Mount Diablo Creek flows northwest from the Mount Diablo for 17.24 miles before reaching Suisun Bay.

Unincorporated county land accounts for 64 percent of the watershed, which also includes the cities of Clayton and Concord. The lower third of the watershed is owned and managed by the U.S. Navy. Naval Weapons Station Seal Beach (previously the Concord Naval Weapons Station) occupies approximately 13,000 acres of open, relatively unaltered floodplain.

The headwaters of Mount Diablo Creek are in Mount Diablo State Park. Major tributaries—Mitchell Creek, Back Creek and Donner Creek—also originate in the state park. The creek and its tributaries flow relatively unencumbered from the headwaters to its outlet in Suisun Bay. The creek is channeled underground through the few areas that are more developed.

11.2.3 Flood Control System
The local flood control system for Concord is managed by the Contra Costa County Flood Control and Water Conservation District, which was founded in 1951 in response to flooding and urban growth (Contra Costa Public Works 2022). The district’s flood control infrastructure consists of about 79 miles of channels, creeks, and other drainage features, along with 30 retention dams and basins. The district’s Walnut Creek Flood Control Channel passes through Concord.

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11.2.4 Federal Flood Programs
National Flood Insurance Program
The City of Concord participates in the National Flood Insurance Program (NFIP), has adopted regulations that meet the program’s requirements, and is currently in good standing with program requirements. Within the city, 242 flood insurance policies provide $72.6 million in coverage at a combined annual premium of $216,932. FEMA statistics show 66 claims have been paid on these policies, for a total of $113,713, an average of $1,723 per claim.

The City entered the NFIP in 1984; its first Flood Insurance Rate Map (FIRM) was issued July 5, 1984. Structures permitted or built in the City of Concord before then are called “pre-FIRM” structures, and structures built afterwards are called “post-FIRM.” The insurance rate is different for the two types of structures. The effective date for the current FIRM is March 21, 2017.

The Community Rating System
The City of Concord has participated in the CRS program since 2008. The City has a Class 6 rating, so policyholders who live in a 1 percent-annual-chance floodplain receive a 20-percent discount on their flood insurance; policyholders outside the 1 percent-annual-chance floodplain receive a 10-percent discount. To maintain or improve its rating, the City goes through an annual recertification and a re-verification every five years.

Repetitive Loss
A repetitive loss property is defined by FEMA as an NFIP-insured property that has experienced any of the following since 1978, regardless of any changes in ownership:
• Four or more paid losses in excess of $1,000
• Two paid losses in excess of $1,000 within any rolling 10-year period • Three or more paid losses that equal or exceed the current value of the insured property The government has instituted programs encouraging communities to identify and mitigate the causes of repetitive losses. Studies have found that many of these properties are outside any mapped 1 percent annual chance (100-year) floodplain. The key identifiers for repetitive loss properties are the existence of flood insurance policies and claims paid by the policies.

Repetitive loss records for Concord are as follows:
• Number of FEMA-identified Repetitive Loss Properties: 2 (single-family homes) • Number of FEMA-identified Severe Repetitive Loss Properties: 0 • Number of Repetitive Loss Properties or Severe Repetitive Loss Properties that have been mitigated:

Unknown
The CRS requires participating communities to identify repetitive loss areas. A repetitive loss area is the portion of a floodplain holding structures that FEMA has identified as meeting the definition of repetitive loss. Identifying repetitive loss areas helps to identify structures that are at risk but are not on FEMA’s list of repetitive loss structures because no flood insurance policy was in force at the time of loss. The most recent information for Concord is provided in the Annual Report on Floodplain Management Components Regarding Repetitive Loss Properties Within the City of Concord (Marstall 2022).

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11.2.5 Past Events
Table 11-1 summarizes flood events in the planning area since 1969. Since 1969, 13 presidential-declared flood events in the planning area have caused in excess of $60 million in property and crop damage. The major floods in the City have resulted from intense rainstorms between November and March.

Table 11-1. History of Flood Events
Date
Declaration
# Type of event Estimated Damage/Event Description
01/14/2023 DR-4683-CA Severe winter storms Flooding
10/24/2021 N/A Flood, heavy rain N/A
01/16/2020 N/A Flood, heavy rain Widespread roadway flooding, downed trees 12/07/2019 N/A Flood, heavy rain Heavy rain, flooding, downed power lines 11/26/2019 N/A Flood, heavy rain Roadway flooding
03/06/2019 N/A Flood, heavy rain Roadway flooding
02/26/2019 N/A Flood, heavy rain Minor roadway flooding 02/13/2019 N/A Flood, heavy rain Atmospheric river, flooding, power outages 02/09/2019 N/A Flood, heavy rain Minor roadway flooding 11/23/2018 N/A Flood, heavy rain Minor debris flows and roadway flooding 03/01/2018 N/A Flood, heavy rain Roadway flooding
01/08/2018 N/A Flood, heavy rain Minor roadway flooding 04/01/2017 DR-4308 Severe winter storms, flooding,
mudslides
N/A
03/16/2017 DR-4305 Severe winter storms, flooding,
mudslides
N/A
02/20/2017 N/A Flood, heavy rain Widespread flooding, overtopping of reservoir spillways 02/07/2017 N/A Flood, heavy rain Atmospheric river, widespread roadway flooding 01/10/2017 N/A Flood, heavy rain N/A
02/14/2014 DR-4301 Severe storms, flooding, mudslides N/A 04/11/2010 N/A Heavy rain Heavy rains led to a car crash with a vehicle upside down in the rain-swollen San Ramon Creek in Walnut Creek.

There were two fatalities.
1/01/2006 DR 1628 Severe storms, flooding, mudslides,
landslides
$22,000,000 property/$8,710,359 crop
12/14/2002 N/A Flood N/A
2/09/1998 DR 1203 Severe winter storms and flooding N/A 2/07/1998 N/A Flood (flash flood) N/A
2/03/1998 N/A Flood (flash flood) N/A
1/22/1997 N/A Flood (flash flood) N/A
1/02/1997 DR 1155 Severe storms, flood N/A
3/12/1995 DR 1046 Flood $11.2 million
1/25/1995 N/A Flood (flash flood) N/A
1/22/1995 N/A Flood (flash flood) N/A
1/10/1995 DR 1044 Severe winter storms, flooding,
landslides, mud flows

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Date
Declaration
# Type of event Estimated Damage/Event Description
1/13/1993 DR 979 Flood (flash flood) $5.5 million property/crop 2/17/1986 DR 758 Flood (flash flood) $5,000,000 property 2/09/1983 DR 677 Flood, severe weather $384,165 property 1/03/1982 DR 651 Flood, severe weather $7,142,857 property 1/18/1969 DR 253 Flood, severe storm/thunder $862,068 property N/A = Information is not available
Sources: Federal Emergency Management Agency, 2022; National Centers for Environmental Information, 2022

11.2.6 Location
The flooding that has occurred in portions of the City has been extensively documented by gage records, high water marks, damage surveys and personal accounts. Concord falls under the countywide Flood Insurance Study and DFIRM effective March 21, 2017, which is the sole source of data used in this risk assessment to map the extent and location of the flood hazard, as shown in Figure 11-1.

11.2.7 Frequency
Recurrence intervals and average annual numbers of events in the planning area were calculated based on data from 2001 to 2021 in NOAA’s Storm Events Database. Concord and neighboring communities have experienced 20 significant events since 2001 classified as flood in the database. Smaller floods may occur more frequently and be categorized as a different event type, typically “flash flood” or “heavy rain.” Based on these data, floods and flash floods have a 90 percent chance of occurring in any given year and heavy rain events have a 71 percent chance.

Generally, flooding will likely continue to be an annual hazard.

11.2.8 Severity
The principal factors affecting flood damage are flood depth and velocity. The deeper and faster flood flows become, the more damage they can cause. Shallow flooding with high velocities can cause as much damage as deep flooding with slow velocity. This is especially true when a channel migrates over a broad floodplain, redirecting high velocity flows and transporting debris and sediment.

Although jurisdictions can implement mitigation and take preventative actions to significantly reduce severity and threat of flood events, some residual risk will always exist (i.e., risk of a hazard event occurring despite technical and scientific measures applied to reduce/prevent it). Threats associated with residual risk could include failure of a reservoir, a dam breach, or other infrastructure failure, or a severe flood event that exceeds flood design standards or drainage capacity.

Flood severity is often evaluated by examining peak discharges; Table 11-2 lists peak flows used by FEMA’s Flood Insurance Study, revised March 21, 2017, to map the floodplains of the planning area.

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UV242
UV4
UV4
§¨¦680
Treat Blvd
Clayton Rd
Willow Pass Rd
Kirker Pass RdMonument Blvd
Oak Grove Rd
Port Chicago Hwy
Cowell Rd
Galindo St
Concord Blvd
Ygnacio Valley Rd
Mallard
Reservoir
Concord

SPECIAL FLOOD HAZARD AREAS
Data Sources:

FEMA Digital Flood Insurance Rate Map
CIty of Concord
Flood Zone
1 PCT Annual Chance Flood Hazard

0.2 PCT Annual Chance Flood Hazard
0 1 2
Miles
4 Figure 11-1

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Table 11-2. Summary of Peak Discharges Within the Planning Area Drainage Discharge (cubic feet/second)
Source/Location Area (sq. mi.) 10-Year 50-Year 100-Year 500-Year Clayton Valley Drain
1,135 feet upstream of Salvio Street 2.10 480 790 930 1,200 At confluence with Walnut Creek 4.40 1,200 1,800 2,100 2,400 Ditch No. 2
At Bart Culvert 2.10 900 1,300 1,450 1,650
At confluence with Pine Creek 3.30 1,100 1,500 1,700 2,000 Farm Bureau Road Drain
At confluence with Contra Costa Canal 1.40 290 510 510 800 Galindo Creek
Approximately 2,500 feet downstream of Newhall
Parkway

4.73 1,200 1,790 1,990 2,400
At Contra Costa Canal 7.73 1,580 2,330 2,570 3,100
At Cowell Road 6.33 1,400 2,050 2,270 2,740
At Newhall Parkway 3.56 900 1,360 1,510 1,830
At San Miguel Road 8.00 1,580 2,330 2,570 3,100
At Treat Boulevard 5.52 1,290 1,930 2,140 2,590
Mount Diablo Creek
Downstream of Bailey Road 21.83 3,670 5,670 6,350 7,760 Pine Creek
At confluence with Contra Costa Canal 13.80 980 2,200 2,800 4,400 At confluence with Walnut Creek 29.10 3,200 6,00 7,300 10,000 At Monument Boulevard 19.40 1,700 3,400 4,300 6,400
Walnut Creek
At corporate limits at State Highway 4 (Arnold
Industrial Highway)
117.30 9,520 18,000 22,300 31,000
At Walnut Creek Stream Gage (upstream of
Concord)

77.20 9,520 17,700 22,000 30,600
Source: (FEMA 2017)

11.2.9 Warning Time
The time it takes to recognize a flooding threat reduces the potential warning time that a community has to take actions to protect lives and property. Due to the sequential pattern of meteorological conditions needed to cause serious flooding, it is unusual for a flood to occur without warning. Warning times for floods can be between 24 and 48 hours. Flash flooding can be less predictable, but potential hazard areas can be warned in advanced of potential flash flooding danger.

Wireless Emergency Alerts from the NWS are notices about potentially hazardous weather that are sent out to all compatible cell phones in affected areas. All of this information is analyzed to evaluate the flood threat and possible evacuation needs. The NWS issues watches, and warnings as follows when forecasts indicate rivers may approach bank-full levels:

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• Minor Flooding—Minimal or no property damage, but possibly some public threat or inconvenience. • Moderate Flooding—Some inundation of structures and roads near streams. Some evacuations of people and/or transfer of property to higher elevations are necessary. • Major Flooding—Extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.

When a watch is issued, the public should prepare for the possibility of a flood. When a warning is issued, the public is advised to stay tuned to a local radio station for further information and be prepared to take quick action if needed.

A warning means a flood is imminent, generally within 12 hours, or is occurring. Local media broadcast NWS warnings.

Flooding is more likely to occur due to a rainstorm when the soil is already wet and/or streams are already running high from recent previous rains (conditions already in place when a storm begins are called “antecedent conditions”).

Contra Costa County Flood Control and Water Conservation District maintains a flood warning system that is tied to monitoring rainfall amounts during storms as well as current antecedent conditions at multiple rain gauges throughout Contra Costa County. Critical antecedent conditions for flood warning are defined as follows:
• 7 inches of rain for the season.
• 5 inches of rain in the last 30 days.
• 3 inches of rain in the last 7 days.

If any of these conditions have been met and 2 inches of rainfall is forecast in the next 24 hours, then flooding is likely in the next 24 hours. This information has been provided to the public via the Contra Costa County Flood Control and Water Conservation District’s “7-5-3-2” outreach campaign (Contra Costa Public Works 2022a).

11.3 EXPOSURE
FEMA mapping of the 1 percent annual chance and 0.2 percent annual chance floods was used to perform the exposure analysis. Summary findings of the risk assessment, showing exposure results for the entire planning area, are provided in the sections below. Appendix D shows results broken down by Council voting district.

11.3.1 Population and Property
Table 11-3 summarizes the estimated population living in the evaluated flood hazard areas and the estimated property exposure. The distribution of exposed structures by use category is shown in Figure 11-2 and Figure 11-3.

11.3.2 Critical Facilities
Figure 11-4 summarizes the number of critical facilities in each mapped flood zone, by category. Figure 11-5 shows the exposed facilities in each flood zone and category as a percent of the planning area total number of facilities in that category.

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Table 11-3. Exposed Population and Property in Evaluated Flood Hazard Zones 1% Annual Chance Flood Zone 0.2% Annual Chance Flood Zone Population
Population Exposed 1,602 4,944
% of Total Planning Area Population 1.3% 3.9%
Property
Acres of Inundation Area 848 1,982
Number of Buildings Exposed 583 1,704
Value of Exposed Structures $652,626,315 $1,618,776,719 Value of Exposed Contents $647,313,980 $1,474,988,144
Total Exposed Property Value $1,299,940,296 $3,093,764,863 Total Exposed Value as % of Planning Area Total 3.7% 8.8%

Figure 11-2. Exposed Structures in 1% Annual Chance Flood Zone by Occupancy Class
Figure 11-3. Exposed Structures in 0.2% Annual Chance Flood Zone by Occupancy Class

Residential
498

85.4%
Commercial
24 4.1%
Industrial
18 3.1%
Agriculture
0 0.0%
Religion
4 0.7%
Government
38 6.5%
Education
1 0.2%
Residential
1,548

90.8%
Commercial
41 2.4%
Industrial
59 3.5%
Agriculture
0 0.0%
Religion
4 0.2%
Government
46 2.7%
Education
6 0.4%

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Figure 11-4. Number of Critical Facilities in Mapped Flood Hazard Areas

Figure 11-5. Critical Facilities in Mapped Flood Hazard Areas as % of Total in Category 0 1 1
0 0 0
10 0
7 1
0 1
3 16
0 10
20 Communication Energy Food, Water,
Shelter
Hazardous
Materials
Medical and HealthSafety and Security Transportation
Number of Facilties in Hazard Area
1% Annual Chance Flood

0.2% Annual Chance Flood
0% 1%
9%
0% 0% 0%
14%
0%
7% 9%
0%
6% 6%
23%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Communication Energy Food, Water,
Shelter
Hazardous
Materials
Medical and Health Safety and
Security
Transportation
Exposed Facilities as % of Total Number in Category
1% Annual Chance Flood

0.2% Annual Chance Flood

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Flooding can significantly impact roads and bridges, which provide the only ingress and egress to some areas. The following major roads in the planning area pass through the 1 percent-annual-chance floodplain and thus are exposed to flooding:
• Babel Lane
• Bailey Road
• California Delta Hwy (State Route 4)
• Clayton Road
• Concord Blvd.
• Cowell Road
• Kinne Blvd.
• Kirker Pass road
• Monument Blvd.
• Port Chicago Highway
• San Miguel Road
• Solano Way
• State Route 242
• Treat Blvd.
• Willow Pass Road
Some of these roads are built above the flood level, and others function as levees to prevent flooding. Still, in severe flood events these roads can be blocked or damaged, preventing access to some areas.

11.3.3 Environment
Parks and open spaces are considered to be wise uses within designated flood hazards areas. The following parks and open spaces are partially or completely within the 1 percent-annual-chance floodplain:
• Diablo Creek Golf Course
• Hillcrest Community Park
• Willow Pass Community Park
• Concord Community Park
• Newhall Community Park

11.4 VULNERABILITY
Summary findings of the risk assessment for flood, showing vulnerability results for the entire planning area, are provided below. Appendix D shows results broken down by Council voting district.

11.4.1 Population
Impacts on Persons and Households
Flood impacts on persons and households were estimated for each event through the Level 2 Hazus analysis.

Table 11-4 summarizes the results.

Table 11-4. Estimated Flood Impacts on Households and Residents 1% Annual Chance Flood Zone 0.2% Annual Chance Flood Zone Displaced Population 18 38
Number of Residents Requiring Short-Term Shelter 4 6
Vulnerable Populations
A geographic analysis of demographics using the SVI mapping described in Section 4.6.2 estimated the following:

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• 8.9 percent of the population living in Census tracts that intersect the 1 percent-annual-chance floodplain are in a high vulnerability area.
• 7.5 percent of the population living in Census tracts that intersect the 0.2 percent-annual-chance floodplain are in a high vulnerability area.

11.4.2 Property
Hazus calculates losses to structures from flooding by looking at depth of flooding and type of structure. Table 11-5 summarizes Hazus estimates of flood damage in the planning area. The debris estimate includes only structural debris and building finishes; it does not include additional debris that may result from a flood event, such as from trees, sediment, building contents, bridges, or utility lines.

Table 11-5. Estimated Impact of a Flood Event in the Planning Area 1% Annual Chance Flood Zone 0.2% Annual Chance Flood Zone Number of Structures Impacted 360 745
Estimated Loss
Structures $79,270,684 $98,889,018
Contents $147,080,022 $184,173,556
Total $226,350,706 $283,062,574
% of Total Planning Area Replacement Value 0.6% 0.8%
Debris to Be Removed 5,385 tons 6,159 tons

11.4.3 Critical Facilities
Significant Facilities Affected
Significant critical facilities predicted by Hazus to be affected by the 1 percent-annual-chance flood include one wastewater pump station, one electric substation, and seven bridges.

Estimated Damage
Hazus was used to estimate the number of critical facilities affected by flooding and the resulting percent of damage to the building and contents. Figure 11-6 compares the predicted number of affected facilities to the number of exposed facilities, for the 1 percent and 0.2 percent-annual chance flood events. Key results are as follows:
• For the 1 percent-annual-chance-event all exposed critical facilities would be affected except for three out of the 10 exposed transportation facilities
• For the 0.2 percent-annual-chance-event all exposed critical facilities would be affected except for six out of the seven exposed energy facilities and nine out of the 16 exposed transportation facilities Figure 11-7 shows the estimated damage to critical facilities for both modeled flood events. For the 1 percent-annual- chance-event, the average amount of damage to structures, measured as a percentage of total value, ranges from 1.2 to

26.8 percent of total value and average damage to contents ranges from 9.0 to 53.2 percent, depending on critical facility category.

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Figure 11-6. Critical Facilities Affected by the 1% and 0.2% Annual Chance Floods

Figure 11-7. Average Damage to Critical Facilities from 1% and 0.2% Annual Chance Floods 0 0
1 7
1 1
0 0 0
1 0
3 10
16 0 0
1 1 1 1
0 0 0
1 0
3 7 7
0 2
4 6
8 10
12 14
16 18
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
Communications Energy Food, Water &
Shelter
Hazardous
Material
Health & Medical Safety & Security Transportation
Number of Faciliities Exposed or Affected
Exposed Facilities
Affected Facilities
0 0
9 11
27 28
0 0 0
3 0 2 1 3
0 0
9 11
53 55
0 0 0
3 0 2 0 0
0 10
20 30
40 50
60 1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
1% Ann.

Chance

0.2%
Ann.

Chance
Communications Energy Food, Water &
Shelter
Hazardous
Material
Health & Medical Safety & Security Transportation
Average % of Damage Due to Flood
Structure Damage
Contents Damage

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City of Concord Hazard Mitigation Plan Flood
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11.4.4 Environment
Flooding is a natural event, and floodplains provide many natural and beneficial functions. Nonetheless, flooding can impact the environment in negative ways.
• Fish can wash into roads or over dikes into flooded fields, with no possibility of escape. • Pollution from roads, such as oil, and hazardous materials can wash into rivers and streams. During floods, these can settle onto normally dry soils, polluting them for agricultural uses. • Human development such as bridge abutments and levees can increase stream bank erosion, causing rivers and streams to migrate into non-natural courses.
• Flooding may disrupt normal drainage systems in cities and can overwhelm sewer systems, causing raw sewage to spill into the flooded area.
• Severe flooding can destroy buildings that may contain toxic materials (paints, pesticides, gasoline, etc.) releasing these materials into the local environment.

Loss estimation platforms such as Hazus are not currently equipped to measure environmental impacts of flood hazards. The best gauge of vulnerability of the environment would be a review of damage from past flood events.

Loss data that segregates damage to the environment was not available at the time of this plan. Capturing this data from future events could be beneficial in measuring the vulnerability of the environment for future updates.

11.5 FUTURE TRENDS
According to the California Department of Finance, the population of Concord is expected to increase over the next 40 years. The City of Concord has potential for expansion through annexation of unincorporated areas and through redevelopment, which creates an opportunity to correct past land use decisions, especially with regards to development within floodplains.

The City will be well-equipped to manage growth in floodplains with its flood damage prevention ordinance, its building code, and the safety element of its General Plan. Proper application of these tools requires accurate hazard mapping. It is the conclusion of this planning effort that currently effective flood hazard mapping accurately reflects the flood risk for the City of Concord. This should be taken into account as future land use decisions are made for areas impacted by flooding.

11.6 SCENARIO
Floods have regularly affected the planning area. The planning area can expect heavy rains and flash flooding about once a year, with flood events every 2 to 3 years. Duration and intensity of heavy winter rains and atmospheric river events that cause flooding may increase due to climate change. The floodplains mapped and identified for the planning area will continue to take the brunt of these floods.

Contra Costa County residents prepare themselves for flooding by seeking and receiving information on flood forecasting (7-5-3-2 Flood), and by making personal evacuation plans. Impacts of flood events should decrease as the City of Concord continues to promote and implement hazard mitigation and preparedness.

The worst-case scenario would be a series of heavy rains events. The rains could flood numerous areas within a short time. This could overwhelm the response and floodplain management capability within the planning area, as the

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planning area would be subject immediately to flash flooding, with subsequent influences on the City’s streams. Major roads could be blocked, preventing critical access for many residents and critical functions. High in-channel flows could cause water courses to scour, possibly washing out roads and creating more isolation problems.

11.7 ISSUES
The planning team has identified the following flood-related issues relevant to the planning area:
• The stormwater/urban drainage flooding risk is not mapped, which makes it difficult to assess this hazard, other than looking at historical loss data.
• Planning tools whose use depends on flood hazard mapping are less effective due to the deficiencies in the currently available mapping.
• There needs to be a sustained effort to gather historical damage data, such as high water marks on structures and damage reports, to measure the cost-effectiveness of future mitigation projects. • Ongoing flood hazard mitigation will require funding from multiple sources. • There needs to be a coordinated hazard mitigation effort between jurisdictions affected by flood hazards across the city.
• Floodplain residents need to continue to be educated about flood preparedness and the resources available during and after floods.
• A lack of concern regarding flood risk by property owners can translate to the lack of political will to make changes.
• The potential impact of climate change on flood conditions needs to be better understood. • The capability for flood threat recognition and warning needs to be enhanced. • Flood warning capability should be tied to flood phases. • There needs to be enhanced modeling to better understand the true flood risk. • Floodplain restoration/reconnection opportunities should be identified as a means to reduce flood risk. • Post-flood disaster response and recovery actions need to be solidified. • Staff capacity is required to maintain the City’s existing level of floodplain management. • Floodplain management actions require interagency coordination. • With the large percentage of pre-FIRM flood insurance policies in force, the City can expect to see significant increases in the costs of flood insurance within the City. This will create challenges in the promotion of flood insurance.
• Open spaces (infiltration) have decreased substantially, with no plans to reverse this trend. More impervious surface leads to more runoff.

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12-1

12. LANDSLIDE

12.1 GENERAL BACKGROUND

12.1.1 Landslide Types
According to the USGS, the term landslide includes a wide range of ground movements. Landslides are commonly categorized by the type of initial ground failure, the material carried, or the nature of the movement. They include the following (see Figure 12-1):
• Block slides—Blocks of rock that slide along a slip plane as a unit down a slope. • Creep—A slow-moving landslide often only noticed through crooked trees and disturbed structures. • Debris avalanche—A debris flow that travels faster than about 10 miles per hour (mph). Speeds in excess of 20 mph are not uncommon, and speeds in excess of 100 mph, although rare, can occur. The slurry can travel miles from its source, growing as it descends, picking up trees, boulders, cars, and anything else in its path. • Earth flows—Fine-grained sediments that flow downhill and typically form a fan structure. • Mudslides or Debris Flows—Rivers of rock, earth, organic matter and other soil materials saturated with water. They develop in the soil overlying bedrock on sloping surfaces when water rapidly accumulates in the ground, such as during heavy rainfall or rapid snowmelt. • Rock falls—Blocks of rock that fall away from a bedrock unit without a rotational component. • Rock topples—Blocks of rock that fall away from a bedrock unit with a rotational component. • Rotational slumps—Blocks of fine-grained sediment that rotate and move down slope. • Transitional slides—Sediments that move along a flat surface without a rotational component.

12.1.2 Landslide Risk Areas
Landslides are typically a function of soil type and steepness of slope. Soil type is a key indicator for landslide potential and is used by geologist and geotechnical engineers to determine soil stability for construction standards.

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Source: (U.S. Geological Survey 2006)

Figure 12-1. Common Landslide Types

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In general, landslide hazard areas are where the land has characteristics that contribute to the risk of the downhill movement of material, such as the following:
• A slope greater than 33 percent
• Post-wildfire areas
• A history of landslide activity or movement during the last 10,000 years • Stream or wave activity, which has caused erosion, undercut a bank or cut into a bank to cause the surrounding land to be unstable
• The presence or potential for snow avalanches
• The presence of an alluvial fan, indicating vulnerability to the flow of debris or sediments • The presence of impermeable soils, such as silt or clay, mixed with granular soils, such as sand or gravel.

The best predictor of where slides might occur is the location of past movements. Past landslides can be recognized by their distinctive topographic shapes, which can remain in place for thousands of years. Most landslides recognizable in this fashion range from a few acres to several square miles. Most show no evidence of recent movement and are not currently active. A small proportion of them may become active in any given year, with movements concentrated within all or part of the landslide masses or around their edges. The recognition of ancient dormant landslide sites is important in the identification of areas susceptible to flows and slides because they can be reactivated by earthquakes or by exceptionally wet weather. Also, because they consist of broken materials and frequently involve disruption of groundwater flow, these dormant sites are vulnerable to construction-triggered sliding.

12.1.3 Landslide Causes
Landslides are caused by a combination of geological and climate conditions and the influence of urbanization. They can be initiated by storms, earthquakes, fires, volcanic eruptions, or human modification of the land. Vulnerable natural conditions are affected by human development and the infrastructure that supports it. In some cases, irrigation increases the landslide potential. The following factors can contribute to slide formation:
• Change in slope of the terrain
• Increased load on the land
• Shocks and vibrations
• Change in water content
• Groundwater movement
• Frost action
• Weathering of rocks
• Removing or changing the type of vegetation covering slopes.

While small landslides are frequently a result of human activity, the largest landslides are often naturally occurring phenomena with little or no human contribution.

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12.1.4 Secondary Impacts
Landslides can cause secondary impacts such as blocking roads, which can isolate residents and businesses and delay commercial, public and private transportation. Other potential problems can result from landslides if vegetation or poles on slopes are knocked over, causing losses to power and communication lines. Landslides also have the potential of destabilizing the foundation of structures, which may result in monetary loss for residents. They can damage rivers or streams, potentially harming water quality, fisheries and spawning habitat.

12.2 HAZARD PROFILE

12.2.1 Past Events
Table 12-1 lists landslide events that impacted the planning area between 1993 and 2022.

12.2.2 Location
The California Geological Survey developed statewide mapping of landslide susceptibility using a combination of regional rock strength and slope data to define classes of susceptibility. The methodology assumed that landslide susceptibility is low on very low slopes in all rock materials and increases with slope and in weak rocks. The analysis also factored in locations of past landslides. Landslide hazard areas are shown in Figure 12-2.

12.2.3 Frequency
Landslides are often triggered by other natural hazards such as earthquakes, heavy rain, floods or wildfires, so landslide frequency is often related to the frequency of these other hazards. In the planning area, landslides typically occur during and after severe storms, so the potential for landslides largely coincides with the potential for sequential severe storms that saturate steep and vulnerable soils.

Based on historical events listed in Table 12-1, the planning area and nearby vicinity have been impacted by severe storms resulting in 10 landslides or mudslides over the past 30 years, representing an annual probability of about 33 percent. The probability of future occurrence can be considered equal to this 33 percent annual probability. Until better data is generated specifically for landslide hazards, the severe storm frequency is appropriate for the purpose of ranking risk associated with the landslide hazard.

12.2.4 Severity
Landslides destroy property and infrastructure and can take human lives. Slope failures in the United States result in about 25 to 50 deaths per year and damages costing over $1 billion (U.S. Geological Survey n.d.). Landslides can pose a serious hazard to properties on or below hillsides. When landslides occur — in response to such changes as increased water content, earthquake shaking, addition of load, or removal of downslope support — they deform and tilt the ground surface. The result can be destruction of foundations, offset of roads, breaking of underground pipes, or overriding of downslope property and structures. In Contra Costa County, landslides and mudslides are a common occurrence and have caused damage to homes, public facilities, roads, parks, and sewer lines in particular.

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Table 12-1. Landslide Events Near the City of Concord
Dates of
Event Event Type
FEMA
Disaster # Location Losses/Impacts
2/14/2019 Mudslide N/A Near
Concord
A mudslide on Bailey Road between Concord and the
Keller Canyon Landfill closed the thoroughfare in both
directions.
2/27 to
3/4/2017
Mudslide N/A Near
Concord and
Brentwood
A slow moving mudslide closed the 3100 block of
Morgan Territory Road from Concord to Brentwood and
Livermore. It caused Contra Costa Water District’s
waterline to break, which affected about 90 customers.
1/03 to
1/12/2017
Severe storms,
flooding, and
mudslides
4301 34 counties Trees and landslides covered roadways throughout the Bay Area.
2011 Winter storm N/A Local Central Contra Costa Sanitary District reported landslides and damage to sewer pipes.
12/17/2005
to 1/3/2006
Severe storms,
flooding, mudslides,
and landslides
1628 30 counties A series of rainstorm events caused significant runoff, with localized evacuations, some slope failures, and road closures throughout the declared counties. Urban
flooding initiated landslides that contributed to the
damage. Much of the damage was in Walnut Creek,
Richmond, San Pablo, Martinez and Orinda. Damaged
facilities included schools, park areas and several
government agency structures.
2/13 to
2/14/2000
Flash flood N/A Countywide Widespread rain occurred over 24 hours with accumulations of more than 5 inches. Several homes in
Daly City had to be abandoned due to mudslides and
consecutive years of above average rainfall.
2/02 to
4/30/1998
Severe winter storms
and El Nino rainstorm
1203 San
Francisco
Bay region
Widespread flooding occurred that caused landslides in
Contra Costa County.
12/28/1996
to 4/01/1997
Severe storms,
flooding, mud,
landslides
1155 47 counties Minor landslide damage in Contra Costa County was attributed to heavy rains and saturated soils.
2/13 to
4/19/1995
Severe winter storms,
flooding, landslides,
mud flows
1046 San
Francisco
Bay area
Minor landslide damage in Contra Costa County was
attributed to heavy rains and saturated soils.
1/03 to
2/10/1995
Severe winter storms,
flooding, landslides,
mud flows
1044 San
Francisco
Bay area
Minor landslide damage in Contra Costa County was
attributed to heavy rains and saturated soils.
1/05 to
3/20/1993
Severe winter storm,
mud and landslides,
flooding
979 27 counties Minor landslide damage in Contra Costa County was attributed to heavy rains and saturated soils.

Sources: Federal Emergency Management Agency 2022; National Centers for Environmental Information 2022; (SFGATE 2019)

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UV242
UV4
UV4
§¨¦680
Treat Blvd
Clayton Rd
Willow Pass Rd
Kirker Pass RdMonument Blvd
Oak Grove Rd
Port Chicago Hwy
Cowell Rd
Galindo St
Concord Blvd
Ygnacio Valley Rd
Mallard
Reservoir
Concord

LANDSLIDE SUSCEPTIBILITY
Data Sources:

CA Geologic Survey
CIty of Concord
0 1 2
Miles
4 Moderate
High
Very High
Figure 12-2

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12.2.5 Warning Time
Landslide velocity can range from inches per year to many feet per second, depending on slope angle, material and water content. Generally accepted warning signs for landslide activity include the following:
• Springs, seeps, or saturated ground in areas that have not typically been wet before • New cracks or unusual bulges in the ground, street pavements or sidewalks • Soil moving away from foundations
• Ancillary structures such as decks and patios tilting and/or moving relative to the main house • Tilting or cracking of concrete floors and foundations • Broken water lines and other underground utilities
• Leaning telephone poles, trees, retaining walls or fences • Offset fence lines
• Sunken or down-dropped roadbeds
• Rapid increase in creek water levels, possibly accompanied by increased soil content • Sudden decrease in creek water levels though rain is still falling or recently stopped • Sticking doors and windows or visible open spaces indicating jambs and frames out of plumb • A faint rumbling sound that increases in volume as the landslide nears • Unusual sounds, such as trees cracking or boulders knocking together.

It is possible to determine areas at risk during general time periods based on geology, vegetation, and amount of predicted precipitation for an area. However, there is no practical warning system for individual landslides. The current procedure is to monitor situations on a case-by-case basis and respond after the event has occurred.

12.3 EXPOSURE
Mapping of the moderate, high, and very high risk landslide hazard areas was used to perform the exposure analysis.

Summary findings of the risk assessment, showing exposure results for the entire planning area, are provided in the sections below. Appendix D shows results broken down by Council voting district.

12.3.1 Population and Property
Table 12-2 summarizes the estimated population living in the landslide hazard areas and the estimated property exposure. The distribution of exposed structures by use category is shown in Figure 12-3 and Figure 12-4 for the moderate and high landslide risk zones, respectively; no chart is shown for the very high landslide risk zone; the nine buildings in that zone are all residential.

12.3.2 Critical Facilities
The risk assessment identified six critical facilities in the high-risk landslide zone, all of them transportation facilities.

This represents 8.7 percent of all transportation critical facilities in the planning area, and 2.4 percent of planning area critical facilities of all types.

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Table 12-2. Exposed Population and Property in Mapped Landslide Risk Zones Moderate Landslide Risk High Landslide Risk Very High Landslide Risk Population
Population Exposed 4,902 2,906 29
% of Total Planning Area Population 3.9% 2.3% 0.0%
Property
Number of Buildings Exposed 1,603 937 9
Value of Exposed Structures $933,493,064 $583,664,418 $3,165,104 Value of Exposed Contents $782,398,391 $448,327,635 $1,582,552 Total Exposed Property Value $1,715,891,455 $1,031,992,053 $4,747,656 Total Value as % of Planning Area Total 4.9% 2.9% 0.0%

Figure 12-3. Exposed Structures in Moderate Landslide Risk Area by Occupancy Class
Figure 12-4. Exposed Structures in High Landslide Risk Area by Occupancy Class

12.3.3 Environment
All natural areas within the mapped landslide hazard zones are considered to be exposed to the hazard.

12.4 VULNERABILITY
Summary findings of the risk assessment for landslide, showing vulnerability results for the entire planning area, are provided below. Appendix D shows results broken down by Council voting district.

12.4.1 Population
All people exposed to the landslide hazard are potentially vulnerable to landslide impacts. Populations with access and functional needs as well as elderly populations and the very young are more vulnerable to the landslide hazards as they may not be able to evacuate quickly enough to avoid the impacts of a landslide. A geographic analysis of demographics using the SVI mapping described in Section 4.6.2 estimated the following:
• 0.6 percent of the population living in Census tracts that intersect the moderate-risk landslide area are in a high vulnerability area.

Residential
1,535

95.8%
Commercial
10 0.6%
Industrial
29 1.8%
Agriculture
0 0.0%
Religion
0 0.0%
Government
25 1.6%
Education
4 0.2%
Residential
894

95.4%
Commercial
18 1.9%
Industrial
3 0.3%
Agriculture
0 0.0%
Religion
4 0.4%
Government
17 1.8%
Education
1 0.1%

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• 16 percent of the population living in Census tracts that intersect the high-risk landslide area are in a high vulnerability area.
• 18 percent of the population living in Census tracts that intersect the very-high-risk landslide area are in a high vulnerability area.

12.4.2 Property
Loss estimations for the landslide hazard are not based on modeling utilizing damage functions, because no such damage functions have been generated. 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 12-3 shows the aggregate general building stock loss estimates from the Very High and High landslide risk areas.

Table 12-3. Loss Potential for Landslide (Aggregate from Very High and High Risk Area Exposure) Total Building Value Exposed (Structure and contents in $) $820,783,000 10% of Total Building Value $82,078,000
30% of Total Building Value $246,235,000
50% of Total Building Value $410,392,000

12.4.3 Critical Facilities
There are six critical facilities exposed to the landslide hazard in the moderate to very high risk areas. A more in-depth analysis of the mitigation measures taken by these facilities to prevent damage from mass movements should be done to determine if they could withstand impacts of a mass movement. At this time all infrastructure and transportation corridors identified as exposed to the landslide hazard are considered vulnerable until more information becomes available.

12.4.4 Environment
Environmental problems as a result of mass movements can be numerous. Landslides that fall into streams may significantly impact fish and wildlife habitat, as well as affecting water quality. Hillsides that provide wildlife habitat can be lost for prolong periods of time due to landslides.

12.5 FUTURE TRENDS IN DEVELOPMENT
The planning area has experienced moderate growth over the past twenty years, averaging a 0.31 percent increase in population each year between 2000 and 2020.

The City of Concord is equipped to handle future growth within landslide hazard areas. The City’s General Plan addresses landslide risk areas in its Safety Element. The City has committed to linking its General Plan to this hazard mitigation plan update. This will create an opportunity for wise land use decisions as future growth impacts landslide hazard areas.

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The State of California has adopted the International Building Code (IBC) by reference in its California Building Standards Code. The IBC includes provisions for geotechnical analyses in steep slope areas that have soil types considered susceptible to landslide hazards. These provisions ensure that new construction is built to standards that reduce the vulnerability to landslide risk.

12.6 SCENARIO
Major landslides in Contra Costa County occur as a result of soil conditions that have been affected by severe storms, groundwater or human development. The worst-case scenario for landslide hazards in the planning area would generally correspond to a severe storm that had heavy rain and caused flooding. Landslides are most likely during late winter when the water table is high. After heavy rains from November to December, soils become saturated with water. As water seeps downward through upper soils that may consist of permeable sands and gravels and accumulates on impermeable silt, it will cause weakness and destabilization in the slope. A short intense storm could cause saturated soil to move, resulting in landslides. As rains continue, the groundwater table rises, adding to the weakening of the slope. Gravity, poor drainage, a rising groundwater table and poor soil exacerbate hazardous conditions.

Mass movements are becoming more of a concern as development moves outside of city centers and into areas less developed in terms of infrastructure. Most mass movements would be isolated events affecting specific areas. It is probable that private and public property, including infrastructure, will be affected. Mass movements could affect bridges that pass over landslide prone ravines and knock out rail service through the county. Road obstructions caused by mass movements would create isolation problems for residents and businesses in sparsely developed areas.

Property owners exposed to steep slopes may suffer damage to property or structures. Landslides carrying vegetation such as shrubs and trees may cause a break in utility lines, cutting off power and communication access to residents.

Continued heavy rains and flooding will complicate the problem further. As emergency response resources are applied to problems with flooding, it is possible they will be unavailable to assist with landslides occurring all over Contra Costa County.

12.7 ISSUES
Important issues associated with landslides in the planning area include the following:
• There are existing homes in landslide risk areas throughout the planning area. The degree of vulnerability of these structures depends on the codes and standards the structures were constructed to. Information to this level of detail is not currently available.
• Future development could lead to more homes in landslide risk areas. • Mapping and assessment of landslide hazards are constantly evolving. As new data and science become available, assessments of landslide risk should be reevaluated. • The impact of climate change on landslides is uncertain. If climate change impacts atmospheric conditions, then exposure to landslide risks is likely to increase. • Landslides may cause negative environmental consequences, including water quality degradation. • The risk associated with the landslide hazard overlaps the risk associated with other hazards such as earthquake, flood and wildfire. This provides an opportunity to seek mitigation alternatives with multiple objectives that can reduce risk for multiple hazards.

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13-1

13. SEVERE WEATHER

13.1 GENERAL BACKGROUND
Severe weather refers to any dangerous meteorological phenomenon with the potential to cause damage, serious social disruption, or loss of human life. It differs from extreme weather, which refers to unusual weather events at the extremes of the historical distribution for a given area.

The most common severe weather events that impact the planning area are heavy rains/thunderstorms, extreme heat, and high winds. These types of severe weather are described in the following sections. Chapter 11 describes flooding associated with severe weather.

13.1.1 Heavy Rain (Atmospheric River or Thunderstorm)
Most severe storms in the planning area consist of heavy rains, often in the form of atmospheric rivers or thunderstorms. The amount of precipitation needed to qualify as heavy rain varies with location and season. Heavy rain is most frequently measured by tracking the frequency of events, analyzing the mean return period, and measuring the amount of precipitation in a certain period (most typically inches of rain within a 24-hour period) (Environmental Protection Agency 2022).

Atmospheric Rivers
A relatively common weather pattern that brings southwest winds and heavy rain to California is often referred to as an atmospheric river. Atmospheric rivers are long, narrow regions in the atmosphere that transport most of the water vapor carried away from the tropics. These columns of vapor move with the weather, carrying large amounts of water vapor and strong winds. When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow, causing flooding and mudslide vents.

Thunderstorms
A thunderstorm is a rain event that includes thunder and lightning. 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.

A thunderstorm is classified as “severe” when it contains one or more of the following: hail with a diameter of three- quarter inch or greater, winds gusting in excess of 50 knots (57.5 mph), or tornado. 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

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• Type and intensity of the precipitation
• Speed and gustiness of the wind
• Appearance of the clouds
• Effect on surface temperature.

Lightning is an electrical discharge that results from the buildup of positive and negative charges within a thunderstorm. When the buildup becomes strong enough, lightning appears as a “bolt” within the clouds or between the clouds and the ground. A bolt of lightning reaches temperatures approaching 50,000ºF instantaneously. The rapid heating and cooling of air near the lightning causes thunder. Lightning is a major threat during a thunderstorm. In the United States, between 75 and 100 Americans are struck and killed by lightning each year.

13.1.2 Extreme Heat
Extreme heat is defined as temperatures that hover 10 ºF or more above the average high temperatures for a region for several weeks. Heat emergencies are often slow to develop and usually hurt vulnerable pop ulations. According to the California Climate Adaptation Strategy , heat waves have claimed more lives in California than all other declared disaster events combined. Despite this history, not a single heat emergency affecting California was proclaimed at t he state or federal level between 1960 and 2022.

Extreme heat is the primary weather-related cause of death in the United States. A 2021 study by the NWS found that, in a 10-year record of weather fatalities across the nation (from 2012 to 2021), excessive heat claimed more lives each year than all other weather hazards assessed (Figure 13-1). In 2021, heat claimed 190 lives nationwide (National Weather Service 2022a, Scientific American 2022).

Source: (National Weather Service 2022a)

Figure 13-1. Weather Fatalities Including Extreme Heat

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Heat waves do not strike victims immediately, but their cumulative effects slowly cause harm to vulnerable populations.

Extreme heat can cause h eat exhaustion, in which the body becomes dehydrated, resulting in an imbalance of electrolytes. Without interventio n, heat exhaustion can lead to collapse and heatstroke. Heatstroke occurs when perspiration cannot occur and the body overheats. Without intervention, heatstroke can lead to confusion, coma, and death.

Extreme heat events do not typically impact buildings; however, losses may be associated with the overheating of HVAC systems. Extreme heat events can lead to drought, impacting water supplies.

13.1.3 High Winds
In this hazard mitigation plan, “high winds” refers to strong straight-line winds; straight-lines winds are those that do not have the rotating characteristic of a tornado. High winds are generally short-duration events involving straight-line winds or gusts of over 50 mph, strong enough to cause property damage. High winds are especially dangerous in areas with significant tree stands and areas with poorly constructed buildings, 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.

Damaging winds are those that exceed 60 mph. 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. The Beaufort Wind Chart (Table 13-1) provides terminology and a description of potential wind impacts at different levels.

Table 13-1. Beaufort Wind Chart
Beaufort
Number
Range
(mph) Terminology Description
0 0 Calm Calm. Smoke rises vertically.
1 1-3 Light air Wind motion visible in smoke.
2 4-7 Light breeze Wind felt on exposed skin. Leaves rustle. 3 8-12 Gentle breeze Leaves and smaller twigs in constant motion. 4 13-18 Moderate
breeze
Dust and loose paper is raised. Small branches begin to move. 5 19-24 Fresh breeze Smaller trees sway
6 25-31 Strong breeze Large branches in motion. Whistling heard in overhead wires. Umbrella use is difficult.
7 32-38 Near gale Whole trees in motion. Some difficulty when walking into the wind. 8 39-46 Gale Twigs broken from trees. Cars veer on road. 9 47-54 Sever gale Light structure damage.
10 55-63 Storm Trees uprooted. Considerable structural damage. 11 64-73 Violent storm Widespread structural damage.
12 74-95 Hurricane Considerable and widespread damage to structures.

Source: (NWS n.d.)
The following are the most common types of damaging straight-line winds:
• Downdrafts—A small-scale column of air that rapidly sinks toward the ground.

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• Downbursts—A strong downdraft with horizontal dimensions larger than 2.5 miles resulting in an outward burst or damaging winds on or near the ground. Downburst winds may begin as a microburst and spread out over a wider area, sometimes producing damage similar to a strong tornado. Although usually associated with thunderstorms, downbursts can occur with showers too weak to produce thunder. • Microbursts—A small, concentrated downburst that produces an outward burst of damaging winds at the surface. Microbursts are generally less than 2.5 miles across and short-lived, lasting only 5 to 10 minutes, with maximum wind speeds up to 168 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 derecho is a widespread thunderstorm wind caused when new thunderstorms form along the leading edge of an outflow boundary (the boundary formed by horizontal spreading of thunderstorm-cooled air). The word “derecho” is of Spanish origin and means “straight ahead.” Thunderstorms feed on the boundary and continue to reproduce. Derechos typically occur in summer when complexes of thunderstorms form over plains, producing heavy rain and severe wind. The damaging winds can last a long time and cover a large area.
• Bow Echo—A bow echo is a linear wind front bent outward in a bow shape. Damaging straight-line winds often occur near the center of a bow echo. Bow echoes can be 200 miles long, last for several hours, and produce extensive wind damage at the ground.

13.1.4 Secondary Impacts
A secondary impact of extreme heat is poor air quality, which can occur during summer months when stagnant atmospheric conditions trap humid air and pollutants near the ground and closer to residents. Ozone, a major component of smog, is c reated in the presence of sunlight via reactions between chemicals in gasoline vapors and industrial smoke stacks. Hot weather can increase ozone levels. High ozone levels often cause or worsen respiratory problems. The longer a given heat wave lasts and t he hotter the temperature is, the greater the risk of adverse impacts on human health or infrastructure.

High winds may cause loss of power if utility service is disrupted. Debris carried by high winds can also result in injury or property damage. Tornadoes may cause fires resulting from damage to natural gas infrastructure. Hazardous materials may be released if a structure is damaged that stores such materials or if such a material is in transport.

Public safety power shutoff events (PSPSs) also are secon dary hazards associated with severe weather. Under certain severe weather conditions, utility service providers shut off power to help prevent wildfire and keep communities safe.

A combination of dry vegetation and high winds can uproot trees, blow branche s onto power lines or create sparks if power lines contact one another. These conditions call for a PSPS. These outages occur across the state to prevent wildfires and keep communities safe. Table 13-2 shows the weather conditions that are monitored by utility service providers that trigger PSPS events. PSPS events can impact areas beyond where severe weather conditions are being observed due to the grid nature of electr ical power distribution systems. Sustained periods of downtime could lead to significant economic impacts.

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Table 13-2. Triggers for Public Safety Power Shutoff Events Monitor Factor Metrics
Red Flag Warning
A warning declared by the National Weather Service that weather conditions could lead to fire and rapid spread.

Low Humidity
20% or lower humidity. Low humidity creates dry vegetation, which fuel fire.

High Winds
Sustained wind speeds above 25 MPH and wind gusts above 45 MPH can cause fire to spread.

Utility Observations
On-the-ground findings from Utility crews.

13.2 HAZARD PROFILE

13.2.1 Past Events
Heavy Rains
Concord and the surrounding area have experienced several damaging heavy rain events over the past 20 years as recorded by NOAA’s National Centers for Environmental Information (NCEI) database and FEMA:
• Winter 2022 – 2023 (current as of the date of this plan) – A series of atmospheric river events resulted in much on Northern California that resulted in a federal disaster declaration (DR-4683-CA). • January 3-12, 2017—A series of atmospheric river events resulted in widespread roadway flooding. Contra Costa County was included in a federal disaster declaration (DR-4301). • February 9, 2015—Heavy rain and gusty winds damaged trees and power lines and caused minor urban flooding in some areas.
• March 13, 2012—Several weather-related traffic accidents occurred due to heavy rains. • June 4, 2011—Heavy rain and strong winds damaged agricultural crops in the area. • April 11, 2010—Brief heavy rain and thunderstorms led to slick roads and flooding streams. At least two fatalities occurred in a weather-related traffic accident. • December 17, 2005 – January 3, 2006—A series of storms with heavy rains produced widespread flooding over much of northern California and caused $300 million in damage. Contra Costa County was included in a federal disaster declaration (DR-1628).

Extreme Heat
Concord and the surrounding area have never been part of a heat-related disaster declaration but have experienced numerous extreme heat events over the past 20 years as recorded by NOAA’s National Centers for Environmental Information (NCEI) database:
• July 21 – 26, 2006—Temperatures soared to as high as 112 ºF in some East Bay valley locations, with overnight lows holding in the mid and upper 70s. Several reports of heat related illness were reported.

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• July 25, 2007—High temperatures in the mid-80s led to the death of a baby in Concord when he was left in a locked vehicle.
• May 17, 2009—Temperatures rose to nearly 100 ºF in the inland valleys. Impacts included heat-exhausted individuals, blown electric transformers, and power outages. • June 27, 2009—Inland areas experienced temperatures well above average. One death and one injury resulted from heat exhaustion and dehydration.
• June 17-23, 2017—Multiple heat records were broken across the region. Rolling blackouts caused more than 2,000 people in Concord to lose power.
• April 24, 2019—Interior valley temperatures soared into the 90s. • August 14-16, 2019—High temperatures caused multiple power outages across the East Bay area. • June 17, 2021—Temperatures soared over 100 ºF in the inland valleys • June 10 – 11, 2022—The Concord airport reached 100 ºF, only dropping to 70 ºF overnight. • August 18, 2022—Daytime highs were recorded up to 110 ºF in the area.

High Winds
Concord and the surrounding area have experienced several high wind events over the past 20 years as recorded by NOAA’s National Centers for Environmental Information (NCEI) database and FEMA:
• December 18, 2005— Wind gusts up to 76 miles per hour were recorded in the area. • December 31, 2005—Wind gusts up to 58 miles per hour were recorded in the area. • January 4, 2008—High winds toppled power lines and trees. In the extended area, more than $2.5 million in damage was sustained from trees falling on cars and structures and damage to roads from the heavy rain. • October 13, 2009—Heavy rain and very strong winds caused trees and utility poles to fall. Over 277,000 customers lost power in the extended area.
• October 27, 2009—Trees were toppled by strong winds, damaging at least one home and car. • January 3-12, 2017—An atmospheric river brought strong southerly winds to the area. One person was killed by a tree that fell in the high winds. Contra Costa County was included in a federal disaster declaration (DR-4301).
• February 7, 2017—An atmospheric river brought strong winds to the area. • February 20, 2017—High winds downed trees, blocking traffic. • January 16, 2019—An atmospheric river impacted the area with destructive winds between 60 and 100 miles per hour. Power lines and trees blew down, resulting in two deaths. • January 19, 2021—Strong winds knocked down power lines and trees. About 137,000 customers lost power across the area.

13.2.2 Location
Severe weather events have the potential to happen anywhere in the planning area. Extreme heat events may be exacerbated in the City where reduced air flow, reduced vegetation, and increased generation of waste heat can

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contribute to temperatures that are several degrees higher than in surrounding less urbanized areas. High wind events affect an entire region, as do heavy rain events.

13.2.3 Frequency
Table 13-3 summarizes search results from the National Center for Environmental Information Storm Events Database for storm events in the planning area over the 20-year period from 2002 through 2022. Based on these results, high wind events are likely to happen almost every two years, extreme heat events once every two years, and heavy rain once every 3 years.

Table 13-3. Severe Weather Events in Concord and the Surrounding Area, January 2002 – September 2022 Number of Days with:

Event Types Includeda
Total Number
of Events Event
Event and Death
or Injury
Event and Property
Damage
Average Years Between
Days with Event
Extreme Heat
Excessive Heat, Heat 10 23 2 1 2
High Wind
High Wind, Strong Wind 12 10 1 2 1.7
Heavy Rain
Heavy Rain 6 6 1 6 3.3
a. Event types are the categories available for search in the National Center for Environmental Information Storm Events Database Source: National Center for Environmental Information Storm Events Database

13.2.4 Severity
Heavy Rain
Heavy rain can have significant impacts, including flash flooding, mudslides and landslides. Stormwater runoff from heavy rains can also impair water quality by washing pollutants into water bodies. Thunderstorms carry the same risks as heavy rain events, and depending on the type of storm, they can also include tornados, lightning, and heavy winds, increasing risk of injury and property damage.

Extreme Heat
During periods of very high temperatures in the summer, those susceptible to extreme heat may suffer heat-related illnesses:
• Heat Exhaustion—Heat exhaustion is a mild form of heat-related illness that can develop after several days of exposure to high temperatures and inadequate or unbalanced replacement of fluids. It is the body’s response to an excessive loss of the water and salt contained in sweat. Those most prone to heat exhaustion are elderly people, people with high blood pressure, and people working or exercising in a hot environment. • Heat Cramps—Heat cramps usually affect people who sweat a lot during strenuous activity. This sweating depletes the body’s salt and moisture. The low salt level in the muscles may be the cause of heat cramps. Heat cramps may also be a symptom of heat exhaustion.
• Heat Stroke—Heat stroke is a severe, dangerous form of heat-related illness. It occurs when the body’s temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. Body temperature may rise to 106°F or higher within 10 to 15 minutes. Heat stroke can cause death or permanent disability if emergency treatment is not provided. This is a medical emergency.

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Heat has caused more than 9,000 deaths in the United States since 1979. Air-conditioning is the number one protective factor against heat-related illness and death. If a home is not air-conditioned, people can reduce their risk for heat-related illness by spending time in public facilities that are air-conditioned.

High Winds
High winds are a frequent problem in the planning area and have been known to damage utilities. The wind speed given in wind warnings issued by the NWS is for a one-minute average; gusts may be 25 to 30 percent higher. Wind speeds up to 100 miles per hour have been recorded in the inland valley areas of Contra Costa County where Concord is located.

13.2.5 Warning Time
Heavy Rain
Meteorologists can often predict the likelihood of a severe rainfall event. This can give several days of warning time.

However, meteorologists cannot predict the exact time of onset or severity of the storm. Some storms may come on more quickly and have only a few hours of warning time. The San Francisco Bay Area Weather Forecast Office of the NWS monitors weather stations and issues watches and warnings when appropriate to alert government agencies and the public of possible or impending weather events. The watches and warnings are broadcast over NOAA weather radio and are forwarded to the local media for retransmission using the Emergency Alert System.

High Winds
NOAA issues watch, warning, and advisory information for high winds. Weather Radio and other weather stations warn residents of upcoming storms so they may prepare and plan accordingly.

Extreme Heat
To better address heat risk and allow people to prepare for upcoming heat events, the NWS has developed the Heat Risk forecast (see Figure 13-2), which provides a quick view of heat risk potential over the upcoming seven days. The heat risk is portrayed in a numeric (0-4) and color (green/yellow/orange/red/magenta) scale, which is similar in approach to the Air Quality Index or the UV Index. It provides one value each day that indicates the approximate level of heat risk concern for any location, along with identifying the groups who are most at risk.

Category Level Meaning
Green 0 No Elevated Risk
Yellow 1 Low Risk for those extremely sensitive to heat, especially those without effective cooling and/or adequate hydration
Orange 2 Moderate Risk for those who are sensitive to heat, especially those without effective cooling and/or adequate hydration
Red 3 High Risk for much of the population, especially those who are heat sensitive and those without effective cooling and/or adequate hydration
Magenta 4 Very High Risk for entire population due to long duration heat, with little to no relief overnight

Figure 13-2. NWS Heat Risk Forecasting System

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The NWS continues to issue excessive heat watches, excessive heat warnings and heat advisories to warn of an extreme heat event (a “heat wave”) within the next 36 hours. If NWS forecasters predict an excessive heat event beyond 36 hours, then the NWS will issue messaging in the form of a special weather statement, emails and social media in the three- to seven -day timeframe. The NWS uses the Heat Risk Forecasting System to determine if an excessive heat watch/warning or heat advisory is warranted. The NWS issues the following types of heat-related advisories:
• Heat Advisory—Tied to events where Heat Risk output is on the orange/red (Level 2-3) thresholds (orange will not be an automatic heat advisory).
• Excessive Heat Watch/Warning— Tied to events where Heat Risk output is on the red/magenta (Level 3- 4) thresholds.

The NWS will issue an excessive heat watch generally two to three days in advance. An excessive heat watch is a way to give the public and emergency officials a warning that extreme temperatures are expected. If significantly hot temperatures remain in the forecast for 24 to 28 hours, the excessive heat watch will be upgraded to an excessive heat warning, indicating that extreme heat has either arrived or is expected soon.

13.3 EXPOSURE
All people and property and the entire environment of the planning area are exposed to some degree to the severe weather hazard.

13.4 VULNERABILITY

13.4.1 Population
Vulnerable populations are the elderly, low income or linguistically isolated populations, people with life-threatening illnesses, people without housing, and residents living in areas that are isolated from major roads. Power outages can be life threatening to those dependent on electricity for life support. Isolation of these populations is a significant concern. These populations face isolation and exposure during severe weather events and could suffer more secondary effects of the hazard. Population vulnerabilities to specific types of severe weather event are as follows:
• Thunderstorms—Nationally, lightning is one of the leading causes of weather-related fatalities (CDC, 2014).

Lightning strikes are far more common in other areas of the country than they are in the west. The majority of injuries and deaths associated with lighting strikes occur when people are outdoors; however, almost one- third of lightning-related injuries occur indoors. Males are five times more likely than females to be struck by lighting and people between the ages of 15 and 34 account for 41 percent of all lightning strike victims (CDC, 2014).
• Extreme Temperatures—Individuals with physical or mobility constraints, cognitive impairments, economic constraints, or social isolation are typically at greater risk from the adverse effects of excessive heat events. The average summertime mortality for excessive heat events is dependent upon the methodology used to derive such estimates. Certain medical conditions, such as heat stroke, can be directly attributable to excessive heat, while others may be exacerbated by excessive heat, resulting in medical emergencies.

Individuals who lack shelter and heating are particularly vulnerable to extreme cold and wind chill. • High Winds—Debris carried by extreme winds and trees felled by gusty conditions can contribute directly to loss of life and indirectly to the failure of protective building envelopes. Utility lines brought down by thunderstorms have also been known to cause fires, which start in dry roadside vegetation. Electric power lines falling down to the pavement create the possibility of lethal electric shock.

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13.4.2 Property
All property is vulnerable to severe weather, but structures in poor condition or in vulnerable locations may risk the most damage. Homes near mature trees or overhead power lines may be more susceptible to wind damage and blackouts. Typically the only impact extreme heat has on general building stock is increased demand on air conditioning equipment, which may cause strain on electrical systems.

Older residential structures in Concord would have been built without the influence of a building code with provisions for wind loads. Those that are located under or near overhead lines or near large trees may be vulnerable to falling ice or may be damaged in the event of a collapse.

Loss estimations for the severe weather hazard are not based on damage functions, because no such damage functions have been generated. 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 potential 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 13-4 lists the loss estimates for the City of Concord.

Table 13-4. Loss Potential for Severe weather
Total Building Value (Structure and Contents) $33,605,400,000 10% of Total Building Value $3,360,500,000
30% of Total Building Value $10,081,600,000
50% of Total Building Value $16,802,700,000

13.4.3 Critical Facilities
Incapacity and loss of roads are the primary transportation failures resulting from severe weather, mostly associated with secondary impacts. Landslides caused by heavy prolonged rains can block roads. High winds can cause significant damage to trees and power lines, blocking roads with debris, incapacitating transportation, and disrupting ingress and egress.

Extreme heat poses a risk to ground transportation infrastructure. For instance, high temperatures can cause railroad tracks and wires, and pavement and joints on roads and bridges to crack, buckle, or sag, resulting in service disruptions, potentially hazardous travel conditions, and the need for costly repairs.

Power outages or roaming blackouts may occur as a result of extreme heat events that strain and overheat circuits.

During a blackout, all critical facilities that are reliant upon electricity for power will be severely impacted unless they are connected to a backup power source. Additional facilities on higher ground may also be exposed to wind damage or damage from falling trees.

13.4.4 Environment
The environment is highly exposed to severe weather events. Natural habitats and park areas are exposed to the elements and risk damage and destruction. Prolonged extreme heat can degrade landscape quality, lakes and vegetation. High winds and tornadoes can cause entire trees to topple.

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13.5 FUTURE TRENDS IN DEVELOPMENT
All future development will be affected by adverse storms. The ability to withstand impacts lies in sound land use practices and consistent enforcement of codes and regulations for new construction. The City of Concord has adopted the International Building Code in response to California mandates. This code is equipped to deal with the impacts of severe weather events. Land use policies identified in the City’s general plan also address many of the secondary impacts of the severe weather hazard. With these tools, the City of Concord is well equipped to deal with future growth and the associated impacts of severe weather.

13.6 SCENARIO
Although severe local storms are infrequent, impacts can be significant, particularly when secondary hazards of flood and landslide occur. A worst-case event would involve prolonged high winds accompanying an atmospheric river event. Such an event would have both short-term and longer-term effects. Initially, schools and roads would be closed due to power outages caused by high winds and downed tree obstructions. In more rural areas, some subdivisions could experience limited ingress and egress. Prolonged rain could produce flooding, overtopped culverts with ponded water on roads, mud over roadways, and landslides on steep slopes. Floods and landslides could further obstruct roads and bridges, further isolating residents.

13.7 ISSUES
Important issues associated with severe weather in the planning area include the following:
• Older building stock in the planning area is built to low code standards or none at all. These structures could be highly vulnerable to severe weather events such as windstorms. • The intensification of heat in the City associated with urban development makes the homeless and vulnerable communities susceptible to heat exhaustion.
• The City may need to open cooling/warming stations during extreme temperature events. • Redundancy of power supply and communications equipment must be evaluated. • The capacity for backup power generation is limited.
• Dead or dying trees as a result of drought conditions are more susceptible to falling during severe storm events.
• Severe weather events are likely to increase as a result of climate change impacts, including the potential for extreme heat.

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14. WILDFIRE

14.1 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, and arson. 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.

14.2 SECONDARY IMPACTS
Wildfires can generate a range of secondary impacts, which in some cases may cause more widespread and prolonged damage than the fire itself. A major fire can lead to ancillary impacts such as landslides in steep ravine areas and flooding due to the impacts of silt in local watersheds. Wildfires cause the contamination of reservoirs, destroy transmission lines and contribute to flooding. They strip slopes of vegetation, exposing them to greater amounts of runoff. This in turn can weaken soils and cause failures on slopes, sometimes several years after a wildfire.

Wildfires can have a significant impact on air quality, especially with prolonged periods of burning combined with climatic conditions. 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.

14.3 HAZARD PROFILE
The City of Concord includes no wildland/urban interface areas, so the risk for wildfire in the City is low. However, the risk could increase with changing conditions and the possibility of extreme events in the future.

14.3.1 Past Events
Incident information from the California Department of Forestry and Fire Protection (CAL FIRE) identifies nearly 50 wildfires in Contra Costa County since 2010. Most of them have been outside of the City of Concord, but smoke from these wildfires impacts a large area that includes the city. There is no history of wildfire damaging or destroying property or structures in the City of Concord. Contra Costa County has not been included in any federal or state- declared fire disasters. The following are recent major wildland/urban interface fires that have affected Contra Costa County (as reported by CAL FIRE unless otherwise noted):
• June 24, 2022, Kirker Fire—Burned 90 acres near Kirker Pass Road and Black Diamond Trail.

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• June 23, 2022, Scenic Fire—Burned 120 acres near Carquinez Scenic Drive and Canyon Lake Drive, east of Crockett.
• June 9, 2022, Marsh Fire—Burned 159 acres near Marsh Creek Road and Walnut Boulevard, South of Brentwood.
• May 20, 2022, Vegetation Fire near Willow Pass Road—20 acres were burned in the City of Concord after a vegetation fire broke out due to strong winds. Some businesses were evacuated, but no injuries were reported.
• July 11, 2021, Diablo Fire—Burned 128 acres at Vasco Road and Camino Diablo, south of Byron. Dry conditions and afternoon winds led to the outbreak of this fire. No damage to life or structures resulted from this fire.
• August 16 – October 1, 2020, SCU Lightning Complex Incident—Burned 396,684 acres in multiple locations across Contra Costa, Santa Clara, Alameda, San Joaquin, Merced and Stanislaus Counties. This wildfire destroyed 225 structures and damaged 26 others, resulting in 6 injuries. • July 7, 2020, Holland Fire—This vegetation fire broke out northeast of Brentwood and was fueled by heavy winds. No structures were destroyed, nor people injured or killed, but evacuations were prompted near the Brentwood Marina.
• July 6, 2020, California Fire—Burned 298 acres at California Street and Springwood Street (east of Rodeo). • October 27, 2019 – October 29, 2019, Sky Fire— Burned around 150 acres and resulted in no structural damage. This incident affected both Contra Costa and Solano counties, causing evacuations but no deaths or injuries.
• August 3, 2019, Marsh Complex Fire—Burned 340 acres at Marsh Creek Road and Morgan Territory Road, southwest of Brentwood.
• June 29, 2018, Valley Fire—Burned 268 acres at Ygnacio Valley Road and Cowell Road in the City of Concord.
• July 8, 2017 – January 9, 2018, Willow Fire—Burned 370 acres near Springwood Court and California Street in Rodeo.

14.3.2 Location
Due to the lack of wildland/urban interface areas in the City of Concord, wildfire mapping has not been developed for the planning area.

14.3.3 Frequency
CAL FIRE records of fires indicate that, from 2010 to 2022, nearly 50 fires have burned in Contra Costa County, representing an average of more than four per year. None of those events have damaged or destroyed property or structures in the City of Concord, but the frequency of the events is enough for wildfire to be a high-probability hazard for the planning area.

14.3.4 Severity
There are no recorded incidents of loss of life or substantial property damage from wildfires in the City of Concord.

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14.3.5 Warning Time
Wildfires are often caused by humans, intentionally or accidentally. There is no way to predict when one might break out. Since fireworks often cause brush fires, extra diligence is warranted around the Fourth of July when the use of fireworks is highest. Dry seasons and droughts are factors that greatly increase fire likelihood. Dry lightning may trigger wildfires. Severe 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.

If a fire does break out and spread rapidly, residents may need to evacuate within days or hours. A fire’s peak burning period generally is between 1 p.m. and 6 p.m. Once a fire has started, fire alerting is reasonably rapid in most cases.

The rapid spread of cellular and two-way radio communications in recent years has further contributed to a significant improvement in warning time. The City has incorporated the use of Zonehaven as an evacuation platform as one of its emergency management tools.

14.4 EXPOSURE AND VULNERABILITY
Based on a lack of events, data, and mapping, the City of Concord currently has no significant exposure or vulnerability to the wildfire hazard.

14.5 FUTURE TRENDS IN DEVELOPMENT
Urbanization tends to alter the natural fire regime and can create the potential for expansion of urbanized areas into wildland areas. Such expansion can be managed with the City’s strong land use and building codes. As the planning area experiences future growth, it is anticipated that the exposure to this hazard will remain as assessed due to these capabilities.

14.6 SCENARIO
A dry summer could follow a wet spring, exacerbated by dry hot winds. Carelessness with combustible materials or a tossed lit cigarette, or a sudden lighting storm could trigger a multitude of small, isolated fires. The embers from these smaller fires could be carried miles by hot, dry winds. The deposition zone for these embers could be within neighborhoods in the city. 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 and may not be able to adequately support local firefighting efforts.

14.7 ISSUES
The major issues for wildfire are 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.

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• Future growth into the foothills interface areas should continue to be managed. • Higher building code standards, such as residential sprinkler requirements and prohibitive combustible roof standards, should be regionally consistent.

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15. CLIMATE CHANGE

15.1 GENERAL BACKGROUND
“Climate change” refers to alterations in the long-term patterns of temperature, precipitation, humidity, wind, and seasons that play a fundamental role in shaping natural ecosystems and the human economies and cultures that depend on them. These shifts may result from natural processes (e.g., cyclical ocean patterns like El Niño, La Niña and the Pacific Decadal Oscillation, volcanic activity, changes in the sun’s energy output, variations in Earth’s orbit), but they can also be driven by human activity. Many of the changes observed in Earth’s climate since the early 20th century have been attributed to human activity.

15.1.1 Greenhouse Gases
The well-established worldwide warming trend of recent decades and its related impacts are caused by increasing concentrations of carbon dioxide and other greenhouse gases in the earth’s atmosphere. Greenhouse gases are gases that trap heat in the atmosphere, resulting in a warming effect. Carbon dioxide is the most commonly known greenhouse gas; however, methane, nitrous oxide and fluorinated gases also contribute to warming.

Emissions of these gases come from a variety of sources, such as fossil fuel combustion for energy and transportation, wastewater treatment, agricultural production, livestock, landfills, and changes in land use. According to the National Aeronautics and Space Administration (NASA), carbon dioxide concentrations in the atmosphere measured about 280 parts per million (ppm) before the industrial era began in the late 1700s and have risen dramatically since then, surpassing 400 ppm in 2013 for the first time in recorded history (see Figure 15-1). The latest atmospheric carbon dioxide measurement, taken in May 2022, was 421 ppm (National Oceanic and Atmospheric Administration 2022).

This is an increase from measurements taken as recently as few months beforehand; in February 2022 a measurement of 418 ppm was taken (NASA 2022). Figure 15-2 shows greenhouse gas emissions by economic sector in California for 2019, the most current data. Transportation is the largest source of CO2 for the state.

15.1.2 How Climate Change Affects Hazard Mitigation
Climate change will affect the people, property, economy, and ecosystems of the planning area in a variety of ways.

Consequences of climate change include increased flood vulnerability and increased heat-related illnesses. 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.

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Source: (NASA 2022)

Figure 15-1. Global Carbon Dioxide Concentrations Over Time Source: (California Air Resources Board 2022)

Figure 15-2. California’s 2020 Greenhouse Gas Emission Inventory by Sector

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An essential aspect of hazard mitigation is predicting the likelihood of hazard events. Typically, predictions are based on statistical projections from records of past events. This approach assumes that the likelihood of hazard events remains essentially unchanged over time. Thus, averages based on the past frequencies of, for example, floods are used to estimate future frequencies: if a river has flooded an average of once every 5 years for the past 100 years, then it can be expected to continue to flood an average of once every 5 years.

For hazards that are affected by climate conditions, the assumption that future behavior will be equivalent to past behavior is not valid if 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. Specifically, as hydrology changes, storms currently considered to be the 100-year flood might strike more often, leaving many communities at greater risk. 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.

15.1.3 Current Indicators of Climate Change
Global Indicators
The major scientific agencies of the United States—including NASA and the National Oceanic and Atmospheric Administration (NOAA)—have presented evidence that climate change is occurring. NASA summarizes key evidence as follows (National Aeronautics and Space Administration 2023):
• Global Temperature Rise—The planet’s average surface temperature has risen about 2.12 ºF since the late 19th century, a change driven largely by increased carbon dioxide emissions into the atmosphere and other human activities. Most of the warming occurred in the past 40 years, with the seven most recent years being the warmest. The years 2016 and 2020 are tied for the warmest year on record. • Warming Oceans—The ocean has absorbed much of the worlds’ increased heat, with the top 300 feet of ocean showing warming of more than 0.6 ºF since 1969. Earth stores 90 percent of its extra energy in the ocean.
• Shrinking Ice Sheets—The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA’s Gravity Recovery and Climate Experiment show Greenland lost an average of 279 billion tons of ice per year between 1993 and 2019, and Antarctica lost about 148 billion tons of ice per year. • Glacial Retreat—Glaciers are retreating almost everywhere around the world—including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.
• Decreased Snow Cover—Satellite observations reveal that the amount of spring snow cover in the northern hemisphere has decreased over the past five decades and that snow is melting earlier. • Sea Level Rise—Global sea level rose about 8 inches in the last century. The rate in the last two decades is nearly double that of the last century and is accelerating slightly every year. • Declining Arctic Sea Ice—Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades.
• Extreme Events—The number of record high temperature events in the United States has been increasing since 1950, while the number of record low temperature events has been decreasing. The U.S. has also witnessed increasing numbers of intense rainfall events.

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• Ocean Acidification—Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 7 to 10 billion tons per year.

California Indicators
Monitoring and research efforts across California have generated data that describe changes already underway in the state. Notable examples across the state include the following (California Office of Environmental Health Hazard Assessment 2018):
• Dissolved oxygen in coastal waters is declining throughout the south coast survey region • Since 1950, the northern Sierra Nevada showed an overall snowpack decline of 7.4 inches. • Unusually warm waters occurred in the Pacific Ocean in 2014-2015, leading to widespread impacts on marine life. This marine heat wave first appeared as a large area of exceptionally high sea surface temperatures in the Gulf of Alaska in November 2013 and later extended along the entire west coast of North America. • The surface area of seven Sierra Nevada glaciers has decreased dramatically since the beginning of the 20th century. In 2014, the size of these glaciers ranged from 14 to 52 percent of their 1903 area. • Sea level has risen by about 7 inches since 1900 at San Francisco and by about 6 inches since 1924 at La Jolla. • Since 1906, the fraction of annual snowmelt runoff that flows into the Sacramento River between April and July has decreased by about 9 percent.
• Compared to the 1930s, forests across much of California today have lower densities of large trees, and higher densities of small trees. Water stress, which increases in a warming climate, poses a greater risk to large trees than to small trees.
• Annual tree mortality in California forests increased in 2014, and steep increases in mortality followed in subsequent years; the highest number, 62 million tree deaths, was recorded in 2016. • Future droughts may be hotter, as warm temperatures coincide with periodic dry years; 2016 and 2020 were the warmest years on record.
• Heat-related deaths and illnesses in California increased dramatically in 2006 following a record-breaking heat wave. At least 140 deaths occurred between July 15 and August 1. Deaths related to this heat wave were largely attributed to elevated nighttime temperatures.
• The number of acres burned by wildfires statewide has been increasing since 1950. Large fires affecting 1,000 acres or more account for most of the area burned each year.

15.1.4 Projected Future Impacts in California
According to California’s Fourth Climate Change Assessment, the state can expect the following climate change impacts (State of California 2022):
• By 2100, the average annual maximum daily temperature is projected to increase by 5.6 to 8.8 ºF. • By 2100, the water supply from snowpack is projected to decline by two-thirds. • By 2050, agricultural production could face climate-related water shortages of up to 16 percent in certain regions.

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• By 2100, the frequency of extreme wildfires will increase, and the average area burned statewide would increase by 77 percent.
• By 2100, the miles of highways susceptible to coastal flooding in a 100-year storm event will triple. • By 2050, heat waves in cities could cause 2 to 3 times more heat-related deaths.

15.1.5 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. Generally, 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 emergency management—as generally addressed in this hazard mitigation plan—is typically defined as the effort to reduce loss of life and property by lessening the impact of disasters. • Mitigation in climate change discussions is defined as a human intervention to reduce impacts on the climate system. It includes strategies to reduce greenhouse gas sources and emissions and enhance greenhouse gas sinks.

In this chapter, mitigation is used as defined by the climate change community. In the other chapters of this plan, mitigation is primarily used in an emergency management context.

Adaptation refers to adjustments in natural or human systems in response to actual or anticipated effects of climate change. These adjustments may moderate harm or exploit beneficial opportunities. 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. Some initiatives and actions can both reduce greenhouse gas emissions and support adaptation to likely future conditions.

Societies across the world need to adapt to climate change. 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. Some ecosystems can adapt to change and buffer surrounding areas from the impacts of change. Forests can bind soils and hold large volumes of water, releasing it through the year; floodplains can absorb water during peak flows; coastal ecosystems can attenuate waves and reduce erosion. Other ecosystem services—such as food provision, timber, materials, medicines, and recreation—can provide buffers 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.

15.2 PROJECTED FUTURE IMPACTS FOR CONCORD
Cal-Adapt, a collaboration between California state agencies, universities, and the private sector, collects peer- reviewed data related to climate change in California and makes it publicly available in easily accessible forms on its website. The available information includes snapshot projections of future climate conditions for individual cities in the state. The report for the City of Concord, showing projections for 11 climate parameters, is included in Appendix E. Key findings are summarized in Table 15-1 for two future scenarios: one with a medium level of carbon dioxide (CO2) emissions and one with a high level.

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Table 15-1. Climate Projections for the City of Concord Historical
Projected Mid-Century
Average (2035 – 2064)
Projected End-of-Century
Average (2070 – 2099)

Average
(1961 – 1990)
Medium CO2
Emissions
High CO2
Emissions
Medium CO2
Emissions
High CO2
Emissions
Average Maximum Temperature (ºF) 72.0 75.5 76.4 76.6 79.6 Average Minimum Temperature (ºF) 47.2 50.3 51.2 51.4 54.5 Extreme Heat Days per Yeara 3 13 17 18 32
Maximum 1-Day Precipitation in a Year (inches) 1.36 1.45 1.46 1.50 1.60 Total Annual Precipitation (inches) 18.5 18.4 18.8 18.8 19.4 Longest Dry Spell in a Year (days)b 119 127 129 129 133 Average Area Burned by Wildfire in a Yearc 374 306 305 275 270 a. Extreme heat days defined as days with high temperature greater than the 1961 – 1990 98th percentile maximum. b. Longest dry spell defined as the greatest number of consecutive days in year with precipitation less than 1 millimeter. c. Wildfire burn area does not include areas of the city outside state or federal responsibility areas for fire protection.

The projections for Concord generally show temperatures, precipitation, and dry spell duration all increasing, with wildfire burn area decreasing. Graphs showing the range of possible projections for each emission scenario, along with the average with those ranges, are shown in Figure 15-3, Figure 15-4, and Figure 15-5 for yearly maximum temperature, annual precipitation, and annual wildfire burn area, respectively.

Source: (Cal-Adapt 2022)

Note: The broad colors indicate the range of future projections; lines indicate the average of the range Figure 15-3. Observed and Projected Yearly Maximum Temperatures in the City of Concord

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Source: (Cal-Adapt 2022)

Figure 15-4. Observed and Projected Average Annual Precipitation in the City of Concord

Source: (Cal-Adapt 2022)

Figure 15-5. Observed and Projected Average Annual Wildfire Burn Area in the City of Concord

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15.3 VULNERABILITY ASSESSMENT— HAZARDS OF CONCERN
The following sections provide information on how each identified natural 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 planning area.

15.3.1 Dam and Levee Failure
Climate Change Impacts on the Hazard
On average, changes in California’s annual precipitation levels are not expected to be dramatic; however, small changes may have significant impacts for water resource systems, including dams and levees. Dams and levees are designed partly based on assumptions about a river’s flow behavior, expressed as hydrographs. Changes in weather patterns can have significant effects on the hydrograph used for the design of a dam or levee. If the hygrograph 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 earlier 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, flood flows on many California rivers have been record-setting since the 1950s. This means that water infrastructure, such as dams, have been forced to manage flows for which they were not designed (DWR, 2007). The California Division of Dam Safety 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 wildfires. According to the Division, climate change also will impact the ability of dam operators to estimate extreme flood events (DWR, 2008).

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 failures.

For 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 (for example 1-percent-annual chance). This means that risk to the area that a levee is protecting from inundation will increase. Levee accreditation may be rescinded, resulting in currently protected areas being mapped within a flood hazard area.

Exposure and Vulnerability
Population
Population exposure and vulnerability to the dam and levee failure hazard are unlikely to change as a result of climate change.

Property
Property exposure and vulnerability to the dam and levee failure hazard are unlikely to change as a result of climate change.

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Critical facilities
The exposure and vulnerability of critical facilities are unlikely to change as result of climate change. Dam and levee 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.

Environment
The exposure and vulnerability of the environment to dam and levee failure are unlikely to change as a result of climate change. 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.

15.3.2 Drought
Climate Change Impacts on the Hazard
The long-term effects of climate change on regional water resources are unknown, but global water resources are already experiencing the following stresses without climate change:
• Growing populations.
• Increased competition for available water.
• Poor water quality.
• Environmental claims.
• Uncertain reserved water rights.
• Groundwater overdraft.
• Aging urban water infrastructure.

With a warmer climate, droughts could become more frequent, more severe, and longer lasting. The Third National Climate Assessment Report for the United States indicates that “higher surface temperatures brought about by global warming increase the potential for drought. Evaporation and the higher rate at which plants lose moisture 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” (U.S. Climate Resilience Toolkit 2021).

Because expected changes in precipitation patterns are still uncertain, the potential impacts and likelihood of drought are uncertain. 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. DWR estimates that the Sierra Nevada snowpack, which provides a large amount of the water supply for the planning area and other parts of the state, will experience a 48- to 65-percent loss by the end of the century compared to historical averages (California Department of Water Resources 2022). In addition to snowpack resources, the planning area’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.

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Exposure and Vulnerability
Population
Population exposure and vulnerability to drought are unlikely to increase as a result of climate change. While greater numbers of people may need to engage in behavior change, such as water saving efforts, significant life or health impacts are unlikely.

Property
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 threaten structures.

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.

Environment
The vulnerability of the environment may increase as a result of increased drought resulting from climate change.

Ecosystems and biodiversity 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.

15.3.3 Earthquake
Climate Change Impacts on the Hazard
The impacts of global climate change on earthquake probability are unknown, although scientists have identified tiny earthquakes triggered by the change of fault stress loads from rain and snow. Similarly, long-term drought can result in a significant change in the stress load on the Earth’s crust.

Pumping of groundwater from underground aquifers by humans, which is exacerbated during times of drought, has also been shown to impact patterns of stress loads by “unweighting” the Earth’s crust. A 2014 study looked at the effects of groundwater extraction in California’s Central Valley on seismicity on the adjacent San Andreas Fault. The researchers found that such extractions can promote lateral changes in stress to the two sides of the San Andreas, which move horizontally against each other along the boundary of two major tectonic plates. This could cause them to unclamp and slip, resulting in an earthquake (National Aeronautics and Space Administration 2019).

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.

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Exposure and Vulnerability
Because impacts of climate change on the earthquake hazard are not well understood, changes in exposure and vulnerability of the local resources are not able to be determined.

15.3.4 Flood
Climate Change Impacts on the Hazard
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, scientists project greater storm intensity with climate change, resulting in more direct runoff and flooding. High frequency flood events (e.g., 10-year floods) in particular will likely 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. 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.

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 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.

Exposure 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.

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 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

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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.

15.3.5 Landslide
Climate Change Impacts on the Hazard
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 occurrences.

Exposure 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. In addition, increased sedimentation resulting from landslides may negatively impact flood control facilities, such as dams.

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.

15.3.6 Severe Weather
Climate Change Impacts on the Hazard
The science for linking the severity of specific severe weather events to climate change is still evolving; however, some trends provide an indication of how climate change may be impacting these events.

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The increase in average surface temperatures can lead to more intense heat waves. Evidence suggests that heat waves are already increasing, especially in western states. Extreme heat days in the planning area are likely to increase.

Climate change impacts on other severe weather events, such as high winds and thunderstorms, are still not well understood.

Climate change impacts on winds are not well understood. Until recently, scientists had predicted rapid inland warming would weaken one of the primary drivers for Santa Ana winds and reduce their frequency. But a 2021 study found that bouts of hot Santa Ana winds are not declining and could even be increasing (Science 2021).

Exposure 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 severe weather hazard. Severe 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. Exposure of the population to higher heat stress and lower air quality could lead to lower quality of health in the City.

Critical Facilities
Critical facility exposure and vulnerability would be unlikely to increase as a result of climate change impacts on the severe weather hazard; however, critical facility owners and operators may experience more frequent disruption to service. 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.

15.3.7 Wildfire
Climate Change Impacts on the Hazard
The frequency and severity of wildland/urban interface fires are determined by climate variability, local topography, and human intervention. Climate change has the potential to affect multiple elements of wildland/urban interface fires: fire behavior, ignitions, fire management, and vegetation fuels. Hot dry spells create the highest fire risk.

Increased temperatures may intensify fire danger by warming and drying out vegetation.

Changes in climate patterns may impact the distribution and perseverance of insect outbreaks that create dead trees (increase fuel). When climate alters fuel loads and fuel moisture, forest susceptibility to fire changes. Climate change also may increase winds that spread fires. Faster fires are harder to contain, and thus are more likely to expand into residential neighborhoods.

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Exposure and Vulnerability
Population
According to Cal-Adapt projections, wildfire risk in the areas surrounding the City of Concord are projected to increase slightly in the medium-emissions scenario and decrease slightly in the high-emissions scenario over the next century. Other areas of California and the western United States are expected to have increased risk to wildfire, with increases in annual acres burned. Although residents may not experience increased risk to wildland/urban interface fire directly, secondary impacts, such as poor air quality may increase.

Property and Critical Facilities
If wildland/urban interface fire risk decreases, the exposure and vulnerability of property and critical facilities would remain the same.

Environment
It is possible that the exposure and vulnerability of the environment will be impacted by changes in wildland/urban interface fire risk due to climate change. Natural fire regimes may change, resulting in more or less frequent or higher intensity burns. These impacts may alter the composition of the ecosystems in areas in and surrounding the planning area.

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

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16. OTHER HAZARDS OF INTEREST

16.1 HUMAN-CAUSED HAZARDS

16.1.1 General Background
Although the DMA does not require an assessment of human-caused hazards, the Steering Committee decided to include a qualitative assessment of the following human-caused hazards that could impact the Concord planning area:
• Terrorism and cyber security threats—These are malicious, intentional, and criminal acts. • Hazardous materials incidents (including pipeline and transportation incidents)—These are accidental events with unintended consequences arising from the manufacture, transportation, storage and use of hazardous materials.
• Utility interruptions—These are electrical, natural gas, sewage, telecommunication, or water failures or interruptions that affect people.
• Active shooter incident—These are criminal attempts to kill people in a confined and populated area. Such incidents have been increasing in numbers and human causalities and have captured significant public and police attention.
• Civil disturbance—These are incidents of violent public activities that disrupt the peace to the degree that law enforcement intervention is required to maintain public safety.

Terrorism
FEMA defines terrorism as the use of weapons of mass destruction (WMDs), including biological, chemical, nuclear and radiological weapons; arson, incendiary, explosive and armed attacks; industrial sabotage and intentional hazardous materials releases; agro-terrorism; and cyber-terrorism (FEMA 2003). The three key elements to defining a terrorist event are as follows:
• Activities involve the use of illegal force.
• Actions are intended to intimidate or coerce.
• Actions are committed in support of political or social objectives.

Types of Terrorism
The Federal Bureau of Investigation (FBI) categorizes two types of terrorism in the United States:
• Domestic terrorism involves groups or individuals without foreign direction whose terrorist activities, including the use of WMDs, are directed at the government or population. The bombing of the Alfred P.

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Murrah federal building in Oklahoma City is an example of domestic terrorism. The FBI, the primary response agency for domestic terrorism, coordinates domestic preparedness programs and activities to limit domestic terrorism.
• International terrorism involves groups or individuals whose terrorist activities are foreign-based and/or directed by countries or groups outside the United States, or whose activities transcend national boundaries.

Examples include the 1993 bombing of the World Trade Center and the attacks of September 11, 2001 at the World Trade Center and the Pentagon.

Terrorism Methods and Impacts
The effects of terrorism can include injuries, loss of life, property damage, or disruption of services such as electricity, water supplies, transportation, or communications. Effects may be immediate or delayed. Terrorists often choose targets that offer limited danger to themselves and areas with relatively easy public access. Foreign terrorists look for visible targets where they can avoid detection before and after an attack, such as international airports, large cities, major special events, and high-profile landmarks. Table 16-1 provides a hazard profile summary of common terrorism methods. Most terrorist events in the United States have been bombing attacks, involving detonated and undetonated explosive devices, tear gas, pipe bombs, and firebombs.

Table 16-1. Event Profiles for Terrorism
Hazard Application Modea Hazard Durationb
Static/Dynamic
Characteristicsc
Mitigating and Exacerbating
Conditionsd
Conventional
Bomb
Detonation of
explosive device on
or near target;
delivery via person,
vehicle, or projectile.

Instantaneous;
additional secondary
devices, or
diversionary activities
may be used,
lengthening the
duration of the hazard
until the attack site is
determined to be
clear.

Extent of damage is
determined by type and
quantity of explosive.

Effects generally static
other than cascading
consequences,
incremental structural
failure, etc.

Overpressure at a given standoff is
inversely proportional to the cube of
the distance from the blast; thus,
each additional increment of
standoff provides progressively
more protection. Terrain,
forestation, structures, etc. can
provide shielding by absorbing
and/or deflecting energy and debris.

Exacerbating conditions include ease
of access to target; lack of barriers
and shielding; poor construction;
and ease of concealment of device.

Chemical Agent Liquid/aerosol
contaminants
dispersed using
sprayers or other
aerosol generators;
liquids vaporizing
from puddles/
containers; or
munitions.

Hours to weeks,
depending on the
agent and the
conditions in which it
exists.

Contamination can be
carried out of the initial
target area by persons,
vehicles, water, and
wind. Chemicals may be
corrosive or otherwise
damaging over time if
not remediated.

Air temperature can affect
evaporation of aerosols. Ground
temperature affects evaporation of
liquids. Humidity can enlarge aerosol
particles, reducing inhalation hazard.

Precipitation can dilute and disperse
agents but can spread
contamination. Wind can disperse
vapors but also cause target area to
be dynamic. The micro-
meteorological effects of buildings
and terrain can alter travel and
duration of agents. Shielding in the
form of sheltering in place can
protect people and property from
harmful effects.

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Hazard Application Modea Hazard Durationb
Static/Dynamic
Characteristicsc
Mitigating and Exacerbating
Conditionsd
Arson/
Incendiary
Attack
Initiation of fire or
explosion on or near
target via direct
contact or remotely
via projectile.

Generally minutes to
hours.

Extent of damage is
determined by type and
quantity of device,
accelerant, and materials
present at or near target.

Effects generally static
other than cascading
consequences,
incremental structural
failure, etc.

Mitigation factors include built-in
fire detection and protection
systems and fire-resistive
construction techniques. Inadequate
security can allow easy access to
target, easy concealment of an
incendiary device, and undetected
initiation of a fire. Non-compliance
with fire and building codes, as well
as failure to maintain existing fire
protection systems, can substantially
increase the effectiveness of a fire
weapon.

Armed Attack Tactical assault or
sniping from remote
location, or random
attack based on fear,
emotion, or mental
instability.

Generally minutes to
days.

Varies based on the
perpetrators’ intent and
capabilities.

Inadequate security can allow easy
access to target, easy concealment
of weapons, and undetected
initiation of an attack.

Biological Agent Liquid or solid
contaminants
dispersed using
sprayers/ aerosol
generators or by
point or line sources
such as munitions,
covert deposits, and
moving sprayers.

Hours to years,
depending on the
agent and the
conditions in which it
exists.

Depending on the agent
used and the
effectiveness with which
it is deployed,
contamination can be
spread via wind and
water. Infection can
spread via humans or
animals.

Altitude of release above ground can
affect dispersion; sunlight is
destructive to many bacteria and
viruses; light to moderate wind will
disperse agents but higher winds
can break up aerosol clouds; the
micro-meteorological effects of
buildings and terrain can influence
aerosolization and travel of agents.

Agro-terrorism Direct, generally
covert contamination
of food supplies or
introduction of pests
and/or disease
agents to crops and
livestock.

Days to months. Varies by type of
incident. Food
contamination events
may be limited to
specific distribution sites,
whereas pests and
diseases may spread
widely. Generally no
effects on built
environment.

Inadequate security can facilitate
adulteration of food and
introduction of pests and disease
agents to crops and livestock.

Radiological
Agent
Radioactive
contaminants
dispersed using
sprayers/ aerosol
generators, or by
point or line sources
such as munitions.

Seconds to years,
depending on material
used.

Initial effects will be
localized to site of
attack; depending on
meteorological
conditions, subsequent
behavior of radioactive
contaminants may be
dynamic.

Duration of exposure, distance from
source of radiation, and the amount
of shielding between source and
target determine exposure to
radiation.

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Hazard Application Modea Hazard Durationb
Static/Dynamic
Characteristicsc
Mitigating and Exacerbating
Conditionsd
Nuclear Bomb Detonation of
nuclear device
underground, at the
surface, in the air, or
at high altitude.

Light/heat flash and
blast/shock wave last
for seconds; nuclear
radiation and fallout
hazards can persist for
years. Electromagnetic
pulse from a high-
altitude detonation
lasts for seconds and
affects only
unprotected
electronic systems.

Initial light, heat, and
blast effects of a
subsurface, ground or air
burst are static and
determined by the
device’s characteristics
and employment; fallout
of radioactive
contaminants may be
dynamic, depending on
meteorological
conditions.

Harmful effects of radiation can be
reduced by minimizing the time of
exposure. Light, heat, and blast
energy decrease logarithmically as a
function of distance from seat of
blast. Terrain, forestation,
structures, etc. can provide shielding
by absorbing and/or deflecting
radiation and radioactive
contaminants.

Intentional
Hazardous
Material
Release (fixed
facility or
transportation)
Solid, liquid, and/or
gaseous
contaminants
released from fixed
or mobile containers
Hours to days. Chemicals may be
corrosive or otherwise
damaging over time.

Explosion and/or fire
may be subsequent.

Contamination may be
carried out of the
incident area by persons,
vehicles, water and
wind.

Weather conditions directly affect
how the hazard develops. The
micro-meteorological effects of
buildings and terrain can alter travel
and duration of agents. Shielding in
the form of sheltering in place can
protect people and property from
harmful effects. Non-compliance
with fire and building codes, as well
as failure to maintain existing fire
protection and containment
features, can substantially increase
the damage from a hazardous
materials release.
a. Application Mode—Application mode describes the human acts or unintended events necessary to cause the hazard event to occur. b. Duration—Duration is the length of time the hazard is present. For example, a chemical warfare agent such as mustard gas, if un- remediated, can persist for hours or weeks under the right conditions. c. Dynamic or Static Characteristics—These characteristics of a hazard describe its tendency, or that of its effects, to either expand, contract, or remain confined in time, magnitude, and space. For example, the physical destruction caused by an earthquake is generally confined to the place in which it occurs, and it does not usually get worse unless aftershocks or other cascading failures occur; in contrast, a cloud of chlorine gas leaking from a storage tank can change location by drifting with the wind and can diminish in danger by dissipating over time.
d. Mitigation and Exacerbating Conditions—Mitigating conditions are characteristics of the target and its physical environment that can reduce the effects of a hazard. For example, earthen berms can provide protection from bombs; exposure to sunlight can render some biological agents ineffective; and effective perimeter lighting and surveillance can minimize the likelihood of someone approaching a target unseen. In contrast, exacerbating conditions are characteristics that can enhance or magnify the effects of a hazard. For example, depressions or low areas in terrain can trap heavy vapors, and a proliferation of street furniture (trash receptacles, newspaper vending machines, mailboxes, etc.) can provide hiding places for explosive devices.

Terrorism Preparation and Response
To prepare for terrorism, the unpredictability of human beings must be considered. People with a desire to perform such acts may seek out targets of opportunity that may not fall into established lists of critical areas or facilities. While education, heightened awareness, and early warning of unusual circumstances may deter terrorism, intentional acts that harm people and property are possible at any time. Public safety entities must react to the threat, locating, isolating, and neutralizing further damage and investigating potential scenes and suspects to bring criminals to justice.

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Those involved with terrorism response, including public health and public information staff, are trained to deal with the public’s emotional reaction swiftly as response to the event occurs. The area of the event must be clearly identified in all emergency alert messages to prevent those not affected by the incident from overwhelming local emergency rooms and response resources, which can reduce service to those actually affected. The public needs to be informed clearly and frequently about what government agencies are doing to mitigate the impacts of the event. The public also needs clear direction on how to protect the health of individuals and families.

Secondary Hazards
A terrorist act can disrupt business activity and have long-term emotional impacts. Recovery can take significant resources and expense at the local level.

Civil Disturbance
Civil disturbance refers to a violent public disturbance of the peace that disrupts a community to the degree that law enforcement intervention is required to maintain public safety. Civil disorder and disturbances have tremendous potential for causing damage to the city. These incidents are generally associated with controversial political, judicial, or economic issues and may occur at any time of the year, although statistics indicate that they are more frequent during summer. The effects of civil disturbances and civil unrest vary with the type, severity, scope, and duration of event. Essential services (e.g., electricity, water, public transportation, communications) may be disrupted, or property damage, injuries, and loss of life may occur. Facilities most at risk are government buildings, schools, utilities, and correctional facilities.

Secondary Hazards
Depending on the size and scope of the incident, civil disturbances may lead to widespread urban fire, utility failure, transportation interruption, and environmental hazards. The most significant secondary impact is interruption of continuity of government.

Cyber Security Threat
Cybersecurity threats can take many forms. Cyber-attacks are the result of one or more cybersecurity threats culminating in an assault on a chosen target. Cyber-attacks are intentional and malicious crimes that compromise the digital infrastructure of a person or organization, often for financial or terror-related reasons. Such attacks vary in nature and are perpetrated using digital mediums or sometimes social engineering to target human operators.

Generally, attacks last minutes to days, but large-scale events and their impacts can last much longer. As information technology continues to grow in capability and interconnectivity, cyber-attacks become increasingly frequent and destructive.

Types of Cyber-Attack
Cyber-threats differ by motive, attack type and perpetrator profile. Motives range from the pursuit of financial gain to political or social aims. Cyber-threats are difficult to identify and comprehend. Types of threats include using viruses to erase entire systems, breaking into systems and altering files, using someone’s personal computer to attack others, or stealing confidential information. The spectrum of cyber-risks is limitless, with threats having a wide-range of effects on the individual, community, organizational, and national threat.

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This risk assessment includes cyber-attacks and cyber-terrorism under the inclusive hazard of cyber-threats. The terms often are used interchangeably, though they are not the same. While all cyber-terrorism is a form of cyber-attack, not all cyber-attacks are cyber-terrorism.

Public and private computer systems are likely to experience a variety of cyber-attacks, from blanket malware infection to targeted attacks on system capabilities. Cyber-attacks specifically seek to breach IT security measures designed to protect an individual or organization. The initial attack is followed by more severe attacks for the purpose of causing harm, stealing data, or financial gain. Organizations are prone to different types of attacks that can be either automated or targeted in nature. Table 16-2 describes the most common cyber-attack mechanisms faced by organizations today.

Table 16-2. Common Mechanisms for Cyber-Attacks
Type Description
Advanced Persistent
Threat (APT)
An attack in which the attacker gains access to a network and remains undetected. APT attacks are designed to steal data instead of cause damage.

Denial of Service
Attacks
Attacks that focus on disrupting service to a network in which attackers send high volumes of data until the network becomes overloaded and can no longer function.

Drive-by Downloads Malware is downloaded unknowingly by the victims when they visit an infected site.

Malvertising Malware downloaded to a system when the victim clicks on an affected ad.

Man in the Middle Man-in-the-Middle attacks mirror victims and endpoints for online information exchange. In this type of attack, the attacker communicates with the victims, who believe they are interacting with a legitimate endpoint website. The attacker is also communicating with the actual endpoint website by impersonating the victim. As the process goes through, the attacker obtains entered and received information from both the victim and endpoint.

Password Attacks Third party attempts to crack a user’s password and subsequently gain access to a system. Password attacks do not typically require malware, but rather stem from software applications on the attacker’s system. These applications may use a variety of methods to gain access, including generating large numbers of generated guesses, or dictionary attacks, in which passwords are systematically tested against all of the words in a dictionary.

Phishing Malicious email messages that ask users to click a link or download a program. Phishing attacks may appear as legitimate emails from trusted third parties.

Ransomware When an individual downloads ransomware, often through phishing, an execution of code results in encryption of all data and personal files stored on the system. The victim then receives a message that demands a fee in the form of electronic currency or cryptocurrency for the decryption code.

Socially Engineered
Trojans
Programs designed to mimic legitimate processes (e.g., updating software, running fake antivirus software) with the end goal of human-interaction caused infection. When the victim runs the fake process, the Trojan is installed on the system.

Unpatched Software Nearly all software has weak points that may be exploited by malware. Most common software exploitations occur with Java, Adobe Reader, and Adobe Flash. These vulnerabilities are often exploited as small amounts of malicious code are often downloaded via drive-by download.

Cyber-Terrorism
Cyber-terrorism is the use of computers and information, particularly over the Internet, to recruit others to an organization’s cause, cause physical or financial harm, or cause a severe disruption of infrastructure service. Such disruptions can be driven by religious, political, or other motives. Like traditional terrorism tactics, cyber-terrorism seeks to evoke very strong emotional reactions, but it does so through information technology rather than a physically violent or disruptive action.

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Cyber-terrorism has three main types of objectives (Kostadinov 2012):
• Organizational—Cyber-terrorism with an organizational objective includes specific functions outside of or in addition to a typical cyber-attack. Terrorist groups today use the internet on a daily basis. This daily use may include recruitment, training, fundraising, communication, or planning. Organizational cyber-terrorism can use platforms such as social media as a tool to spread a message beyond country borders and instigate physical forms of terrorism. Additionally, organizational goals may use systematic attacks as a tool for training new members of a faction in cyber-warfare.
• Undermining—Cyber-terrorism with undermining as an objective seeks to hinder the normal functioning of computer systems, services, or websites. Such methods include defacing, denying, and exposing information.

While undermining tactics are typically used due to high dependence on online structures to support vital operational functions, they typically do not result in grave consequences unless undertaken as part of a larger attack. Undermining attacks on computers include the following (Waldron 2011):
➢ Directing conventional kinetic weapons against computer equipment, a computer facility, or transmission lines to create a physical attack that disrupts the reliability of equipment. ➢ Using electromagnetic energy, most commonly in the form of an electromagnetic pulse, to create an electronic attack against computer equipment or data transmissions. By overheating circuitry or jamming communications, an electronic attack disrupts the reliability of equipment and the integrity of data. ➢ Using malicious code directed against computer processing code, instruction logic, or data. The code can generate a stream of malicious network packets that disrupt data or logic by exploiting vulnerability in computer software, or a weakness in computer security practices. This type of cyber-attack can disrupt the reliability of equipment, the integrity of data, and the confidentiality of communications (Wilson 2008)
• Destructive—The destructive objective for cyber-terrorism is what organizations fear most. Through the use of computer technology and the Internet, the terrorists seek to inflict destruction or damage on tangible property or assets, and even death or injury to individuals. There are no cases of pure cyber-terrorism as of the date of this plan.

Secondary Hazards
Computer security breaches associated with data and telecommunications losses can have significant economic impact.

Hazardous Materials Incident
Hazardous materials are present in nearly every city and county in the United States in facilities that produce, store, or use them. For example, water treatment plants use chlorine on-site to eliminate bacterial contaminants. Hazardous materials are transported along interstate highways and railways daily. Even the natural gas used in every home and business is a dangerous substance when a leak occurs. Many businesses, through intentional action, lack of awareness or accidental occurrences, have contamination in and around their property.

Title 49 of the CFR lists thousands of hazardous materials, including gasoline, insecticides, household cleaning products, and radioactive materials. State-regulated substances that have the greatest probability of adversely impacting the community are listed in the CCR, Title 19.

Types of Incidents
The following are the most common type of hazardous material incidents:

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• Fixed-Facility Hazardous Materials Incident—This is the uncontrolled release of materials from a fixed site capable of posing a risk to health, safety and property. It is possible to identify and prepare for a fixed-site incident because laws require facilities to notify state and local authorities about what is being used or produced at the site.
• Hazardous Materials Transportation Incident—A hazardous materials transportation incident is any event resulting in uncontrolled release of materials during transport that can pose a risk to health, safety, and property. Transportation incidents are difficult to prepare for because there is little if any notice about what materials could be involved should an accident happen. Hazardous materials transportation incidents can occur anywhere, although most occur on interstate highways or major federal or state highways, or on the major rail lines. In addition to materials such as chlorine that are shipped throughout the country by rail, thousands of shipments of radiological materials, mostly medical materials and low-level radioactive waste, take place via ground transportation across the United States. Many incidents occur in sparsely populated areas and affect very few people.
• Interstate Pipeline Hazardous Materials Incident—A significant number of interstate natural gas, heating oil, and petroleum pipelines run through California cities including Concord. These are used to provide natural gas to utilities in California and to transport these materials from production facilities to end-users.

Oversight
Business practices and the laws that regulate them have changed dramatically over the years. Hazardous materials management is regulated by federal and state codes. The state fire marshal and the Pipeline and Hazardous Materials Safety Administration enforce oil and gas pipeline safety regulations. The federal government enforces hazardous material transport pursuant to its interstate commerce regulation authority.

The Department of Toxic Substances Control (DTSC), a Division of the California Environmental Protection Agency, acts to protect California from exposure to hazardous wastes by cleaning up existing contamination and looking for ways to reduce the hazardous waste produced in the state. The DTSC regulates hazardous waste in California primarily under the authority of the federal Resource Conservation and Recovery Act, and the California Health and Safety Code. Other laws that affect hazardous waste are specific to handling, storage, transportation, disposal, treatment, reduction, cleanup, and emergency planning.

DTSC reviews and monitors legislation to ensure that proposed regulations reflect DTSC goals. DTSC’s major program areas develop regulations and consistent policies and procedures. Under the Resource Conservation and Recovery Act, DTSC has the authority to implement permitting, inspection, compliance and corrective action programs to ensure that people who manage hazardous waste follow state and federal requirements. As such, the management of hazardous sites in the planning area is under regulation by the DTSC, to ensure that state and federal regulations pertaining to hazardous waste are followed.

Businesses are required to disclose all hazardous materials and waste above certain designated quantities that they use, store, or handle at their facility. They must prepare chemical inventory and business emergency plans, review the plans regularly, and perform annual training. Any release or possible release of hazardous material must be reported to the Cal OES Warning Center. Businesses using certain regulated substances (a list of about 260 specific flammable or toxic chemicals) must develop a risk management plan. The risk management plan includes analysis of operations on- site, and projection of off-site consequences with accompanying mitigation plans.

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Secondary Hazards
Roadway or railroad closures due to a transportation-related hazardous material spill would have serious effects on the local economy and ability to provide services. Loss of major travel routes would result in loss of commerce and could impact the ability to provide emergency services to citizens. The ability to receive fuel deliveries could be impacted.

Utility Interruption
Power Failure
A power failure is any interruption or loss of electrical service due to disruption of power generation or transmission caused by an accident, sabotage, natural hazards, equipment failure, or fuel shortage. These interruptions can last anywhere from a few seconds to several days. Power failures are considered significant only if the local emergency management organization is required to coordinate basic services such as the provision of food, water, and heating as a result. Power failures are common with severe weather and winter storm activity.

Pacific Gas and Electric (PG&E) is responsible for operating and maintaining the electrical transmission and distribution system in the planning area. Calpine Corporation energy centers in the Cities of Antioch and Pittsburg generate electricity from natural gas and geothermal resources and sell it to PG&E. Crockett Cogeneration operates a natural gas fired plant in Crockett, California and sells to PG&E. Refineries in the planning area have power generation plants that supply their operations. A co-generation facility next to the Tesoro refinery produces electricity for Tesoro and can sell it to PG&E.

Water or Wastewater Disruption
Water or wastewater disruption is a secondary impact from a natural disaster or intentional act. In the planning area, water service is provided by the Contra Costa Water District. A breach in district pipelines that carry water through the planning area would have significant temporary impacts until alternative water sources are pumped and treated.

Long-term disruption would have significant impacts on residences and businesses in the planning area if demand exceeds secondary supplies and water conservation measures do not provide enough relief to reduce demand to equal the secondary supplies.

Disruption of the planning area’s wastewater collection and wastewater treatment plants would have significant regional impacts. Such disruption could result if the system were to be overwhelmed by a significant storm or discharge of materials in such quantities that the treatment plant could not adequately treat the waste. Natural hazards such as earthquake or flood, major power outages, or terrorism directed at the facilities and systems could disrupt the process of collecting and treating millions of gallons of sewage. Wastewater treatment plants may also have emergencies internal to the plant such as oxygen deficiencies that render them incapable of treating waste. The disruption of service may also have significant environmental impacts on the waterways adjacent to the treatment plants.

Data and Telecommunications Interruptions
The loss of data or telecommunications is often a secondary hazard to natural and other human-caused hazards. Data and telecommunications provide a primary method for service to the community by the government and the private sector. A loss of data and telecommunications could result in loss of emergency dispatch capabilities, emergency planning services, infrastructure monitoring capabilities, access to statistical data, and access to financial and personnel records. Some systems have built in redundancies that might minimize the loss of any data.

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Pipeline Interruptions
Pipelines are often considered the safest and most reliable way to transport natural gas, crude oil, liquid petroleum products, and chemical products, but there is still an inherent risk due to the nature of the hazardous materials.

Failures of pipelines can occur when pipes corrode, are damaged during excavation, are incorrectly operated, or are damaged by other forces. One of the worst hazardous material incidents in the County involved a pipeline carrying gasoline in November 2004 in Walnut Creek. The released fuel ignited, and five people were killed. The affected pipeline runs through Concord and had to be shut off in Concord and Alamo to kill the fire.

Intra-state liquid petroleum pipelines are regulated by the Office of the State Fire Marshal Pipeline Safety Division.

Natural gas pipelines are regulated by the California Public Utilities Commission. Pipelines are also monitored by supervisory control and data acquisition systems that measure flow rate, temperature and pressure. These systems transfer real-time data via satellite from the pipelines to a control center where valves, pumps, and motors are remotely operated. If tampering with the pipeline occurs, an alarm sounds. The ensuing valve reaction is instantaneous, with the system isolating any rupture and setting off a chain reaction that shuts down pipeline pumps and alerts pipeline operators within seconds.

Transmission pipelines and distribution pipelines provide different services. Transmission pipelines transport raw material for further refinement. These pipes are large and far reaching, operating under high pressure. Distribution pipelines provide processed materials to end users. These are smaller in diameter, some as small as a half an inch, and operate under lower pressure. More serious accidents occur on distribution pipelines than on any other type due to their number, intricate networking, and location in highly populated areas.

Secondary Hazards
Utility losses can cause a reduction in employment and in wholesale and retail sales, require utility repairs, and increase medical risk. Local government may lose tax revenue, and the finances of private utility companies and the businesses that rely on them can be disrupted.

Active Shooter Incident
Active shooter attacks are typically motivated by the desire to maximize human casualties. They are differentiated from other attack types by the indiscriminate nature of the victim’s targets of opportunity rather than actions directed toward a specific target. Active shooter attacks have evolved over the last decade ranging from “lone wolf” shooters who act alone and without any organizational affiliation to organized groups acting in concert to achieve a specific objective.

Active shooter threat force tactics employ a blend of lone shooters and multi-person teams as part of a larger assault, as seen in the attacks in Paris in November 2015. They may use small arms (revolvers, automatic pistols, rifles, shotguns, assault rifles, light machine guns, etc.), light weapons (medium caliber and explosive ordinance, grenade launchers, rocket propelled grenades, etc.), or both, depending on the type of attack. The following are characteristics that police and sheriff departments have often seen associated with active shooters. • Active shooters may focus on specific individuals or they may be intent on killing as many randomly chosen people as possible.
• Their purpose is usually an expression of hatred or rage, rather than financial gain or motives associated with other types of crimes. Thus, police tactics of containment and negotiation may be an inadequate response to an active shooter.

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• They chose a site that they are familiar with and have made detailed plans for the attack. In many cases, they are very well armed.
• Active shooters often, but not always, are suicidal. Escaping the police is not usually a priority and in general, they have not attempted to hide their identity.
• The location chosen for the incident usually has a tactical advantage.

Active shooter incidents are unpredictable and evolve quickly. Because active shooter incidents are often over within 5 to 10 minutes, before law enforcement arrives on the scene, individuals at the scene must be prepared both mentally and physically to deal with the shooting in progress situation. In most cases, active shooters use firearms and there is no pattern or method to their selection of victims.

Secondary Hazards
Depending on the severity of the incident, a mass-casualty active shooter event may lead to community distrust in law enforcement. Active shooter events may also lead to economic impacts depending on the community’s willingness to revisit businesses in an area recently affected by an active shooter event.

16.1.2 Hazard Profile
Past Events
Terrorism
According to the Cal OES Terrorism Response Plan, the State of California has had a long history of defending the public against domestic and foreign terrorists. Domestic terrorist groups in California have been focused on political or social issues, while the limited internationally based incidents have targeted the state’s immigrant communities due to foreign disputes. Advanced technologies and communication have allowed these groups to become more sophisticated and better organized, with remote members linked electronically.

Terrorism incidents in Concord have been limited. The following past terrorism events have affected the city or nearby communities:
• June 10, 2019, Concord Mass Shooting Plot Foiled—Local and federal law enforcement authorities foiled a plot by a 23-year-old Concord man to indiscriminately kill people of Jewish faith. The suspect had planned to carry out a copycat attack on a Jewish synagogue, similar to the Poway synagogue shooting on April 27, 2019. Police recovered books about Hitler Youth and Nazi Life in the Concord home along with a rifle, 13 magazines, ammunition, and various other items the suspect planned to use in the attack (Hurd 2019). • December 23, 2015, Richmond Mosque Bomb Threat —A Richmond man was arrested after a pipe bomb was found in his home. The suspect had threatened members of the Islamic Society of West Contra Costa County by yelling “I’m going to kill you” and other threats from the adjacent Burger King parking lot before the investigation began that uncovered the explosive device (ABC 7 News 2015). • August 2, 2008, UC Santa Cruz Firebombing —The vehicles of two UC Santa Cruz scientists were firebombed by animal rights extremists enraged by animal testing at the university (Wilson 2008). • June 22, 1993, UCSF Professor’s Home Bombed by Unabomber—A UCSF professor received a package at home containing an explosive device mailed by “Unabomber” Ted Kaczynski. The professor was killed by the blast. The Unabomber was captured three years after this event (University of California, San Francisco Police Department 2021).

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Civil Unrest
The following are the major past civil unrest events that have affected the planning area or nearby communities:
• November 2021 Kyle Rittenhouse Protests—Nearly 100 people gathered in Oakland to protest the not- guilty verdict in the Kyle Rittenhouse trial. The protests were peaceful and did not result in violence or damage to property.
• May-June 2020 George Floyd Protests—Hundreds of demonstrators gathered on June 2, 2020, across the Bay Area as part of a nationwide protest over the death of George Floyd. Civil rights groups mobilized for protests in cities across the United States amid charged emotions over the death of Floyd in Minneapolis, Minnesota. Certain protestors went on to loot, vandalize, and destroy businesses in the area, leading to an imposed curfew across numerous Bay Area cities (CBS San Francisco 2020).

Cyber Security Threat
The following recent local cyber-attack affected Concord residents (Contra Costa County 2022):
• March 15, 2022 (Contra Costa County)—A cybersecurity breach into county employee email accounts compromised the social security numbers, medical information, and financial account numbers of numerous county employees as well as a few individuals that had communicated with the Employment and Human Services Department. Those affected by this breach were notified and the investigation was completed.

Hazardous Material Incident
Table 16-3 lists the number of hazardous material incidents in the City of Concord reported to the Cal OES Warning Center from 2018 through 2022. Additional historical hazardous material spill report data is available on the Cal OES website. The records show 1,242 hazardous materials spills in the City of Concord over the 5-year timeframe.

Table 16-3. Hazardous Materials Spills in the City of Concord Reported to Cal OES, 2018-2022 Spill Site 2018 2019 2020 2021 2022 Total
Airport 0 0 0 0 0 0
Industrial Plant 0 1 1 0 0 2
Merchant/Business 3 1 4 2 3 13
Military Base 0 1 0 0 0 1
Oil Field 0 0 0 0 0 0
Other 3 2 3 3 1 12
Pipeline 2 0 1 0 0 3
Railroad 0 0 0 0 0 0
Refinery 0 0 0 0 0 0
Residence 4 3 2 3 3 15
Road 4 5 2 2 4 17
School 0 0 0 0 0 0
Service Station 1 2 1 0 2 6
Ship/Harbor/Port 0 1 0 0 0 1
Treatment/Sewage Facility 0 0 0 0 0 0
Utilities/Substation 0 1 2 0 0 3
Waterways 0 4 2 2 3 11
Total 17 21 18 12 16 84
Source: (Cal OES 2023a)

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Notable recent hazardous materials incidents include the following (Contra Costa Health Services 2018):
• November 16, 2022, Concord Gas Pipeline Accident—A construction crew working in the City of Concord struck a gas pipeline, which burst into flames near Highway 242. A highway off-ramp and a portion of Grant and Frederick Street were closed or blocked due to this incident. No injuries were reported, and no structures were threatened.
• July 6, 2018, Shell Martinez Refinery—Two separate events occurred on this day:
➢ A drop in pressure of refinery instrument air resulted in flaring and extinguishing of flare pilots ➢ A small lube oil fire forced shutdown of a unit. HAZMAT personnel responded, but no odors were detected in the area.
• December 19, 2016, Shell Martinez Refinery—One of the refinery’s three main electrical substations’ main breakers tripped during maintenance, causing loss of power to two distribution substations. This resulted in a loss of power to multiple units. No injuries resulted from this incident and no damage was reported. • December 15, 2015, Tesoro Golden Eagle Refinery— The six-boiler unit, which provides steam, tripped offline due to a loss of fuel gas. The loss of steam caused a rise in pressure in a flare knockout pot, which caused flare gas recovery compressors to trip offline. This resulted in flaring from three flares, which also generated smoke due to the loss of steam to the flares. No injuries were reported.

Utility Interruption
Contra Costa Water District services have been interrupted by landslides and storm-related damage. The most recent occurred in January and February 2017, when severe storms caused surficial slides on the face of the Los Vaqueros Dam, the Contra Costa Canal system, trails and other district facilities. Landslides on Morgan Territory Road in Clayton damaged the roadway, resulting in multiple breaks in the District’s 8-inch pipeline and creating temporary water service outage for over 100 customers.

Active Shooter Incident
The following is a past active shooter event that affected the planning area:
• October 5, 2022, Active Shooter Threat at Sunvalley Shopping Center —A 49-year-old man was arrested after entering the Sunvalley Shopping Center with a large duffle bag and claiming he would shoot anyone who came near him. Police utilized an aerial drone to communicate with the suspect, who eventually surrendered without incident. No firearms or explosive devices were recovered on his person (Kelley 2022).

Location
Terrorism
The City of Concord has identified certain high-profile targets for potential terrorists. Large population centers, high visibility tourist attractions, and critical infrastructure accessible to the public present security challenges of an ongoing nature in the planning area.

Civil Disturbance
Civil unrest can take the form of small gatherings or large groups blocking or impeding access to a building or disrupting normal activities by generating noise and intimidating people throughout the entire city. Demonstrations

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can range from a peaceful sit-in to a full-scale riot, in which a mob burns or otherwise destroys property and terrorizes individuals. Even in more passive forms, groups that block roadways, sidewalks, or buildings interfere with public order. Often protests intended to be peaceful escalate into general chaos.

Cyber Security Threat
Cyber-attacks can originate from any computer to affect any other computer in the world. If a system is connected to the Internet or operating on a wireless frequency, it is susceptible to exploitation. Targets of cyber-attacks can be individual computers, networks, organizations, business sectors, or governments. Financial institutions and retailers are often targeted to extract personal and financial data that can be used to steal money from individuals and banks.

The most affected sectors are finance, energy and utilities, and defense and aerospace, as well as communication, retail, and health care. Both public and private operations in Concord are threatened on a near-daily basis by millions of cyberattacks developed to automatically seek technological vulnerabilities.

Hazardous Material Incident
The following locations have the potential of hazardous materials releases:
• Business and Industrial Areas—Retail, manufacturing and industrial firms are areas of concern. These facilities have high concentration of hazardous materials due to their manufacturing operations. Each business is required to file a detailed plan with the Contra Costa Health Services Hazardous Materials Program regarding materials on-site and safety measures taken to protect the public. • Agricultural Areas—Accidental releases of pesticides, fertilizers, and other agricultural chemicals may be harmful to both humans and the environment. Agricultural pesticides are transported daily in and around the planning area en route to destinations in rural areas.
• Illegal Drug Operations—Illegal operations such as laboratories for methamphetamine can pose a threat.

Laboratory residues are often dumped along roadways or left in rented hotel rooms, creating a serious health threat to unsuspecting individuals and to the environment. • Illegal Dumping Sites—Hazardous wastes such as used motor oil, solvents, or paint are occasionally dumped in remote areas or along roadways, creating a potential health threat to unsuspecting individuals and to the environment.
• Transportation Routes—The County’s transportation system consists of a network of federal, state, and county roads, airports, and rail service that all have the potential for hazardous material incidents:
➢ Interstates 80, 580, and 680, State Routes 4, 24, 123, and 242 ➢ Amtrak long distance and intercity trains through the County ➢ Railroad lines—Union Pacific owns 60 miles of lines, BNSF Railway has 55 miles of line, and two smaller lines (Sacramento Northern and Bay Point) operate in the County ➢ General Aviation Airports—Buchanan Field, in the unincorporated county near Concord and Pleasant Hill; and Byron Airport near the Town of Byron.
• Pipelines—Figure 16-1 shows gas and hazardous liquid pipelines in Concord, as well as the locations of accidents and incidents. This information is provided by the National Pipeline Mapping System and is available to the general public.
• Refineries—Six refineries that can pose hazard risks in Contra Costa County are subject to the County’s Industrial Safety Ordinance: Air Products (within the Shell Refinery), Air Products (within the Tesoro Refinery), Phillips 66 Rodeo Refinery, Air Liquide-Rodeo Hydrogen Plant, Shell Oil Martinez Refinery, the DOW Chemical Refinery and Tesoro Golden Eagle Refinery.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-15
Source: PHMSA National Pipeline Mapping System 2017

Figure 16-1. Pipelines in Concord
Utility Interruption
Electrical generation, transmission, and distribution system are located throughout the planning area.

Active Shooter Incident
Depending on the intent of the perpetrator, active shooter events can take place at any location and at any time. If the intent of the perpetrator is to kill or injure as many people as possible, an active shooter event will likely take place in a crowded public place with few exits and low levels of security. Shopping malls, schools, public events, parties, and any other type of medium to large gathering are likely targets. Targeted active shooting events are much smaller in magnitude and are generally confined to one area until the chosen target (whom the shooter likely knows personally) is injured or killed. According to recent studies, 77 percent of active shooter incidents occur in commercial, education, or government environments. Usually, the shooter is familiar with the chosen area and the area offers a tactical advantage.

Frequency
Terrorism
The likelihood of a terrorist event varies with the method of attack, as follows:

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-16
• Chemical—The risk of a chemical event is present in the planning area. The petroleum and agricultural community uses and stores significant amounts of chemicals that could be used in destructive ways. • Explosives—The elements necessary to construct a WMD explosive are readily available. Agricultural communities maintain sufficient products for use in explosive devices. Pipe bomb and suspicious package events have occurred in Concord, though none have been specifically identified as a WMD. • Radiological/Nuclear—The major transportation arteries for vehicles or rail that cross through or near the planning area contribute to the risk of a radiological event. Such products can pass through any of the regional transportation corridors.
• Biological—Anthrax incidents that occurred in the U.S. in October 2001 demonstrate the potential for spreading terror through biological weapons. An agent also could be introduced to livestock, causing harm to public health and the economy.
• Combined Hazards—WMD agents can be combined to have a greater total effect. Given the risks associated with chemical agents in Concord, the possibility of a combined event exists.

Civil Disturbance
Large civil unrest events with injuries and fatalities and public property damage occur infrequently. This type of large event gets a lot of national and international media coverage. Smaller gathering events occur more frequently in the planning area, but with fewer injuries and less property damage.

Cyber Security Threat
Cyber security threats are experienced on a daily basis, often without being noticed. Up-to-date virus protection software used in public and private sectors prevents most cyber-attacks from becoming successful. Programs that promote public education on virus protection are an effective way to mitigate cyber-threats. Cyberterrorism is much less common than cyber-attacks, though the frequency is unknown.

Hazardous Material Incident
Hazardous material incidents may occur at any time in the planning area, given the presence of transportation routes dividing the planning area, the location of businesses and industry that use hazardous materials, the presence of scattered illegitimate businesses such as clandestine drug laboratories, and the improper disposal of hazardous waste.

Table 16-3 lists 84 incidents that occurred in the planning area over a 5-year timeframe.

Utility Interruption
The frequency of utility failure and power interruption is likely to remain constant, but the length of time a utility is shut down should lessen in the future as more redundancies are built into infrastructure and utilities. In addition, leak detection sensors alert utilities to faults and failures more quickly.

Active Shooter Incident
Although recent events have highlighted the severity and impact that mass-casualty active shooter events can have on communities, such events are uncommon. They may happen in clusters as perpetrators feel motivated by other televised acts of violence, but they are generally random and do not normally occur on a consistent or predictable basis.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-17
Severity
Terrorism
A multi-casualty incident is defined as any incident with three or more fatalities or critically injured. Because large numbers of victims may be involved, such incidents may tax local emergency medical and hospital resources, and therefore require a regional response. First responders, including fire, police, and emergency room staffs at local hospitals, follow established protocols for multi-casualty incidents. Mutual aid is requested should local officials be unable to respond appropriately with available personnel and equipment.

Civil Disturbance
Civil unrest and disturbances are human-caused disasters with tremendous potential for causing damage to the City.

They are especially harmful with their effects on human lives. Should disturbances exceed the capabilities of the City’s police services, the City would rely on mutual aid from neighboring law enforcement agencies.

Cyber Security Threat
There is no official index for measuring the severity of a cyber-attack. At the beginning of the COVID-19 pandemic in March 2020, cybersecurity threats spiked by over 400 percent compared to previous months. According to recent data by IBM, it takes an average of 280 days to find and contain the average cyber-attack, and the average attack costs $3.86 million (Fortinet 2022).

Hazardous Materials
Hazardous materials come in the form of explosives, flammable and combustible substances, poisons and radioactive materials. Hazards can occur during production, storage, transportation, use or disposal. The release or spill of hazardous materials requires a different response depending on factors such as the amount, type and location of the spill. Each location should have its own specific cleanup procedure, and all personnel handling such material should have received instruction on that procedure. There has been no fatality in the County from hazardous material release since the Walnut Creek pipeline explosion in 2004. The last hazardous material release that had a fatality at a fixed facility was the MBA Polymers dust explosion in 2000.

Utility Interruption
The severity of utility failure and power interruptions varies too widely to be able to be measured. Electricity, for example, may be out for a few hours to several weeks, depending on the cause of the event.

Active Shooter Incident
Active shooter events have the potential to be mass-casualty incidents, depending on the intent, training, and available ammunition possessed by the attacker. The deadliest active shooter event in modern U.S. history occurred in October 2017, where a gunman killed 58 people and injured over 850 others at a country music festival in Las Vegas, Nevada (Abadi, Pasley and Ardrey 2022).

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-18
Warning Time
Terrorism
According to experts, fewer than 5 percent of all terrorism incidents are preceded by a warning or threat.

Civil Disturbance
Civil disturbances usually have minimal warning time, but when a controversial event has media coverage with a large gathering of people, the Concord Police Department is on high alert, along with other Emergency Operations Organization divisions.

Cyber Security Threat
There is no warning time for cyber-attacks. The top vector for spreading cyber-ransom threats is email.

Hazardous Material Incident
Hazardous material incidents occur without predictability under circumstances that give responders little time to prepare. Contra Costa County uses the Community Warning System to disseminate information to the public in the event of a release or threatened release of a hazardous material. The system includes the integration of warning sirens, the local media, NOAA weather radios, computer terminals, emergency response personnel pages, and emergency phone notification through the telephone emergency notification system. The system also sends out text messages and provides information over Facebook and Twitter. Contra Costa Health Services’ Hazardous Materials Incident Response Team provides general data to first responders to advise evacuations or sheltering in place.

Utility Interruption
Utility failure and power interruptions occur at any time without warning. However, they usually are a secondary effect from a storm event, landslide, earthquake, and human-caused issues.

Active Shooter Incident
Behavioral warning signs are generally the only type of advanced warning for these events. Behavioral warning signs may include animal abuse, the sharing of violent or explicit content online, posing with firearms in a threatening manner on social media, and other indicators.

16.1.3 Exposure
Population and Property
Terrorism
Numerous potential targets for terrorism exist in Concord. A terrorist event could range from an individual attack to a coordinated attack by multiple agents upon multiple targets. Large -scale incidents have the potential to kill or injure many people in the immediate vicinity and may also affect people a relative distance from th e initial event. Variables affecting exposure for a WMD attack include the physical and chemical properties of the WMD, the ambient temperature, wind speed, wind direction, barometric pressure, and humidity.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-19
All structures and property in the City of Concord are exposed to this hazard. The emphasis on accessibility, the opportunity for roof access, driveways underneath some structures, unmonitored areas, the proximity of many structures to transportation corridors and underground pipelines, and the potential for a terrorist to strike any structure randomly all have an impact on the vulnerability of structures.

Civil Disturbance
The entire population of the Concord is exposed to the civil unrest hazard. Those who live in densely populated areas, those living near colleges/universities, correctional facilities, landmarks, courthouses, and other areas of significance may have a higher exposure and are thus more vulnerable to the effects of civil unrest.

All City pr operty is exposed during civil unrest and may be damaged or destroyed during a riot. All City assets are susceptible to damage during civil unrest. Concord Police Department facilities are likely the most at risk since several demonstrations or rallies have originated at this location in the past.

Previous experience indicates that critical response facilities (police stations, fire stations) are at risk during periods o f civil unrest. In addition, critical operating facilities, such as Concord City Hall, the Mayor’s Office, etc. are at risk of damage or destruction, or may be rendered inoperative for some time. Depending on the nature of the event, however, all City-owned assets may be considered vulnerable to damage or destruction as a result of civil unre st. Because of the unpredictability of civil unrest events, no specific estimates can be made concerning potential losses.

Cyber Security Threat
The entire planning area population is exposed to cyber security threat personally or at places of employment. All populations who directly use a computer or receive services from automated systems are exposed to cyber-terrorism.

Structures are usually not impacted by cyber security threats, but systems operated by electronics and computers are exposed.

Hazardous Material Incident
According to the California Department of Finance, there are 47,683 housing units in the City of Concord as of January 1, 2022. Variables affecting exposure in the event of a hazardous materials incident include the type of product, the physical and chemical properties of the substance, the physical state of the product (solid, liquid, or gas), the ambient temperature, wind speed, wind direction, barometric pressure, and humidity. With so many variables, distances are difficult to forecast. In general, those close to transportation corridors or businesses with acutely hazardous materials are more at risk for some sort of effect; but each chemical incident is different and the scenarios are numerous.

Hazardous materials pose a significant risk to emergency response personnel. All potential first responders and follow-on emergency personnel in the planning area currently are and will be properly trained to the level of emergency response actions required of their individual position at the response scene. Hazardous materials also pose a serious long-term threat to public health and safety, property and the environment.

Utility Interruption
All residents and visitors are exposed to utility interruptions. This will continue as people are dependent on basic utility services such as electricity, water, wastewater, gasoline, natural gas, etc. All property is exposed to some type of utility infrastructure throughout the planning area.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-20
Active Shooter Incident
The entire population of Concord is exposed to the potential hazard of an active shooter event. Active shooter events generally do not involve damage to property aside from stray or over-penetrating bullets that may punch holes in walls or other property nearby. Property may be affected i f the attacker uses explosives or other destructive devices in the assault, which is very uncommon.

Critical Facilities and Infrastructure
Terrorism and Hazardous Material Incident
Hazardous materials may be stored at or transported along critical facilities. In the industrial corridor along the northern and northwestern portions of the county, Chevron, Phillips 66, Shell, Tesoro Golden Eagle Refinery, Dow Chemical, and USS-Posco Industries all house hazardous materials. These facilities are susceptible to accidents and are visible targets for terrorism. The exposure of critical facilities and infrastructure to a terrorism event or hazardous material incident is based on the facility’s criticality and physical vulnerability:
• Criticality is a measure of the potential consequence of an accidental or terrorist event as well as the attractiveness of the facility to a potential adversary or threat. The criticality for each critical facility is based on the factors shown in Table 16-4.
• Vulnerability is a measure of the physical opportunity for an accident or an adversarial attack. This assessment takes into consideration physical design, existing countermeasures, and site layout. The vulnerability for each critical facility is based on the criteria shown in Table 16-5.

Table 16-4. Criticality Factors
Criterion Low Criticality Medium Criticality High Criticality Awarenessa Not known/Neighborhood City/Region/County State/National Hazardous
Materialsb
None / limited and secure Moderate to large and secure Large, minimum or no security Collateral Damage
Potentialc
None or low Moderate/immediate area or
within 1 mile radius
High/immediate area or within
1 mile radius
Site Populationd 0 – 300 301 – 1,000 1,001 or greater
Public/ Emergency
Functione
No emergency function, or could be
used for emergency function in the
future
Support emergency function—
redundant site
Emergency function—critical
service with or without
redundancy
a. Awareness—How aware is the public of the existence of the facility, site, system, or location? b. Hazardous Materials—Are flammable, explosive, biological, chemical and/or radiological materials present on site? c. Collateral Damage Potential—What are the potential consequences for the surrounding area if the asset is attacked or damaged? d. Site Population—What is the potential for mass causalities, based on the capacity of the facility. e. Public or Emergency Functions—Does the facility perform a function during an emergency? Is this facility or function capable of being replicated elsewhere?

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-21
Table 16-5. Vulnerability Criteria
Criterion Low Vulnerability Medium Vulnerability High Vulnerability Accessibilitya Remote location, secure
perimeter, tightly controlled
access
Controlled access, protected or
unprotected entry
Open access, unrestricted,
patrolling security, sign
restrictions
Automobile
Proximityb
Not within 75’ – 100’ Not within 25’ – 50’ Adjacent or not within 10’ Asset Mobilityc Moves or is relocated
frequently
Moves or is relocated occasionally Permanent/Fixed
Proximity to other
Critical Facilitiesd
Greater than 1.5 – 2 miles Greater than 3/4 - 1 mile Within 1/2 – 3/4 mile Secure Designe No areas for concealment of
packages, air intakes are on
roof, access ways are not
under the structure.

Area of concealment present,
greater than 25’ from the
structure; Air intakes located at
least 10’ above ground, may have
under structure access drives.

Areas of concealment within
25’, air intakes at ground level,
under structure access drives.
a. Accessibility—How accessible is the facility or site to the public? b. Automobile Proximity—How close can an automobile get to the facility? How vulnerable is the facility to a car bomb attack? c. Asset Mobility—Is the facility or asset’s location fixed or mobile? If mobile, how often is it moved, relocated, or repositioned? d. Proximity to other critical facilities—If the facility is close to other critical facilities then there could be an increased probability of the facility receiving collateral damage.
e. Secure design—General evaluation of areas of obstruction, air intake locations, parking lot and road design and locations and other site design aspects.

Civil Disturbance
Critical facilities are exposed during a riot event. Civil unrest can damage or destroy any facility and block roads and infrastructure from being used.

Cyber Security Threat
All critical facilities and infrastructure that operate by electricity and/or a computer system are exposed to cyber security threats.

Utility Interruption
Critical facilities are exposed to utility interruption. Damage to critical facilities can disrupt health care, fire and police services and impair search and rescue and emergency medical care.

Active Shooter Incident
Critical facilities do not play a role for an active shooter incident. The location of infrastructure such as roads and highways may play a role in the chosen site for an active shooter, but the intent is to obtain inflict extensive personal harm before police arrive and shooters are usually not planning to flee the scene.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-22
Environment
Terrorism
The environment is exposed to terrorism events, which, depending on the methods used, can kill wildlife, destroy habitat, and contaminate critical resources in the food chain.

Civil Disturbance
The environment is not generally affected by civil unrest. Most of the damage is to people and property.

Cyber Security Threat
The environment is not exposed to cyber security threats and thus would not risk damage. It would only be through a secondary effect that the environment could be effected by a cyber-attack. For example: a cyber-attack that shuts down a hydroelectric dam so that a river would be affected.

Hazardous Material Incident
The risk of hazardous material spills to the environment is considerable. Hazardous materials spilled along roads or railways can pollute rivers, streams, wetlands, riparian areas and adjoining fields. Other hazardous materials released into the air can severely impact plant and animal species. Reducing risk exposure to the built environment will also mitigate potential losses to the natural environment.

Utility Interruption
The environment is usually not exposed to utility interruption unless it is a spill that contaminates water or open land or creates a wildfire that burns acres.

Active Shooter Incident
The environment does not play a role for an active shooter incident.

16.1.4 Vulnerability
Population
Terrorism
Although terrorism has not resulted in a large number of deaths in the planning area, it can be deadly and widespread.

Any individuals exposed to human-caused hazards are considered to be at risk, particularly those working as first responders.

Civil Disturbance
All individuals in the planning area are considered vulnerable in the event of civil unrest or a civil disturbance. Police officers, other first responders, magistrates, judges, and other public or private officials may be targeted and especially vulnerable depending on the focus of the demonstrations, riots, or other gatherings.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-23
Cyber Security Threat
All populations who directly use a computer or receive services from automated systems are vulnerable to cyber security threats. Certain types of attacks would impact specific segments of the population. If the cyber security threat targeted the PG&E power or utility grid, individuals with medical needs would be impacted the greatest. These populations are most vulnerable because many of the life-saving systems they rely on require power. If an attack occurred during extreme hot weather, those 65 and older would be vulnerable to the effects of the lack of air conditioning. These individuals might require an air-conditioned shelter operating on a back-up generator. If a cyber- attack targeted a facility storing or manufacturing hazardous materials, individuals living adjacent to these facilities would be vulnerable.

Hazardous Material Incident
People near facilities producing, storing, or transporting hazardous substances are at higher risk. Populations downstream, downwind, and downhill of a released substance are particularly vulnerable. A spill of a toxic airborne chemical in a populated area could have greater potential for loss of life. Depending on the characteristics of the substance released, more people in a larger area may be in danger from explosion, absorption, injection, ingestion, or inhalation. Often, people in the radius area (outside the immediate affected area) are evacuated as a precaution or told to shelter-in-place, depending on the release type and wind conditions.

Utility Interruption
The entire planning area is vulnerable to utility interruptions. FEMA has developed standard loss-of-use estimates in conjunction with its benefit/cost analysis methodologies to estimate the cost of lost utilities on a per-person, per-use basis, as summarized in Table 16-6.

Table 16-6. FEMA Standard Value for Loss of Service for Utilities and Roads/Bridges Interruption Total Economic Impact
Complete Loss of Electric Power $126 per person per day Complete Loss of Potable Water
Service
$93 per person per day
Complete Loss of Wastewater Service $41 per person per day Complete Loss of Road/Bridge Service $38.15 per vehicle per hour of vehicle delay detour time $0.55 per mile of vehicle delay (or current federal mileage rate) Source: FEMA BCA Reference Guide, June 2009, Appendix C Active Shooter Incident
All individuals in the planning area are considered to be at risk to active shooter incidents.

Property
Terrorism
All structures in the planning area are physically vulnerable to a terrorism event. Factors that affect vulnerability include an emphasis on accessibility, opportunities for roof access, driveways underneath structures, unmonitored areas, and the proximity of structures to transportation corridors and underground pipelines.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-24
Civil Disturbance
All property in the planning area is vulnerable to the effects of civil unrest and civil disturbance including businesses, government buildings, etc.

Cyber Security Threat
The entire City’s population is vulnerable to a cyber-attack. Because it is difficult to predict the particular target of cyber-terrorism, assessing vulnerability to the hazard is also difficult. All populations who directly use a computer or receive services from automated systems are vulnerable to cyber-terrorism. Although all individuals in the City are vulnerable to an attack, certain types of attacks would impact specific segments of the population. • If the cyber-attack targeted the City’s power or utility grid, individuals with medical needs would be impacted the greatest. These populations are most vulnerable because many of the life-saving systems they rely on require power.
• If an attack occurred during months of extreme hot weather, those 65 years of age and older would be vulnerable to the effects of the lack of climate control. These individuals might require an air-conditioned shelter operating on a back-up generator.
• If a cyber-attack targeted a facility storing or manufacturing hazardous materials, individuals living adjacent to these facilities would be vulnerable to the secondary effects, should the attack successfully cause a critical failure at that facility.

Hazardous Material Incident
The impact of a fixed-facility hazardous materials incident will likely be localized to the property where it occurs. The impact of a spill of a small amount of a liquid chemical may be limited to remediation of soil.

Utility Interruption
All property is exposed and vulnerable to some type of utility infrastructure failure throughout the planning area.

Active Shooter Incident
The intent of an active shooter is to harm persons; property may be incidentally damaged, but the shooter’s intent does not generally focus on property.

Critical Facilities and Infrastructure
Terrorism
The U.S. Office of Homeland Security created the 2003 National Strategy for the Physical Protection of Critical Infrastructure of Critical Infrastructure and Key Assets, which lays a foundation to work together to prepare and protect critical infrastructure and key assets nationwide from terrorist events. Owners of critical facilities and infrastructure know that they are vulnerable to terrorism and have executed preparedness planning and exercises for years and fortified these facilities to minimize their vulnerability. Critical facilities being targeted during a terrorist attack can result in other human-caused hazards such as hazardous material incidents, pipeline accidents, and cybersecurity concerns.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-25
Civil Disturbance
Critical facilities are unlikely to experience significant damage from an incident of civil disturbance or unrest.

Cyber Security Threat
A catastrophic cyber security threat can have far-ranging effects on public and private infrastructure systems. All critical facilities and infrastructure that are operated by electricity and/or a computer system are vulnerable to the cyber security threat. Cyber-threats may affect structures if any critical electronic systems suffer service disruption. For instance, a cyber-attack may cripple the electronic system that controls a cooling system or pressure system, resulting in physical damage to the structure from components overheating, or an explosion if pressure relief systems are rendered inoperable.

Hazardous Material Incident
The impact of a hazardous material spill or transportation incident will likely be localized to the particular facility, hospital, port, airport, railroad, road, highway, or interstate. The potential losses vary because of the variable nature of the hazardous material spill, but costs from product loss, property damage and decontamination and other costs can add up to millions of dollars.

Utility Interruption
Critical facilities are vulnerable to utility interruption. But the adverse effect of damaged critical facilities can extend beyond direct physical damage. It can disrupt health care, fire, and police services, impair search and rescue, and emergency medical care.

Active Shooter Incident
Critical facilities are unlikely to experience significant damage from an active shooter incident.

Environment
Terrorism
A terrorism event using a WMD could cause harm to the environment, but no platforms currently exist for estimating the level of harm. The best gauge of vulnerability of the environment would be a review of damage from past terrorism events. Capturing such data from future events could be beneficial in measuring the vulnerability of the environment.

Civil Disturbance
The environment is unlikely to experience significant damage from an incident of civil disturbance or unrest.

Cyber Security Threat
While effects of cyber-threats on the natural environment are unlikely, they can occur. Such effects may come from a system failure that, for example, allows a release of hazardous materials or improper disposal of waste.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-26
Hazardous Material Incident
Depending on the characteristic of the hazardous material or the volume of product involved, the affected area can be as small as a room in a building or as large as many square miles that require soil remediation. More widespread effects occur when a product contaminates the municipal water supply or water system such as a port, river, lake, or aquifer.

Such environmental damage can linger for decades.

Utility Interruption
The environment is vulnerable to utility interruption if the utility has a spill that contaminants water and/or open land or creates a wildfire that burns acres.

Active Shooter Incident
The environment is unlikely to experience significant damage from an active shooter incident.

Economic Impacts
Terrorism
Economic impacts from a terrorist event could be significant. The cost of a terrorist act would be felt in terms of loss of life and property and disruption of business activity. Recovery would take significant resources and expense at the local level.

Civil Disturbance
Economic impacts can occur from loss of patrons coming to a local business where an incident occurred, down time from a closed business, and loss of wages for individuals forced to close their businesses due to events of civil unrest.

Cyber Security Threat
Cyber-threats can have extensive fiscal impacts. Companies and government services can lose large sums of unrecoverable revenue from site downtime and compromise of sensitive confidential data. The economic impact of data and telecommunications losses can be high as computer security breaches, crime conducted via the internet such as identify theft, and many other forms of cyber-attack occur daily. Millions of dollars are lost each year as criminals and cyber-terrorists steal sensitive information and funds from individuals and organizations.

Hazardous Material Incident
Large hazardous material spills can drive away tourists. Transportation incidents can temporarily shut down transportation routes. Studies that look at economic effects from bridge and highway losses consistently report job loss and economic losses in the billions of dollars. For example, 43 percent of businesses reporting losses after the 1994 Northridge Earthquake said they were due to transportation issues.

Utility Interruption
Utility losses could cause a reduction in employment and wholesale and retail sales, a need for utility repairs, and increased medical risks. Local governments might lose tax revenues, and the finances of private utility companies and the businesses that rely on them would be disrupted.

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City of Concord Hazard Mitigation Plan Other Hazards of Interest 16-27
Active Shooter Incident
Economic impacts can occur from loss of patrons coming to a local business where an incident occurred, down time from a closed business, and loss of wages for an individual who was injured or killed.

16.1.5 Future Trends in Development
Terrorism
The agencies and organizations involved with terrorism in the City of Concord, specifically threat analyses and threat reduction capability studies, are examining the challenges presented by future development and expansion.

Individually, and in collaboration with task forces and other facilities, plans are underway for continuation, changes and/or expansion of current initiatives. Buildings and other structures constructed to resist earthquakes and fires usually have qualities that also limit damage from blasts and resist fire spread and spread of noxious fumes in the event of a terrorist attack.

Civil Disturbance
There is a correlation between civil unrest and higher population density in larger cities. Larger more densely populated cities with culturally diverse populations tend to be more vulnerable to this hazard.

Because it is evident that societal trends and emerging social issues have led to these types of events in the past, cities with cultural diversity such as Concord may be subject to civil unrest in the future.

Cyber Security Threat
The City of Concord will continue to be impacted by and compelled to respond to cyber-attacks in the future. The nature of these attacks is projected to evolve in sophistication over time. The City will remain vigilant in its efforts to prevent attacks from occurring or disrupting business operations. The reality remains that many computers and networks in organizations of all sizes and industries around the U.S. will continue to suffer intrusion attempts on a daily basis from viruses and malware that are passed through websites and emails.

Hazardous Material Incident
The number and types of hazardous chemicals stored in and transported through the City of Concord will likely continue to increase. As population grows, the number of people vulnerable to the impacts of hazardous materials spills and transportation incidents will increase. Population and business growth along major transportation corridors increases the vulnerability to transportation-related hazardous material spills.

Utility Interruption
The likelihood of utility interruption in the future will continue as development and population growth continue in the City. The majority of utilities in the City are privately owned, and market forces are, as a rule, insufficient to induce needed investments in protection. Private organizational strategies and policies will need to work together to ensure reliable and resilient services for the long term.

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Concord City CouncilMarch 10, 2026

Concord City Council
March 10, 2026