Exh 1. 2024 Contra Costa County LHMP Volume 1 — San Pablo City Council, April 7, 2025 (part 1 of 3)

VOLUME I
2024 HazardMitigationPlan
Contra Costa County,California
Planning Area-wide Elements

2024 Hazard Mitigation Plan
Contra Costa County, California

Table of Contents i

TABLE OF CONTENTS
Executive Summary ................................................................................................................................ 1 Chapter 1. Introduction ................................................................................................................. 3

1.1 Purpose of the Plan ................................................................................................................... 3

1.2 Hazard Mitigation Program ....................................................................................................... 3

1.3 Planning Area ............................................................................................................................ 4

1.4 Participating Jurisdictions .......................................................................................................... 4

1.5 Plan Participation ...................................................................................................................... 5

1.5.1. Core Planning Team ............................................................................................................................ 5

1.5.2. Steering Committee ............................................................................................................................. 6

1.5.3. Local Planning Teams and Community Representatives .................................................................... 7

1.5.4. Supporting Organizations .................................................................................................................... 7

1.6 Plan Approval and Adoption ...................................................................................................... 7 Chapter 2. Planning Process ........................................................................................................ 8

2.1 Review of Existing Programs and Plans ................................................................................. 10

2.2 Equity Consideration for the Underserved Population ............................................................ 11 Chapter 3. Community Profile .................................................................................................... 14

3.1 Contra Costa County History .................................................................................................. 15

3.2 Topography ............................................................................................................................. 15

3.3 Climate .................................................................................................................................... 16

3.4 Land Use ................................................................................................................................. 18

3.5 Changes in Development & Development Trends .................................................................. 20

3.5.1. Implications of Development on Risk ................................................................................................. 20

3.6 Future Trends in Development ................................................................................................ 21

3.7 Demographics ......................................................................................................................... 21

3.7.2. Underserved Population .................................................................................................................... 24

3.8 Economy ................................................................................................................................. 26

3.9 Critical Infrastructure ............................................................................................................... 28

3.10 Capability Assessment ............................................................................................................ 30

3.10.1. Planning and Regulatory Capabilities ........................................................................................... 30

3.10.2. Administrative and Technical Capabilities ..................................................................................... 33

3.10.3. Financial Capabilities ..................................................................................................................... 36

3.10.4. Education and Outreach Capabilities ............................................................................................ 37

3.11 Hazard Mitigation Integration .................................................................................................. 38

3.11.1. Existing Plan Integration ................................................................................................................ 39

3.11.2. Potential Future Integration ........................................................................................................... 39

3.12 National Flood Insurance Program ......................................................................................... 40 2024 Hazard Mitigation Plan
Contra Costa County, California

Table of Contents ii

3.12.1. Contra Costa County Floodplain Management Program .............................................................. 41

3.12.2. Floodplain Managers ..................................................................................................................... 42

3.12.3. Participation Activities .................................................................................................................... 43 Chapter 4. Hazard Identification and Risk Assessment ........................................................... 44

4.1 Identified Hazards ................................................................................................................... 44

4.2 Presidential Disaster and Emergency Declarations ................................................................ 46

4.3 Risk Assessment Methodology ............................................................................................... 48

4.3.1. Probability of Occurrence ................................................................................................................... 49

4.3.2. Extent Factors .................................................................................................................................... 50

4.3.3. Vulnerability Factors .......................................................................................................................... 51

4.3.4. Impact Factors ................................................................................................................................... 52

4.4 FEMA National Risk Index Scores .......................................................................................... 56

4.4.1. Expected Annual Loss ....................................................................................................................... 56

4.4.2. Social Vulnerability ............................................................................................................................. 57

4.4.3. Community Resilience ....................................................................................................................... 57

4.5 Total Risk Scores .................................................................................................................... 58

4.6 Hazard Profiles ........................................................................................................................ 61

4.6.1. Climate Change ................................................................................................................................. 61

4.6.2. Dam and Levee Failure ...................................................................................................................... 76

4.6.3. Drought ............................................................................................................................................ 103

4.6.4. Earthquake ....................................................................................................................................... 119

4.6.5. Flood ................................................................................................................................................ 142

4.6.6. Landslide .......................................................................................................................................... 167

4.6.7. Sea Level Rise ................................................................................................................................. 182

4.6.8. Severe Weather ............................................................................................................................... 196

4.6.9. Tsunami ........................................................................................................................................... 233

4.6.10. Wildfire ......................................................................................................................................... 247

4.6.11. Other Hazard of Concern ............................................................................................................ 264 Chapter 5. Mitigation Strategy .................................................................................................. 285

5.1 Mitigation Goals .................................................................................................................... 285

5.2 Mitigation Strategies and Actions .......................................................................................... 286

5.2.1. Mitigation Action Plan ...................................................................................................................... 287

5.3 Changes in Priority ................................................................................................................ 291 Chapter 6. Plan Maintenance .................................................................................................... 294

6.1 Plan Update .......................................................................................................................... 294

6.1.1. Monitoring, Evaluating ..................................................................................................................... 294

2024 Hazard Mitigation Plan
Contra Costa County, California

Table of Contents i

APPENDICES
Appendix A. Mitigation Actions ................................................................................................... 299 Appendix B. Stakeholder Engagement ....................................................................................... 356 Appendix C. Public Engagement ................................................................................................. 389 Appendix D. Plan Adoption .......................................................................................................... 512

LIST OF TABLES
Table 1-1. Participating Jurisdictions .................................................................................................................... 5 Table 1-2. Core Planning Team Members ............................................................................................................ 5 Table 1-3. Hazard Mitigation Steering Committee Members ................................................................................ 6 Table 3-1. Contra Costa County Monthly Climate Summary (1970 – 2023) ...................................................... 17 Table 3-2. Acreages of Land Use Designations ................................................................................................. 18 Table 3-3. Population Estimates .................................................................................................................... 22 Table 3-4. Poverty Thresholds for 2022 by Size of Family ................................................................................. 23 Table 3-5. Age Distribution (2022) ................................................................................................................. 23 Table 3-6. Racial and Ethnic Distribution (2022) ........................................................................................... 24 Table 3-7. Social Vulnerability Index (2020) ....................................................................................................... 25 Table 3-8. Employment by Industry (2022) ......................................................................................................... 27 Table 3-9. Employment Status (2022) ................................................................................................................ 27 Table 3-10. Occupation (2022) ......................................................................................................................... 27 Table 3-11. Income and Benefits (2022) .......................................................................................................... 28 Table 3-12. Critical Infrastructure in Contra Costa County ............................................................................... 28 Table 3-13. Countywide Planning and Regulatory Capabilities........................................................................ 30 Table 3-14. Administrative and Technical Capabilities ..................................................................................... 34 Table 3-15. Financial Resources ...................................................................................................................... 36 Table 3-16. Education and Outreach Resources ............................................................................................. 37 Table 3-17. Current Plan Integration ................................................................................................................ 39 Table 3-18. Potential Future Integration ........................................................................................................... 40 Table 3-19. NFIP Participation Information ....................................................................................................... 40 Table 3-20. Floodplain Managers ..................................................................................................................... 42 Table 4-1. Contra Costa County Hazards ........................................................................................................... 45 Table 4-2. State and Federal Disaster Declarations for Contra Costa County ................................................... 46 Table 4-3. Probability of Occurrence ................................................................................................................... 49 Table 4-4. Extent/Intensity Factor ....................................................................................................................... 50 Table 4-5. Catastrophic Factor ............................................................................................................................ 50 Table 4-6. Population Exposure Factor............................................................................................................... 51 Table 4-7. Property Exposure Factor .................................................................................................................. 51 Table 4-8. Changes in Development Factor ....................................................................................................... 51 Table 4-9. Population and Life Safety Factor ...................................................................................................... 52 Table 4-10. Underserved/Equity Factor ............................................................................................................ 52 Table 4-11. Property Damage Factor ............................................................................................................... 53 Table 4-12. Economic Factor ............................................................................................................................ 53 Table 4-13. Environmental Factor .................................................................................................................... 54 Table 4-14. Essential Operations Factor .......................................................................................................... 54 Table 4-15. Future Development Factor ........................................................................................................... 55 Table 4-16. Climate Change Factor .................................................................................................................. 55 Table 4-17. Risk Index Score for Contra Costa County (FEMA National Risk Index) ...................................... 56 Table 4-18. Expected Annual Loss for Contra Costa County (FEMA National Risk Index) ............................. 57 Table 4-19. Social Vulnerability for Contra Costa County (FEMA National Risk Index) .................................. 57 Table 4-20. Community Resilience for Contra Costa County (FEMA National Risk Index) ............................. 58 Table 4-21. 2024 Hazard Risk Score for Contra Costa County........................................................................ 59 2024 Hazard Mitigation Plan
Contra Costa County, California

Table of Contents ii
Table 4-22. Climate Change Indicators in the United States ............................................................................ 62 Table 4-23. IPCC Scenarios ............................................................................................................................. 64 Table 4-24. Climate Change Impacts in California ..................................................................................... 66 Table 4-25. Neighborhoods At Risk Table (Contra Costa County, CA) ........................................................... 71 Table 4-26. Probability of Occurrence .............................................................................................................. 73 Table 4-27. Extent Factors................................................................................................................................ 73 Table 4-28. Vulnerability Factors ...................................................................................................................... 73 Table 4-29. Impact Factors ............................................................................................................................... 73 Table 4-30. Climate Change Total Risk Score ................................................................................................. 75 Table 4-31. Dam Failure Types ................................................................................................................... 76 Table 4-32. High Hazard Dams in Contra Costa County .................................................................................. 78 Table 4-33. Additional Dams in Contra Costa County ...................................................................................... 80 Table 4-34. Dams Outside of Contra Costa County ......................................................................................... 81 Table 4-35. Dams Within Jurisdiction in Contra Costa County with DSOD Downstream Hazard Potential Classifications ....................................................................................................................................................... 82 Table 4-36. Project Levees in Contra Costa County ........................................................................................ 83 Table 4-37. Non-Project Reclamation District Levees in Contra Costa County ............................................... 83 Table 4-38. USACE Dam Hazard Categories .................................................................................................. 85 Table 4-39. DSOD’s Downstream Hazard Potential Classifications ................................................................ 86 Table 4-40. USACE Levee Safety Action Classification (LSAC) ................................................................ 86 Table 4-41. Dam and Levee Failure Past Events ............................................................................................. 88 Table 4-42. Vulnerability and At Risk Population ............................................................................................. 90 Table 4-43. Critical Assets in Vulnerable to Dam Failure ................................................................................. 91 Table 4-44. Levee and Vulnerability in the Leveed Area .................................................................................. 91 Table 4-45. 25-Year Precipitation Projections for Contra Costa County .................................................... 98 Table 4-46. Future Climate Indicators for Contra Costa County ...................................................................... 98 Table 4-47. Probability of Occurrence ............................................................................................................ 100 Table 4-48. Extent Factors.............................................................................................................................. 100 Table 4-49. Vulnerability Factors .................................................................................................................... 100 Table 4-50. Impact Factors ............................................................................................................................. 100 Table 4-51. Dam and Levee Failure Total Risk Score .................................................................................... 102 Table 4-52. Types of Drought ......................................................................................................................... 103 Table 4-53. Palmer Drought Severity Index .................................................................................................... 104 Table 4-54. U.S. Drought Monitor Classification ............................................................................................ 106 Table 4-55. Drought Annualized Frequency for Contra Costa County (FEMA National Risk Index) ............. 108 Table 4-56. Drought Past Events .................................................................................................................... 109 Table 4-57. 25-Year Climate Projections for Contra Costa County ................................................................ 113 Table 4-58. Future Climate Indicators for Contra Costa County .................................................................... 114 Table 4-59. Probability of Occurrence ............................................................................................................ 115 Table 4-60. Extent Factors.............................................................................................................................. 115 Table 4-61. Vulnerability Factors .................................................................................................................... 115 Table 4-62. Impact Factors ............................................................................................................................. 115 Table 4-63. Drought Expected Annual Loss (FEMA National Risk Index) ..................................................... 117 Table 4-64. Drought Risk Index (FEMA National Risk Index) ........................................................................ 117 Table 4-65. Drought Total Risk Score ............................................................................................................ 118 Table 4-66. Active Faults Within the Contra Costa County Area.................................................................... 120 Table 4-67. Modified Mercalli Scale vs. Richter Scale ................................................................................... 123 Table 4-68. Earthquake Warning California Alerting Thresholds ................................................................... 124 Table 4-69. Earthquake Probabilities for the San Francisco Bay Area (2014 – 2043) ................................... 125 Table 4-70. Earthquake Annualized Frequency (FEMA National Risk Index) ................................................ 126 Table 4-71. Earthquake Past Events Within or Near Contra Costa County (Magnitude 5.0 or Greater) .. 127 Table 4-72. Disability Characteristics (2022) .................................................................................................. 128 Table 4-73. Vulnerability and At Risk Population ........................................................................................... 129 Table 4-74. Physical Housing Characteristics in Contra Costa County ......................................................... 130 Table 4-75. Critical Assets Vulnerable to Earthquakes .................................................................................. 131 2024 Hazard Mitigation Plan
Contra Costa County, California

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Table 4-76. Probability of Occurrence ............................................................................................................ 133 Table 4-77. Extent Factors.............................................................................................................................. 133 Table 4-78. Vulnerability Factors .................................................................................................................... 133 Table 4-79. Impact Factors ............................................................................................................................. 133 Table 4-80. Contra Costa County Population and Building Value Data ......................................................... 135 Table 4-81. Expected Building Damage by Occupancy ................................................................................. 135 Table 4-82. Expected Building Damage by Building Type ............................................................................. 136 Table 4-83. HAZUS Earthquake Expected Damage to Essential Facilities ................................................... 136 Table 4-84. Expected Damage to Utility Systems .......................................................................................... 137 Table 4-85. Expected Damage to the Transportation Systems ...................................................................... 137 Table 4-86. Building Related Economic Loss Estimates (Millions of Dollars) ................................................ 138 Table 4-87. HAZUS Earthquake Transportation System Economic Losses (Millions of Dollars) .................. 139 Table 4-88. Earthquake Expected Annual Loss (FEMA National Risk Index) ................................................ 140 Table 4-89. Earthquake Risk Index (FEMA National Risk Index) ................................................................... 140 Table 4-90. Earthquake Total Risk Score ....................................................................................................... 141 Table 4-91. Flood Types ........................................................................................................................... 142 Table 4-92. Contra Costa County Flooding Sources ...................................................................................... 143 Table 4-93. NWS Flood Advisories ................................................................................................................. 146 Table 4-94. NWS Flash Flood Impact Based Warnings ................................................................................. 146 Table 4-95. NWS River Flood Severity Categories ........................................................................................ 147 Table 4-96. Recurrence Intervals and Probabilities of Occurrences .............................................................. 147 Table 4-97. Riverine Flooding Annualized Frequency (FEMA National Risk Index) ...................................... 147 Table 4-98. Contra Costa County Repetitive Loss and Severe Repetitive Loss Properties .......................... 149 Table 4-99. Flood Events (1950 – 2023) ........................................................................................................ 150 Table 4-100. Vulnerability and At Risk Population ........................................................................................... 155 Table 4-101. Critical Assets in the 100-Year and 500-Year Floodplains .......................................................... 156 Table 4-102. 25-Year Precipitation Projections for Contra Costa County .................................................. 159 Table 4-103. Future Climate Indicators for Contra Costa County .................................................................... 159 Table 4-104. Probability of Occurrence ............................................................................................................ 160 Table 4-105. Extent Factors.............................................................................................................................. 160 Table 4-106. Vulnerability Factors .................................................................................................................... 160 Table 4-107. Impact Factors ............................................................................................................................. 161 Table 4-108. Contra Costa County Population and Building Value Data ......................................................... 163 Table 4-109. 100-Year Flood Expected Building Damage by Occupancy ....................................................... 163 Table 4-110. Expected Building Damage by Building Type ............................................................................. 164 Table 4-111. 100-Year Flood Expected Damage to Essential Facilities .......................................................... 164 Table 4-112. 100-Year Flood Building Related Economic Loss Estimates (Millions of Dollars) ...................... 165 Table 4-113. Riverine Flooding Expected Annual Loss (FEMA National Risk Index) ...................................... 166 Table 4-114. Riverine Flooding Risk Index (FEMA National Risk Index) ......................................................... 166 Table 4-115. Flooding Total Risk Score ........................................................................................................... 166 Table 4-116. Types of Slope Movement ........................................................................................................... 167 Table 4-117. Types of Common Landslide ................................................................................................. 168 Table 4-118. USGS Landslide Advisories ........................................................................................................ 171 Table 4-119. Landslide Annualized Frequency (FEMA National Risk Index) ................................................... 171 Table 4-120. Significant Landslide Events ........................................................................................................ 172 Table 4-121. Vulnerability and At Risk Population ........................................................................................... 174 Table 4-122. Critical Assets Vulnerable to Landslides ..................................................................................... 175 Table 4-123. 25-Year Climate Projections for Contra Costa County .......................................................... 177 Table 4-124. Probability of Occurrence ............................................................................................................ 178 Table 4-125. Extent Factors.............................................................................................................................. 178 Table 4-126. Vulnerability Factors .................................................................................................................... 178 Table 4-127. Impact Factors ............................................................................................................................. 178 Table 4-128. Landslide Expected Annual Loss (FEMA National Risk Index) ................................................... 180 Table 4-129. Landslide Risk Index (FEMA National Risk Index) ...................................................................... 180 Table 4-130. Landslide Total Risk Score .......................................................................................................... 181 2024 Hazard Mitigation Plan
Contra Costa County, California

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Table 4-131. Projected Sea Level Rise for San Francisco ............................................................................... 184 Table 4-132. Probability that Sea level Rise Will Meet or Exceed a Particular Height in San Francisco (High Emissions – RCP 8.5)............................................................................................................................................ 186 Table 4-133. Probability that Sea level Rise Will Meet or Exceed a Particular Height in San Francisco (Low Emissions – RCP 2.6)............................................................................................................................................ 186 Table 4-134. Coastal Flooding Annualized Frequency (FEMA National Risk Index) ....................................... 186 Table 4-135. Vulnerability and At Risk Population ........................................................................................... 187 Table 4-136. Critical Assets in Vulnerable to 1 Foot of Sea Level Rise ........................................................... 189 Table 4-137. Probability of Occurrence ............................................................................................................ 192 Table 4-138. Extent Factors.............................................................................................................................. 192 Table 4-139. Vulnerability Factors .................................................................................................................... 192 Table 4-140. Impact Factors ............................................................................................................................. 192 Table 4-141. Coastal Flooding Expected Annual Loss (FEMA National Risk Index) ....................................... 194 Table 4-142. Coastal Flooding Risk Index (FEMA National Risk Index) .......................................................... 194 Table 4-143. Sea Level Rise Total Risk Score ................................................................................................. 195 Table 4-144. Hail Speed Estimates .................................................................................................................. 196 Table 4-145. Types of Strong Winds ................................................................................................................ 197 Table 4-146. Types of Tornadoes ..................................................................................................................... 198 Table 4-147. Converting Traditional Hail Size Descriptions ............................................................................. 203 Table 4-148. Beaufort Wind Scale .................................................................................................................... 204 Table 4-149. Enhanced Fujita Scale ................................................................................................................. 205 Table 4-150. NWS HeatRisk Categories .......................................................................................................... 205 Table 4-151. Atmospheric River Scale ............................................................................................................. 206 Table 4-152. NWS Severe Weather Advisories................................................................................................ 206 Table 4-153. NWS Excessive Heat Advisories ................................................................................................. 207 Table 4-154. Hail Annualized Frequency (FEMA National Risk Index) ............................................................ 208 Table 4-155. Strong Wind Annualized Frequency (FEMA National Risk Index) .............................................. 208 Table 4-156. Tornado Annualized Frequency (FEMA National Risk Index) ..................................................... 208 Table 4-157. Heat Wave Annualized Frequency (FEMA National Risk Index) ................................................ 209 Table 4-158. Strong Winds Events (1950 – 2023) ........................................................................................... 209 Table 4-159. Tornado Events (1950 – 2023) .................................................................................................... 213 Table 4-160. Heavy Rainfall Past Events ......................................................................................................... 214 Table 4-161. Heat Events (1950 – 2023) .......................................................................................................... 215 Table 4-162. Vulnerability and At Risk Population ........................................................................................... 219 Table 4-163. Critical Assets Vulnerable to Severe Weather ............................................................................ 221 Table 4-164. Probability of Occurrence ............................................................................................................ 224 Table 4-165. Extent Factors.............................................................................................................................. 224 Table 4-166. Vulnerability Factors .................................................................................................................... 225 Table 4-167. Impact Factors ............................................................................................................................. 226 Table 4-168. Hail Expected Annual Loss (FEMA National Risk Index) ............................................................ 229 Table 4-169. Strong Wind Expected Annual Loss (FEMA National Risk Index) .............................................. 229 Table 4-170. Tornado Expected Annual Loss (FEMA National Risk Index) ..................................................... 229 Table 4-171. Riverine Flooding Expected Annual Loss (FEMA National Risk Index) ...................................... 230 Table 4-172. Heat Wave Expected Annual Loss (FEMA National Risk Index) ................................................ 230 Table 4-173. Hail Risk Index (FEMA National Risk Index) ............................................................................... 230 Table 4-174. Strong Wind Risk Index (FEMA National Risk Index) ................................................................. 231 Table 4-175. Tornado Wind Risk Index (FEMA National Risk Index) .............................................................. 231 Table 4-176. Riverine Flooding Risk Index (FEMA National Risk Index) ......................................................... 231 Table 4-177. Heat Wave Risk Index (FEMA National Risk Index) ................................................................... 231 Table 4-178. Severe Weather Total Risk Score ............................................................................................... 232 Table 4-179. Papadopoulos and Imamura Tsunami Scale .............................................................................. 235 Table 4-180. National Tsunami Warning Center Alerts .................................................................................... 237 Table 4-181. Tsunami Annualized Frequency (FEMA National Risk Index) .................................................... 237 Table 4-182. Tsunami Events (1950 – 2023) ................................................................................................... 238 Table 4-183. Vulnerability and At Risk Population ........................................................................................... 239 2024 Hazard Mitigation Plan
Contra Costa County, California

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Table 4-184. Critical Assets Vulnerable to Tsunami ......................................................................................... 241 Table 4-185. Probability of Occurrence ............................................................................................................ 243 Table 4-186. Extent Factors.............................................................................................................................. 243 Table 4-187. Vulnerability Factors .................................................................................................................... 243 Table 4-188. Impact Factors ............................................................................................................................. 243 Table 4-189. Tsunami Expected Annual Loss (FEMA National Risk Index) .................................................... 245 Table 4-190. Tsunami Risk Index (FEMA National Risk Index) ....................................................................... 245 Table 4-191. Tsunami Total Risk Score ........................................................................................................... 246 Table 4-192. Types of Wildfires ........................................................................................................................ 247 Table 4-193. Air Quality Index for Ozone and Particle Pollution ...................................................................... 250 Table 4-194. National Weather Service Fire Advisories ................................................................................... 250 Table 4-195. Wildfire Annualized Frequency (FEMA National Risk Index) ...................................................... 251 Table 4-196. Wildfire Events (1950 – 2023) ..................................................................................................... 251 Table 4-197. Critical Assets in Vulnerable to Wildfire ....................................................................................... 256 Table 4-198. 25-Year Climate Projections for Contra Costa County ................................................................ 258 Table 4-199. Future Climate Indicators for Contra Costa County .................................................................... 259 Table 4-200. Probability of Occurrence ............................................................................................................ 260 Table 4-201. Extent Factors.............................................................................................................................. 260 Table 4-202. Vulnerability Factors .................................................................................................................... 260 Table 4-203. Impact Factors ............................................................................................................................. 260 Table 4-204. Wildfire Expected Annual Loss (FEMA National Risk Index) ...................................................... 262 Table 4-205. Wildfire Risk Index (FEMA National Risk Index) ......................................................................... 262 Table 4-206. Wildfire Total Risk Score ............................................................................................................. 263 Table 4-207. Common Types of Cyberattacks ................................................................................................. 265 Table 4-208. Counterterrorism Objectives ........................................................................................................ 266 Table 4-209. Cybersecurity Total Risk Score ................................................................................................... 269 Table 4-210. Hazardous Materials Incident Types ........................................................................................... 270 Table 4-211. Hazardous Materials Incidents (Reported to CalOES) ................................................................ 272 Table 4-212. Hazardous Materials Incidents Total Risk Score ......................................................................... 274 Table 4-213. Utility Interruption Past Events .................................................................................................... 277 Table 4-214. Utility Interruptions Total Risk Score ........................................................................................... 278 Table 4-215. Active Shooter Total Risk Score .................................................................................................. 281 Table 4-216. Terrorism Total Risk Score .......................................................................................................... 284 Table 5-1. Contra Costa County Mitigation Goals and Objectives ................................................................... 285 Table 5-2. Contra Costa County Mitigation Actions Summary ......................................................................... 287 Table 5-3. Mitigation Action Estimated Cost Parameters ................................................................................. 288 Table 5-4. Mitigation Action Benefits Parameters ............................................................................................. 288 Table 5-5. Mitigation Action Project Duration Parameters ................................................................................ 288 Table 5-6. Existing Mitigation Action Priority Parameters ................................................................................. 289 Table 5-7. STAPLEE+E Method ....................................................................................................................... 289 Table 5-8. New Mitigation Action Priority Parameters ...................................................................................... 291 Table 6-1. Five-Year Action Plan ...................................................................................................................... 297 Table 6-2. Contra Costa County Mitigation Actions Summary ......................................................................... 299

LIST OF FIGURES
Figure 3-1. Contra Costa County Planning Area ............................................................................................. 14 Figure 3-2. Topographical Map ........................................................................................................................ 16 Figure 3-3. Land Use Map ............................................................................................................................... 19 Figure 3-4. Existing Development in Unincorporated Contra Costa County Flood Zones ......................... 21 Figure 3-5. Impacted Communities .................................................................................................................. 26 Figure 3-6. Critical Infrastructure in Contra Costa County ............................................................................... 29 Figure 4-1. Global Temperature Trends (1993 – 2022) ............................................................................. 63 Figure 4-2. Projected Annual Global Carbon Emissions ................................................................................. 65 Figure 4-3. Projected Global Temperatures..................................................................................................... 65 2024 Hazard Mitigation Plan
Contra Costa County, California

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Figure 4-4. Temperature and Atmospheric CO2 Variation the Past 400,000 Years ........................................ 67 Figure 4-5. Global Average Surface Temperature (1880 – 2022) ................................................................... 67 Figure 4-6. High and Significant Hazard Dams in the Contra Costa County Area .......................................... 80 Figure 4-7. Dams Inundation Areas in the Contra Costa County Area ............................................................ 81 Figure 4-8. Levee Systems in Contra Costa County Area ............................................................................... 84 Figure 4-9. Palmer Drought Severity Index Map (March 2024) ..................................................................... 105 Figure 4-10. California U.S. Drought Monitor (April 9, 2024) ........................................................................... 107 Figure 4-11. U.S. Drought Monitor for Contra Costa County ..................................................................... 108 Figure 4-12. Faults Located in the San Francisco Bay Region ....................................................................... 121 Figure 4-13. Earthquake History in Contra Costa County Area ....................................................................... 122 Figure 4-14. USGS National Seismic Hazard Map .......................................................................................... 126 Figure 4-15. Contra Costa County Floodplain ................................................................................................. 145 Figure 4-16. Landslide Susceptibility in Contra Costa County ......................................................................... 170 Figure 4-17. Expected Sea Level Rise 2050 Projection .................................................................................. 183 Figure 4-18. Expected Sea Level Rise 2100 Projection .................................................................................. 184 Figure 4-19. National Weather Service Heat Index Chart ............................................................................... 199 Figure 4-20. Contra Costa County Hail History (1950 – 2023) ........................................................................ 200 Figure 4-21. Contra Costa County Strong Wind History (1950 – 2023) .......................................................... 201 Figure 4-22. Contra Costa County Tornado History (1950 – 2023) ................................................................. 202 Figure 4-23. SPC Severe Thunderstorm Outlook Categories ......................................................................... 203 Figure 4-24. Contra Costa County Tsunami Hazard Areas ............................................................................. 234 Figure 4-25. Contra Costa County Fire Hazard Severity Zones ...................................................................... 248 Figure 4-26. Contra Costa County Wildland-Urban Interface .......................................................................... 249 Figure 4-27. Contra Costa County Historic Wildfire Perimeters ...................................................................... 253

2024 Hazard Mitigation Plan
Contra Costa County, California

Executive Summary 1

EXECUTIVE SUMMARY
The Contra Costa County Hazard Mitigation Plan (the Plan) was developed to guide Contra Costa County in a risk-based approach to become more resilient to the impacts of natural and technological hazards through mitigation planning. The Plan identifies potential hazards that could negatively impact County operations and assesses the risk and vulnerability of life safety and County assets for each hazard. This Plan also establishes strategies and priorities to mitigate risk from natural, human-caused, and technological hazards, identifies specific mitigation projects to pursue for each identified hazard, guides the County in associated risk management activities, and establishes eligibility for future mitigation program funds. The development of this Plan was a collaborative effort among the Contra Costa County Core Planning Team and Steering Committee with support from Integrated Solutions Consulting (ISC).

The five (5) goals for this Plan, identified by the Contra Costa County Steering Committee, are listed below. The goals represent the County’s long term and strategic vision to accomplish and achieve successful mitigation efforts. Additionally, the Steering Committee identified 19 objectives which are specific strategies and steps identified to assist the communities in attaining the listed goals.

Goals
1 Save (or protect) lives and reduce injury.
2 Increase resilience of infrastructure and critical facilities. 3 Avoid (minimize or reduce) damage to property.
4 Encourage the development and implementation of long-term, cost-effective, and environmentally sound mitigation projects.
5 Build and support capacity to enable local government and the public to prepare for, respond to and recover from the impact of natural hazards.

There are a number of hazards that pose a threat to human life, health, and well -being, and this Plan is not meant to compile an exhaustive list. Contra Costa County identified 10 natural hazards and five (5) human-caused/technological hazards for this Plan. Although FEMA only requires and reviews natural hazards in hazard mitigation plans, Contra Costa County decided to rank and mitigate against a comprehensive list of hazard events that could impact the County. Due to the nature of non- natural hazards and the discretionary status regarding their inclusion, the following hazards of interest have been briefly and qualitatively assessed for the sake of public education and informing their inclusion within the hazard ranking and mitigation process. Hazards that have been identified as significant in Contra Costa County and that will be considered in this Plan are listed below.

Identified Hazards
Natural Hazards
Climate Change
Dam and Levee Failure
Drought
Earthquake
Flood
2024 Hazard Mitigation Plan
Contra Costa County, California

Executive Summary 2
Identified Hazards
Landslide
Sea Level Rise (Coastal Flooding)
Severe Weather (Severe Thunderstorms – Hail, Strong Winds, Tornadoes – Heavy Rainfall, Heat Wave/Extreme Heat) Tsunami
Wildfire
Human-Caused/Technological Hazards
Cybersecurity Threats
Hazardous Materials Incidents
Utility Interruptions
Active Shooter Incidents
Terrorism (Weapons of Mass Destruction)

The following key elements are included in the 2024 Contra Costa County Hazard Mitigation Plan.

• Planning Process: The Core Planning Team, Steering Committee, and planning process are described and documented.
• Community Profile: Demographics (including underserved population) , social, and economic data, as well as existing and future land use descriptions, are updated to reflect the status of Contra Costa County and its jurisdictions.
• Hazard Risk Assessment: Outlines the process of measuring the potential loss of life, personal injury, economic injury, and property damage resulting from natural hazards. In this section, the process focuses on the following elements – hazard identification, vulnerability identification, and cost evaluation.
• Mitigation Strategy: The mitigation strategy describes how the community will accomplish the overall purpose of the planning process. In this section, mitigation goals and objectives were reevaluated and updated; and mitigation actions were updated, identified, evaluated, and prioritized.
• Plan Maintenance: The Hazard Mitigation Plan requires monitoring, evaluati on, and updati ng every five (5) years. This section includes a schedule for annual monitoring and evaluation of the programmatic outcomes established in the Plan and for producing a formal Plan revision every five (5) years.
• Appendices: Includes the Contra Costa County’s mitigation actions, stakeholder and public engagement details and supporting documentation, and the plan adoption. • Annexes: This Plan includes 40 plan participants – 16 municipalities and 24 special districts – and each jurisdiction developed its own annex. All jurisdiction specific information and supporting documentation (e.g., hazard vulnerability and impacts, mitigation actions, stakeholder and public engagement) can be found in the respective annexes.

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CHAPTER 1. INTRODUCTION
The Contra Costa County Hazard Mitigation Plan (Plan) was developed to guide the County in a risk - based approach to become more resilient to the impacts of natural , human-caused, and technological hazards through mitigation planning. The Plan documents historical disasters, assesses probabilistic disasters through Hazus and GIS analys is, and addresses specific strategies to mitigate the potential impacts of these disasters.

This five (5) year update was a collaborative effort among the Contra Costa County Core Planning Team.

The Plan accomplishes the following:

• Identifies areas of risk and assesses the probability, extent, vulnerability, and impacts for each natural hazard.
• Establishes strategies and priorities to mitigate risk from natural hazards. • Identifies specific mitigation projects to pursue for each identified natural hazard. • Guides the communities in their risk management activities and minimizes conflicts among agencies.
• Establishes eligibility for future mitigation program funds.

1.1 PURPOSE OF THE PLAN
The Plan identifies activities that can be undertaken by both the public and private sectors to reduce risk to natural, human-caused, and technological hazards, property damage, and economic disruption caused by these hazards. This Plan reviews mitigation activities and selects those that will be most beneficial for Contra Costa County.

The Federal Disaster Mitigation Act of 2000 requires jurisdictions to develop and maintain a Hazard Mitigation Plan to remain eligible for certain Federal disaster assistance and hazard mitigation funding programs (e.g., Hazard Mitigation Grant Program, Building Resilient Infrastructure and Communities).

Renewal of the Plan every five (5) years is required to encourage continual awareness of mitigation strategies. Additionally, communities that participate in the Federal Emergency Management Agency (FEMA) Community Rating System (CRS), a voluntary program that reduces National Flood Insurance Program (NFIP) premiums and are designated as a Category C repetitive loss community, must prepare a Floodplain Management Plan (FMP) or a Repetitive Loss Area Analysis (RLAA). However, the CRS Program allows multi-hazard and multi-jurisdictional mitigation plans to fulfill this requirement.

This Plan fulfills the federal requirements for mitigation funding outlined in 44 Code of Federal Regulations (CFR), section 201.6 (44 CFR § 201.6) and United States Code (USC) 42, section 5165 (42 USC § 5165), the CRS Program and provides the jurisdiction with a blueprint for reducing the impacts of natural, human- caused, and technological hazards.

1.2 HAZARD MITIGATION PROGRAM
Hazard mitigation is defined as any sustainable action taken to reduce or eliminate long-term risk to people and property from future disasters. Mitigation planning breaks the cycle of disaster damage, reconstruction, and repeated damage. Hazard mitigati on includes long-term solutions that reduce the impact of disasters in the future.
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• Keep the hazards away from people, property, and structures. • Keep people, property, or structures away from the hazard. • Reduce the impact of the hazards on victims (e.g., insurance).

1.3 PLANNING AREA
The planning area was defined to consist of the unincorporated county, 16 incorporated jurisdictions (i.e., cities and towns), and 23 special districts within the geographical boundary of Contra Costa County. All partners to this Plan have jurisdictional authority within this planning area.

All incorporated jurisdictions were invited to participate in the planning process. The cities of Pittsburg and Concord declined participation because each city has a FEMA -approved Hazard Mitigation Plan.

Additionally, the City of Antioch opted to not participate in this Hazard Mitigation Plan. Therefore, the cities of Antioch, Concord, and Pittsburg are not included as participating jurisdictions in this Plan. For countywide interest and statistical purposes, some Antioch, Concord, and Pittsburg demographics, and hazard-related data are included in this Plan. The intent of this inclusion is to create a more informative plan regarding the hazards, risks, and vulnerabilities across all of Contra Costa County.

1.4 PARTICIPATING JURISDICTIONS
All participating jurisdictions (i.e., cities, towns, and special districts) listed in Table 1-1 were represented by one (1) or more representatives. Responsibilities for each of the participati ng jurisdiction’s representatives included the following:

• Assist with gathering the appropriate data and historical information. • Complete the community preparedness survey.
• Participate in their jurisdiction’s hazard analysis.
• Identify new mitigation actions.
• Update existing mitigation actions.
• Participate in workshops, mitigation meetings, and webinars. • Review draft documents, as necessary.

Contact information for each of the representatives and documentation of participation in the Plan update are available in Appendix B. The County also invited key organizati ons to assist and review the plan update process; supporting documentation is available in Appendix C.

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Table 1-1. Participating Jurisdictions
Cities, Towns, and Unincorporated Contra Costa County
Contra Costa County City of Lafayette City of Pleasant Hill City of Brentwood City of Martinez City of Richmond
City of Clayton Town of Moraga City of San Pablo
Town of Danville City of Oakley City of San Ramon
City of El Cerrito City of Orinda City of Walnut Creek
City of Hercules City of Pinole
Special Districts
Bethel Island Municipal
Improvement District
Kensington Police Protection and
Community Services District
Reclamation District No. 2122
(Winter Island)
Central Contra Costa Sanitary
District Mt. View Sanitary District Reclamation District No. 2137 Contra Costa County Fire
Protection District
Pleasant Hill Parks and Recreation
District
Rodeo-Hercules Fire Protection
District
Contra Costa County Flood Control
and Water Conservation District
Reclamation District No. 799
(Hotchkiss Tract)
San Ramon Valley Fire Protection
District
Contra Costa Water District Reclamation District No. 830 (Jersey Island)
San Ramon Valley Unified School
District
Diablo Water District Reclamation District No. 2025
(Holland Tract)
Town of Discovery Bay Community
Services District
Ironhouse Sanitary District Reclamation District No. 2026 (Webb Tract) West County Wastewater District
Kensington Fire Protection District Reclamation District No. 2065 (Veale Tract)

1.5 PLAN PARTICIPATION
Updating this Plan involved assistance in identifying and evaluating hazards and mitigation actions from five (5) main groups – Core Planning Team, Steering Committee, representatives from County jurisdictions, members of the public, and other stakeholders.

1.5.1. Core Planning Team
The Core Planning Team consisted of key members from the Contra Costa County Office of Emergency Services (OES) and staff from Integrates Solutions Consulting (ISC). The Core Planning Team also served on the Steering Committee and helped guide the planning process. Table 1-2 lists the Core Planning Team members from Contra Costa County OES.

Table 1-2. Core Planning Team Members
Name Title Jurisdiction/Organization
Rick Kovar Emergency Services Manager Contra Costa County Office of Emergency Services
Beatriz Portillo Senior Emergency Planning
Coordinator
Contra Costa County Office of
Emergency Services
Lorena Herrera Senior Emergency Planning
Coordinator
Contra Costa County Office of
Emergency Services
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Name Title Jurisdiction/Organization
Jennifer Cannon Senior Emergency Planning
Coordinator
Contra Costa County Office of
Emergency Services

1.5.2. Steering Committee
Hazard mitigation planning enhances collaboration and support among diverse parties whose interests can be affected by hazard losses. A Hazard Mitigation Steering Committee (the Steering Committee) was formed to oversee all phases of the planning process.

Throughout this Plan update, the Steering Committee agreed to meet as often as needed through the planning process. The Core Planning Team facilitated each meeting, which addressed a set of objectives based on the work plan established. All members of the Steering Committee were actively involved in attending meetings and responsible for the following:

• Identifying and prioritizing natural, human-caused, and technological hazards that impact Contra Costa County.
• Defining and identifying critical facilities.
• Identifying the Plan’s goals and objectives.
• The planning area’s capability assessment and consideration of mitigation alternatives. • Identifying and prioritizing mitigation actions and projects. • Coordinating and conducting outreach with key stakeholders, planning partners, and the public.

The Steering Committee members are listed on Table 1-3 and the Steering Committee Meetings sign-in sheets are available in Appendix B.

Table 1-3. Hazard Mitigation Steering Committee Members Name Title Jurisdiction/Organization
Beatriz Portillo Senior Emergency Planning
Coordinator
Contra Costa County Office of
Emergency Services
Brian Helmick Deputy Fire Chief Contra Costa County Fire Protection District
Carol McCray AFN Co-Coordinator VistAbility
Daniel Barrios Senior Planner Department of Conservation and Development
Gilbert Salinas Chief Equity Officer Contra Costa Health (DEI) Glenn Kimball Community & Media Relations
Specialist
Contra Costa County Office of
Communication and Media
Jeff Valeros Senior Civil Engineer Contra Costa Public Works Jody London Sustainability Coordinator Department of Conservation and Development
Kristi Jourdan Director Contra Costa County Office of
Communication and Media
Larry Fong Volunteer American Red Cross, Contra Costa
Search and Rescue, and CERT
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Name Title Jurisdiction/Organization
Lissette Davis Community & Media Relations
Specialist
Contra Costa County Office of
Communication and Media
Lorena Herrera Senior Emergency Planning
Coordinator
Contra Costa County Office of
Emergency Services
Rick Kovar Emergency Services Manager Contra Costa County Office of Emergency Services
Robyn Cole Emergency Services Coordinator
California Office of Emergency
Services - Coastal Region
Response Ops
Seana Fields Senior Planner (Community
Development) City of Hercules
Thomas Rossberg Lieutenant Contra Costa County Office of the Sheriff

1.5.3. Local Planning Teams and Community Representatives Each of the participating jurisdictions identified representatives to serve on their Local Planning Teams.

The Local Planning Teams were instrumental in identi fying community -specific risks/hazards and identifying and priori tizing mi tigation ac tions that would reduce the costs of disaster response and recovery, protect people and infrastructure, and minimize overall disrupti on to their respec tive communities in the event of a disaster.

1.5.4. Supporting Organizations
Throughout the planning process, key stakeholders, departments, and community organizations , including local community organizations that provide support to underserved communities, were involved in providing key input, data, disseminating information about the Plan, survey, meetings, and reviewing the draft of the Plan (i.e., public comment period). Details regarding stakeholder engagement throughout the planning process and a list of stakeholders can be found in Appendix B.

1.6 PLAN APPROVAL AND ADOPTION
The Plan presents a comprehensive description of Contra Costa County’s commitment to significantly reduce or eliminate the potential impacts of disasters through planning and mitigation. Adoption by the local governing body within the State of California legitimizes the Plan and authorizes Contra Costa County and its jurisdictions to implement mitigation responsibilities and activities.

A hazard mitigation plan must document that it has been formally adopted by the governing bodies of the jurisdictions requesting federal approval of the plan (44 CFR Section 201.6(c)(5)). For multi-jurisdictional plans, such as this, each jurisdiction requesting approval must formally adopt the Plan. This Plan will be submitted for a pre-adoption review to Cal OES and FEMA Region IX prior to adoption. Once pre- adoption approval has been provided, all participating jurisdictions will formally adopt the Plan. Federal Disaster Mitigation Act of 2000 compliance and its benefits cannot be achieved until the Plan is adopted.

Copies of the resolutions adopting this Plan for all planning partners can be found in Appendix D.

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CHAPTER 2. PLANNING PROCESS
The Contra Costa County Hazard Mitigation Plan was developed to provide a basis for identifying and managing natural, human-caused, and technological hazards, and to meet federal, state, and local requirements for hazard mitigation and FEMA mitigation grant funding.

Updating this Plan began with an initial kick -off meeting with the Contra Costa County Office of Emergency Services (OES) on September 7, 2023. Following this meeting, a series of Stakeholder and Jurisdiction Introductory Webinars were held on September 25 and 27, 2023, and October 3 and 4, 2023.

The main purpose of these webinars was to provide information regarding FEMA ’s Hazard Mitigation Program directive and how participating in this Plan will enable jurisdictions (i.e., cities, towns, and special districts) to become eligible for FEMA hazard mitigation grant programs. Furthermore, the planning process involved the following:

• Review of the existing Plan.
• Updating Contra Costa County’s hazard history.
• Gathering information on local hazards from individual communities. • Gathering input on hazard priorities.
• Identifying specific vulnerabilities and desired mitigation strategies. • Evaluating the previous Plan goals, objectives, and mitigation strategies. • Determining the status of previous mitigation strategies and action plans. • Identifying Repetitive Loss and Severe Repetitive Loss properties. • Facilitating the activities of the Steering Committee. • Conducting multiple public meetings and outreach activities.

Information regarding Contra Costa County’s hazards and applicable mitigation strategies was obtained through two (2) Stakeholder Workshops held in the Contra Costa County Emergency Operations Center on December 4 and 6, 2023. Additionally, a comprehensive public survey reached 1,894 residents and resulted in 1,387 completed responses.

The 2024 Contra Costa County Haza rd Mitigation Questionnaire (i.e., Public Survey) was available in English, Spanish, Traditional Chinese, Simplified Chinese, and Tagalog. The English and Spanish survey opened on October 19, 2023. While the Traditional Chinese, Simplified Chinese, and Tagalog opened on November 15, 2023. As part of this survey, Steering Committee members, community representatives, and members of the public were asked to rate each of the hazards in terms of perceived risk.

Furthermore, they were asked to rate “mitigation importance” for each of the identified hazards in the Plan. The information gathered from this survey was used to inform the hazard risk prioritization process, and to ensure the Plan adequately addressed the public’s concerns and priorities. Three (3) Public Meetings were held throughout the County on December 4, 5, and 6, 2023. These meetings were advertised for residents to have an opportunity to provide input into the Plan. Additionally, a draft of the Plan was made available on the Contra Costa County OES website for public review and comment from April 22, 2024, through May 31, 2024.

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The purpose of the two (2) Stakeholder Workshops was to ensure local jurisdictions had the opportunity to identify their community ’s risks and identify/update their mitigation strategies and priorities. These Workshops included local planning team members from each city, town, and special district. Participants validated the County’s risk assessment findings, described specific hazard risks and concerns for their communities, updated existing mitigation actions/strategies from the 2018 Plan, and worked with their local planning teams to identify new mitigation i nitiatives. Through a combination of ranking exercises, worksheets, and discussions, workshop participants evaluated hazard risk results , action plans, and rankings; and selected options for mitigating specific hazards to be included in the 2024 Plan update.

In summary, the planning process consisted of the following key tasks:

Task 1: Organize Resources
Contra Costa County OES created a Core Planning Team to attend meetings, gather data and historical information, review drafts, and participate in mitigation brainstorming sessions. Additionally, a Steering Committee was formed to provide overall guidance and direction throughout the mitigation planning process. A series of Steering Committee meetings were held throughout the Plan update process.

Participating jurisdictions were invited to form Local Planning Teams to ensure their jurisdiction’s mitigation needs and priorities were addressed. Refer to Plan Participation under Chapter 1 (Introduction) for a list of Core Planning Team and Steering Committee members.

Task 2: Risk Assessment
The Core Planning Team identified the hazards to include in this Plan, as well as hazard profiles to address the probability, extent, vulnerabilities, and impacts associated with each hazard. Furthermore, the Team used local resources to inventory Contra C osta County’s assets and estimated losses. The Core Planning Team and Steering Committee provided input and subject matter expertise throughout this process.

Task 3: Public Involvement and Participation
The public was given an opportunity to be involved throughout the planning process via a public survey, in-person and virtual public meetings, and public engagement activities to review the Plan draft. The public was invited to attend one (1) of three (3) Public Meetings to review the risk assessment results and discuss mitigation strategies. The Public Meetings were conducted in person with options to attend virtually and were advertised locally in advanc e. A comprehensive Public Survey that reached 1,895 residents and resulted in 1,387 completed responses, up until January 30, 2024, was also conducted.

The survey results were used to inform the hazard risk prioritization process and to ensure the Plan adequately addresses the public’s concerns and priorities. The complete survey and a summary of its findings can be found in Appendix C. Once the draft Plan was completed, the public was given an opportunity to review and provide comments on Volume 1 ( Planning Area-wide Elements) and each of the jurisdiction annexes. The public comment period began on April 22, 2024. Each plan participant developed a public outreach strategy to engage stakeholders and the public during the public comment period. Further details on public engagement and participation along with supporting documentation can be found in Appendix C. Public engagement participation and supporting documentation for each plan participant can be found in their respective annexes.

To further facilitate con tinued public involvement in the planning process, the public will have an opportunity to provide continual feedback and input. As future needs and concerns arise, or if the public would like to provide feedback regarding the latest version of the Contra Costa County Hazard Mitigation Plan, the public is invited to use the form provided on the County’s website to provide comments.

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Task 4: Develop Mitigation Strategies
The Core Planning Team met with representatives from each community (Local Planning Team) to develop and prioritize mitigation strategies and actions items that would reduce the costs of disaster response and recovery, protect people and infrastructure, and minimize overall disruption to the County in the event of a disaster. A list of mitigation actions for each plan participant can be found in their respective annexes.

Task 5: Complete the Plan
The Core Planning Team compiled all the relevant sections of the Plan to produce a Draft Plan for review.

Contra Costa County stakeholders, which include members of the public, had multiple opportunities to review and revise the Plan before submitting it to the California Office of Emergency Services and FEMA for review.

Task 6: Plan Adoption
Contra Costa County OES coordinated the effort to ensure the Approvable Pending Adoption (APA) was formally adopted by each participating jurisdiction (i.e., city, town, and special district) and that at least one (1) jurisdiction adopted the Plan within one (1) year of the APA notification from FEMA.

Updating this Plan involved assistance in identifying and evaluating hazards and mitigation options from five (5) key groups – Core Planning Team, Steering Committee, local planning teams from the participating jurisdictions/districts, members of the public, and other stakeholders.

2.1 REVIEW OF EXISTING PROGRAMS AND PLANS
Since a Hazard Mitigation Plan is only a part of the emergency planning, mitigation, preparedness, response, and recovery process, a second objective of the planning process was to coordinate Plan preparation with existing Contra Costa County emergency plans, programs, procedures, and organizations. The following programs can affect mitigation within the planning area:

• California Fire Code
• The California Fire Alliance
• California Building Code
• California State Hazard Mitigation Forum
• Adapting to Rising Tides
• Contra Costa County Climate Action Plan
• Local Capital Improvement Programs
• Local Emergency Operations Plans
• Local General Plans
o Housing Element
o Safety Element
• Local Zoning Ordinances
• Local Coastal Program Policies

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An assessment for each jurisdiction’s capabilities that can contribute to the reduction of long-term vulnerabilities to hazards are addressed in their respective annexes . It should be noted that this Plan does not replace any existing plans or programs but is intended to provide a reference on hazard mitigation to be used in planning and program development.

2.2 EQUITY CONSIDERATION FOR THE UNDERSERVED POPULATION Some disasters occur on larger scales and are more impacted by built environments and are most likely to continually impact those most at risk because of existing health conditions, lack of resources, being underserved by past mitigation planning work, fac ing historical disinvestment in their communities, or other factors. In this case, people in widely different locations can be the most harmed by repeating disaster cycles, so mitigation strategies should also work to break cycles of loss caused by social and economic disparities. Hazard mitigation strategies can reduce existing risk by, for example, relocating a building out of an area that frequently floods. In each case, an attempt has been made to lessen the harm of a future flood before the event happens. Strategies may also seek to make future development less vulnerable to hazards at the time it is built. Examples would be requiring new structures to be elevated above predicted flood levels or building structures to better withstand future hazards. Hazard mitigation plans are designed to involve the input of stakeholders from different perspectives to ensure plans use the best available data, are aligned with the needs of the entire community, and are in alignment with other plans, such as general plans, capital improvement plans, and climate action plans.

The Contra Costa County Hazard Mitigation Plan recognizes that all members of the community are not impacted in the same way by natural, human-caused, and technological disasters. Some community members are at more risk, for a number of possible reasons. A mitigation strategy that uses a ‘one size fits all’ approach and does not recognize different levels of risk will not adequately or efficiently support historically underserved populations and can actually make inequalities worse after a disaster.

This Plan highlights equity as a key component of the Plan’s overall vision and seeks to continue to develop a shared understanding among participants of how hazard mitigation can be made more inclusive and be proactive in creating strategies that reduce existing disparities in risk and hazard recovery. Addressing the whole community requires an understanding that while a single solution for all seems fair, it does not address historical inequalities and current differences in age, financial resources, housing stability, neighborhood investment, health or ability, and access to government services. In mitigation planning, this means that successfully reducing risk in the most meaningful and efficient way requires understanding how the distribution of resources will actually reduce risk and for whom.

Equitable mitigation success should be measured by assessing who was most impacted in loss of life or financial harm by past and future disasters, quantifiable reductions of vulnerability to those most at risk, and increasing engagement with historically u nderserved populations and community organizations to better understand how plans and processes and natural hazard events are affecting different communities. The following highlights how this Plan addresses this priority.

Chapter 3 (Community Profile): This section describes different demographic and economic factors in Contra Costa County. Additionally, Centers for Disease Control and Prevention (CDC) Social Vulnerability Index (SVI) data was included.

Chapter 4 (Hazard Identification and Risk Assessment): This section includes FEMA’s National Risk Index scores for the County for social vulnerability and community resilience. Social vulnerability is defined as the susceptibility of social groups to the adverse impacts of natural hazards, including 2024 Hazard Mitigation Plan
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disproportionate death, injury, loss, or disruption of livelihood. 1 Community resilience is defined as the ability of a community to prepare for anticipated natural hazards, adapt to changing conditions, and withstand and recover rapidly from disruptions.
2 Additionally, it includes a hazard ranking methodology that specifically assessed the impact of the hazard on underserved populations. Furthermore, each hazard profile includes a narrative of the vulnerability and impacts for the underserved and at-risk population, FEMA’s Expected Annual Loss analysis, and the National Risk Index score for the County.

The Risk Index score is based on the following components: Social Vulnerability, Community Resilience, and Estimate Annual Loss (based on Exposure, Annualized Frequency, and Historic Loss Ratio (HLR) factors, for a total of five (5) risk factors).
3 Under the Climate Change hazard profile in Chapter 4 (Hazard Identification and Risk Assessment), it includes an analysis of the 42 C ensus Tracts in Contra Costa County which are identified as disadvantaged by the United States Council on Environmental Quality (ACEQ). According to the ACEQ, a disadvantaged community is identified if is located in a Census Tract that is at or above the threshold for one (1) or more environmental, climate, or other burdens, and at or above the threshold for associated socioeconomic burdens, including poverty and language barriers. 4 Mitigation goals were updated to encourage greater participation and engagement from underserved populations and groups and aligns with the Contra Costa County General Plan, which prioritizes diversity, inclusion, and equity. During Stakeholder Workshops, in which new and ongoing mitigation strategies were discussed, jurisdictional representatives were encouraged to consider how the mitigation actions directly and/or indirectly resulted in equitable outcomes.

During this Plan update process, a comprehensive community preparedness questionnaire was developed and disseminated. The questionnaire was developed with a specific focus to better understand the challenges and concerns related to access and functional needs, access to information, abi lity to recover, and services needed, especially for those who may be underserved or lack access to key resources. The survey was available in English, Spanish, Traditional and Simplified Chinese, and Tagalog. Additionally, Spanish translation assistance was provided during all Public Meetings that were held, which is a key demographic in Contra Costa County.

The County and participating jurisdictions have a responsibility to ensure equitable outcomes in the implementation of this Plan and to ensure that action is taken to reduce vulnerabilities to disasters experienced disproportionately by marginalized populations.

When conducting community engagement related to implementation of or update to this Plan, Contra Costa County will ensure that the whole community has an opportunity to participate in the process and discussion. FEMA defines the whole community as the groups and organizations that should share the responsibility for emergency preparedness and mitigation, to include:
5 1 Federal Emergency Management Agency. (2023). Social Vulnerability. Retrieved from https://hazards.fema.gov/nri/social-vulnerability.
2 Federal Emergency Management Agency. (2023). Community Resilience. Retrieved from https://hazards.fema.gov/nri/community-resilience.
3 Federal Emergency Management Agency. (2023). Determining Risk. Retrieved from https://hazards.fema.gov/nri/determining-risk.
4 United States Council of Environmental Quality. (n.d.). Climate and Economic Justice Screening Tool:

Methodology. Retrieved from https://screeningtool.geoplatform.gov/en/methodology. 5 Federal Emergency Management Agency. (n.d.). Guide to Expanding Mitigation. Retrieved from https://www.fema.gov/sites/default/files/documents/fema_mitigation-guide_whole-community.pdf. 2024 Hazard Mitigation Plan
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• Individuals
• Families
• Businesses
• Faith-based and
community
organizations
• Non-profit groups
• Schools and academia
• Media
• Local and state
government
• Artists and arts
organizations
• Tribal government and
associations
• Territories
• Other federal agencies

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CHAPTER 3. COMMUNITY PROFILE
Contra Costa County is located in the Bay Area region of California and is considered an East Bay region. 6 The County is the ninth most populous County in the State of California with a population of 1,157,019 and 19 municipalities including 17 cities and two ( 2) towns. 7 The population per square mile is approximately 1,614. 8 The major population centers include the cities of Concord, Antioch, and Richmond and the County seat is the City of Martinez, located in the northwest part of the County. 9

The name “contra costa” is Spanish for “opposite coast” due to its location across San Francisco. 10 Like most locations in the United States, Contra Costa County is vulnerable to natural, human-caused, and technological hazards that threaten life safety, public health, business, economy, and its critical infrastructure. Figure 3-1 illustrates the Contra Costa County planning area.

Figure 3-1. Contra Costa County Planning Area

6 Contra Costa County. (n.d.). Our County. Retrieved from https://www.contracosta.ca.gov/31/Our-County. 7 United States Census Bureau. (2022). Quick Facts: Contra Costa County. Retrieve from https://www.census.gov/quickfacts/fact/table/contracostacountycalifornia/. 8 Ibid.
9 State of California Department of Finance. (2023). Population and Housing Estimates for Cities, Counties, and the State - January 1, 2022 and 2023. Retrieved from https://dof.ca.gov/forecasting/demographics/estimates-e1/. 10 Contra Costa County. (2023). Public Review Draft Contra Costa County 2045 General Plan – Planning Context.

Retrieved from https://envisioncontracosta2040.org/wp-c ontent/uploads/2023/10/Contra-Costa-County-General- Plan_Public-Review-Draft_Combined-2.pdf.

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3.1 CONTRA COSTA COUNTY HISTORY
The first inhabitants in Contra Costa County were members of the Bay Miwok, Northern Valley Yokuts, and Ohlone Tribes and land was used for a variety of reasons. 11

The Spanish colonization of what is now known as California began in 1769 and the area was controlled by Spain until 1821 when Mexico won its independence. Under Mexican rule, the County was divided into 15 land grants (i.e., ranchos), which were granted to settlers. Many names of the County’s cities and areas are derived from the ranchos or their owners.
12 In 1848, after the Mexican American War, California
was relinquished by the United States. Two (2) years later, in 1850, Contra Costa County became one of the original 27 counties established in the State of California with Martinez as the County seat. Less than 5,000 people resided in the County at the time.

Cattle ranching was always present since the ranchos. However, the latest economic activity in the 19 th
century was agriculture. Although crops grown changed throughout the years, wheat, grapes, and walnuts were prominent. Additionally, the presence of deep water along the western coastline and the Carquinez Strait made industrial development possible with the Standard Oil refinery in Richmond. 13

Rapid industrialization during World War II sparked urban development and economic expansion and diversification in the area.
14 Contra Costa County is usually considered as comprising of three (3) regions – West County, Central County, and East County. The West County area was the first area to develop with urban and industrial uses. Prior to World War II, several cities and unincorporated areas existed, but they were relatively small. Richmond was the largest city with a population of 23,093 in the 1940 United States Census.

Nonetheless, West County became a central point for industrial activity during the War, which led to fast and extensive urbanization. Kaiser Shipyards was located in Richmond and produced 750 ships, more than any other shipyard in the United States. In 1950, the City of Richmond had a population of approximately 100,000. Post World War II (1950s through 1960s), a wave of suburbanization was experienced in Central County. Rural agricultural communities were transformed into cities where middle and upper -class residents were able to live in new construction with the ability to commute via the expanding freeway network. In the 1980s, suburban development began extending into the agricultural landscape of East County, and due to the lower housing costs in the area and scenic open spaces, residents tended to gravitate more towards this area. The City of Brentwood grew rapidly, and the City of Oakley was incorporated in 1999. 15

3.2 TOPOGRAPHY
Contra Costa County is located in northern California bordered by Alameda County to the south, San Joaquin County to the east, Sacramento and Solano counties to the north, and East Bay of the San Francisco Bay to the west. The County stretches approximately 40 miles from west to east and 20 miles

11 Ibid.
12 Contra Costa County Historical Society. (n.d.). Contra Costa County History. Retrieved from https://www.cocohistory.org/contra-costa-county-history. 13 Ibid.
14 Contra Costa County. (2023). Public Review Draft Contra Costa County 2045 General Plan – Planning Context.

Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/Contra-Costa-County-General- Plan_Public-Review-Draft_Combined-2.pdf.
15 Ibid.
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from north to south. Contra Costa County has a total land area of 716.9 square miles. 16 Contra Costa County’s topography is comprised of the San Francisco and San Pablo bays, and the Sacramento-San Joaquin Delta. Furthermore, near the County’s center is Mount Diablo with a peak of 3,849 feet.17 Mount Diablo is part of the Diablo Range which is a dominant topographic feature in northern California, and it is a localized uplift associated with the San Andreas Fault system . 18 Other topographic features include the Oakland/Beverly Hills.

Figure 3-2 illustrates the topographical map for Contra Costa County.

Figure 3-2. Topographical Map

3.3 CLIMATE
Based on the Modified Köppen Climate Classification System, Contra Costa County is a Mediterranean (temperate, warm, dry summers) climate that is characterized by hot, dry summers and cool, wet winters.

However, the location’s distance from the coast has a significant effect on the location’s climate. Coastal Contra Costa County has moderate temperatures throughout the year with mild and wet winters, and

16 United States Census Bureau. (2022). Contra Costa County, California Profile. Retrieved from https://data.census.gov/profile/Contra_Costa_County,_California?g=050XX00US06013. 17 Contra Costa County. (2015). Contra Costa County Climate Action Plan. Retrieved from https://www.contracosta.ca.gov/DocumentCenter/View/39791/Contra-Costa-County-Climate-Action-Plan?bidId=. 18 California Geological Survey and California State Parks. (2015). CGS Special Report 230: Geological Gems of California State Parks. Retrieved from
https://www.parks.ca.gov/pages/734/files/GeoGems%20FINAL%20WEB.pdf.

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foggy conditions during the summer months. Central and easter portion of the County, in the inland valley, summers tend to be hotter while the winters are colder. 19, 20

In the winter (December through February), the average daily temperature is 52.7°F with temperatures reaching low 60s during the day and mid 40s during the evening. During the summer (June through August), the average daily temperature is 64.6°F with temperatures reaching the low 70s during the day and high 50s in the evening. The coldest month in Contra Costa County is January and the warmest month is September. The monthly climate summary, based on the Oakland Museum weather station, is listed on Table 3-1.

Table 3-1. Contra Costa County Monthly Climate Summary (1970 – 2023) Average Daily Temperature 21 (° F)
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Annual

51.7 54.7 56.3 58.3 61.0 63.6 64.4 65.8 66.4 63.7 57.2 51.7 59.4 Average Maximum Temperature 22 (° F)
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Annual

58.8 62.1 63.8 66.4 68.9 71.7 72.0 73.4 74.8 72.4 65.0 58.4 67.1 Average Minimum Temperature 23 (° F)
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Annual

44.7 47.2 48.8 50.3 53.2 55.5 56.8 58.1 58.0 55.1 49.5 45.0 51.8 Average Total Precipitation 24 (inches)
Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Annual

4.13 3.90 3.47 1.28 0.58 0.15 0.04 0.06 0.24 1.29 2.87 4.26 22.10 The closest National Weather Service weather station to Contra Costa County is the Oakland Museum where weather observations have been continuous since October 1970.

19 Contra Costa County. (2015). Contra Costa County Climate Action Plan. Retrieved from https://www.contracosta.ca.gov/DocumentCenter/View/39791/Contra-Costa-County-Climate-Action-Plan?bidId=. 20 State of California The Resource Agency Department of Fish and Wildlife. (2021). Atlas of the Biodiversity of California. Retrieved from https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=211302&inline. 21 National Oceanic and Atmospheric Administration. (2023). NOWData – NOAA Online Weather Data (Monthly Mean Average Temperature for Oakland Museum, CA). Retrieved from https://www.weather.gov/wrh/climate?wfo=mtr.
22 National Oceanic and Atmospheric Administration. (2023). NOWData – NOAA Online Weather Data (Monthly Mean Max Temperature for Oakland Museum, CA). Retrieved from https://www.weather.gov/wrh/climate?wfo=mtr.
23 National Oceanic and Atmospheric Administration. (2023). NOWData – NOAA Online Weather Data (Monthly Mean Min Temperature for Oakland Museum, CA). Retrieved from https://www.weather.gov/wrh/climate?wfo=mtr. 24 National Oceanic and Atmospheric Administration. (2023). NOWData – NOAA Online Weather Data (Monthly Sum Precipitation for Oakland Museum, CA). Retrieved from https://www.weather.gov/wrh/climate?wfo=mtr. 2024 Hazard Mitigation Plan
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3.4 LAND USE
Contra Costa County, including incorporated and unincorporated County, has a total area of 515,840 acres (806 square miles ) of which 57,600 acres ( 90 square miles ) are water. Table 3-2 outlines the acreage of unincorporated county area designated for each land use type. 25 Residential densities are expressed in terms of dwelling units per net acre, which is the area remaining after land is dedicated for rights-of-way, easements, and other public or common uses. As a rule of thumb, the County assumes net acreage to be 75% of the gross for single-family residential projects and 80% of the gross for multiple- family residential and mixed-use projects. A project’s actual density is calculated during the development review process and must usually fall within the density range for the applicable land use designation.

Development intensities for nonresidential uses are expressed in terms of floor area ratio (FAR), which is the ratio of gross building floor square footage to gross land area, expressed as a decimal number.

When a building’s square footage is equal to the area of the parcel it occupies, the FAR is 1.0. FARs are lower in suburban areas, where buildings are shorter and often surrounded with parking and landscaping, than in urban areas, where buildings are taller and occupy more of their respective parcels. Nonresidential development cannot exceed the FAR for the applicable land use designation.

Table 3-2. Acreages of Land Use Designations
Land Use Designation Area (acres) Percent of Total
Residential Very Low Density 2,518 0.81%
Residential Low Density 6,302 2.03%
Residential Low-Medium Density 5,810 1.87%
Residential Medium Density 3,504 1.13%
Residential Medium-High Density 771 0.25%
Residential High Density 125 0.04%
Residential very High Density 55 0.02%
Commercial and Office 269 0.09%
Light Industry 1,285 0.41%
Heavy Industry 3,408 1.10%
Mixed-Use Low Density 233 0.08%
Mixed-Use Medium Density 69 0.02%
Mixed-Use High Density 108 0.34%
Mixed-Use Community-Specific Density 363 0.12%
Public and Semi-Public 16,884 5.44%
Agriculture Core 11,902 3.83%
Agriculture Lands 95,852 30.86%
Parks and Recreation 72,796 23.44%

25 Contra Costa County. (2023). Public Review Draft Contra Costa County 2045 General Plan – Planning Context.

Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/Contra-Costa-County-General- Plan_Public-Review-Draft_Combined-2.pdf.
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Land Use Designation Area (acres) Percent of Total
Commercial Recreation 1,838 0.59%
Resource Conservation 59,900 19.29%
Water 26,564 8.55%
Total 310,554 100.0%

Figure 3-3 illustrates the general land use map within Contra Costa County.

Figure 3-3. Land Use Map

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Chapter 3: Community Profile 20

3.5 CHANGES IN DEVELOPMENT & DEVELOPMENT TRENDS
The State of California requires, by law, that every county and city adopt a general plan that outlines the goals, policies, and specific implementation measures expected to guide the decision on future growth, development, and resource conservation for the next 20 years. 26 Additionally, each general plan serves are the “charter” or “constitution” governing development, and governments are required, by law, to implement the plan once it is adopted. Each general plan must contain the eight (8) State-mandated elements – Land Use, Circulation, Housing, Conservation, Open Space, Safety, Noise, and Environmental Justice. 27

The Contra Costa County Hazard M itigation Plan will work together with the general plans to support wise land use in the future by providing vital information on the risks associated with natural hazards in the planning area. Furthermore, all municipal planning partners will incorporate this H azard Mitigation Plan in their general plans by reference. This will ensure that future development trends can be established with the benefits of the information on risk and vulnerability to the hazards identified in this Plan.

The Contra Costa County General Plan can be accessed via the following link https://www.contracosta.ca.gov/4732/General-Plan
. The County’s General Plan was undergoing an
update during the development of this Hazard Mitigation Plan. Further details of the update can be accessed via the following link
https://envisioncontracosta2040.org/.

3.5.1. Implications of Development on Risk
Growth patterns directly affect hazard impacts, risk, and vulnerability. Growth can lead to an increase in the number of people and developed properties exposed to hazards. Figure 3-4 illustrates existing development in flood zones within Unincorporated Contra Costa County areas.

26 Contra Costa County. (n.d.). General Plan: Overview. Retrieved from https://www.contracosta.ca.gov/4732/General-Plan.
27 Contra Costa County. (2023). Public Review Draft Contra Costa County 2045 General Plan – Planning Context.

Chapter 3: Community Profile 21
Figure 3-4. Existing Development in Unincorporated Contra Costa County Flood Zones 28

3.6 FUTURE TRENDS IN DEVELOPMENT
The State of California is a strong growth management state that equips its local governments with general plans to address future developments, including safety and housing elements. Regional housing needs assessments are mandated by State law as part of the periodic process of updating local general plan housing elements. Safety elements have similar mandates, including those that promote integration with local hazard mitigation plans. These initiatives provide a strong footing for Contra Costa County to manage and address development pressures as it interfaces known hazard areas. These land use initiatives, and the adoption and enforcement of strong building codes and standards are key ingredients to overall community resilience.

3.7 DEMOGRAPHICS
Population and Population Density: Contra Costa County had a population of 1,156,966 as of July 1, 2022. The majority of this population resides within incorporated areas. Between 2010 and 2020 , the population increased by approximately 11.1%; however, a population decrease of 0.8% occurred between 2020 and 2022.29 Table 3-4 shows Contra Costa County’s population distribution by jurisdiction between 2010 and 2022.

28 Ibid.
29 United States Census Bureau. (2022). Quick Facts: Contra Costa County, California. Retrieve from https://www.census.gov/quickfacts/fact/table/contracostacountycalifornia/PST045222.

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Table 3-3. Population Estimates 30
Jurisdiction 2010 2020 2022 Population Change
(2010 – 2022)
Contra Costa County 1,046,025 1,165,927 1,156,966 10.6% City of Antioch 102,372 115,291 115,264 12.6%
City of Brentwood 51,481 64,292 66,127 28.4%
City of Clayton 10,897 11,070 10,904 0.1%
City of Concord 122,067 125,410 122,265 0.2%
Town of Danville 42,039 43,582 42,732 1.6%
City of El Cerrito 23,549 25,962 25,583 8.6%
City of Hercules 24,060 26,016 25,920 7.7%
City of Lafayette 23,893 25,391 25,044 4.8%
City of Martinez 35,824 37,287 36,447 1.7%
Town of Moraga 16,016 16,870 16,707 4.3%
City of Oakley 35,432 43,357 44,688 26.1%
City of Orinda 17,643 19,514 19,355 9.7%
City of Pinole 18,390 19,022 18,582 1.0%
City of Pittsburg 63,264 76,416 77,572 22.6%
City of Pleasant Hill 33,152 34,613 33,913 2.3%
City of Richmond 103,701 116,448 114,301 10.2%
City of San Pablo 29,139 32,127 31,389 7.7%
City of San Ramon 72,148 84,605 85,953 19.1%
City of Walnut Creek 64,173 70,127 68,969 7.5%

Income and Socioeconomic Status: In 2022, the median household income in Contra Costa County was $120,061. 31 About 6.6% of the households in the Contra Costa County have an annual income of less than $ 15,000 per year and are therefore below the poverty level. Table 3-5 outlines the poverty thresholds for 2022 by size of family. 32

30 United States Census Bureau. (2022). Quick Facts. Retrieved from https://www.census.gov/quickfacts/. 31 United States Census Bureau. (2022). S1901: Income in the Past 12 Months (in 2022 Inflation-Adjusted Dollars). Retrieve from https://www.census.gov/quickfacts/fact/table/contracostacountycalifornia/PST045222. 32 United States Census Bureau. (2022). Poverty Threshold (By Size of Family and Number of Children).

Retrieved from https://www.census.gov/data/tables/time-series/demo/income-poverty/historical-poverty- thresholds.html.
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Table 3-4. Poverty Thresholds for 2022 by Size of Family Size of Family Unit Weighted Average Threshold
One (1) Person $14,880
Two (2) People $18,900
Three (3) People $23,280
Four (4) People $29,950
Five (5) People $35,510
The source of the weighted average thresholds is the 2023 Current Population Survey Annual Social and Economic Supplement (CPS ASEC).

Sex and Age Distribution: 17.4% of Contra Costa County’s population is 65 years old and over, compared to the State average of 15.8%. It is also estimated that 21.7% of the County’s population is 18 or younger, compared to the State average of 21.8 %. 33 Additionally, approximately 21.4% of Contra Costa County population has a disability type (i.e., hearing, vision, cognitive, or ambulatory, self-care, and independent living difficulty).34 Females make up 50.8%, which is slightly above the national average of 50.4%, while males make up 49.2% of the Contra Costa County population. 35 The age group with the highest percentage is the 35 to 39 age group, with the 40 to 44 age group as the second highest. The overall age distribution for Contra Costa County is outlined in Table 3-6.

Table 3-5. Age Distribution (2022) 36
Age Group Estimate Percent
Under 5 Years 61,175 5.3%
5 to 9 Years 68,924 6.0%
10 to 14 Years 72,660 6.3%
15 to 19 Years 74,953 6.5%
20 to 24 Years 67,593 5.8%
25 to 29 Years 65,654 5.7%
30 to 34 Years 75,126 6.5%
35 to 39 Years 82,400 7.1%
40 to 44 Years 80,566 7.0%
45 to 49 Years 77,407 6.7%
50 to 54 Years 79,534 6.9%
55 to 59 Years 75,803 6.6%

33 United States Census Bureau. (2022). Quick Facts: California. Retrieve from https://www.census.gov/quickfacts/fact/table/CA/.
34 United States Census Bureau. (2022). S1810: Disability Characteristics (2022: ACS 1-Year Estimates Subject Tables). Retrieved from https://data.census.gov/table/ACSST1Y2022.S1810?g=050XX00US06013. 35 United States Census Bureau. (2022). Quick Facts: Contra Costa County, California. Retrieve from https://www.census.gov/quickfacts/fact/table/contracostacountycalifornia. 36 United States Census Bureau. (2022). S0101: Age and Sex (2022: ACS 1-Year Estimates Subject Tables).

Retrieved from https://data.census.gov/table/ACSST1Y2022.S0101?g=050XX00US06013. 2024 Hazard Mitigation Plan
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Chapter 3: Community Profile 24
Age Group Estimate Percent
60 to 64 Years 74,035 6.4%
65 to 69 Years 61,568 5.3%
70 to 74 Years 53,717 4.6%
75 to 79 Years 38,877 3.4%
80 to 84 Years 22,488 1.9%
85 Years and Over 24,486 2.1%

Race and Ethnic Distribution: The majority of the population in Contra Costa County is White (40.9%), with the next highest percent being Hispanic or Latino (27.0%) and Asian (19.3%). Table 3-7 outlines the racial and ethnic distribution in Contra Costa County. 27.0% of the population in Contra Costa County is foreign-born.
37 Other than English, the most commonly spoken language in Contra Costa County is Spanish ( 18.7%). The United States Census Bureau estimates that 14.5% of the County’s residents speak English “less than very well.”38
Table 3-6. Racial and Ethnic Distribution (2022) 39
Race and Ethnicity Estimate Percent
White (not Hispanic or Latino) 472,779 40.9%
Black or African American 100,358 8.7%
American Indian and Alaska Native 8,043 0.7%
Asian 223,114 19.3%
Native Hawaiian and Other Pacific Islander 5,970 0.5%
Two (2) or More Races 182,593 15.8%
Some Other Race Alone 164,109 14.2%
Hispanic or Latino 311,808 27.0%

3.7.2. Underserved Population
The 2023 California State Hazard Mitigation Plan identifies the Centers for Disease Control and Prevention (CDC) Social Vulnerability Index (SVI) as the most appropriate and authoritative dataset to identify areas where efforts can be prioritized to ensure equitable outcomes from mitigation planning and actions.

37 United States Census Bureau. (2022). DP02: Selected Social Characteristics in the United States (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP02?g=050XX00US06013. 38 United States Census Bureau. (2022). S1601: Language Spoken at Home (2022: ACS 1-Year Estimates Subject Tables). Retrieved from https://data.census.gov/table/ACSST1Y2022.S1601?g=050XX00US06013. 39 United States Census Bureau. (2022). DP05: ACS Demographic and Housing Estimates (2022:ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP05?g=050XX00US06013. 2024 Hazard Mitigation Plan
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Chapter 3: Community Profile 25
CDC’s SVI combines 16 social factors, within four (4) themes (i.e., socioeconomic status, household characteristics, racial and ethnic minority status, and housing type and transportation), to identify areas of social vulnerability. Table 3-8 outlines the SVI information for Contra Costa County.

Table 3-7. Social Vulnerability Index (2020)
Theme Social Factors Population Percent
Socioeconomic
Status
People below 150% poverty estimate 156,345 13.4%
Unemployed
(Civilian 16 years old and older) 32,666 2.8%
Housing Cost Burden 98,841 8.5%
No High School Diploma 80,257 6.9%
No Health Insurance 57,133 4.9%
Household
Characteristics
65 years old and older 181,578 15.6%
17 years and younger 260,191 22.3%
Civilian with a Disability 127,957 11.0%
Single-Parent Household 23,103 2.0%
English Language Proficiency 65,454 5.6%
Racial and Ethnic
Minority Status
• Hispanic or Latino (of any race)
• Black or African American
• Asian
• American Indian or Alaska Native
• Native Hawaiian or Pacific Islander
• Two or More Races
• Other Races
658,653 56.5%
Housing Type and
Transportation
Multi-Unit Structures 53,171 4.6%
Mobile Homes 6,533 0.6%
Crowding 19,927 1.7%
No Vehicle 21,003 1.8%
Group Quarters 9,828 0.8%

3.7.2.1. Impacted Communities
The term impacted communities was introduced into the 2024 Contra Costa County Climate Action Plan.

Impacted communities (e.g., low income, disabled, seniors, communities of color) have faced extensive discrimination, negligence, and economic disempowerment. Members of these communities often live in areas that are uniquely vulnerable to climate change related to natural hazards. Furthermore, these individuals often lack the financial means and other resources or authority to act on climate change initiatives. Figure 3-5 illustrates where the impacted communities are located within unincorporated Contra Costa County which are concentrated along the County’s northern waterfront.

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Chapter 3: Community Profile 26
Figure 3-5. Impacted Communities

3.8 ECONOMY

64.5% of the 16 and over population was in the labor force. Of the 604,766 civilian-employed population,

77.4% were employed in the private sector. Contra Costa County is currently experiencing an average unemployment rate of 5.1%. Educational services, health care, and social assistance represent the largest sector, employing over 22.5% of the workforce. Tables 3-9 through 3-11 provide a breakdown of the economic characteristics of Contra Costa County.
40 40 United States Census Bureau. (2022). DP03: Selected Economic Characteristics (2022:ACS 1-Year Estimates Data Profiles). Retrieved from https://data.census.gov/table/ACSDP1Y2022.DP03?g=050XX00US06013.

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Table 3-8. Employment by Industry (2022)
Industrial Sector Estimate Percent
Agriculture, forestry, fishing, hunting, and mining 3,771 0.7% Construction 45,553 7.9%
Manufacturing 33,037 5.8%
Wholesale funds 11,224 2.0%
Retail trade 61,311 10.7%
Transportation, warehousing, and utilities 34,306 6.0%
Information 14,469 2.5%
Finance and insurance, real estate, and leasing 42,417 7.4% Professional, scientific, management, and administrative 102,135 17.8% Educational services, health care, and social assistance 129,074 22.5% Arts, entertainment, recreation, accommodation, and food 45,803 8.0% Other services (except public administration) 24,092 4.2% Public administration 26,892 4.7%
Civilian Employed Population 16 Years and Over 574,084
Table 3-9. Employment Status (2022)
Employment Status Estimate Percent
Civilian Labor Force 604,766 64.5%
Employed 574,084 61.2%
Unemployed 30,682 3.3%
Armed Forces 513 0.1%
Not in Labor Force 33,2497 35.5%
Total Employed Population 16 and Over 937,776
Table 3-10. Occupation (2022)
Employment Status Estimate Percent
Management, Business, Science, and Arts 27,8075 48.4%
Service Occupations 92,665 16.1%
Sales and Office Occupations 110,681 19.3%
Natural Resources, Construction, and Maintenance 42,251 7.4% Production, Transportation, and Material Moving 50,412 8.8% Civilian Employed Population 16 and Over 574,084

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The median household income in Contra Costa County estimated in 2022 was $120,061, while 6.6% of the households in the Contra Costa County have an annual income of less than $15,000 per year and are therefore below the poverty level. Table 3-12 outlines the breakdown of income and benefits in Contra Costa County. 41
Table 3-11. Income and Benefits (2022)
Income
Number of
Households
(Estimate)
Percent
Less than $10,000 17,255 4.2%
$10,000 to $14,999 10,498 2.5%
$15,000 to $24,999 15,288 3.7%
$25,000 to $34,999 17,830 4.3%
$35,000 to $49,999 28,484 6.9%
$50,000 to $74,999 40,705 9.8%
$75,000 to $99,999 45,025 10.8%
$100,000 to $149,999 74,364 17.9%
$150,000 to $199,999 52,049 12.5%
$200,000 or more 113,696 27.4%
Median Household Income $120,061
Total Households 415,194

3.9 CRITICAL INFRASTRUCTURE
Critical infrastructure is comprised of assets, systems, and networks, whether physical or virtual, which are so vital to the United States that their incapacitation or destruction would have a debilitating effect on security, national economic security, national public health or safety, or any combination thereof.42 Table 3-13 summarizes the number of critical infrastructure within each broad category. Due to the sensitivity of this information, a detailed list of facilities is not provided as part of this Plan. The list is on file with Contra Costa County OES. Figure 3-6 shows locations of the critical infrastructure within Contra Costa County.

Table 3-12. Critical Infrastructure in Contra Costa County Critical Infrastructure Category Number of Facilities
Medical and Health 27
Government Functions 9
Protective Functions 152
School and Educational Facilities 493
HazMat 45

41 Ibid.
42 Cybersecurity & Infrastructure Security Agency. (n.d.). Critical Infrastructure Sectors. Retrieved from https://www.cisa.gov/topics/critical-infrastructure-security-and-resilience/critical-infrastructure-sectors. 2024 Hazard Mitigation Plan
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Chapter 3: Community Profile 29
Critical Infrastructure Category Number of Facilities
Bridges 407
Water Supply 157
Wastewater 66
Power 52
Communications 109
Other Critical Functions 17
Other Critical Infrastructure 117
TOTAL 1,651
Figure 3-6. Critical Infrastructure in Contra Costa County

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Chapter 3: Community Profile 30

3.10 CAPABILITY ASSESSMENT
Federal regulations require hazard mitigation plans to identify goals for reducing long-term vulnerabilities to the identified hazards in the planning area (Section 201.6(c)(3)(i)). A critical step in the development of specific hazard mitigation actions and projects is assessing existing authorities, policies, programs, resources, and capabilities to use or modify local tools to reduce losses and vulnerability from profiled hazards.

A capability assessment was conducted for Contra Costa County and participating jurisdictions’ authorities, policies, programs, and resources. Goals and mitigation actions were developed using input from this assessment. This section also includes information regarding the County’s jurisdictions’ implementation of and continued participation in the National Flood Insurance Program (NFIP). Capability assessments for each participating jurisdiction can be found in their respective annexes.

The Core Planning Team assessed Contra Costa County’s capabilities that can contribute to the reduction of long-term vulnerabilities to hazards. The capabilities include the following categories:

• Planning and Regulatory Capabilities
• Administrative and Technical Capabilities
• Financial Capabilities
• Education and Outreach Capabilities

Additionally, ways to expand on and improve these existing policies and programs to integrate hazard mitigation into the day-to-day activities and programs of the County were considered.

3.10.1. Planning and Regulatory Capabilities
These include local ordinances, policies, and laws to manage growth and development (e.g., land use plans, capital improvement plans, transportation plans, emergency preparedness and response plans, building codes, and zoning ordinances). The County and c ities will adopt the approved 2024 Hazard Mitigation Plan into their General Plan Safety Element for AB 2140 compliance. Table 3-14 contains a list of legal and regulatory capabilities. The d escription section of each Planning and Regulatory Capability includes a paragraph on expansion, implementation, and improvement. These sections describe the processes to integrate this Hazard Mitigation Plan into other planning mechanisms.

Table 3-13. Countywide Planning and Regulatory Capabilities County Ordinance Code Title 7 County Code, Building Regulations Includes: Building Code, Electrical Code, Plumbing Code, Mechanical Code, Housing Code, House Moving, Grading, Community Preservation, Fire Code
Building Regulations (incorporate d by reference and is based upon the 2022 California Building Code, 2022 California Residential Code, 2022 California Green Building Standards Code, and 2022 California Existing Building Code [all codified in California Code of Regulations, Title 24]); adopted November 17, 2022.

Expansion, Implementation, and Improvement: Building and Fire codes will be reviewed based on developing trends in identified hazards and mitigation measures that can make them more effective at preventing losses.

They will be updated to comply with the latest International and State building codes.

Lead
Department
Department of Conservation and
Development
Hazards
Addressed All hazards
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Chapter 3: Community Profile 31
County Ordinance Code Title 8 – Zoning
The Zoning Code addresses land use in precise detail. It sets standards for building and construction types and usage for all parcels in the County.

Expansion, Implementation, and Improvement: Zoning Code must be modified and updated to reflect changes in development. Zoning Code may be used to address land use regulations that support mitigation actions such as development.

Lead
Department
Department of Conservation and
Development
Hazards
Addressed
Climate Change, Dam/Levee
Failure, Drought, Earthquake,
Flooding, Severe Weather,
Wildfire
County Ordinance Code Title 9 – Subdivisions
The Subdivision Code addresses the development of groups of residences and commercial property. It describes requirements for transportation, water, and wastewater services. It sets limits on residential property density.

Expansion, Implementation, and Improvement: Subdivision Code should be modified and updated to support changes in land use development. Additionally, it should be implemented to require adequate infrastructure to support residential area populations.

Lead
Department
Department of Conservation and
Development
Hazards
Addressed
Climate Change, Dam/Levee
Failure, Drought, Earthquake,
Flooding, Severe Weather,
Wildfire
County Ordinance Code Title 10 – Public Works and Flood Control The purpose is to provide for public health, safety, and general welfare and to minimize public and private losses due to flood conditions in specific areas. It also addresses the intent to protect and enhance the water quality of the County's unincorporated area watercourses pursuant to and consistent with the Porter-Cologne Water Quality Control Act (Water Code Section 13000 et seq.), the Federal Clean Water Act (33 U.S.C. Section 1251 et seq.) and applicable implementing regulations.

Expansion, Implementation, and Improvement: The FEMA Flood Inundation Risk Maps (FIRMs) will be used in selecting mitigation items related to flooding. Development in the 100 and 500- year floodplains will be monitored and adhered to flood safe practices. As the FIRM s are updated, new mitigation activities will be considered.

Lead
Department Department of Public Works Hazards
Addressed Flood
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Chapter 3: Community Profile 32
General Plan
The purpose of the Contra Costa County General Plan is to express the broad goals and policies, and specific implementation measures, which will guide decisions on future growth, development, and the conservation of resources over 20 years into the future. This Plan includes eight (8) state-mandated elements and two (2) optional elements.

• Land Use
• Circulation (i.e., Transportation)
• Housing
• Conservation (i.e., Conservation, Open Space, and Working Lands) • Open Space (i.e., Conservation, Open Space, and Working Lands) • Safety (i.e., Health and Safety)
• Noise (i.e., Health and Safety)
• Environmental Justice (i.e., Stronger Communities)
• Public Facilities and Services
• Growth Management

The Contra Costa County 2045 General Plan was undergoing public review during the update period of this Hazard Mitigation Plan.

Expansion, Implementation, and Improvement: The Contra Costa County Hazard Mitigation Plan will be incorporated in the General Plan Safety Element. The General Plan will include specific actions that support mitigation throughout unincorporated Contra Costa County, and will be closely aligned with the Hazard Mitigation Plan.

Lead
Department
Department of Conservation and
Development
Hazards
Addressed All hazards
County Climate Action Plan (CAP)
The Climate Action Plan ( CAP), adopted in December 2015, is the County’s strategic approach to reduce greenhouse gas (GHG) emissions from sources throughout the unincorporated area. The CAP reflects the County’s programs and actions to decrease energy use, improve energy efficiency, develop renewable energy, reduce vehicle miles traveled, increase multi -modal travel options, expand green infrastructure, reduce waste, and improve the efficiency of government operations.

Expansion, Implementation, and Improvement: The CAP will be updated in parallel with the General Plan.

The General Plan will provide the long-term resiliency framework of goals and policies, and the CAP will provide strategic implementation programs to show how the County will reduce GHG emissions in support of the State’s adopted reduction targets for 2030 and 2050, reducing GHG emissions 40 % below 1990 levels by 2030, with consideration of the State’s long-term goal to reduce GHG emissions to 80% below 1990 levels by 2050.

Lead
Department
Contra Costa County Department
of Conservation and Development
Hazards
Addressed
Climate Change, Drought,
Flooding, Severe Weather,
Wildland Fire, Sea Level Rise
Contra Costa Hazardous Materials Plan / Hazardous Material Business Plan Addresses the storage, use, and emergency planning for hazardous materials and extremely hazardous substances in the community and at businesses.

Expansion, Implementation, and Improvement: The Hazard Mitigation Plan will support mitigation measures compatible with the County Hazardous Materials Plan to reduce potential hazardous material releases.

Lead
Department
Contra Costa Health Services,
Hazardous Materials Program
Office; Contra Costa County Fire
Protection District
Hazards
Addressed Hazardous Materials
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Alameda and Contra Costa County Regional Wildfire Prevention Plan The Contra Costa Resource Conservation District (CCRCD) and the Alameda City Resource Conservation District (ACRCD) worked jointly with funding from the Coastal Conservancy to develop a Regional Priority Plan (RPP) for Contra Costa and Alameda counties. The goal of the Regional Priority Plan process was to identify regional natural resource concerns that could be exacerbated by catastrophic wildfire and develop projects or other methods to remedy those issues ahead of the next fire. The planning process started in November 2020 and completed in September 2022.

Expansion, Implementation, and Improvement: The Hazard Mitigation Plan and Regional Wildfire Prevention Plan should be aligned and mitigation actions in the Hazard Mitigation Plan should support the goals of the Regional Wildfire Prevention Plan. Analysis of the fire hazard in the Hazard Mitigation Plan can inform updates and revisions to the Wildfire Prevention Plan.

Lead
Department
Contra Costa County Fire
Protection District
Hazards
Addressed Wildland Fire
Community Wildfire Protection Plan – Contra Costa County The 2019 update of the Contra Costa County Wildfire Protection Plan (CWPP) provides an analysis on wildfire hazards and risk in the wildland urban interface (WUI) in Contra Costa County. The Plan follows the standards for CWPPs established by the federal Healthy Forest Restoration Act.

Expansion, Implementation, and Improvement: The Hazard Mitigation Plan and County Community Wildfire Protection Plan should be aligned and mitigation actions in the Hazard Mitigation Plan should support the goals of the CWPP. Analysis of the fire hazard in the Hazard Mitigation Plan can inform updates and revisions to the CWPP.

Lead
Department
Contra Costa County Fire
Protection District
Hazards
Addressed Wildland Fire
Capital Improvement Plan (CIP)
The Capital Improvement Plan ( CIP) provides broad direction for development of County facilities and infrastructure. It describes a strategy to maintain adequate support for the County’s communities and commerce.

Additionally, it addresses transportation, greenhouse gases, stormwater, and other environmental factors.

Expansion, Implementation, and Improvement: The CIP should include mitigation measures that will be funded by the County such as improvements to stormwater collection systems, elevation of roadways at risk for flooding and strengthening of structures.

Lead
Department
Contra Costa County Fire
Protection District
Hazards
Addressed
Climate Change, Dam and Levee
Failure, Drought, Earthquake,
Flood, Landslide, Sea Level Rise,
Severe Weather, Tsunami,
Wildfire
Continuity of Operations Plan
This Plan is under development.

Lead
Department
Contra Costa County Office of
Emergency Services

Hazards
Addressed
Climate Change, Dam and Levee
Failure, Drought, Earthquake,
Flood, Landslide, Sea Level Rise,
Severe Weather, Tsunami,
Wildfire

3.10.2. Administrative and Technical Capabilities
The administrative and technical capabilities include community ( i.e., public and private) staff and their skills and tools, which can be used for mitigation planning and implementation. This capability includes engineers, planners, emergency managers, GIS analysts, building inspectors, grant writers, and 2024 Hazard Mitigation Plan
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floodplain managers. S mall communities may rely on other government entities, such as counties or special districts, for resources. These capabilities may be used to support mitigation activities. Table 3- 15 lists administrative and technical capabilities.

Table 3-14. Administrative and Technical Capabilities
Planners, Engineers, Building Officials, Code Enforcement Planners, engineers, building officials, and/or c ode enforcement issue building permits, review plans for new construction and improvements; conduct plan checks; work with architects, engineers, designers, and building owners during pre- construction; inspect all phases of residential and commercial/industrial construction for compliance; enforce municipal code violations.

Expansion and Improvement: Provide opportunities for continued education to Community Development staff to maintain state of the art knowledge of the new code and regulatory requirements.

Department Department of Conservation and Development
Planners, Engineers, Analysts, General Staff
Planners, engineers, analysts, and general staff plan future County land use; development and implementation of the Envision 2040 General Plan; land use regulations through zoning and subdivision codes, and environmental review of development; administration of the Community Development Block Grant Program (CDBG), conduct the Code Compliance program with the Building Division; conduct conditional use permits, variances, land subdivision, California Environmental Quality Act (CEQA) review, public hearings, noise permits, and zoning information.

Expansion and Improvement: Provide opportunities for continued education to Community Development staff to maintain state of the art knowledge of the new code and regulatory requirements.

Department Department of Conservation and Development
Director, Assistant Director, Superintendent, Supervisor, Engineers, Analysts, General Staff Directors, assistant directors, superintendents, supervisors, engineers, analysts, and general staff oversee public and private improvements in the public right of way; develop and implement the Capital Improvement Program by providing staff support to the County Infrastructure and Transportation Subcommittee regarding County streets, sanitary sewer, storm drains, water system facilities, traffic signals, park, and recreational facilities; maintain and upgrade public infrastructure; provide services related to traffic issues; monitors the street lighting system maintained by the County and Pacific Gas and Electric Company (PG&E); keeps and maintains record drawings of County owned infrastructure; conducts traffic committee meetings with the Police Department; and provides engineering support to other County departments and divisions within the Public Works Department.

Expansion and Improvement: Provide opportunities for continued education to Public Works staff to maintain state-of-the-art knowledge of the new code and regulatory requirements.

Department Department of Public Works
Office of Emergency Services (OES)
The Office of Emergency Services (OES) provides coordinated response and recovery from major emergencies and disasters; develop, administer, and coordinate the emergency planning preparedness program in conformity with local, State, and Federal requirements; develop emergency management and hazard mitigation plans; provide training to County staff in emergency planning and preparedness; operate the County Emergency Operations Center; provide businesses and residents with emergency planning and preparedness material to help reduce the loss of life and property resulting from a disaster; coordinate with County, State, and Federal counterparts; prepare emergency management grants; coordinate the efforts of volunteer organizations.

Expansion and Improvement: Provide training to officers, EOC staff, and other key personnel to better prepare them to respond and recover.

Department Contra Costa County Office of the Sheriff
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Code Enforcement Officer
Investigates citizen complaints regarding the enforcement of municipal code violations, conduct inspections, notification, communication, and the issuance of citations to proactively respond to citizens’ concerns.

Expansion and Improvement: Provide opportunities for continued education to Community Development staff to maintain state of the art knowledge of the new code and regulatory requirements.

Department Department of Conservation and Development
Fire Marshal
The Fire Marshal performs fire inspections for construction, commercial, multi-family occupancies, and high-rise buildings; conduct s fire prevention, emergency evacuation, and extinguisher training to businesses and the public; conducts enforcement and identifies and issues notices for fire code violations; updates Fire Prevention Regulations to conform with currently adopted Codes, Regulations, and Standards; coordinates with industries for fire prevention.

Expansion and Improvement: Continue to coordinate with the County Fire Marshal to update building codes and conduct inspections of new construction.

Department Contra Costa County Fire Protection District Floodplain Administrator
As a member of the National Flood Insurance Program (NFIP), the Floodplain Manager is responsible for collaborating with stakeholders to ensure the Floodplain Management Ordinance is followed within the County.

Expansion and Improvement: Continue to manage the County’s NFIP participation. Support the development of mitigation activities consistent with the best practices for floodplain management.

Department Director of Public Works
Public Information Officer (PIO)
The Public Information Officer (PIO) provides public and media information regarding the County’s disaster response, mitigation, and recovery efforts.

Expansion and Improvement: Continue to use PIOs to promote awareness of the Hazard Mitigation Plan and activities associated with individual mitigation projects as they are implemented.

Department Office of Communications and Media
Information Technology (IT) and Geographic Information System (GIS) Information technology (IT) and Geographic Information System (GIS) provide the technical resources and support necessary to operate all of the applications relating to the County's information resources; respond to the service needs to all departments based on countywide priorities as established by the County Administrator’s Office (CAO); responsible for the training and effective use of all County technology computer hardware, software, and peripherals; provide internal coordination of technology efforts Countywide including substantial interface with all technology vendors to assure cost-effective, secure, and reliable technologies compatible with the long-range needs of the County; provide high-quality spatial data to County departments.

Expansion and Improvement: Acquire and conduct training for GIS technicians on the latest versions of ArcGIS.

Department Department of Information Technology
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Risk Management
Risk Management provides services to assist County departments in managing their risk of injury to employees, County property, and the public at large; purchase insurance for County departments and act in an advisory capacity with respect to workers' compensation, public liability, County property, and County contracts.

Expansion and Improvement: Continue to have the Risk Manager provide input to support the analysis of potential losses due to hazards. Update Hazard Mitigation Plan based on current insurance values.

Department Contra Costa County Risk Management

3.10.3. Financial Capabilities
Table 3-16 contains a list of financial capabilities available to the County. These financial resources may be used to support mitigation activities based on procedures for each resource.

Table 3-15. Financial Resources
General Fund
The General Fund Program funds operations and specific projects.

Expansion and Improvement: Hazard mitigation projects may be considered during the annual budgeting process for funding from the general fund.

Administrator Department Specific
Board of Supervisors Administered Special Funds
The Board of Supervisors Administered Special Funds most special revenue funds were established to mitigate the impact of projects approved in certain areas of the County and that most funds have been intended for uses that will benefit the quality of life for the communities in which the project is approved and special revenue funds originated.

Expansion and Improvement: Focus Administered Special Funds on projects that provide mitigation to natural hazards.

Administrator Board of Supervisors
National Pollutant Discharge Elimination System (NPDES) The National Pollutant Discharge Elimination System (NPDES) is a joint effort of the Planning, Engineering, and Public Works departments through the Contra Costa County Clean Water Program. Since 1993, Contra Costa County Flood Control and Water Conservation District, and 16 cities in the county have worked together to meet federal mandates for minimizing pollutants in stormwater runoff. This revenue is used to fund its pro- rated share of the Clean Water Program’s staffing, overhead costs, and local-level activities necessary to comply with the joint Municipal Regional Permit (MRP) provisions.

Expansion and Improvement: Where permissible, the NPDES Fund may be considered during the annual budgeting process for funding mitigation projects.

Administrator Department of Conservation and Development 2024 Hazard Mitigation Plan
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Community Development Block Grant (CDBG)
The Community Development Block Grant ( CDBG) Program provides funding for eligible senior activities such as in-home care, art classes, counseling, and home-delivered meals. United States Department of Housing and Urban Development (HUD) also provides Disaster Recovery Assistance in the form of flexible grants to help cities, counties, and states recover from Presidentially declared disasters, especially in low-income areas, subject to the availability of supplemental appropriations.

Expansion and Improvement: Where applicable, CDBG should be used to fund mitigation projects that enhance the resilience of low-income and underserved communities.

Administrator Federal Emergency Management Agency, Department of Conservation and Development Hazard Mitigation Grant Program (HMGP)
The Hazard Mitigation Grant Program (HMPG) provides support for post-disaster mitigation plans and projects.

Expansion and Improvement: Train staff on notice of intent (NOI) procedures and track opportunities on the California OES mitigation website to initiate applications for grant funding.

Administrator Federal Emergency Management Agency
Building Resilient Infrastructure and Communities (BRIC) Building Resilient Infrastructure and Communities (BRIC) provides support for pre-disaster mitigation plans and projects.

Expansion and Improvement: Train staff on notice of intent (NOI) procedures and track opportunities on the California OES mitigation website to initiate applications for grant funding.

Administrator Federal Emergency Management Agency
Flood Mitigation Assistance (FMA) Grant Program
The Flood Mitigation Assistance (FMA) Grant Program mitigates structures and infrastructure with repetitive losses.

Expansion and Improvement: Train staff on notice of intent (NOI) procedures and track opportunities on the California OES mitigation website to initiate applications for grant funding.

Administrator Federal Emergency Management Agency

3.10.4. Education and Outreach Capabilities
Table 3-17 lists the County's public outreach capabilities. These capabilities include fire safety programs, hazard awareness campaigns, public information, and communications offices. Education and outreach capabilities can be used to inform the public about current and potential mitigation activities.

Table 3-16. Education and Outreach Resources
County Emergency/Disaster Readiness Website
https://www.cocosheriff.org/disaster-preparedness/emergency-services-division The County Sheriff’s website has educational material on numerous programs, including making an emergency plan, stocking supplies, staying informed, and getting involved in community preparedness programs.

Expansion and Improvement: Provide links to the County website on all County websites. Post material on social media accounts provide a link to the appropriate FEMA website page.

Lead Organization Contra Costa County Office of Emergency Services 2024 Hazard Mitigation Plan
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County Public Safety and Emergency Information
https://www.contracosta.ca.gov/5435/Public-Safety-Emergency-Info Provides resources and links for public safety and emergency information in Contra Costa County.

Expansion and Improvement: Provide additional links to other organizations such as FEMA and PG&E.

Lead Organization Contra Costa County Office of Emergency Services County Community Emergency Response Team (CERT) Coalition The Community Emergency Response Team (CERT) Program is a 20-hour all risk, all hazard training offered by the County Fire Department. This valuable course is designed to help you protect yourself, your family, your neighbors, and your neighborhood before, during, and after an emergency.

Expansion and Improvement: Conduct coordinated training and exercises with all County CERT s to improve interoperability.

Lead Organization Contra Costa County Cities Citizen Corps County Office of Communications and Media
https://www.contracosta.ca.gov/128/Office-of-Communications-and-Media The Contra Costa County's Office of Communications and Media, a division of County Administration, oversees public information and media relations. It is responsible for coordinating emergency communications countywide.

Expansion and Improvement: Use Office of Communications and Media resources to increase enrollment in the County Community Warning System. Feature mitigation activities in programming on public access channels.

Lead Organization County Administration
Contra Costa Television (CCTV)
Contra Costa Television (CCTV) is the flagship channel of Contra Costa County’s cable television programming, bringing special events, government meetings, and produced shows. CCTV broadcasts on channels Comcast Cable 27, ATT/U-Verse 99, and Astound 32 & 1027.

Expansion and Improvement: Use CCTV to provide information on how the public can support mitigation activities including limiting creating greenhouse gases and providing fire safety zones around residences.

Lead Organization County Administration
Community Warning System (CWS)
The Community Warning System (CWS) can alert residents and businesses within Contra Costa County that are impacted by or are in danger of being impacted by an emergency. The CWS message will include basic information about the incident and what specific protective actions (e.g., shelter in place, lockdown, evacuate, avoid the area) are necessary for life safety and health.

Expansion and Improvement: Coordinate community evacuation drills using CWS to implement the exercise.

Conduct post-exercise information fairs at evacuation collection points.

Lead Organization Contra Costa County Office of the Sheriff

3.11 HAZARD MITIGATION INTEGRATION
The information on hazards, risk, vulnerability, and mitigation contained in this Hazard Mitigation Plan is based on the best available data at the time of the Plan update. Plan integration consists of the incorporation of hazard mitigation into other relevant planning mechanisms (e.g., general planning and capital improvement planning). It includes the integration of natural hazard information and mitigation 2024 Hazard Mitigation Plan
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Chapter 3: Community Profile 39
policies, principles, and actions into local planning mechanisms and vice versa. Additionally, plan integration is achieved through the involvement of key staff and community officials in collaborative hazard mitigation planning.

3.11.1. Existing Plan Integration
In the performance period since the adoption of the previous Hazard Mitigation Plan, Contra Costa County made progress on integrating components of the hazard mitigation strategy (e.g., goals, objectives, and actions) into the planning initiatives listed in Table 3-18.

Table 3-17. Current Plan Integration
Planning Initiative Description
Capital Improvement Plan
The Plan includes projects that can help mitigate potential hazards. The County will strive to ensure consistency between the Hazard Mitigation Plan and the current and future Capital Improvement Plan. The Hazard Mitigation Plan may identify new possible funding sources for capital improvement projects and may result in modifications to proposed projects based on results of the risk assessment.

Building Code The County’s adoption of the 2022 California Building Code incorporated local modifications addressing seismic and fire hazards.

General Plan
The County General Plan includes a Safety Element to protect the community from unreasonable risk by establishing policies and actions to avoid or minimize geological and seismic, fire, hazardous materials, and flooding hazards. Contra Costa County is in the process of updating the General Plan, and efforts to continue integrating and improving the Safety Element are ongoing.

The 2045 General Plan’s Safety Element includes all the hazards that impact the County; Community Profiles (for each unincorporated neighborhood) that identify the community’s local hazards; Impacted Communities where the population is exposed to hazards at higher levels than others; and policies and actions.

Climate Action Plan Highlights potential programs that could be implemented to reduce greenhouse gas emissions and discusses possible impacts of climate change.

County Debris Management
Plan
The County of Contra Costa Disaster Debris Management Plan (DDMP) provides a comprehensive framework for managing debris following a disaster for all debris-generating hazards. It addresses the roles and responsibilities of government organizations, private firms, and non-governmental organizations that might have a role in debris operations.

Envision Contra Costa
Envision Contra Costa 2040 is the County’s plan to address land use, transportation, housing, climate change, environmental justice, and other important issues over the next 20 years. At the time of this Hazard Mitigation Plan update, the 2045 General Plan and the 2024 Climate Action Plan were undergoing public comment. In an effort to integrate both of these plans into hazard mitigation, the outcomes of the extensive public outreach for the ongoing Envision Contra Costa 2040 process were incorporated into this Plan.

3.11.2. Potential Future Integration
As the Hazard Mitigation Plan is implemented, Contra Costa County will use information from the Plan as the best available science and data on hazards. The capability assessment presented in Section

3.10.1 of this Annex identifies codes, plans, and programs that provide opportunities for integration. The countywide and local action plans developed for this Plan are related to plan integration. The capability 2024 Hazard Mitigation Plan
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Chapter 3: Community Profile 40
assessment identified plans and programs, listed in Table 3-19, that do not currently integrate goals and recommendations of this Plan but provide opportunities to do so in the future.

Table 3-18. Potential Future Integration
Planning Initiative Description
Flood Control Capital
Improvement Plan
Capital improvement project proposals may take into consideration hazard mitigation potential as a means of evaluating project prioritization.

Capital Road Improvement
and Protection Plan
Capital improvement project proposals may take into consideration hazard mitigation potential as a means of evaluating project prioritization.

County General Plan
The County is conducting a comprehensive update to its General Plan. The opportunity to incorporate additional hazard mitigation and abatement measures will be considered for inclusion in the updated General Plan.

County Emergency
Operations Plan (EOP)
The County EOP establishes the emergency organization, assigns tasks, specifies policies and general procedures, and provides for the coordination of planning efforts of the various emergency staff and service elements utilizing the Standardized Emergency Management System (SEMS). The EOP and the Hazard Mitigation Plan are currently integrated and will continue to be integrated, as appropriate. Specifically, the new hazard ranking methodology and rankings may be one area for inclusion.

Post-Disaster Recovery Plan
The County does not have a recovery plan and intends to develop one as a mitigation planning action during the next five (5) years. The Recovery Plan will build on the mitigation goals and objectives identified in the Hazard Mitigation Plan.

3.12 NATIONAL FLOOD INSURANCE PROGRAM
As of January 2024, Unincorporated Contra Costa County and all 19 jurisdictions within the County are members of the National Flood Insurance Program (NFIP). Table 3-20 identifies each community and the date each participant joined the NFIP. 43

Seven (7) of the NFIP communities also participate in the Community Rating System (CRS) which is a voluntary incentive program that recognizes and encourages community floodplain management activities that exceed the minimum NFIP requirements. As a result, flood insurance premium rates are discounted to reflect the reduced flood risk resulting from the community actions, meeting the three (3) goals of the CRS:

• Reduce flood losses.
• Facilitate accurate insurance ratings.
• Promote flood insurance awareness.

Table 3-19. NFIP Participation Information
CID Community
Name
NFIP
Participation
Date
Current
Effective
FIRM Date
CRS Entry
Date
CRS
Current
Effective
Date
CRS
Class
060025 Unincorporated
Contra Costa 11/1/1974 3/21/2017 10/1/1991 10/1/2022 6

43 Federal Emergency Management Agency, National Flood Insurance Program. (2024). Community Status Book Report. Retrieved from https://www.fema.gov/cis/CA.pdf. 2024 Hazard Mitigation Plan
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CID Community
Name
NFIP
Participation
Date
Current
Effective
FIRM Date
CRS Entry
Date
CRS
Current
Effective
Date
CRS
Class
060026 City of Antioch 6/28/1974 3/21/2017 N/A N/A N/A
060439 City of Brentwood 2/7/1975 3/21/2017 N/A N/A N/A 060027 City of Clayton 5/17/1974 3/21/2017 N/A N/A N/A
065022 City of Concord 6/28/1974 3/21/2017 10/1/2008 5/1/2022 6 060707 Town of Danville N/A 3/21/2017 N/A N/A N/A
065027 City of El Cerrito 6/28/1974 3/21/2017 N/A N/A N/A 060434 City of Hercules 3/26/1976 3/21/2017 N/A N/A N/A 065037 City of Lafayette 7/26/1974 3/21/2017 N/A N/A N/A 065044 City of Martinez 6/28/1974 3/21/2017 N/A N/A N/A 060637 Town of Moraga 11/19/1976 6/16/2009 N/A N/A N/A
060766 City of Oakley 11/1/1974 3/21/2017 N/A N/A N/A
060722 City of Orinda N/A 6/16/2009 N/A N/A N/A
060032 City of Pinole 5/24/1974 3/21/2017 N/A N/A N/A
060033 City of Pittsburg 6/21/1974 3/21/2017 N/A N/A N/A 060034 City of Pleasant
Hill 5/24/1974 3/21/2017 5/1/2003 10/1/2018 9
060035 City of Richmond 6/28/1974 NSFHA 10/1/1995 5/1/2015 10 060036 City of San Pablo 3/15/1974 3/21/2017 10/1/2013 10/1/2013 8 060710 City of San Ramon N/A 6/16/2009 10/1/1991 9/26/2023 6 065070 City of Walnut
Creek 11/8/1974 3/21/2017 10/1/1991 5/1/2011 8

3.12.1. Contra Costa County Floodplain Management Program The Contra Costa County Floodplain Management Program, coordinated by the Contra Costa County Public Works Department, Engineering Services Division, provides floodplain information for existing structures and proposed projects within the Special Flood Hazard Area (SFHZ). The Program is meant for Unincorporated County areas only.

FEMA produced a Flood Insurance Study (FIS) and printed Flood Insurance Rate Maps (FIRMs) for Contra Costa County in July 1987. These watersheds are studied, updated, and remapped periodically, showing areas with a 1% chance of flooding each year. These areas are commonly referred to as 100- year floodplains and are shown as SFHAs on the FIRMs. Flood insurance is mandatory for residential, commercial, and industrial developments within SFHAs, and for federally backed mortgages. Flood insurance may also be required by lenders.

In compliance with the NFIP, the County adopted a Floodplain Management Ordinance. This Ordinance requires that the lowest floor, including basement, for all new structures or substantial improvements to existing structures within a SFHA, shall be elevated one (1) to two (2) feet above the 100-year Base 2024 Hazard Mitigation Plan
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Chapter 3: Community Profile 42
Flood Elevation (BFE) for that area. Lower insurance rates are available when the lowest floor is above the BFE.
44 3.12.2. Floodplain Managers
All NFIP participating jurisdictions have a designated Floodplain Manager that is charged with enforcing floodplain regulations, routinely monitoring the floodplains, and providing community assistance such as encouraging owners to maintain flood insurance. A list of Contra Costa County Floodplain Managers (County and cities) can be found in Table 3-21.

Table 3-20. Floodplain Managers
Jurisdiction Department Name Title Phone Number
Contra Costa
County Public Works Larry Gossett Civil Engineer (925) 313-2016 City of Antioch Public Works Scott Buenting City Engineer (925) 779-7035 City of Brentwood Engineering
Development Allen Baquilar Director/
City Engineer (925) 516-5405
City of Clayton Engineering
Department Larry Theis City Engineer (925) 673-7300
City of Concord Community
Development Kevin Marstall Director (925) 671-3257
Town of Danville Engineering
Division Steven Jones City Engineer (925) 314-3310
City of El Cerrito Building Raylee Glasser Building Official (510) 215-4635 City of Hercules Public Works Mike Roberts Director (510) 799-8200 City of Lafayette Engineering
Department Mike Moran City Engineer (925) 299-3247
City of Martinez Public Works Joe Enke Director (925) 372-3562 Town of Moraga Public Works Shawn Knapp Town Engineer (925) 888-7027 City of Oakley Public Works Kevin Rohani City Engineer (925) 625-7003 City of Orinda Public Works Sivakumar
Natarajan City Engineer (925) 253-4231
City of Pinole Public Works Sanjay Mishra City Engineer (510) 724-9017 City of Pittsburg Public Works John Samuelson City Engineer (925) 252-4930 City of Pleasant Hill Engineering Omar Adina Assistant
Engineer (510) 620-6868
City of Richmond Community
Services Oscar Dalvalos Chief Building
Inspector (510) 215-3030
City of San Pablo Public Works Allan Panganiban Director/ City Engineer (925) 215-3062
City of San Ramon
Public Works
(Engineering
Services Division)
Chen-hsuan Hsieh City Engineer (925) 973-2681
City of Walnut
Creek Public Works Heather Ballenger Director (925) 943-5854

44 Contra Costa County Public Works. (n.d.). FEMA Floodplain Management Program: Overview. Retrieved from https://www.contracosta.ca.gov/332/FEMA-Floodplain-Program. 2024 Hazard Mitigation Plan
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3.12.3. Participation Activities
Contra Costa County NFIP participation activities over the last five (5) years include the following:

• Provides the following services – permit review, GIS, inspections, and engineering capability. • The City educates private owners and other stakeholders about the importance of flood insurance through public outreach events, workshops, and/or seminars. • Enforces local floodplain regulations and monitors compliance. • Floodplain management regulations meet or exceed FEMA or State minimum requirements.

3.12.3.1. Substantial Damage
Substantial Damage means damage of any origin sustained by a structure whereby the cost of restoring the structure to its before damaged condition would equal or exceed 50% of the market value of the structure before the damage occurred (County Code Title 8, Chapter 82-28 – Floodplain Management).

3.12.3.2. Substantial Improvement
Substantial Improvement means any reconstruction, rehabilitation, addition or improvement of a structure, the cost of which equals or exceeds 50% of the market value of the structure before the "start of construction" of the improvement. This term includes structures that have incurred substantial damage regardless of the actual repair work performed.

The percentage figure must be added to any successive building permits that may be issued or have been issued within a contiguous 10 year span. Substantial improvement is considered to occur when the first alteration of any wall, ceiling, floor or other structural part of the building commences, whether or not that alteration affects the external dimensions of the structure. However, the term does not include:

• Any project for improvement of a structure to comply (not required because of flood damage) with existing state or local health, sanitary or safety code specifications which are the minimum necessary to assure safe living conditions.
• Any alteration of an "historic structure," provided that the alteration will not preclude the structures continued designation as an "historic structure." (County Code Title 8, Chapter 82-28 – Floodplain Management)

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Chapter 4: Hazard Identification and Risk Assessment 44 CHAPTER 4. HAZARD IDENTIFICATION AND RISK

ASSESSMENT
A risk assessment is the process of measuring the potential loss of life, personal injury, economic injury, and property damage resulting from natural hazards. It allows emergency management personnel to establish early response priorities by identifying potential hazards and vulnerable assets. The process focuses on the following elements.

• Hazard Identification: Use all available information to determine what types of disasters may affect a jurisdiction, how often they can occur, and their potential severity. • Vulnerability Identification: Determine the impact of natural, human-caused, and technological hazard events on the population, environment, economy, and lands of the region. • Cost Evaluation: Estimate the cost of potential damage or cost that can be avoided by mitigation.

This Plan is designated to comply with requirements of the Robert T. Stafford Disaster Relief and Emergency Assistance Act, as amended, and Related Authorities and 44 CFR Part 201 (44 CFR § 201.6), which states that local governments must have an approved Hazard Mitigation Plan in place for eligibility of pre-disaster and/or post-disaster mitigation grant funds. This Plan is also designed to comply with the FEMA and the California Office of Emergency Services guidance documents (particularly the Local Mitigation Planning Policy Guide, effective April 19, 2023) and other applicable federal, state, and local regulations. This was accomplished by evaluating the impacts of known natural, human-caused, and technological hazards, prioritizing mitigation alternativ es, and coordinating hazard mitigation with other Contra Costa County programs and policies.

4.1 IDENTIFIED HAZARDS
There are a number of hazards that pose a threat to human life, health, and well -being, and this Plan is not meant to compile an exhaustive list. Those addressed in disaster planning are generally categorized as natural, human-caused, or technological. Some hazards are a threat to all geographic areas while others (e.g., flooding) are more limited in their extent.

The Contra Costa County hazards were identified, and their frequency of occurrence was evaluated through a historical analysis using a number of resources, including:

• 2018 Contra Costa County Hazard Mitigation Plan
• 2018 and 2023 State of California Hazard Mitigation Plan • Hazard planning documents developed by state, federal, and private agencies • National Centers for Environmental Information data from 2012 through 2022 • National Oceanic and Atmospheric Administration/National Weather Service Space Weather Prediction Center
• United States Geological Survey data
• FEMA National Risk Index data
Although FEMA only requires and reviews natural hazards in hazard mitigation plans, Contra Costa County decided to rank and mitigate against a comprehensive list of hazard events that could impact the 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 45 County. Due to the nature of non-natural hazards and the discretionary status regarding their inclusion, the following hazards of interest have been briefly and qualitatively assessed for the sake of public education and informing their inclusion within the hazard ranking and mitigation process. Hazards that have been identified as significant in Contra Costa County and that will be considered in this Plan are listed in Table 4-1.

Table 4-1. Contra Costa County Hazards
Natural Hazards
Climate Change
Dam and Levee Failure
Drought
Earthquake
Flood
Landslide
Sea Level Rise (Coastal Flooding)
Severe Weather (Severe Thunderstorms – Hail, Strong Winds, Tornadoes – Heavy Rainfall, Heat Wave/Extreme Heat) Tsunami
Wildfire
Human-Caused/Technological Hazards
Cybersecurity Threats
Hazardous Materials Incidents
Utility Interruptions
Active Shooter Incidents
Terrorism (Weapons of Mass Destruction)

Per FEMA’s requirement to consider all natural hazards, the following natural hazards were not included because these hazards are not considered significant for the Contra Costa County planning area due to its geographic location and lack of significant historical occurrences.

• Avalanche
• Hurricane
• Ice Storm
• Volcanic Activity
• Winter Weather (specifically related to snow and blizzards)

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Chapter 4: Hazard Identification and Risk Assessment 46

4.2 PRESIDENTIAL DISASTER AND EMERGENCY DECLARATIONS
Table 4-2 lists all federal disaster and emer gency declarations in Contra Costa County between 1950 and 2023, according to FEMA. This lists shows the foundation for identifying what hazards pose the most significant risk within the County. 45

Table 4-2. State and Federal Disaster Declarations for Contra Costa County Event
State
Proclamation
Date
Disaster
Number
Federal
Declaration
Date
FEMA
Disaster
Number
Location
Severe Winter Storms,
Flooding, Landslides,
and Mudslides
1/4/2023 2023-01 1/14/2023 DR-4683
Contra Costa
County
(Countywide)
Severe Winter Storms,
Flooding, and
Mudslides
1/4/2023 N/A 1/9/2023
EM-3591
(consolidated
into DR-4683)
Contra Costa
County
(Countywide)
California Covid-19
Pandemic 3/4/2020 2020-01 3/22/2020 DR-4482
Contra Costa
County
(Countywide)
California Covid-19
Pandemic 3/4/2020 2020-01 3/13/2020
EM-3428
(consolidated
into DR-4482)

Contra Costa
County
(Countywide)
Severe Winter Storms,
Flooding, Mudslides 3/7/2017 2017-03 4/1/2017 DR-4308
Contra Costa
County
(Countywide)
Severe Winter Storms,
Flooding, and
Mudslides
2/10/2017 2017-02 3/16/2017 DR-4305
Contra Costa
County
(Countywide)
Severe Storms,
Flooding, and
Mudslides
1/23/2017 2017-01 2/14/2017 DR-4301
Contra Costa
County
(Countywide)
Bay Area Oil Spill 11/9/2007 2007-15 Not Declared N/A
Contra Costa
County
(Countywide)
Severe Storms,
Flooding, Mudslides,
and Landslides
1/12/2006 2006-01 2/3/2006 DR-1628
Contra Costa
County
(Countywide)
Severe Winter Storms
and Flooding Not Available 98-01 2/9/1998 DR-1203
Contra Costa
County
(Countywide)
Severe Storms,
Flooding, Mud and
Landslides
1/2/1997 –
1/31/1997 97-01 1/4/1997 DR-1155
Contra Costa
County
(Countywide)
Winter Storms
Varies from
1/2/1997 –
1/31/1997
97-01 Not Declared N/A
Contra Costa
County
(Countywide)
Severe Winter Storms,
Flooding Landslides,
Mud Flow
Varies from
3/12/1995 –
3/24/1995
95-03 3/12/1995 DR-1046
Contra Costa
County
(Countywide)

45 Federal Emergency Management Agency. (2023). Disaster Declarations for States and Counties. Retrieved from https://www.fema.gov/data-visualization/disaster-declarations-states-and-counties. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 47 Event
State
Proclamation
Date
Disaster
Number
Federal
Declaration
Date
FEMA
Disaster
Number
Location
Severe Winter Storms,
Flooding, Landslides,
Mud Flows
Varies from
1/9/1995 –
2/17/1995
95-01 1/10/1995 DR-1044
Contra Costa
County
(Countywide)
Severe Winter Storm,
Mud and Land Slides,
and Flooding
1/7/1993 –
2/19/1993 93-01 1/15/1993 DR-979
Contra Costa
County
(Countywide)
Loma Prieta
Earthquake
10/18/1989 –
10/30/1989 89-05 10/18/1989 DR-845
Contra Costa
County
(Countywide)
Severe Storms and
Flooding
2/18/1986 –
3/12/1986 86-01 2/18/1986 DR-758
Contra Costa
County
(Countywide)
High Tides/Storms 1/1/1984 83-06 Not Declared N/A
Contra Costa
County
(Countywide)
Bradford Levee Failure 12/9/1983
1/18/1984 83-05 Not Declared N/A
Contra Costa
County
(Countywide)
Coastal Storms,
Floods, Slides, and
Tornadoes
12/8/1982 –
3/21/1983 82-18 2/9/1983 DR-677
Contra Costa
County
(Countywide)
High Tides and Rains 12/8/1982 N/A Not Declared N/A
Contra Costa
County
(Countywide)
Severe Storms, Flood,
Mudslides, and High
Tide
1/5/1982 –
1/9/1982 N/A 1/7/1982 DR-651
Contra Costa
County
(Countywide)
Torrential Rain, High
Tide, and Winds Not Proclaimed N/A 2/1/1980 EM-3078
Contra Costa
County
(Countywide)
Delta Levee Break 1/23/1980 N/A 1/23/1980 EM-3078
Contra Costa
County
(Countywide)
Drought Not Proclaimed N/A 1/20/1977 EM-3023
Contra Costa
County
(Countywide)
1976 Drought
2/9/1976
2/13/1976
2/24/1976
3/26/1976
7/6/1976
N/A Not Declared N/A
Contra Costa
County
(Countywide)
1970 Storms and
Floods 4/10/1970 N/A Not Declared N/A
Contra Costa
County
(Countywide)
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Chapter 4: Hazard Identification and Risk Assessment 48 Event
State
Proclamation
Date
Disaster
Number
Federal
Declaration
Date
FEMA
Disaster
Number
Location
Severe Storms and
Flooding
1/23/1969
1/25/1969
1/28/1969
1/29/1969
2/8/1969
2/10/1969
2/16/1969
3/12/1969
N/A 1/26/1969 DR-253
Contra Costa
County
(Countywide)
California Severe
Storms, Flooding
10/17/1962
10/25/1962
10/30/1962
11/4/1962
N/A 10/24/1962 DR-138
Contra Costa
County
(Countywide)

4.3 RISK ASSESSMENT METHODOLOGY
As part of the Contra Costa County Office of Emergency Services (OES), the risk assessment identifies the natural, human-caused, and technological hazards that have potential impacts on all or portions of the County. Hazard identification, historical occurrences, and risk modeling (where applicable and available for specific hazards) information was collected from multiple sources including, but not limited to:

• Environmental Systems Research Institute (Esri)
• Federal Emergency Management Agency (FEMA)
• National Centers for Environmental Information (NCEI) • National Weather Services (NWS)
• United States Geological Survey (USGS)
• Local repositories
This information was analyzed to assess the risk and vulnerability of people, property, the environment, and the jurisdiction’s essential operations from these hazards. Furthermore, a risk ranking was performed for the hazards of concern described in this Plan. The risk ranking is an important step in developing an action plan, as it allows jurisdic tions to compare the risk factors from one hazard to another. That comparison provides critical information to use in selecting hazard mitigation actions and their priorities.

This process is not only intended to help focus actions on the hazards with the highest ranking, but also to ensure that jurisdictions are aware of the hazards that ranked low yet still pose significant risk.

In order to provide an informed and comprehensive ranking of the hazards addressed in this Plan, a number of factors were considered: probability, extent, vulnerability, and impact. The sum of all the weighted factors for the extent, vulnerability, and impact categories was combined into a final consequence score. Probability multiplied by consequence resulted in a total risk score for each hazard.

Extent + Vulnerability + Impact = Consequence

Consequence x Probability = Total Risk Score
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Chapter 4: Hazard Identification and Risk Assessment 49 These results were determined by following a data driven quantitative assessment, reviewing, and ranking local knowledge from local subject matter experts, and developing other risk elements by the Core Planning Team based on the data collected. These elements were then aggregated to inform the analysis.

At the fundamental level, consequence is an assessment of the potential impact(s) if the hazard incident actually occurs. In this assessment, the consequence of an event (or the impact) will be interdependent on the following factors:

• Vulnerabilities (i.e., social, physical, and community conditions) • Capabilities and capacities
• Mitigation
• Characteristics of the hazard event (i.e., magnitude, scale) The frequency/probability of the hazard is not included in assessing the consequence because without the event, there is no consequence or impact.

4.3.1. Probability of Occurrence
The probability of occurrence of a hazard is indicated by a probability factor based on the likelihood of annual occurrence. Numerical probability factors were assigned as follows.

Table 4-3 outlines the probability of occurrence factors used in the risk assessment calculations for this Plan. A significant hazard event is defined as any hazard occurrence that directly or indirectly damages structures or infrastructure, impedes normal business operations, and/or is likely to cause serious or fatal injuries.

Table 4-3. Probability of Occurrence
Probability Description Probability
Factor
High Significant hazard event is likely to occur annually. 3 Medium Significant hazard event is likely to occur within 25 years. 2 Low Significant hazard event is likely to occur within 100 years. 1 Unlikely There is little to no probability of significant occurrence, or the recurrence interval is greater than every 100 years. 0

The assessment of hazard frequency is generally based on past hazard events in the area and professional judgment of local subject matter experts.

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Chapter 4: Hazard Identification and Risk Assessment 50

4.3.2. Extent Factors
Extent was assessed in two (2) categories – extent/intensity potential and catastrophic probability of the hazard. Numerical extent factors were assigned as follows.

4.3.2.1. Extent/Intensity Factor
Extent is defined as the range of anticipated intensities of the identified hazards. This category is most commonly expressed using various scientific scales (e.g., Saffir -Simpson, Enhanced Fujita, Modified Mercalli). Extent/Intensity Factors are hazard-specific and are detailed in each hazard profile. Table 4-4 outlines the extent/intensity factors used in the risk assessment calculations for this Plan.

Table 4-4. Extent/Intensity Factor
Probability Description Extent
Factor
High Historical and/or probabilistic models/studies for this hazard indicate the possibility of a high-intensity incident. 3
Medium Historical and/or probabilistic models/studies for this hazard indicate the possibility of a medium-intensity incident. 2
Low Historical and/or probabilistic models/studies for this hazard indicate the possibility of a low-intensity incident. 1
Unlikely Historical and/or probabilistic models/studies for this hazard indicate the possibility of little to no intensity. 0

4.3.2.2. Catastrophic Factor
The probability that a hazard could be catastrophic. Catastrophes are defined as significant incidents that cause sudden and great harm or destruction. Table 4-5 outlines the catastrophic factors used in the risk assessment calculations for this Plan.

Table 4-5. Catastrophic Factor
Probability Description Extent
Factor
High Catastrophic hazard event is likely to occur at least once in 10 years. 3 Medium Catastrophic hazard event is likely to occur at least once between 11 and 50 years. 2
Low Catastrophic hazard event is likely to occur at least once in 51 or more years. 1
No Impact Virtually no probability that this hazard could be catastrophic. 0

Each category was assigned a weighting factor to reflect its significance, consistent with this typically used for measuring the benefits of hazard mitigation actions – a weighting factor of three (3) was assigned for Extent/Intensity and its potential for Catastrophe.

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Chapter 4: Hazard Identification and Risk Assessment 51

4.3.3. Vulnerability Factors
Vulnerabilities were assessed in three (3) categories – population exposure, property exposure, and exposure based on changes in development. Numerical vulnerability factors were assigned as follows.

4.3.3.1. Population Exposure Factor
Population exposure values were assigned based on the percentage of the total population exposed to the hazard event. Table 4-6 outlines the population exposure factors used in the risk assessment calculations for this Plan.

Table 4-6. Population Exposure Factor
Probability Description Vulnerability
Factor
High 30% or more of the population is exposed to the hazard. 3 Medium 15% to 29% of the population is exposed to the hazard. 2 Low 14% or less of the population is exposed to the hazard. 1 No Vulnerability None of the population is exposed to the hazard. 0

4.3.3.2. Property Exposure Factor
Property exposure values were assigned based on the percentage of the total property value exposed to the hazard event. Table 4-7 outlines the property exposure factors used in the risk assessment calculations for this Plan.

Table 4-7. Property Exposure Factor
Probability Description Vulnerability
Factor
High 25% or more of the total assessed property value is exposed to the hazard. 3
Medium 10% to 24% of the total assessed property value is exposed to a hazard. 2
Low 9% or less of the total assessed property value is exposed to a hazard. 1
No Vulnerability None of the total assessed property value is exposed to a hazard. 0

4.3.3.3. Changes in Development
Changes in development in the past five (5) years have increased or decreased the community’s vulnerability/exposure to the hazard. Table 4-8 outlines the changes in development factors used in the risk assessment calculations for this Plan.

Table 4-8. Changes in Development Factor
Probability Description Vulnerability
Factor
High Changes in development have increased the vulnerability/exposure of the community to the hazard by 10% or more. 3
Medium Changes in development have increased the vulnerability/exposure of the community to the hazard between 5% and 9%. 2
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Chapter 4: Hazard Identification and Risk Assessment 52 Probability Description Vulnerability
Factor
Low Changes in development have increased the vulnerability/exposure of the community to the hazard by 4% or less. 1
No Vulnerability Changes in development had no effect and/or have decreased the vulnerability/exposure of the community to the hazard. 0

Each category was assigned a weighting factor to reflect the significance, consistent with those typically used for measuring the benefits of hazard mitigation actions – a weighting factor of three (3) was assigned for Population Exposure, and a weighting factor of one (1) was assigned for Property Exposed and Changes in Development.

4.3.4. Impact Factors
Hazard impacts were assessed in eight (8) categories – population and life/safety, underserved/equity, property damages, economic, environmental, essential operations, future development, and climate change. Numerical impact factors were assigned as follows.

4.3.4.1. Population and Life Safety Factor
Population and life safety values were assigned based on the best available data (historical and probabilistic) for people vulnerable to the hazard event and whether the affected population is likely to experience adverse impacts from the hazard incident. Table 4-9 outlines the population and life safety factors used in the risk assessment calculations for this Plan.

Table 4-9. Population and Life Safety Factor
Probability Description Impact
Factor
High Populations exposed to this hazard are likely to experience significant adverse impacts, such as fatalities and severe injuries. 3 Medium Populations exposed to this hazard are likely to experience some adverse impacts, such as injuries requiring acute medical care. 2 Low Populations exposed to this hazard are likely to experience minimal adverse impacts, such as ambulatory injuries. 1
No Impact Populations exposed to this hazard are not likely to experience significant adverse impacts. 0

4.3.4.2. Underserved/Equity Factor
Underserved/equity values were assigned based on the best available data for underserved populations vulnerable to the hazard event and whether the affected population is likely to experience adverse/disproportionate impacts from the hazard incident resulting in greater disparity in equity. Table 4-10 outlines the underserved/equity factors used in the risk assessment calculations for this Plan.

Table 4-10. Underserved/Equity Factor
Probability Description Impact
Factor
High
Underserved populations exposed to the hazard are likely to experience significant adverse/disproportionate impacts, such as fatalities and severe injuries.
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Chapter 4: Hazard Identification and Risk Assessment 53 Probability Description Impact
Factor
Medium
Underserved populations exposed to the hazard are likely to experience some adverse/disproportionate impacts, such as injuries requiring acute medical care.
2 Low
Underserved populations exposed to the hazard are likely to experience minimal adverse/disproportionate impacts, such as ambulatory injuries.
1 No Impact Underserved populations exposed to the hazard are not likely to experience significant adverse/disproportionate impacts. 0

4.3.4.3. Property Damage Factor
Property damage values were assigned based on the expected total property damage incurred from a hazard incident. It is important to note that values represent estimates of the loss from a major incident based on historical data or probabilistic models/studies. Table 4-11 outlines the property damage factors used in the risk assessment calculations for this Plan.

Table 4-11. Property Damage Factor
Probability Description Impact
Factor
High
More than $5 Million in property damages is expected from a single major hazard event, or damages are expected to occur to 15% or more of the property value within the jurisdiction.
3 Medium
More than $500,000 but less than $5 Million in property damages is expected from a single major hazard event, or damages are expected to occur to more than 5% but less than 15% of the property value within the jurisdiction.
2 Low
Less than $500,000 in property damages is expected from a single major hazard event or less than 5% of the property value within the jurisdiction.
1 No Impact Little to no property damage is expected from a single major hazard event. 0

4.3.4.4. Economic Factor
An estimation of the impact, expressed in terms of dollars, on the local economy is based on a loss of business revenue, crops, worker wages, and local tax revenues or on the impact on the local gross domestic product (GDP). Table 4- 12 outlines the economic factors used in the risk assessment calculations for this Plan.

Table 4-12. Economic Factor
Probability Description Impact
Factor
High Where the total economic impact is likely to be greater than $10 Million. 3
Medium Total economic impact is likely to be greater than $500,000, but less than or equal to $10 Million. 2
Low Total economic impact is not likely to be greater than $100,000. 1 No Impact Virtually no significant economic impact. 0

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Chapter 4: Hazard Identification and Risk Assessment 54

4.3.4.5. Environmental Factor
An estimate of the environmental impact from a major hazard event requiring outside resources and support; and/or repair, clean-up, restoration, and/or preservation work. Table 4-13 outlines the environmental factors used in the risk assessment calculations for this Plan.

Table 4-13. Environmental Factor
Probability Description Impact
Factor
High
Environmental impact from a single major hazard event is likely to be significant, requiring extensive outside resources and support; and/or repair, clean-up, restoration, and/or preservation work. 3 Medium
Environmental impact from a single major hazard event is likely to be localized, requiring some outside resources and support; and/or repair, clean-up, restoration, or preservation work.
2 Low
Environmental impact from a single major hazard event is likely to be minimal, requiring little to no outside resources and support, and/or minimal repair, clean-up, restoration, or preservation work. 1 No Impact No environmental impacts from a single major hazard event are likely. 0

4.3.4.6. Essential Operations Factors
The essential operations factor is the impact on the ability of the jurisdiction to meet the essential day-to- day operational demands and needs of the community after a single major hazard event. Table 4-14 outlines the essential operations factors used in the risk assessment calculations for this Plan.

Table 4-14. Essential Operations Factor
Probability Description Impact
Factor
High
Impact greater than 72 hours on the ability of the jurisdiction to meet the essential day-to-day operational demands and needs of the community from a single major hazard event.
3 Medium
Impact between 24 and 72 hours on the ability of the jurisdiction to meet the essential day-to-day operational demands and needs of the community from a single major hazard event.
2 Low
Impact less than 24 hours on the ability of the jurisdiction to meet the essential day-to-day operational demands and needs of the community from a single major hazard event.
1 No Impact
No impact on the ability of the jurisdiction to meet the essential day- to-day operational demands and needs of the community from a single major hazard event.
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Chapter 4: Hazard Identification and Risk Assessment 55

4.3.4.7. Future Development Factor
The future development factor is the potential that future development will have on increasing or decreasing the impact/consequence of the hazard. Table 4-15 outlines the future development factors used in the risk assessment calculations for this Plan.

Table 4-15. Future Development Factor
Probability Description Impact
Factor
High Future development trends will significantly increase the impact/consequence of this hazard. 3
Medium Future development trends will increase the impact/consequence of this hazard, but not significantly. 2
Low Future development trends will minimally increase
impact/consequence of this hazard. 1
No Impact
Future development trends will not increase the impact/consequence of the hazard, and/or may even decrease the impact/consequence of this hazard.
0 4.3.4.8. Climate Change Factor
The potential that climate change will increase the risk of the hazard (i.e., type, location, and range of anticipated intensities of the hazard and impacts). Table 4-16 outlines the climate change factors used in the risk assessment calculations for this Plan.

Table 4-16. Climate Change Factor
Probability Description Impact
Factor
High Climate Change trends will significantly increase the risk of this hazard and its impacts. 3
Medium Climate Change trends will increase the risk of this hazard and its impacts, but not significantly. 2
Low Climate Change trends will minimally increase the risk of this hazard and its impacts. 1
No Impact Climate change trends will not increase the risk of the hazard and its impacts. 0

Each category was assigned a weighting factor to reflect its significance, consistent with those typically used for measuring the benefits of hazard mitigation actions – a weighting factor of three (3) was assigned for Population and Life Safety, and Underserved/Equity, and a weighting factor of two (2) was assigned for Property Damage. A weighting factor of one (1) was assigned for Economic, Environmental, Essential Operations, Future Development, and Climate Change.

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Chapter 4: Hazard Identification and Risk Assessment 56

4.4 FEMA NATIONAL RISK INDEX SCORES
The National Risk Index (NRI) is a dataset and online tool to help illustrate the United States communities most at risk for 18 natural hazards. These include:

• Avalanche
• Coastal Flooding
• Cold Wave
• Drought
• Earthquake
• Hail
• Heat Wave
• Hurricane
• Ice Storm
• Landslide
• Lightning
• Riverine Flooding
• Strong Wind
• Tornado
• Tsunami
• Volcanic Activity
• Wildfire
• Winter Weather

Not all the hazards on this list are applicable to Contra Costa County; therefore, only those hazards with a defined risk to the County will be included in this Plan, as listed in Section 4.1 (Identified Hazards). The NRI’s goal is to fill gaps in available data and analyses to better inform federal, state, local, tribal, and territorial decision-makers as they develop risk reduction strategies.

In the NRI, risk is defined as the potential for negative impacts as a result of a natural hazard. The Risk Index is based on three (3) components – a natural hazards component (Expected Annual Loss), a consequence enhancing component (Social Vulnerability), and a consequence reduction component (Community Resilience). Using these components, the composite and hazard type Risk Index values are calculated for each community (county and Census Tract). Risk Index values form an absolute basis for measuring Risk within the NRI and are used to generate Risk Index percentiles and ratings across communities.
46 Table 4-17 illustrates the Risk Index rating and score for Contra Costa County.

Table 4-17. Risk Index Score for Contra Costa County (FEMA National Risk Index) Jurisdiction Rating Score
Contra Costa County Very High 99.6
Risk Index scores are calculated using an equation that combines scores for Expected Annual Loss due to natural hazards, Social Vulnerability and Community Resilience (Expected Annual Loss x Social Vulnerability / Community Resilience = Risk Index).

4.4.1. Expected Annual Loss
The Expected Annual Loss (EAL), the natural hazards component of the NRI, represents the average economic loss in dollars resulting from natural hazards each year. It is calculated for each hazard type and quantified loss for relevant consequence types such as, buildings, people, and agriculture. The EAL score and rating represents a community’s relative level of expected losses each year when compared to other communities at the same level. Since the score is associated to a community’s risk; the higher EAL score results in a higher Risk Index score.
47 Table 4-18 illustrates the EAL rating and score for
Contra Costa County.

46 Federal Emergency Management Agency. (2023). Determining Risk. Retrieved from https://hazards.fema.gov/nri/determining-risk.
47 Federal Emergency Management Agency. (2023). Expected Annual Loss. Retrieved from https://hazards.fema.gov/nri/expected-annual-loss.
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Chapter 4: Hazard Identification and Risk Assessment 57 Table 4-18. Expected Annual Loss for Contra Costa County (FEMA National Risk Index) Jurisdiction Rating Score
Contra Costa County Very High 99.6
Expected Annual Loss scores are calculated utilizing an equation that combines values for exposure, annualized frequency, and historic loss ratios (Expected Annual Loss = Exposure x Annualized Frequency x Historic Loss Ratio).

An EAL score and rating is calculated independently for each consequence type (i.e., buildings, population, and agriculture) for each county and Census Tract. The population EAL is measured in fatalities and injuries while the building and agriculture values are measured in dollars. However, for consistency in the unit of measurement, the population EAL was monetized into population equivalence using a value of statistical life (VSL) approach where each fatality or 10 injuries is treated as $11.6 Million of economic loss.

4.4.2. Social Vulnerability
Social vulnerability, the consequence enhancing risk component of the NRI, measures the susceptibility of social groups to the adverse impacts of natural hazards, including disproportionate death, injury, loss, or disruption of livelihood. The Social Vulnerability score and rating represent the relative level of a community’s social vulnerability compared to all other communities at the same level. A higher Social Vulnerability score results in a higher Risk Index score. 48 Table 4-19 illustrates the Social Vulnerability
rating and score for Contra Costa County.

Table 4-19. Social Vulnerability for Contra Costa County (FEMA National Risk Index) Jurisdiction Rating Score
Contra Costa County Relatively Moderate 47.4
Social Vulnerability is measured using the Social Vulnerability Index (SoVI) published by the University of South Carolina’s Hazards and Vulnerability Research Institute (HVRI).

4.4.3. Community Resilience
Community resilience, the consequence reduction risk component, measures the ability of a community to prepare for anticipated natural hazards, adapt to changing conditions, and withstand and recover rapidly from disruptions. The Community Resilience score and rating represent the relative level of a community’s resilience compared to all other communities at the same level. Since the score is inversely proportional to a community’s risk; the higher Community Resilience score results in a lower Risk Index score.
49 Table 4-20 illustrates the Community Resilience rating and score for Contra Costa County.

48 Federal Emergency Management Agency. (2023). Social Vulnerability. Retrieved from https://hazards.fema.gov/nri/social-vulnerability.
49 Federal Emergency Management Agency. (2023). Community Resilience. Retrieved from https://hazards.fema.gov/nri/community-resilience.
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Chapter 4: Hazard Identification and Risk Assessment 58 Table 4-20. Community Resilience for Contra Costa County (FEMA National Risk Index) Jurisdiction Rating Score
Contra Costa County Relatively High 75.0
Community Resilience is measured using the Baseline Resilience Indicators for Communities (HVRI BRIC) published by the University of South Carolina's Hazards and Vulnerability Research Institute (HVRI).

4.5 TOTAL RISK SCORES
Table 4-21 represents the overall risk scores for Contra Costa County, based on the Risk Assessment Methodology defined at the beginning of this section. Following a data- driven quantitative assessment, reviewing and ranking local knowledge from local subject matter experts, and developing other risk elements by the Core Planning Team based on data collected. These elements were aggregated to inform the analysis. The hazards are ranked from highest to lowest based on the Total Risk Score.

However, if the Risk Score is the same, then it is ranked by the Probability Factor. If the Probability Factor is the same, then it is ranked by the sum of the Impact Factor. If the Impact Factor is the same, then it is ranked by the sum of the Vulnerability Factor.

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Chapter 4: Hazard Identification and Risk Assessment 59 Table 4-21. 2024 Hazard Risk Score for Contra Costa County Hazard
Event
Probability Consequence
(Sum of weighted factors) Total Risk
Probability
Factor
Extent
(sum of the weighted
Extent factors)
Vulnerability
(sum of the weighted
Vulnerability factors)
Impact
(sum of the weighted
Impact factors)
Consequence
Score
Total Risk
Score
(Probability x
Consequence)
Earthquake 2 18 17 36 71 68
Wildfire 2 18 12 31 61 59
Heavy Rainfall
(Severe Weather) 3 9 14 15 38 56
Flood
(Urban/Flash Flood) 2 15 12 29 56 55
Landslide 3 9 6 22 37 55
Strong Winds/ Damaging
Winds
(Severe Weather)
3 9 11 16 36 54
Severe Thunderstorm
(Severe Weather) 3 6 16 14 36 54
Utility Interruptions 3 9 7 18 34 51
Heat Wave/Extreme Heat
(Severe Weather) 3 9 10 15 34 51
Drought 2 18 12 20 50 50
Flood
(Riverine/Creek Flood) 2 12 7 29 48 48
Hazardous Materials
Incidents 2 15 9 16 40 41
Climate Change 2 9 12 15 36 38
Sea Level Rise 2 12 6 17 35 37
Cybersecurity
Threats 2 12 7 13 32 34
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Chapter 4: Hazard Identification and Risk Assessment 60 Hazard
Event
Probability Consequence
(Sum of weighted factors) Total Risk
Probability
Factor
Extent
(sum of the weighted
Extent factors)
Vulnerability
(sum of the weighted
Vulnerability factors)
Impact
(sum of the weighted
Impact factors)
Consequence
Score
Total Risk
Score
(Probability x
Consequence)
Active Shooter
Incidents 2 9 5 15 29 32
Terrorism
(Weapons of Mass
Destruction)
1 18 11 27 56 31
Dam and Levee Failure 1 18 6 31 55 30
Tsunami 1 6 6 22 34 20
Tornado
(Severe Weather) 1 6 6 14 26 16
Total Risk Score Legend
Classification Probability
Factor
Extent
(sum if the weighted
Extent factors)
Vulnerability
(sum if the weighted
Vulnerability factors)
Impact
(sum if the weighted
Impact factors)
Consequence
Score
Total Risk
Score
Low (L) 1 0 – 6 0 – 6 0 – 12 0 – 24 0 – 24
Medium (M) 2 7 – 12 7 – 12 13 – 26 25 – 50 25 – 54
High (H) 3 13 – 18 13 – 18 27 – 39 51 – 75 55 and above The legend— specifically the assignment of low, medium, and high— provides an additional means to qualitatively assess the probability factor, sum of weighted factors, and the total risk scores for each hazard. The Consequence Score represents the sum of the Extent, Vulnerability, and Impact Factors. The Total Risk Score is a measure of Probability and Consequence.

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Chapter 4: Hazard Identification and Risk Assessment 61

4.6 HAZARD PROFILES

4.6.1. Climate Change

4.6.1.1. Description
The National Oceanic and Atmospheric Administration (NOAA) defines climate change as any significant change in the measures of climate for extended periods of time, usually over decades or longer (e.g., major long-term changes in temperature, precipitation, ocean heat, sea level, sea ice extent) that affect life on Earth.
50 In California, annual temperatures have increased over one (1) degree Fahrenheit (1°F) while some areas have exceeded two (2) degrees Fahrenheit (2°F) .
51 The State can expect warmer and drier
conditions, reduction in winter snow, an increase in winter rainfall, sea level rise, changes in the water cycle, and an increase in extreme weather events. However, due to the geographical differences throughout the State, impact may vary from location to location. In Contra Costa County, an increase in extreme heat events, reduced air quality, sea level changes , water supply issues, and an increase in storm severity and frequency resulting in flood events are expected due to climate change. 52 The San
Francisco Bay Region, which includes Contra Costa County, average temperatures are expected to increase between three (3) and 4.5 degrees Fahrenheit by 2050. 53

The five (5) main greenhouse gases consist of carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and water vapor. These gases are naturally part of the Earth’s atmosphere creating the greenhouse effect which allows conditions to be livable. However, increasing the levels of these greenhouse gases in the atmosphere results in heat being trapped near the Earth’s surface causing the global average temperature to increase.
54 Carbon dioxide is a crucial component of the Earth’s atmosphere and human activities have increased its amount in the air by 5 0% since the start of the Industrial Revolution, in the late 1700s . Additionally, other greenhouse gases amounts continue to increase. 55
Climate Change Indicators
Earth’s climate has changed throughout its history, it is part of Earth’s cycle. However, scientists from agencies such as NASA, NOAA, and the Intergovernmental Panel on Climate Change (IPCC) agree that climate change is occurring at a faster rate than expected. Global surface temperatures continue to rise unequivocally as a result of greenhouse gas emissions from human activities. Between 2011 and 2020, global surface temperatures were 1.1 degrees Celsius (1.1°C) higher than between 1850 through 1900 average, with larger increases over land (1.6°C) than over the ocean ( 0.9°C). Global surface temperatures have increased at a faster rate since 1970 than any other 50-year period over the last 2,000

50 National Oceanic and Atmospheric Administration. (n.d.). What’s the Difference Between Climate and Weather? Retrieved from https://www.noaa.gov/explainers/what-s-difference-between-climate-and-weather. 51 California Climate Adaptation Strategy. (2023). Summary of Projected Climate Change Impacts on California.

Retrieved from https://climateresilience.ca.gov/overview/impacts.html. 52 Contra Costa County. (2015) Contra Costa County Climate Action Plan. Retrieved from https://www.contracosta.ca.gov/DocumentCenter/View/39791/Contra-Costa-County-Climate-Action-Plan?bidId=. 53 California Climate Adaptation Strategy. (2023). Region: San Francisco Bay Area. Retrieved from https://climateresilience.ca.gov/regions/sf-bay-area.html. 54 National Aeronautics and Space Administration. (n.d.). What is the Greenhouse Effect? Retrieved from https://climate.nasa.gov/faq/19/what-is-the-greenhouse-effect/. 55 National Aeronautics and Space Administration. (n.d.). The Causes of Climate Change. Retrieved from https://scied.ucar.edu/learning-zone/how-climate-works/carbon-dioxide. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 62 years. 56 The warmest years on record were between 2015 and 2023 with 2023 on track to be the warmest year on record. 57

Increasing global temperatures have affected weather patterns throughout the planet. In the United States, since 1950, the number of extreme heat events have increased while record low temperatures events have decreased, and an increase of heavy rainfall events has been recorded. Other climate change impacts include increasing ocean temperatures and ocean acidification , shrinking ice sheets, retreading glaciers, decreasing snow cover, sea level rise, and declining artic sea ice. 58 The United
States Environmental Protection Agency, in collaboration with other data contributors, compiled seven (7) climate indicators that provide evidence of changes and their impacts on the population and environment. The seven (7) climate indicators are listed in Table 4-22. 59 Table 4-22. Climate Change Indicators in the United States Indicator Description
Greenhouse Gases
This indicator characterizes emissions of major greenhouse gases (i.e., carbon dioxide, nitrous oxide, methane, chlorofluorocarbons (CFCs), and water vapor) resulting from human activities, the concentration of these gases in the atmosphere, and how emissions and concentrations have changed over time.

Weather and Climate
Rising global temperatures are associated with widespread changes in weather patterns. Extreme weather events (e.g., heat waves and heavy precipitation) are likely to become more frequent or more intense as a result of climate change.

Oceans Weather is heavily influenced on local and global scales by oceans while changes in climate change can alter many of the ocean’s properties.

Snow and Ice
Earth’s snow and ice coverage can be significantly altered with relatively minor changes in temperatures. As a result of increasing temperatures, snow and ice coverage has decreased globally.

Health and Society Changes in climate can have adverse effects on public health, agriculture, water supplies, energy production and use, land use and development, and recreation.

Ecosystems Ecosystems are what provides humans with food, clean water, and a variety of other services. Changes in climate can disrupt the functioning ecosystems.

4.6.1.2. Hazard Location
Climate change is occurring globally with wide variations based on location and latitude. The polar regions have experienced particularly rapid changes in climate with increased ice melting and more sea ice free days. Figure 4-1 illustrates the global average temperature between 1993 and 2022 in degrees Fahrenheit per decade.

56 Intergovernmental Panel on Climate Change. (2023). Climate Change 2023 Synthesis Report: Summary for Policymakers. Retrieved from https://www.ipcc.ch/report/ar6/syr/downloads/report/IPCC_AR6_SYR_SPM.pdf. 57 World Meteorological Organization. (2023). 2023 Shatters Climate Records, With Major Impacts. Retrieved from https://wmo.int/news/media-centre/2023-shatters-climate-records-major-impacts. 58 National Aeronautics and Space Administration. (n.d.). How Do We Know Climate Change Is Real? Retrieved from https://climate.nasa.gov/evidence/.
59 United States Environmental Protection Agency. (n.d.). Climate Change Indicators: View the Indicators.

Retrieved from https://www.epa.gov/climate-indicators/view-indicators. 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 63 Figure 4-1. Global Temperature Trends (1993 – 2022) 60

4.6.1.3. Hazard Extent/Intensity
In 1990 and 1992, the Intergovernmental Panel on Climate Change (IPCC) developed long-term emission scenarios which have been extensively used in climate change, its impact, and climate change mitigation analysis.
61 Throughout the year s, these scenarios have been evaluated and updated based on the current scientific data and technology available at the time of the update. These scenarios were developed to account for the uncertainty on how societies and government will deal with human emission of greenhouse gases in the future. Table 4-23 provides an overview of the five (5) major IPCC scenarios used in the 2021 Report.
62 60 Climate.gov. (2023). Climate Change: Global Temperature. Retrieved from https://www.climate.gov/news- features/understanding-climate/climate-change-global-temperature. 61 Intergovernmental Panel of Climate Change. (2000). IPCC Special Report: Emissions Scenarios. Retrieved from https://www.ipcc.ch/site/assets/uploads/2018/03/sres-en.pdf. 62 University Corporation for Atmospheric Research. (2021). Compare IPCC Scenarios Interactive. Retrieved from https://scied.ucar.edu/interactive/compare-ipcc-scenarios.

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Chapter 4: Hazard Identification and Risk Assessment 64 Table 4-23. IPCC Scenarios
Scenario Description Expected Temperature
Increase
SSP1-1.9
(Most Optimistic)
No increase in greenhouse gas emissions. Global carbon
dioxide emissions do not increase (are cut to net zero) by approximately 2050.

1.5°C
SSP1-2.6
(Next Best)
Small levels of greenhouse gas emissions. Severe carbon dioxide emissions cuts, and no longer increase (are cut to net zero) after 2050.

1.8°C
SSP2-4.5
(Middle of the
Road)
Medium greenhouse gas emissions scenario. Carbon dioxide emissions start to fall around mid-century but do not reach net zero until after 2100.

2.7°C
SSP3-7.0
(Dangerous)
Medium to high greenhouse gas emissions scenario.

Emissions rise steadily, with total carbon dioxide double the current level by 2100.

3.6°C
SSP5-8.5
(Avoid at All
Costs)
Highest greenhouse gas emissions scenario. Yearly
emissions amounts are double current levels by 2100. 4.4°C The Scenarios are based on Shared Socioeconomic Pathways (SSPs), which determine likely emissions of greenhouse gases based o n different climate policies.

4.6.1.4. Warning Time
Though warming has not been uniform across the planet, the upward trend in the globally averaged temperature shows that more areas are warming than cooling. According to NOAA's 2021 Annual Climate Report the combined land and ocean temperature has increased at an average rate of 0.14 degrees Fahrenheit (0.08 degrees Celsius) per decade since 1880; however, the average rate of increase since 1981 has been more than twice as fast: 0.32 °F (0.18 °C) per decade.

The amount of future warming Earth will experience depends on how much carbon dioxide and other greenhouse gases we emit in coming decades. Today, our activities —burning fossil fuels and clearing forests—add about 11 billion metric tons of carbon (equivalent to a little over 40 billion metric tons of carbon dioxide) to the atmosphere each year. Because that is more carbon than natural processes can remove, atmospheric carbon dioxide increases each year.

4.6.1.5. Probability and Frequency
According to the 2017 U.S. Climate Science Special Report, if yearly emissions continue to rapidly increase, as they have since 2000, models project that by the end of this century, global temperature will be at least 5 degrees Fahrenheit (5°F ) warmer than the 1901 – 1960 average, and possibly as much as

10.2 degrees Fahrenheit (10.2°F) warmer. If annual emissions increase at a slower rate and begin to significantly decline by 2050, models project temperatures would still be at least 2.4 degrees (2.4°F) warmer than the first half of the 20
th century, and possibly up to 5.9 degrees Fahrenheit (5.9°F) warmer.

Figure 4-2 illustrates hypothetical pathways of carbon emissions ( i.e., representative concentration pathways or RCPs) throughout the 21
st century based on different possible energy policies and economic growth patterns. Figure 4-3 illustrates projected temperature increase relative to the 1901-1960 average depending on which RCP we eventually follow. 63

63 U.S. Global Change Research Program. (2017). Fourth National Climate Assessment: Executive Summary.

Retrieved from https://science2017.globalchange.gov/chapter/executive-summary/. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 65 Figure 4-2. Projected Annual Global Carbon Emissions

Figure 4-3. Projected Global Temperatures

Probability of Future Hazard Events
In California and western North America, climate observations have shown a trend toward warmer temperatures with an increase in extremely hot days and nights , an increase in the area burned by wildfires, a smaller fraction of precipitation falling as snow , an increase in frequency of drought and an increase in consecutive dry years , and sea level rise is expected to continue to increase flooding and erosion on beaches, bluffs, and cliffs. Research suggests that California will continue to experience hotter and drier conditions, reductions in winter snow and increases in winter rains, sea level rise, significant changes to the water cycle, and an increase in extr eme weather events. Table 4-24 summarizes the potential impacts in California due to climate change.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 66 Table 4-24. Climate Change Impacts in California 64
Climate Impact Historical Trends Future Direction
of Change
Confidence for
Future Change
Temperature Warming Warming Very High
Sea Level Rise Rising Rising Very High
Annual Precipitation No significant trends Unknown Low Intensity of Heavy Precipitation
Events No significant trends Increasing Medium-High
Frequency of Droughts Increasing No significant trends Increasing Medium-High Acres Burned by Wildfire Increasing Increasing Medium-High

4.6.1.6. Past Events
Climate change has occurred throughout Earth’s history due to variations in the Earth’s inclination to the sun, volcanic activity, and other factors (e.g., asteroid impacts and the amount of solar radiation reaching the earth’s surface rises and falls). Earth’s temperature correlates to the amount of solar radiation arriving at the surface and the climate with it.

In relatively recent history, the last glacial period (i.e., the Ice Age), occurred from c. 110,000 to 12,000 years ago. This most recent glacial period is part of a larger pattern of glacial and interglacial periods known as the Quaternary glaciation (c. 2,588,000 years ago to present). From this point of view, scientists consider this "ice age" to be merely the latest glaciation event in a much larger ice age that dates back over two (2) million years and is still ongoing.

During this last glacial period, there were several changes between glacier advance and retreat. The Last Glacial Maximum, the maximum extent of glaciation within the last glacial period, was approximately 22,000 years ago. While the general pattern of global cooling and glacier advance was similar, local differences in the development of glacier advance and retreat make it difficult to compare the details from continent to continent. Generally, temperature variation and glaciation patterns have lagged in atmospheric carbon dioxide (CO
2) content.

Figure 4-4 depicts global variations during the past 400,000 years as a correlation between temperature and atmospheric CO
2 content in part per million. 65

64 Contra Costa County. (2023). Draft Contra Costa County Climate Action Plan. Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
65 Hogg, A.M. (2008). Glacial Cycles and Carbon Dioxide: A Conceptual Model. Retrieved from https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007GL032071. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 67 Figure 4-4. Temperature and Atmospheric CO2 Variation the Past 400,000 Years

For 22,000 years ago, the planet has slowly warmed, and the glaciers retreated to high northern latitudes and mountains. In the last several decades, human activity has likely led to a rapid increase in atmospheric CO
2 and a matching rise in global temperature. The result has been that climate change may be accelerating. Figure 4-5 provides a graphical depiction of yearly average surface temperature compared to the 20th century average.

Figure 4-5. Global Average Surface Temperature (1880 – 2022)

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 68

4.6.1.7. Vulnerability and Impacts
Climate change is expected to alter many aspects of the County’s climate, including temperature, precipitation patterns, and sea levels, potentially exacerbating both the severity and geographic scope of climate hazards. Contra Costa County is most vulnerable to hazards associated with changes in air quality, drought, extreme heat, flooding, human health hazards, landslides, severe storms, sea level rise, shoreline flooding, and wildfire.
66 Drought, flood, landslides, sea level rise, severe weather (includes heat wave/extreme heat), and wildfire are individual hazards in this Hazard Mitigation Plan. Vulnerability and impacts for each of these hazards are discussed in further detail under each hazard profile.

Life Safety and Health: Although climate change will affect everyone, some populations in the County are likely to be affected more than others. This can include the risk of injury, death, property damage or destruction, and can also include economic impacts and loss of income, behavioral and mental health impacts, and an overall decrease in quality of life. Impacted Communities, who have been historically under-resourced and are already more likely to face constraints (e.g., limited financial resources, reduced access to education and job opportunities, and increased exposure to environmental hazards), are likely to be further impacted as climate change related hazards increases in frequency and severity.

Populations especially vulnerable to climate change are concentrated along the northern waterfront of the County , within unincorporated communities such as North Richmond, Bay Point, and Pacheco.

Additionally, this population faces greater vulnerabilities because they may be less able to withstand a temporary loss of income if jobs are affected by these hazards.

Lack of access to resources not only includes financial resources, but also communication, transportation, education, and other community services. Even people who are relatively financially stable can be disproportionately affected by climate change related hazards if physically or socially isolated. For example, individuals with limited English proficiency may not be able to interact with officials, and those without lifelines (e.g., transportation, broadband internet or other forms of reliable communication), may not be able to get accurate and timely information about hazardous situations (e.g., evacuation order).

This often delays this population’s ability to obtain the resources needed to prepare for or respond to an emergency. Renters face similar vulnerabilities and impacts because even if they have the financial resources to adapt to changing conditions, they have limited control over their home.

Physical constraints can also make people more susceptible to climate change. Individuals with disabilities may find it harder to prepare for hazardous events, and some hazards can exacerbate chronic health conditions and create a greater threat for people with these conditions. Young children (under 10 years old) and senior s (65 years old and over) are disproportionately affected by some hazards (e.g., extreme heat and air pollution) even if they are entirely healthy. The senior population that lives alone is often at greater risk because they are more likely to be socially isolated. People with physical constraints are also more likely to need assistance during evacuations. The health equity of populations is also closely associated with racism, historic discrimination, and a wide range of socioeconomic conditions.

The Contra Costa County Climate Action Plan, updated in 2024, has identified the following underserved and at risk population that could be uniquely vulnerable to the climate change related hazards within this Plan:
67 66 Contra Costa County. (2023). Draft Contra Costa County Climate Action Plan. Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
67 Ibid.
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Chapter 4: Hazard Identification and Risk Assessment 69 • Children (under 10 years old) are susceptible to allergens and pollution due to wildfires, extreme heat, flooding, and landslides. Children are known to spend more time outdoors which exposes them to more of these hazards. Furthermore, children are physiologically less able to regulate their body temperatures than adults and may not be able to recognize the need to hydrate and cool down when overheated. In Contra Costa County, there are approximately 130,099 ( 11.2%) children under 10 years old as of 2022.
68 The highest concentration of children lives in parts of the cities of Concord, Richmond, Pittsburg, Brentwood, and San Ramon. • Households in Poverty are households with an income below the poverty line which is $24,300 for a household of four (4) people. This population is exposed to extreme heat, flooding, landslides, severe weather, sea level rise, and wildfires . Approximately 7,600 households in Contra Costa County live in poverty. T he areas with the highest concentrations of poverty in Contra Costa County occur in central Richmond, North Richmond and San Pablo, tracts of Concord and Martinez, and in Bay Point, Pittsburg, and Antioch. • Low Income Households are those with an income of 80% or less of the median income in Contra Costa County ($104,400). Approximately 25,340 households (41.0%) in the County are within the low income category. Low income households may have fewer financial resources to devote to preparing for and recovering from the effects of climate change. This population is extremely vulnerable to flooding because many of these households are located within or near a flood zone or dam inundation areas, especially in the north and east portions of the County. High concentrations of low income households vulnerable to shoreline flooding occur in Rodeo, Crockett, the islands in the Delta, and Discovery Bay.
• Outdoor Workers are directly exposed to poor air quality, extreme heat, and drought, are facing increased health risks and economic hardships. These include, but are not limited to, constructions workers, agriculture workers, and recreation. • Individuals Experiencing Homelessness are those who do not have a permanent home, including those who live in their vehicles or temporary shelters. This population is highly exposed to extreme heat, flooding, sea level rise, severe weather, and wildfires. Furthermore, they face the risk of health complications, minimal access to healthcare, and loss of temporary shelters. In 2024, there are 2,843 people experiencing homelessness in Contra Costa County, an 18.5% increase from 2023.
69 • Individuals Living on Single Access Roads are those living in areas with a single route in and out (i.e., accessible via one (1) roadway) of the neighborhood or area. This includes several communities in the Delta and in the hillside areas of central and western Contra Costa County.

This population is uniquely vulnerable to landslides, wildfires, flooding, and sea level rise because these hazards can cause damage and/or block essential roadways . These communities can become isolated from the community and emergency services. For example, in Contra Costa County, Bethel Island and Delta islands are accessible via a single road. • Seniors (65 years old and over) and Seniors Living Alone are uniquely vulnerable to extreme heat, flooding, severe weather, landslides, and wildfires. The physiology of seniors makes them especially vulnerable to the health effects of extreme heat and wildfires. Furthermore, physical limitations may not allow seniors to evacuate in the event of an emergency. In Contra Costa

68 United States Census Bureau. (2022). S0101: Age and Sex (2022: ACS 1-Year Estimates Subject Tables).

Retrieved from https://data.census.gov/table/ACSST1Y2022.S0101?g=050XX00US06013. 69 Contra Costa Health. (2024). Health, Housing, and Homelessness Data Reports (Point-in-Time Count).

Retrieved from https://www.cchealth.org/services-and-programs/homeless-services/data. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 70 County, there are approximately 201,136 seniors (17.4%).70 Due to institutional and residential retirement communities, central Contra Costa County, Bethel Island, the easter n part of the City of Richmond, and several part of the City of Walnut Creek have a particularly high concentration of seniors. Seniors living alone may have caretakers, but for the most part are living alone. This population is generally more vulnerable compared to other seniors because they may lack access to social connections and community support to assist in preparedness and responding to emergency events (e.g., evacuations). In 2022, there were approximately 33,102 (8.0%) seniors living alone.
71 • Individuals with Chronic Illnesses are those that have long term or permanent health conditions that can be exacerbated by climate change related hazards. These health problems include, but are not limited to cancer, respiratory and cardiovascular diseases, and arthritis. This population is uniquely vulnerable to flooding, extreme heat, severe weather, and wildfires. • People with Limited English Proficiency may not be aware of climate related hazards and emergency situations in a timely manner . Other languages spoken in the County are primarily Spanish, Mandarin, Cantonese, Tagalog, and Persian. Other than English, the most commonly spoken language in Contra Costa County is Spanish (18.7%). The United States Census Bureau estimates that 14.5% of the County’s residents speak English “less than very well.” 72 The higher
proportion with limited English proficiency occurs in the cities of Richmond, Concord, and San Pablo.
• Individuals without Access to Lifelines are those who do not have access to basic technology or services (e.g., transportation or modern communication). These individuals may live in areas where these lifelines are not available or feasible, may not be able to afford these, or for personal reasons may choose to not have them. This population is uniquely vulnerable to flooding and wildfire. Furthermore, those without access to lifelines may be unaware of an approaching emergency, may be unable to evacuate in a timely manner, and may become isolated if power services or transit systems are not working.
• Undocumented Individuals includes people who do not have formal permission to live in the United States (i.e., do not have citizenship, permanent residency, visas, or other similar status) .

This population is uniquely vulnerable to extreme heat, flooding, landslides, severe weather, and wildfire. Many individuals within this population have outdoor occupations or work in highly unregulated environments which make them vulnerable to extreme heat and poor air quality due to wildfires. Additionally, many of the undocumented population are likely to fall in the household in poverty or low income categories and are more likely to live in low lying areas making vulnerable to flood and severe weather events. There are no official counts of the number of undocumented individuals within Contra Costa County.

Table 4-25 outlines the population in Contra Costa County where vulnerabilities to climate change exceed the County median, as compared to United States percentages and the differences thereof. There are 42 Census Tracts in Contra Costa County that are identified as disadvantaged by the United States Council on Environmental Quality (ACEQ). According to the ACEQ, a disadvantaged community is

70 United States Census Bureau. (2022). S0101: Age and Sex (2022: ACS 1-Year Estimates Subject Tables).

Retrieved from https://data.census.gov/table/ACSST1Y2022.S0101?g=050XX00US06013. 71 United States Census Bureau. (2022). DP02: Selected Social Characteristics in the United States (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP02?g=050XX00US06013. 72 United States Census Bureau. (2022). S1601: Language Spoken at Home (2022: ACS 1-Year Estimates Subject Tables). Retrieved from https://data.census.gov/table/ACSST1Y2022.S1601?g=050XX00US06013. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 71 identified if it is located in a Census Tract that is at or above the threshold for one (1) or more environmental, climate, or other burdens, and at or above the threshold for associated socioeconomic burdens, including poverty and language barriers.
73 Table 4-25. Neighborhoods At Risk Table (Contra Costa County, CA) Indicators 2022* Population Percentage United States
Percentage
Percent
Difference
(County vs. United States)
People under 5
years old 62,829 6.0% 5.7% 5.0%
People over 65
years old 190,307 12.5% 16.5% -28.0%
People of color
(including Hispanic) 690,897 80.6% 41.1% 65.0%
People who do not
speak English well 65,143 11.6% 4.1% 96.0%
People without a
high school degree 83,135 20.1% 10.9% 59.0%
Families in poverty 16,650 10.2% 8.8% 15.0%
Housing units that
are rentals 134,149 51.0% 35.2% 37.0%
Households with no
car 20,801 7.3% 8.3% -13.0%
People with
disabilities 130,100 12.5% 12.9% -3.0%
People without
health insurance 53,839 8.4% 8.7% -4.0%
* ACS 5-year estimates: 2022 represents average characteristics between 2018 and 2022.

Table 4-28 outlines the vulnerability of the total population exposed to climate change, and Table 4-29 outlines the climate change impacts to population and life safety, underserved/equity population, and essential operations, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Property Damage and Critical Infrastructure: The loss of key buildings and infrastructure systems can create potentially severe effects throughout the C ounty. The loss of homes in a natural disaster means that a potentially large group of people must be temporarily housed while their homes go through the lengthy reconstruction process. Meanwhile, some people may choose not to return to their former community. Damages to businesses can cause economic harm to business owners and employees as well as members of various communities. For example, sea level rise and coastal flooding can interrupt many of the industrial and manufacturing centers located along the Contra Costa County shoreline, creating temporary or permanent loss of income for their employees, with possible cascading impacts such as harming the tax base and well-being of various communities.

Contra Costa County’s infrastructure networks are connected to much larger regional, State, and national systems. These systems are vulnerable to disruption from outside of Contra Costa County, resulting in a loss of service to community members. For example, most of the water used in the unincorporated areas of the County is imported from the Sierra Nevada through a complex system of pumps, aqueducts, and reservoirs. Damage at any point along this system can affect Contra Costa County’s water supply,

73 United States Council of Environmental Quality. (n.d.). Climate and Economic Justice Screening Tool:

Methodology. Retrieved from https://screeningtool.geoplatform.gov/en/methodology. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 72 causing restricted water service. Many components of this system pass through eastern Contra Costa County and other low-lying areas of the Delta region, where they are particularly vulnerable to sea level rise. Buildings and infrastructure do not need to be physically damaged to trigger a loss of service. For example, extreme heat makes the machinery of the power grid run less efficiently and simultaneously increases demand to meet greater cooling needs. This combination raises the risk of grid overloading and causing brownouts or blackouts. Similarly, drought conditions harm water delivery services but do not cause physical damage to pipes or water treatment plants. Economic drivers can also be affected without experiencing physical damage, such as when businesses are forced to close because of a public health emergency.
74 Table 4-28 outlines the total property value exposed to climate change and how the changes in development in the past five (5) years, have affected the vulnerability of the community to climate change.

Table 4-29 outlines the climate change impact on total property damage, potential future development, and the economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Environment: The unprecedented rate of change in the climate system can rapidly create local conditions unfavorable to ecosystems, killing them or forcing them out of the area before they have the chance to adapt. Damage or loss of local ecosystems and natural resources is harmful for its own sake, but it also affects the people and economy of Contra Costa County. Many ecosystems provide important services for communities, such as protection against floods and high winds, groundwater recharge and filtration, and home for pollinators and beneficial species. The natural environment provides recreational and tourism opportunities, contributes to the valued character of Contra Costa County, and helps maintain a high quality of life.

Climate change often results in species and even entire ecosystems being forced out of their historical range and moving to areas that provide their preferred living conditions. In some cases, there may no longer be places in Contra Costa County that can support these ecosystems, and they disappear from the area. For example, the conifer forests in the hills of the western portion of the County depend on fog and its cooling benefit in summer temperatures. As temperatures increase and coastal fog is expected to decrease, these trees may not survive. Habitat loss can also exacerbate this problem. For example, in a natural system, wetlands will migrate inland as sea levels rise. However, if the inland areas are blocked by development or other barriers, the wetlands cannot migrate and could disappear.

Even if overall temperature and precipitation patterns remain favorable to key ecosystems and natural resources, the increased frequency and severity of some climate change related hazards can harm these important community assets. For example, many ecosystems in the State (e.g., forests) rely on naturally occurring wildfires to remove dead vegetation and return nutrients to the soil, and some species rely on fires reproduction. However, as wildfires are increasing in intensity, trees that could survive relatively low level fires may not be able to survive much more severe blazes.

Table 4-29 outlines climate change’s impact on the environment, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

74 Contra Costa County. (2023). Draft Contra Costa County Climate Action Plan. Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
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Chapter 4: Hazard Identification and Risk Assessment 73 Table 4-26. Probability of Occurrence
Hazard Event Probability of Occurrence Probability
Factor
Weighted
Factor
Climate Change Medium Significant hazard event is likely to occur within 25 years. 2 N/A Table 4-27. Extent Factors
Hazard Event Extent Factor Extent Extent
Factor
Weighted
Factor
Climate Change
Extent/Intensity Medium Historical and/or probabilistic models/studies for this hazard indicate the possibility of a medium-intensity incident. 2 6 Catastrophic Low Catastrophic hazard event is likely to occur at least once in 51 or more years. 1 3
Table 4-28. Vulnerability Factors
Hazard Event Vulnerability Factor Vulnerability Vulnerability Factor
Weighted
Factor
Climate Change
Population Exposure High 30% or more of the population is exposed to the hazard. 3 9 Property Exposure Low 9% or less of the total assessed property value is exposed to a hazard. 1 2
Changes in
Development Low
Changes in development have increased the
vulnerability/exposure of the community to the hazard by 4% or less.
1 1
Table 4-29. Impact Factors
Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Climate Change
Population and Life
Safety Low Populations exposed to this hazard are likely to experience minimal adverse impacts, such as ambulatory injuries. 1 3 Underserved/Equity Low
Underserved populations exposed to the hazard are likely to experience minimal adverse/disproportionate impacts, such as ambulatory injuries.
1 3
Property Damage Low
Less than $500,000 in property damages is expected from a single major hazard event or less than 5% of the property value within the jurisdiction.
1 2
Economic Low Total economic impact is not likely to be greater than $100,000. 1 1
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Chapter 4: Hazard Identification and Risk Assessment 74 Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Environmental Low
Environmental impact from a single major hazard event is likely to be minimal, requiring little to no outside resources and support, and/or minimal repair, clean-up, restoration, or preservation work.
1 1
Essential Operations Low
Impact less than 24 hours on the ability of the jurisdiction to meet the essential day-to-day operational demands and
needs of the community from a single major hazard event. 1 1
Future Development Low Future development trends will minimally increase impact/consequence of this hazard. 1 1
Climate Change High Climate Change trends will significantly increase the risk of this hazard and its impacts. 3 3

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Chapter 4: Hazard Identification and Risk Assessment 75

4.6.1.8. FEMA NRI Expected Annual Loss Estimates
There are no clear, quantitative assessments of losses due solely to climate change. Losses from drought, flood, landslides, severe weather, sea level rise, and wildfire are almost certainly exacerbated by climate change. The impacts of climate change not only result in more frequent and intense disaster incidents, but they also result in secondary impacts in areas such as public health, water quality, and the cost of food and other essential resources.

4.6.1.9. FEMA Climate Change Risk Index Scores
The FEMA NRI does not assess climate change events. Table 4-30 represents the Climate Change Total Risk Score for Contra Costa County, based on the Risk Assessment Methodology, as defined in this Plan. For further details on how the probability, extent, vulnerability, and impact factors were calculated, please refer to Table 4-26 through Table 4-29. Additional details on how the Total Risk Score was calculated can be found in the Risk Assessment Methodology in Section 4.3 of this Plan.

Table 4-30. Climate Change Total Risk Score
Hazard
Event
Probability Consequence Total Risk
Probability
Factor Extent Vulnerability Impact Consequence
Score
Total Risk
Score*
Climate Change 2 9 12 15 36 38
Consequence: Sum of all weighted factors.

Extent: Sum of the weighted Extent factors.

Vulnerability: Sum of the weighted Vulnerability factors.

Impact: Sum of the weighted Impact factors.

Total Risk Score = Probability x Consequence
* Normalized to 100
Total Risk Score Legend
Classification Probability
Factor Extent Vulnerability Impact Consequence
Score
Total Risk
Score
Low (L) 1 0 – 6 0 – 6 0 – 12 0 – 24 0 – 24
Medium (M) 2 7 – 12 7 – 12 13 – 26 25 – 50 25 – 54
High (H) 3 13 – 18 13 – 18 27 – 39 51 – 75 55 and above The legend— specifically the assignment of low, medium, and high— provides an additional means to qualitatively assess the probability factor, sum of weighted factors, and the total risk scores for each hazard. The Consequence Score represents the sum of the Extent, Vulnerability, and Impact Factors.

The Total Risk Score is a measure of Probability and Consequence.

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Chapter 4: Hazard Identification and Risk Assessment 76

4.6.2. Dam and Levee Failure

4.6.2.1. Description
Dams are a critical and vital part of the nation’s infrastructure as they provide a range of benefits, such as irrigation, electrical generation, flood control, renewable/clean energy, water storage, sediment/hazardous materials control, navigation, fisheries, and recreation. 75 Dams are
artificial/manmade structures built across a watercourse for the purpose of retaining water. 76 A levee is a human-made structure, usually an earthen embankment or concrete floodwall, designed and constructed to contain, control, or divert the flow of water to provide reasonable assurance of excluding temporary flooding from the levee area.
77 Dam Failure
The sudden rapid and uncontrolled release of impounded water or liquid-borne solids characterizes failure. The term “dam failure” encompasses a wide variety of circumstances. Situations that would constitute a dam failure vary widely, from developing problems to a partial or catastrophic collapse of the entire dam. Potential causes of dam failure are numerous and can be attributed to deficiencies in the original design of the dam, the quality of construction, the maintenance of the dam, operation of the appurtenances and acts of nature including precipitation in excess of the design, flood, and damage from earthquakes. Dam failures are most likely to happen for one (1) of five (5) reasons listed in Table 4-31.

Table 4-31. Dam Failure Types
78 Failure Type Description
Overtopping
Caused by water spilling over the top of a dam. Overtopping of a dam is often a precursor of dam failure. National statistics show that overtopping due to inadequate spillway design, debris blockage of spillways, or settlement of the dam crest account for approximately 34% of all dam failures in the United States.

Foundation Defects Include settlement and slope instability, cause about 30% of all dam failures.

Cracking Caused by movements like the natural settling of a dam.

Inadequate Maintenance
and Upkeep Inadequate Maintenance and Upkeep
Piping
When seepage through a dam is not properly filtered and soil particles continue to progress, and form sink holes in the dam. Another 20% of United States dam failures have been caused by piping (internal erosion caused by seepage).

Seepage often occurs around hydraulic structures, such as pipes and spillways, through animal burrows, around roots of woody vegetation, and through cracks in dams, dam appurtenances, and dam foundations.

Dam failure is potentially extremely dangerous if it occurs catastrophically with little or no warning. Dam inundation areas may contain large populations and significant critical infrastructure. During a catastrophic failure, the water flow may be dozens of feet high and move at high velocity. For large dams, evacuation procedures may not be adequate to prevent large loss of life and property damage.

75 FEMA. (2020). The National Dam Safety Program: 25 Years of Excellence. Retrieved from https://www.fema.gov/sites/default/files/2020-08/national-dam-safety-25-years.pdf. 76 Merriam-Webster. (n.d.). Dam. Retrieved from https://www.merriam-webster.com/dictionary/dam https://www.oregon.gov/owrd/programs/streamslakessanddams/dams/Pages/default.aspx. 77 United States Army Corps of Engineers. (n.d.). Levees and Flood Risk Management. Retrieved from https://www.nwp.usace.army.mil/Missions/Flood-Risk-Management/Levees/. 78 Association of State Dam Safety Officials. (n.d.). Understanding Dam Failures. Retrieved from https://damsafety.org/dam-failures.
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Chapter 4: Hazard Identification and Risk Assessment 77 A jurisdictional dam (one that falls under the jurisdiction of the State dam regulations) is defined by the California Water Code as a dam with a height greater than six (6) feet that impounds 50 acre-feet or more, or a height greater than 25 feet with storage capacity of 15 acre-feet or more. Over 1,250 jurisdictional dams are under the jurisdiction of California’s Department of Water Resources (DWR), Division of Safety of Dams (DSOD). Dams and reservoirs operated by the Federal government are not subject to State jurisdiction except as otherwise provided by Federal Law. In California, there are currently 220 dams operated by federal government agencies such as the United States Forest Service, United States Bureau of Reclamation, United States Army Corps of Engineers (USACE). 79 Levee Failure
A levee failure can occur when flood waters exceed the height of a levee and flow over its crown (i.e., overtopping); or when breaching occurs. A levee breach can occur gradually or suddenly when part of the levee gives way, resulting in an opening through which floodwater may pass. The most dangerous breaches happen quickly during periods of high water. The resulting stream of water can quickly flood a large area behind the failed levee with little to no warning. 80

Earthen levees can be damaged in several ways and if severe enough these scenarios can lead to a zone of weakness that could cause a levee breach.

• Strong river currents and waves can erode the surface. • Trees growing on a levee can blow over, leaving a hole where the root ball and soil used to be. • Burrowing animals (e.g., California ground squirrel, the salt marsh harvest mouse, or the western burrowing owl) can create holes that enable water to pass through a levee. • In seismically active areas like Contra Costa County, earthquakes and ground shaking can cause a loss of soil strength, weakening the levee potentially resulting in a levee failure. Seismic activity can also cause levees to slide or slump, both of which can lead to failure. 81 USACE operates, maintains, and evaluates flood protection levees to determine if they meet accreditation requirements. Most levees are owned by local communities and flood control districts that must ensure proper operation and maintenance of the levee system as well. Two (2) types of levees are present in the San Joaquin-Sacramento River Delta area of Contra Costa County.

• Levees that are part of an authorized federal flood control project on the Sacramento-San Joaquin River Delta systems that deliver irrigation and drinking water are designated as “project” levees.

The 385 miles of project levees are built to the highest level of flood protection standards, are maintained mainly by the County, and are inspected by USACE. • All other levees in the Delta are “non-project” or “local” levees. These levees, totaling 730 miles in length, are maintained by local reclamation districts. The non-project levees incorporate modern techniques and materials as the reclamation districts work to bring the old agricultural levees up to current standards. As land has subsided and sea levels have risen, a lot of the land

79 California Governor’s Office of Emergency Services. (2023). California State Hazard Mitigation Plan. Retrieved from https://www.caloes.ca.gov/wp-content/uploads/Hazard-Mitigation/Documents/2023-California- SHMP_Volume-1_11.10.2023.pdf.
80 American Society of Civil Engineers. (2010). So, You Live Behind a Levee! Retrieved from https://www.spl.usace.army.mil/Portals/17/SoYouLiveBehindLevee.pdf. 81 Ibid.
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Chapter 4: Hazard Identification and Risk Assessment 78 behind these levees is now 10 to 15 feet below sea level, making the efforts of continual improvements essential to avoid overtopping and consequent flooding.

Levees in Contra Costa County are maintained by the Contra Costa Flood Control and Water Conservation District ( CCFCWCD), USACE, 13 reclamation districts, and private landowners. These levees and drainage systems protect agricultural and rural areas, critical infrastructure like highways, and important environmental resources.
82 4.6.2.2. Hazard Location
The National Inventory of Dams (NID) consists of dams meeting at least one (1) of the following criteria:

• High hazard potential classification – loss of human life is likely if the dam fails. • Significant hazard potential classification – no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or impact other concerns. • Equal or exceed 25 feet in height and exceed 15 acre-feet in storage. • Equal or exceed 50 acre-feet storage and exceed six (6) feet in height.

Although the goal of the NID is to include all dams in the United States that meet these criteria, in reality, this inventory is limited to information that can be gathered and properly interpreted. In most cases, dams within the NID criteria are regulated (e.g., construction permit, inspection, and/or enforcement) by federal or state agencies, who have basic information on the dams within their jurisdiction. All high hazard dams have Emergency Action Plans (EAP) in place, however due to data privacy and protected information, this information is not included in this Plan. Existing EAPs include inundation data for all listed High Hazard dams. According to the NID, most High Hazard dams do not include a USACE risk assessment as outlined via the NID tool’s risk tab. Those that have risk assessments available are noted in the Summary Vulnerability Assessment section on the following pages.

According to the NID, there are 27 dams within Contra Costa County of which 23 are classified as high hazard dams. Table 4-32 lists the high hazard dams within Contra Costa County and Table 4-33 lists additional dams within the County classified as low hazard potential. 83 Figure 4-6 displays the high and
significant dams located within five (5) miles of Contra Costa County.

Table 4-32. High Hazard Dams in Contra Costa County
Name National
ID Location Owner Type Condition
Assessment
Condition
Assessment
Date
Height
(feet)
Normal
Storage
(acre-feet)
Max
Discharge
(cubic feet /
second)
EAP
Antioch
Reservoir CA00057
Contra
Costa
County
City of
Antioch Earth Satisfactory 9/1/2017 30 722 Not
Available Yes
Argyle
No. 2 CA00186
Contra
Costa
County
East Bay
Municipal
Utility District
Other Satisfactory 9/1/2017 27 22 Not
Available
Briones CA00172
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Satisfactory 9/1/2017 273 67,520 Not
Available Yes

82 Contra Costa County. (2023). Public Review Draft Contra Costa County 2045 General Plan. Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2024/02/Contra-Costa-County-General-Plan_Public- Review-Draft_Combined.pdf.
83 United States Army Corps of Engineers. (n.d.). National Inventory Dams. Retrieved from https://nid.sec.usace.army.mil/#/.
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Chapter 4: Hazard Identification and Risk Assessment 79 Name National
ID Location Owner Type Condition
Assessment
Condition
Assessment
Date
Height
(feet)
Normal
Storage
(acre-feet)
Max
Discharge
(cubic feet /
second)
EAP
C.L.

Tilden
Park
CA00161
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Satisfactory 9/1/2017 88 268 Not
Available Yes
Contra
Loma CA10143
Contra
Costa
County
United States
Bureau of
Reclamation
Earth Not Available Not Available 107 2,630 838 Yes
Danville CA00184
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Satisfactory 9/1/2017 75 45 Not
Available Yes
Dry Creek CA00811
Contra
Costa
County
Contra Costa
County Flood
Control and
Water
Conservation
District
Earth Satisfactory 9/1/2017 30 330 Not
Available Yes
Lafayette CA00163
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Fair 9/1/2017 132 4,250 Not
Available Yes
Lake
Orinda CA00659
Contra
Costa
County
Orinda
Country Club Earth Satisfactory 8/20/2019 45 111 474 Yes Leland CA00177
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Satisfactory 9/1/2017 41 60 Not
Available Yes
Los
Vaqueros CA01396
Contra
Costa
County
Contra Costa
Water District Earth Satisfactory 9/1/2017 231 160,000 Not Available Yes
Mallard CA00838
Contra
Costa
County
Contra Costa
Water District Earth Satisfactory 9/1/2017 30 3,113 Not Available Yes
Maloney CA00180
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Satisfactory 9/1/2017 107 68 Not
Available Yes
Marsh
Creek CA00809
Contra
Costa
County
Contra Costa
County Flood
Control and
Water
Conservation
District
Earth Satisfactory 9/1/2017 59 4,425 Not
Applicable Yes
Martinez CA10168
Contra
Costa
County
United States
Bureau of
Reclamation
Earth Not Available Not Available 62 296 272 Yes
Moraga CA00178
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Satisfactory 9/1/2017 37 36 Not
Available Yes
North CA00183
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Satisfactory 9/1/2017 82 244 Not
Available Yes
Pine
Creek CA00808
Contra
Costa
County
Contra Costa
County Flood
Control and
Water
Conservation
District
Earth Satisfactory 9/1/2017 87 225 Not
Available Yes
Pine
Creek
Detention
CA01252
Contra
Costa
County
Contra Costa
County Flood
Control and
Water
Conservation
District
Gravity Satisfactory 9/1/2017 30 320 Not
Available Yes
San Pablo CA00166
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Satisfactory 9/1/2017 170 43,193 Not
Available Yes
Sobrante
Clearwell CA00179
Contra
Costa
County
East Bay
Municipal
Utility District
Earth Satisfactory 9/1/2017 28 25 Not
Available Yes
Upper
Sand
Creek
Detention
Basin
CA01555
Contra
Costa
County
Contra Costa
County Flood
Control and
Water
Conservation
District
Earth Satisfactory 9/1/2017 40 895 Not
Available Yes
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Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 80 Name National
ID Location Owner Type Condition
Assessment
Condition
Assessment
Date
Height
(feet)
Normal
Storage
(acre-feet)
Max
Discharge
(cubic feet /
second)
EAP
Vista Del
Mar
Detention
Basin
CA01489
Contra
Costa
County
William Lyon
Homes, Inc. Earth Satisfactory 9/1/2017 42 33 Not
Available Yes
Table 4-33. Additional Dams in Contra Costa County
Name National
ID Location Owner Type Condition
Assessment
Condition
Assessment
Date
Height
(feet)
Normal
Storage
(acre-feet)
Max
Discharge
(cubic feet /
second)
Clearwell
Phase 2 CA01109
Contra
Costa
County
Central Contra Costa
Sanitary District Earth Satisfactory 9/1/2017 30 100 Not Available
Clifton
Court
Forebay
CA00050
Contra
Costa
County
California Department
of Water Resources Earth Fair 1/8/2021 34 29,000 Not
Available
Deer
Creek CA00810
Contra
Costa
County
Contra Costa County
Flood Control and
Water Conservation
District
Earth Satisfactory 9/1/2017 29 233 Not
Available
San Pablo
Clearwell CA00185
Contra
Costa
County
East Bay Municipal
Utility District Earth Satisfactory 9/1/2017 42 17 Not
Available
Figure 4-6. High and Significant Hazard Dams in the Contra Costa County Area

Additionally, there are six (6) high hazard dams, listed in Table 4-34, that although located outside of the County, they have inundation areas within the County. Figure 4-7 illustrates areas in the County that would be inundated in the event that a dam fails.

2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 81 Table 4-34. Dams Outside of Contra Costa County
Name National
ID Location Owner Type Condition
Assessment
Condition
Assessment
Date
Height
(feet)
Normal
Storage
(acre-feet)
Max
Discharge
(cubic feet /
second)
EAP
Exchequer
Main CA00240 Mariposa,
California
Merced
Irrigation
District
Rockfill,
Earth Not Available Not Available 490 1,100,000 531,600 Yes New
Hogan CA10109 Calaveras,
California
USACE
(Sacramento
District)
Rockfill,
Earth Not Available Not Available 210 348,598 106,400 Yes New
Melones CA10246 Calaveras,
California
United States
Bureau of
Reclamation
Rockfill,
Earth Not Available Not Available 625 2,870,000 Not
Available Yes
Pine Flat CA10112 Fresno,
California
USACE
(Sacramento
District)
Gravity Not Available Not Available 440 1,091,700 391,000 Yes San Luis
Reservoir
(B.F. Sisk)
CA10183 Merced,
California
United States
Bureau of
Reclamation
Earth Not Available Not Available 382 2,118,380 Not
Available Yes
Summit CA00146 Solano,
California City of Vallejo Earth Satisfactory 9/1/2017 124 220 Not Available Yes
Figure 4-7. Dams Inundation Areas in the Contra Costa County Area

DSOD classifies dams slightly differently than NID. The DSOD scale defines the intensity or potential severity of dam failure solely based on potential downstream impacts to life and property and the hazard is not related to the condition of the dam or its pertinent structures. Refer to the Hazard Extent/Intensity section for further details on the DSOD’s classification. Table 4-35 lists the 25 dams within jurisdiction in Contra Costa County with DSOD’s classification.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 82 Table 4-35. Dams Within Jurisdiction in Contra Costa County with DSOD Downstream Hazard Potential Classifications
Name National ID Downstream Hazard Potential
Antioch Reservoir CA00057 Extremely High
Argyle No. 2 CA00186 High
Briones CA00172 Extremely High
C.L. Tilden Park CA00161 Extremely High
Clearwell Phase 2 CA01109 Low
Clifton Court Forebay CA00050 Low
Danville CA00184 Extremely High
Dry Creek CA00811 High
Lafayette CA00163 Extremely High
Lake Orinda CA00659 High
Leland CA00177 High
Los Vaqueros CA01396 Extremely High
Mallard CA00838 High
Maloney CA00180 Extremely High
Marsh Creek CA00809 Extremely High
Moraga CA00178 High
North CA00183 Extremely High
Pine Creek CA00808 High
Pine Creek Detention CA01252 High
San Pablo CA00166 Extremely High
San Pablo Clearwell CA00185 Low
Sobrante Clearwell CA00179 High
Upper Sand Creek Detention Basin CA01555 Extremely High Vista Del Mar Detention Basin CA01489 High

According to the National Levee Database, there are 17 project levees in the County that are included in the USACE Levee Program, listed in Table 4-36.
84 An additional 18 non-project levees owned by
reclamation districts in the County are listed in Table 4-37. 85 There are over 1,100 miles of earthen levees

84 United States Army Corps of Engineers. (n.d.). National Levee Database. Retrieved from https://levees.sec.usace.army.mil/#/.
85 Contra Costa County Department of Conservation & Development Draft Levee Shapefile. 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 83 and revetments managed by CCFCWCD and reclamation districts in the County. 86 Figure 4-8 displays the levee systems within five (5) miles of Contra Costa County, per USACE.

Table 4-36. Project Levees in Contra Costa County
Levee Name Levee Owner Segment Length
(miles)
Wildcat Creek (Right Bank) Contra Costa County Public Works 0.86 Wildcat Creek (Left Bank) Contra Costa County Public Works 0.29 Walnut Creek and Pacheco Creek
(Right Bank)
Contra Costa County Flood Control and
Water Conservation District 1.74
Walnut Creek and Pacheco Creek
(Left Bank)
Contra Costa County Flood Control and
Water Conservation District 1.86
Walnut Creek and Grayson Creek
(Right Bank)
Contra Costa County Flood Control and
Water Conservation District 2.88
Walnut Creek and Grayson Creek
(Left Bank)
Contra Costa County Flood Control and
Water Conservation District 1.49
Walnut Creek and Clayton Valley Drain
(Right Bank)
Contra Costa County Flood Control and
Water Conservation District 0.56
Walnut Creek and Clayton Valley Drain
(Left Bank)
Contra Costa County Flood Control and
Water Conservation District 1.68
San Pablo Creek (Right Bank) Contra Costa County Public Works 1.00 San Pablo Creek (Left Bank) Contra Costa County Public Works 0.92 Rodeo Creek (Right Bank) Contra Costa County Public Works 0.19 Rodeo Creek (Left Bank) Contra Costa County Public Works 0.25 Rheem Creek (Right Bank) Contra Costa County Public Works 0.46 Rheem Creek (Left Bank) Contra Costa County Public Works 0.47 Reclamation District No. 800
(Byron Tract)
Reclamation District No. 800
(Byron Tract) 8.90
Pinole Creek (Right Bank) Contra Costa County Public Works 0.35 Pinole Creek (Left Bank) Contra Costa County Public Works 0.41 Table 4-37. Non-Project Reclamation District Levees in Contra Costa County Levee Name Segment Length
(miles)
Bixler Tract 2.04
Bethel Island 11.62
Bradford Island 7.41
Byron Tract / Discovery Bay 9.40
Coney Island 5.49

86 Contra Costa County. (2023). Public Review Draft Contra Costa County 2045 General Plan. Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2024/02/Contra-Costa-County-General-Plan_Public- Review-Draft_Combined.pdf.
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Chapter 4: Hazard Identification and Risk Assessment 84 Levee Name Segment Length
(miles)
Contra Costa Canal 8.15
Cypress Corridor 3.82
Cypress Flood Control 1.32
Cypress Flood Control 1.88
Holland Tract 10.97
Hotchkiss Tract 6.91
Jersey Island 15.52
Palm Tract / Orwood Tract 14.42
Quimby Island 7.02
Summer Lake 3.10
Veale Tract 6.01
Webb Tract 12.96
Figure 4-8. Levee Systems in Contra Costa County Area

4.6.2.3. Hazard Extent/Intensity
Federal guidelines provide for a three (3) level classification system that defines low, significant, and high-hazard potential classifications depending on the potential for loss of life, economic loss, and

2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 85 environmental damage resulting from a hypothetical dam failure. The USACE dam hazard categories are listed in Table 4-38.

Table 4-38. USACE Dam Hazard Categories
Hazard
Category Direct Loss of Life Lifeline Losses Property Losses Environmental Losses
Low
None (rural location, no
permanent structures for
human habitation).

No disruption of
services (cosmetic or
rapidly repairable
damage).

Private agricultural
lands, equipment, and
isolated buildings.

Minimal incremental
damage.

Significant
Rural location, only
transient or day-use
facilities.

Disruption of essential
facilities and access.

Major public and
private facilities.

Major mitigation
required.

High
Certain (one or more)
extensive residential,
commercial, or
industrial
development.

Disruption of essential
facilities and access.

Extensive public and
private facilities.

Extensive mitigation
cost or impossible to
mitigate.

The hazard categories are assigned to overall projects, not individual structures at a project. The four (4) general categories are described below.

• Direct Loss of Life: The loss of life potential based on inundation mapping of area downstream of the project. Analyses of loss of life potential should take into account the population at risk, time of flood wave travel, and warning time.
• Lifeline Losses: Indirect threats to life caused by the interruption of lifeline services due to project failure or operational disruption; for example, loss of critical medical facilities or access to them. • Property Losses: Damage to project facilities and downstream property and indirect impact due to loss of project services, such as impact due to loss of a dam and navigation pool, or impact due to loss of water or power supply.
• Environmental Losses: Environmental impact downstream caused by the incremental flood wave produced by the project failure, beyond what would normally for the magnitude flood event under which the failure occurs.

DSOD uses its own scale for defining the intensity or potential severity of dam failure solely based on potential downstream impacts to life and property. Additionally, the hazard is not related to the condition of the dam or its pertinent structures. This scale has four (4) categories which include the Federal categories and adds a fourth category of “extremely high”. Table 4-39 outlines the downstream hazard potential classifications used by DSOD.
87 87 California Department of Water Resources, Division of Safety of Dams. (2021). Downstream Hazard. Retrieved from https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/All-Programs/Division-of-Safety-of- Dams/Files/Publications/Division-of-Safety-of-Dams-Definitions-for-Downstream-Hazard-and-Condition- Assessment.pdf.
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 86 Table 4-39. DSOD’s Downstream Hazard Potential Classifications Downstream Hazard
Potential Classifications Potential Downstream Impacts to Life and Safety Low No probable loss of human life and low economic and environmental losses.

Losses are expected to be principally limited to the owner’s property.

Significant No probable loss of human life but can cause economic loss, environmental damage, impacts to critical facilities, or other significant impacts.

High Expected to cause loss of at least one human life.

Extremely High Expected to cause considerable loss of human life or would result in an inundation area with a population of 1,000 or more.

The United States Army Corps of Engineers (USACE) Levee Safety Program key activities include levee inspections, risk assessments, and sharing levee information. 88 To better inform stakeholders and residents of the residual risk within their communities, USACE utilizes the Levee Safety Action Classification (LSAC) tool.
89 Table 4-40 outlines the LSAC risk levels, actions, and risk characteristics for each level. The LSAC is not a levee rating or grade, but a classification system designed to consider the following:

• Probability of the levee being loaded (hazard).
• Existing condition of the levee.
• The current and future maintenance of the levee (performance). • The consequences if the levee were to fail or be overwhelmed.

For example, a levee that reduces risk for a dense population will have a different classification from an equally constructed levee with a smaller population because the consequences associated with failure are greater.
90 Table 4-40. USACE Levee Safety Action Classification (LSAC) 91 Risk
Actions for Levee Systems and Leveed
Areas in this Class
(Adapt actions to specific levee system conditions)
Risk Characteristics
of this Class
Very
High
(1)
Based on risk drivers, take immediate action to implement interim risk reduction measures. Increase frequency of levee monitoring, communicate risk characteristics to the community within an expedited timeframe; verify emergency plans and flood inundation maps are current; ensure community is aware of flood warning systems and evacuation procedures; and recommend purchase of flood insurance. Support risk
reduction actions as very high priority.

Likelihood of inundation due to
breach and/or system
component malfunction in
combination with loss of life,
economic, or environmental
consequences result in very high
risk.

88 United States Army Corps of Engineers. (n.d.). Levee Safety Program. Retrieved from https://www.usace.army.mil/Missions/Civil-Works/Levee-Safety-Program/. 89 United States Army Corps of Engineers. (n.d.). Levee Safety Action Classification (LSAC). Retrieved from https://www.mvn.usace.army.mil/LSAC/.
90 Ibid.
91 United States Army Corps of Engineers. (n.d.). Levee Safety Action Classification (LSAC). Retrieved from https://www.mvn.usace.army.mil/Portals/56/docs/PAO/LSACs/LSAC%20Table.pdf. 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 87 Risk
Actions for Levee Systems and Leveed
Areas in this Class
(Adapt actions to specific levee system conditions)
Risk Characteristics
of this Class
High
(2)
Based on risk drivers, implement interim risk reduction measures. Increase frequency of levee monitoring;
communicate risk characteristics to the community within an expedited timeframe; verify emergency plans and flood
inundation maps are current; ensure community is aware of flood warning and evacuation procedures; and recommend
purchase of flood insurance. Support risk reduction actions as high priority.

Likelihood of inundation due to
breach and/or system
component malfunction in
combination with loss of life,
economic, or environmental
consequences results in high
risk.

Moderate
(3)
Based on risk drivers, implement interim risk reduction measures as appropriate. Verify risk information is current and implement routine monitoring program; assure O&M is up to date; communicate risk characteristics to the community in a timely manner; verify emergency plans and flood inundation maps are current; ensure community is aware of flood warning and evacuation procedures; and recommend purchase of
flood insurance. Support risk reduction actions as a priority.

Likelihood of inundation due to
breach and/or system
component malfunction in
combination with loss of life,
economic, or environmental
consequences results in
moderate risk.

Low
(4)
Verify risk information is current and implement routine monitoring program and interim risk reduction measures if appropriate; assure O&M is up to date; communicate risk characteristics to the community as appropriate; verify emergency plans and flood inundation maps are current;
ensure community is aware of flood warning and evacuation procedures; and recommend purchase of flood insurance.

Support risk reduction actions to further reduce risk to as low as practicable.

Likelihood of inundation due to
breach and/or system
component malfunction in
combination with loss of life,
economic, or environmental
consequences results in low risk.

Very
Low
(5)
Continue to implement routine levee monitoring program, including operation and maintenance, inspections, and
monitoring of risk. Communicate risk characteristics to the community as appropriate; verify emergency plans and flood inundation maps are current; ensure community is aware of flood warning and evacuation procedures; and recommend
purchase of flood insurance.

Likelihood of inundation due to
breach and/or system
component malfunction in
combination with loss of life,
economic, or environmental
consequences results in very low
risk.

No
Verdict Not enough information is available to assign an LSAC. *Levee risk is the risk that exists due to the presence of the levee system, and this is the risk used to inform the decision on the LSAC assignment.

The information presented in this table does not reflect the overtopping without breach risk associated with the presence or operation of the levee system.

4.6.2.4. Warning Time
Dam and levee failure may occur with little or no warning time.

For a dam failure, warning time varies depending on the cause of the failure. For example, i n the event of extreme precipitation or massive snowmelt, evacuations can be planned with sufficient time. On the other hand, in the event of a structural failure due to earthquake, there may be no warning time. A dam’s structural type also affects warning time. Earthen dams tend to not fail completely or instantaneously, the time of breach formation ranges from a few minutes to a few hours. Once a breach is initiated, discharging water erodes the breach until either the reservoir water is depleted, or the breach resists further erosion.

Concrete gravity dams also tend to have a partial breach as one or more monolith sections are forced apart by escaping water.
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 88 Contra Costa County and its planning partners have established protocols for flood warning and response to imminent dam failure in the flood warning portion of its adopted Emergency Operations Plan. These protocols are tied to the emergency action plans created by the dam owners.

Warning time for levee failures also depends on the cause of the failure. A levee failure caused by structural failure can be sudden and occur with little to no warning. If heavy rains are impacting a levee system, communities located in the immediate danger zone can be evacuated before a failure occurs. If the levee failure is caused by overtopping, the community may or may not be able to recognize the impending failure and evacuate. If a levee failure occurs suddenly, evacuation may not be possible.

4.6.2.5. Probability and Frequency
Dam failure has a low probability of occurrence and it usually coincides with events that cause them (e.g., earthquakes, landslides, excessive rain, and snowmelt). Between 1950 and 2023, there have been three (3) Federal disaster declarations due to dam failure, one (1) of which has occurred in California. 92 This represents an average of one (1) event every 23 years. However, dam safety incidents, which are less severe than dam failures, have occurred.

Like dams, levee failures have a low probability of occurrence and usually coincide with events that cause them (e.g., earthquakes and heavy rainfall). Between 1950 and 2023, there has been one (1) Federal disaster declarations due to a levee failure, which occurred in California in 2004. 93 According to the 2023
California State Hazard Mitigation Plan, in the last 120 years, there have been 124 levee failures in the State. This represents about one (1) occurrence per year.

Probability of Future Hazard Events
As previously states, dam failure and levee failure are infrequent. A levee failure is more likely to occur than a dam failure.

4.6.2.6. Past Events
There are no dam failure events reported in Contra Costa County. However, there have been two (2) recent levee failures in the San Joaquin-Sacramento River Delta, listed in Table 4-41.

Table 4-41. Dam and Levee Failure Past Events
Date Event Summary
August 27, 2009
A levee breach occurred when a bulk carrier ship was outbound from Port of Stockton and it lost steering, grounded, and hit the levee at Bradford Island. The collision damaged approximately 150 feet of levee, causing a serious breach. Of note, Bradford Island has been flooded numerous times over the past 100 years due to levee failure.

June 3, 2004
The Upper Jones Tract levee near Woodward Island failed, inundating the entire island with more than 150,000 acre feet of water. Repairs required three (3) weeks. The island, which lies 10 feet below sea level, required an additional five (5) months of de- watering. The failure resulted in approximately $90 Million in repairs.

4.6.2.7. Vulnerability and Impacts
Life Safety and Health: All residents within dam and levee inundation areas would be vulnerable and impacted by a dam or levee f ailure event. The potential for loss of life is affected by the capacity and number of evacuation routes available to those living in potential dam inundation areas. In a dam and

92 Federal Emergency Management Agency. (n.d.). Declared Disasters. Retrieved from https://www.fema.gov/disaster/declarations.
93 Ibid.
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 89 levee failure event, the vulnerable populations are all of those downstream from the dam or levee failure that are unable to evacuate the area within the allowable time frame. However, the underserved and at risk population face unique vulnerabilities and impacts in the event of flooding are a result of a dam or levee failure. These groups include, but are not limited to, households in poverty, low income population, population living in single access roads, people with limited English proficiency, individuals without access to lifelines, the elderly population (including those with access and functional needs ), and undocumented individuals.94

• Households in Poverty and Low Income Population: Households in poverty include those with an income at or below $24,300 for a household of four (4). In Contra Costa County, most households considered to live in poverty are located within or near 100-year flood zones. Flooding from a dam and levee failure can damage homes, cause mildew , and mold to grow . The low income population includes households with an income of 80% or less of the median income ($104,400) in Contra Costa County. This population tends to be less likely to evacuate in response to emergency incidents, such as a dam and levee failure. Furthermore, households in poverty and low income households may have fewer financial resources to complete preparedness and recovery activities (i.e., fix flood damage) and the structures are not waterproofed or built above the current 100-year flood elevation. High concentration of this population is located within or near a flood zone or dam inundation area, mostly in the north and east portion of the County. • Individuals Living on Single Access Roads: Includes the population living in areas with a single route in and out (i.e., accessible via one (1) roadway) of the neighborhood or area. This population is uniquely vulnerable to dam and levee failure because the flooding can block, damage, and destroy roadways which can isolate this population from the community and emergency services.

In Contra Costa County, several neighborhoods and communities in the Delta and in the hillside areas in the central and western side of the County are only accessible via one (1) roadway. • Limited English Proficiency: This group includes those that speak English “less than very well”, per the United States Census Bureau definition. In Conta Costa County, 158,965 people (38.2%) have limited English proficiency (i.e., speak English “less than very well”). This population are more likely to live in low income areas which are also most likely to be located within low lying areas. Flooding due to dam and levee failures can cause significant damage to homes resulting in uninhabitable and unhealthy conditions to live in. Additionally, individuals with limited English proficiency may have limited access to information and resources designed to prevent or mitigate flooding risk due to language or cultural differences.
• Individuals Without Access to Lifelines: Includes individuals who do not have access to basic technology or services (e.g., transportation, modern communication). This population is vulnerable because not having access to these can create barriers to prepare and respond to emergency events, including dam and levee failure, may be unable to evacuate in a timely manner, and may become isolated if transit services are not operating. For example, this population may be unaware of an impending or occurring failure of a dam or levee potentially resulting in being unable to evacuate in a timely manner in the event an evacuation order is issued.
• Senior (65 years old and over): The elderly population (i.e., seniors ), especially those with access and functional needs, may have physical limitations that make it harder to evacuate in the event of an emergency, such as a dam and levee failure. Furthermore, the elderly population may

94 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 90 lack access to social connections and community support that can assist in preparing for and responding to emergency events, evacuating, improving home resiliency, managing medical needs, and locating support services. A high concentration of the elderly population lives in central Contra Costa County, Bethel Island, eastern part of Richmond, and several parts of Walnut Creek. • Undocumented Individuals: Includes people who do not have formal permission to live in the United States (i.e., do not have citizenship, permanent residency, visas, or other similar status).

This population is most likely to fall in the households in poverty and low income categories, which are considered to be at risk populations during a flooding event and are more likely to live in low lying areas in structures that are not waterproofed or build above the 100-year flood elevations.

Table 4-42 summarizes the vulnerable and at-risk population for dam and levee failure in Contra Costa County.

Table 4-42. Vulnerability and At Risk Population
Category Estimate Percent
Households in Poverty95 7,600 12.0%
Low Income Households96 25,340 41.0%
Spanish Spoken at Home97 204,442 18.7%
Speak English “Less than very
well”98 158,965 38.2%
Language Other than English99 416,505 38.0%
Foreign Born100 312,050 27.0%
Households Without Vehicle101 8,872 1.6%
65 Years and Over102 201,136 17.4%
Seniors (65 years and over) Living
Alone103 45,672 22.7%
Undocumented Individuals104 There are no official counts of how many undocumented individuals live in Contra Costa County, but in 2019 there was an estimate of 63,000.

95 Ibid.
96 Ibid.
97 United States Census Bureau. (2022). S1601: Language Spoken at Home (2022: ACS 1-Year Estimates Subject Tables). Retrieved from https://data.census.gov/table/ACSST1Y2022.S1601?g=050XX00US06013. 98 Ibid.
99 Ibid.
100 United States Census Bureau. (2022). DP02: Selected Social Characteristics in the United States (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP02?g=050XX00US06013. 101 United States Census Bureau. (2022). S0801: Commuting Characteristics by Sex. Retrieved from https://data.census.gov/table/ACSST1Y2022.S0801?g=050XX00US06013. 102 United States Census Bureau. (2022). DP05: Demographics and Housing Estimates (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP05?g=050XX00US06013. 103 United States Census Bureau. (2022). DP02: Selected Social Characteristics in the United States (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP02?g=050XX00US06013. 104 Migration Policy Institute. (2019). Profile of the Unauthorized Population: Contra Costa County, CA. Retrieved from https://www.migrationpolicy.org/data/unauthorized-immigrant-population/county/6013. 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 91 Table 4-49 outlines the vulnerability of the total population exposed to dam and levee failure, and Table 4-50 outlines the dam and levee failure impacts to population and life safety, underserved/equity population, and essential operations, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Property Damage and Critical Infrastructure: Vulnerable properties are those closest to the dam and levee, and within the inundation area. These properties would experience the largest, most destructive surge of water. Low lying areas are also vulnerable since they are where the dam and levee waters would collect. In Contra Costa County, there is a range from the large, state-owned bridges that carry interstate freeways, to locally owned bridges that carry rural roads and pedestrians over small creeks. Countywide, there are over 400 bridges where approximately 80 are owned by the County and 160 owned by Caltrans.

There are 26 bridges that are within the 100-year flood zone and dam inundation areas. Some of these bridges are located in low lying areas that could become flooded during a dam or levee failure event if located within the inundation areas. Additionally, Interstate 680 and 80, and State Route 4, along with many regional roadways, are within dam and levee inundation areas. Flooding to these roadways and local roadways can cause major disruptions to local and regional transportation, transit, and commuters.

There are 10 wastewater treatment plants in the County which treat wastewater for residents within cities and unincorporated County. O ne (1) of the wastewater treatment plants is located within a dam inundation area. In Contra Costa County, there are 99 industrial buildings that are within dam inundation areas. Other industrial buildings located outside the 100-year floodplain, and dam and levee inundation areas are unlikely to be waterproofed or flood resistant. If any of these structures are damaged due to flooding, it can increase the potential of a hazardous materials release.

There are a total of 554 critical assets (i.e., schools, nursing homes, fire stations, police stations, and hospitals) throughout the County and 41 (7.4%) are located within a dam inundation area. Table 4-43 provides a breakdown of critical assets that are located within dam inundation areas in Contra Costa County.

Table 4-43. Critical Assets in Vulnerable to Dam Failure Asset Estimate Percent
(of total asset)
Schools (public schools, private schools) 27 7.5%
Nursing Homes 2 2.6%
Fire Stations 8 9.9%
Police Stations 4 16.7%
Hospitals 0 0.0%

According to the National Levee Database, there are 58 levees in the County , which are included in the USACE Levee Program. Table 4-44 lists the levees within the County along with the number of buildings, population, property value, and number of critical infrastructure that is deemed vulnerable in the event of a levee failure.
105
Table 4-44. Levee and Vulnerability in the Leveed Area

105 United States Army Corps of Engineers. (n.d.). National Levee Database. Retrieved from https://levees.sec.usace.army.mil/.
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 92 Levee Name System ID
Operations /
Maintenance
Organization
(or Floodplain
Management)
Location Flooding
Source Behind Levee
Contra Costa
County Levee 6 1905004482
Contra Costa Flood
Control and Water
Conservation
District
City of Oakley Marsh Creek
7 Buildings
9 People
$10 M Property Value
0 Critical Structures
Contra Costa
County Levee 7 1905004044 FEMA Region 9 Knightsen Not Available 81 Buildings
187 People
$60 M Property Value
0 Critical Structures
Contra Costa
County Levee 9 1905004332 FEMA Region 9 Town of
Discovery Bay Not Available
7 Buildings
65 People
$50 M Property Value
0 Critical Structures
Contra Costa
County Levee
14 1905004480
Contra Costa Flood
Control and Water
Conservation
District
City of Oakley Marsh Creek
13 Buildings
37 People
$50 M Property Value
1 Critical Structures
Contra Costa
County Levee
15 1905004159 FEMA Region 9 Bethel Island Not Available 14 Buildings
42 People
$8 M Property Value
0 Critical Structures
Contra Costa
County Levee
16 1905004423 Reclamation
District No. 799 City of Oakley Unknown
131 Buildings
708 People
$100 M Property Value
0 Critical Structures
Contra Costa
County Levee
17 1905004133 FEMA Region 9 Bethel Island Not Available 3 Buildings
18 People
$2 M Property Value
0 Critical Structures
Contra Costa
County Levee
19 1905004126 Reclamation
District No. 830 Bethel Island Not Available
16 Buildings
8 People
$30 M Property Value
0 Critical Structures
Contra Costa
County Levee
20 1905004130 FEMA Region 9 Bethel Island Not Available 1,114 Buildings
2,419 People
$700 M Property Value
2 Critical Structures
Contra Costa
County Levee
22 1905004016 FEMA Region 9 City of Oakley Not Available 609 Buildings
1,666 People
$500 M Property Value
0 Critical Structures
Contra Costa
County Levee
24 1905004051 FEMA Region 9 City of Oakley Not Available 15 Buildings
0 People
$30 M Property Value
0 Critical Structures
Contra Costa
County Levee
25 1905004400
Town of Discovery
Bay Community
Services District
Town of
Discovery Bay Not Available
134 Buildings
1,627 People
$100 M Property Value
0 Critical Structures
Contra Costa
County Levee
28 1905004333 FEMA Region 9 Town of
Discovery Bay Not Available
2 Buildings
74 People
$2 M Property Value
0 Critical Structures
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 93 Levee Name System ID
Operations /
Maintenance
Organization
(or Floodplain
Management)
Location Flooding
Source Behind Levee
Contra Costa
County Levee
29 1905004019 City of Oakley City of Oakley Not Available 336 Buildings
24 People
$200 M Property Value
0 Critical Structures
Contra Costa
County Levee
32 1905004008 City of Oakley City of Oakley Contra Costa Canal
825 Buildings
1,196 People
$500 M Property Value
0 Critical Structures
Contra Costa
County Levee
35 1905004443 FEMA Region 9 Knightsen Not Available
2 Buildings
15 People
$1 M Property Value
0 Critical Structures
Contra Costa
County Levee
39 1905004334 FEMA Region 9 Town of
Discovery Bay Not Available
16 Buildings
80 People
$20 M Property Value
1 Critical Structures
Contra Costa
County Levee
40 1905004020 FEMA Region 9 City of Oakley Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
41 1905004158 FEMA Region 9 Bethel Island Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
42 1905004095 FEMA Region 9 Byron Unknown
0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
47 1905004157 FEMA Region 9 City of Pittsburg Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
52 1905004129 FEMA Region 9 City of Pittsburg Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
55 1905004081 FEMA Region 9 City of Pittsburg Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
64 1905004119 FEMA Region 9 City of Martinez Not Available 3 Buildings
1 People
$3 M Property Value
0 Critical Structures
Contra Costa
County Levee
73 1905004261 FEMA Region 9 City of
Richmond Not Available
0 Buildings
0 People
$0 M Property Value
0 Critical Structures
Contra Costa
County Levee
81 1905004310 FEMA Region 9 City of Antioch Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 94 Levee Name System ID
Operations /
Maintenance
Organization
(or Floodplain
Management)
Location Flooding
Source Behind Levee
Contra Costa
County Levee
88 1905004270 FEMA Region 9 City of
Richmond Not Available
0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
108
1905004272 FEMA Region 9 City of
Richmond Not Available
0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
151
1905004322 FEMA Region 9 City of Antioch Not Available
1 Buildings
3 People
$100,000 Property
Value
0 Critical Structures
Contra Costa
County Levee
198
1905004090 FEMA Region 9 City of Pittsburg Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
208
1905004149 FEMA Region 9 City of Pittsburg Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
215
1905004420 FEMA Region 9 City of Martinez Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
217
1905004420 FEMA Region 9 City of Pittsburg Not Available 0 Buildings
0 People
$0 M Property Value
0 Critical Structures
Contra Costa
County Levee
218
1905004271 FEMA Region 9 City of
Richmond Not Available
0 Buildings
0 People
$0 M Property Value
0 Critical Structures
Contra Costa
County Levee
245
1905004262 FEMA Region 9 City of
Richmond Not Available
1 Buildings
0 People
$20 M Property Value
0 Critical Structures
Contra Costa
County Levee
251
1905004125 FEMA Region 9 Byron Not Available
0 Buildings
0 People
$0 Property Value
0 Critical Structures
Contra Costa
County Levee
253
1905004365 FEMA Region 9 Mountain House Not Available
2 Buildings
13 People
$1 M Property Value
0 Critical Structures
Contra Costa
County Levee
255
1905004452 FEMA Region 9 Byron Not Available
5 Buildings
0 People
$10 M Property Value
0 Critical Structures
Lakeshore Dry
Levee 1905004128
Town of Discovery
Bay Community
Services District
Town of
Discovery Bay Unknown
207 Buildings
1,245 People
$200 M Property Value
0 Critical Structures
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 95 Levee Name System ID
Operations /
Maintenance
Organization
(or Floodplain
Management)
Location Flooding
Source Behind Levee
Pinole Creek
(Left Bank) 5305000027
Contra Costa
County Public
Works Department
City of Pinole Pinole Creek
20 Buildings
47 People
$6 M Property Value
0 Critical Structures
Pinole Creek
(Right Bank) 5305000028
Contra Costa
County Public
Works Department
City of Pinole Pinole Creek
16 Buildings
52 People
$6 M Property Value
0 Critical Structures
Reclamation
District No. 800
(Byron Tract)
5205000071 Reclamation
District No. 800
Town of
Discovery Bay
Discovery Bay,
Italian Slough,
Old River,
Vasco Hills
runoff, Vasco
Hills runoff drain
1,704 Buildings
3,599 People
$1 B Property Value
7 Critical Structures
Rheem Creek
(Left Bank) 5305000031
Contra Costa
County Public
Works Department
City of
Richmond Rheem Creek
0 Buildings
12 People
$0 Property Value
0 Critical Structures
Rheem Creek
(Right Bank) 5305000032
Contra Costa
County Public
Works Department
City of
Richmond Rheem Creek
0 Buildings
4 People
$0 Property Value
0 Critical Structures
Rodeo Creek
(Left Bank) 5305000033
Contra Costa
County Public
Works Department
Rodeo Rodeo Creek
198 Buildings
412 People
$70 M Property Value
0 Critical Structures
Rodeo Creek
(Right Bank) 5305000034
Contra Costa
County Public
Works Department
Rodeo Rodeo Creek
12 Buildings
40 People
$4 M Property Value
0 Critical Structures
Sacramento
County Levee 1 1905004132 FEMA Region 9 Bethel Island Not Available 0 Buildings
0 People
$0 Property Value
0 Critical Structures
San Pablo
Creek (Left
Bank)
5305000043
Contra Costa
County Public
Works Department
North Richmond San Pablo
Creek
0 Buildings
12 People
$0 Property Value
0 Critical Structures
San Pablo
Creek (Right
Bank)
5305000044
Contra Costa
County Public
Works Department
North Richmond San Pablo
Creek
18 Buildings
470 People
$30 M Property Value
0 Critical Structures
Walnut Creek –
Clayton Valley
Drain (Left
Bank)
5205001391
Contra Costa Flood
Control and Water
Conservation
District, Contra
Costa County
Public Works
Department
City of Concord Walnut Creek
168 Buildings
1,365 People
$100 M Property Value
0 Critical Structures
Walnut Creek –
Clayton Valley
Drain (Right
Bank)
5205001392
Contra Costa Flood
Control and Water
Conservation
District, Contra
Costa County
Public Works
Department
City of Concord Walnut Creek
142 Buildings
528 People
$70 M Property Value
0 Critical Structures
2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 96 Levee Name System ID
Operations /
Maintenance
Organization
(or Floodplain
Management)
Location Flooding
Source Behind Levee
Walnut Creek –
Grayson Creek
(Left Bank)
5205001394
Contra Costa Flood
Control and Water
Conservation
District, Contra
Costa County
Public Works
Department
Vine Hill Walnut Creek
22 Buildings
638 People
$80 M Property Value
1 Critical Structures
Walnut Creek –
Grayson Creek
(Right Bank)
5205001393
Contra Costa Flood
Control and Water
Conservation
District, Contra
Costa County
Public Works
Department
Pacheco Walnut Creek
785 Buildings
2,375 People
$200 M Property Value
1 Critical Structures
Wildcat Creek 1905004525
Contra Costa Flood
Control and Water
Conservation
District
North Richmond Wildcat Creek
0 Buildings
0 People
$0 Property Value
0 Critical Structures
Wildcat Creek 1905004520
Contra Costa Flood
Control and Water
Conservation
District
City of
Richmond Wildcat Creek
4 Buildings
0 People
$30 M Property Value
1 Critical Structures
Wildcat Creek 1905004521
Contra Costa Flood
Control and Water
Conservation
District
North Richmond Wildcat Creek
0 Buildings
0 People
$0 Property Value
0 Critical Structures
Wildcat Creek
(Left Bank) 5305000045
Contra Costa
County Public
Works Department
North Richmond Wildcat Creek
1,120 Buildings
3,894 People
$300 M Property Value
6 Critical Structures
Wildcat Creek
(Right Bank) 5305000046
Contra Costa
County Public
Works Department
City of
Richmond Wildcat Creek
16 Buildings
159 People
$20 M Property Value
1 Critical Structures

Table 4-49 outlines the total property value exposed to dam and levee failures and how the changes in development in the past five (5) years have affected the vulnerability of the community to dam and levee failures. Table 4-50 outlines the dam and levee failure impacts on total property damage, potential future development, and the economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Environment: All of the environmental assets that are within dam and levee inundation areas are vulnerable to flooding as a result of a dam or levee failure. Loss estimation platforms (e.g., 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 dam and levee failures events.

Data on losses that segregate 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 Plan updates.

Agriculture, a major economic driver for the County, is located with in low lying areas that are located within dam inundation areas. Field crops (i.e., tomatoes, sweet corn, and other vegetables), fruit and nut orchards, vineyards, and plant nurseries are part of the agriculture in the County. Flooding can cause significant damage to crop production by damaging plants, washing away topsoil nutrients, and degrading 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 97 essential microbial activity. As a result, plants can be harmed, and agricultural productivit y will be reduced; subsequently harming the agricultural economy. Furthermore, rangeland, lands where livestock species (i.e., cattle) are raised, located in Bethel Island and the Delta areas are within the 100-year floodplain and dam inundation areas. In Contra Costa County, rangeland is primarily located in the eastern portion of the County. Flood waters can damage important rangeland infrastructure and the natural grassland that feeds cattle and livestock which can harm the local economy in the County.

Table 4-50 outlines dam and levee failure impacts on the environment and the economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Changes in Development and Impact of Future Development: There have been no significant changes in development that have affected the risks associated with dam and levee failure. Future increases in population within dam and levee inundation areas may expose more of the population to these events. Growth over the past decade has considerably increased. Between 2010 and 2022, as outlined in Table 3-3, the population in Contra Costa County grew 10.6%, from 1,046,025 to 1,156,966 residents. The Bay Area Association of Governments (ABAG) growth forecasts predict a steady increase in households through 2050. From 2015 to 2050, ABAG projects that the County’s number of households will grow by 44%.
106 This increase in population can add an additional strain to first responders in the event of a dam and levee failure evacuation. The impact of future development should not significantly change the vulnerability to dam or levee failure. Most of the expected development will occur in the eastern portions of the County which are less susceptible to these hazards.

Table 4-49 outlines how the changes in development in the past five (5) years h ave affected the vulnerability of the community to dam and levee failure. Table 4-50 outlines the dam and levee failure impacts on potential future development, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Effects of Climate Change in Severity of Impacts: Although climate change does not have a direct impact on dam and levee failures, flood frequency and magnitude are expected to increase as a result of climate change. Subsequently increasing the probability of dam and levee failures. Table 4-45 indicates the 25-year precipitation projections in Contra Costa County. 107 Table 4-46 outlines the flood associated
climate indicators for Contra Costa County projected through the end of the century.108

106 Bay Area Association of Government. (2020). Plan Bay Area 2050 Final Blueprint Growth Pattern. Retrieved from https://planbayarea.org/digital-library/plan-bay-area-2050-final-blueprint-growth-pattern. 107 Northeast Regional Climate Center. (n.d.). Neighborhoods at Risk: Climate Projections. Retrieved from https://nar.headwaterseconomics.org/.
108 Climate Mapping for Resilience and Adaptation. (n.d.). Climate Mapping for Resilience and Adaptation Assessment Tool. Retrieved from https://livingatlas.arcgis.com/assessment-tool/explore/details. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 98 Table 4-45. 25-Year Precipitation Projections for Contra Costa County Higher Emissions (RCP8.5)
Contra Costa County is expected to experience a 7% increase in days with heavy precipitation within 25 years.

By 2048, Contra Costa County is expected to experience 0.18 more days of heavy precipitation per year (from

2.77 days to 2.95 days per year).

Lower Emissions (RCP4.5)
Contra Costa County is expected to experience an 8% increase in days with heavy precipitation within 25 years.

By 2048, Contra Costa County is expected to experience 0.2 more days of heavy precipitation per year (from

2.5 days to 2.7 days per year).

Table 4-46. Future Climate Indicators for Contra Costa County Indicators
Modeled
History
(1976 – 2005)
Early Century
(2015 – 2044)
Mid Century
(2035 – 2064)
Late Century
(2070 – 2099)
Lower
Emissions
Higher
Emissions
Lower
Emissions
Higher
Emissions
Lower
Emissions
Higher
Emissions
Min – Max Min – Max Min – Max Min – Max Min – Max Min – Max Min – Max Precipitation
Average annual total
precipitation
19 inches 19 inches 20 inches 20 inches 20 inches 20 inches 21 inches 17 – 21 16 – 25 17 – 24 17 – 26 16 – 25 16 – 25 14 – 27 Days per year with
precipitation
(Wet Days)
84 days 82 days 82 days 80 days 80 days 80 days 77 days 80 – 88 74 – 91 74 – 91 68 – 91 69 – 98 70 – 90 58 – 94 Maximum period of
consecutive wet days
11 days 11 days 12 days 11 days 11 days 11 days 11 days 10 – 12 10 – 14 10 – 14 9 – 14 9 – 15 10 – 15 8 – 17
Temperature Thresholds
Annual days with total
precipitation greater
than 1 inch
2 days 3 days 3 days 3 days 3 days 3 days 4 days
2 – 3 2 – 4 2 – 4 2 – 5 2 – 5 2 – 5 2 – 7
Annual days with total
precipitation greater
than 2 inches
0 days 0 days 0 days 0 days 0 days 0 days 0 days
0 – 0 0 – 1 0 – 1 0 – 1 0 – 1 0 – 1 0 – 1
Annual days with total
precipitation greater
than 3 inches
0 days 0 days 0 days 0 days 0 days 0 days 0 days
0 – 0 0 – 0 0 – 0 0 – 0 0 – 0 0 – 0 0 – 0
Annual days that
exceed 99
th percentile
precipitation
4 days 5 days 5 days 5 days 5 days 5 days 6 days
3 – 7 3 – 8 3 – 8 3 – 8 3 – 9 3 – 9 4 – 11
Days with maximum
temperature below
32°F
0 days 0 days 0 days 0 days 0 days 0 days 0 days
0 – 0 0 – 0 0 – 0 0 – 0 0 – 0 0 – 0 0 – 0
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Chapter 4: Hazard Identification and Risk Assessment 99 Table 4-50 outlines the climate change impacts to dam and levee failures in Contra Costa County , as outlined in the risk assessment methodology in Section 4.3 of this Plan.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 100 Table 4-47. Probability of Occurrence
Hazard Event Probability of Occurrence Probability
Factor
Weighted
Factor
Dam and Levee Failure Low Significant hazard event is likely to occur within 100 years. 1 N/A Table 4-48. Extent Factors
Hazard Event Extent Factor Extent Extent
Factor
Weighted
Factor
Dam and Levee Failure
Extent/Intensity High Historical and/or probabilistic models/studies for this hazard indicate the possibility of a high-intensity incident. 3 9 Catastrophic High Catastrophic hazard event is likely to occur at least once in 10 years. 3 9
Table 4-49. Vulnerability Factors
Hazard Event Vulnerability Factor Vulnerability Vulnerability Factor
Weighted
Factor
Dam and Levee Failure
Population Exposure Low 14% or less of the population is exposed to the hazard. 1 3 Property Exposure Low 9% or less of the total assessed property value is exposed to a hazard. 1 2
Changes in
Development Low
Changes in development have increased the
vulnerability/exposure of the community to the hazard by 4% or less.
1 1
Table 4-50. Impact Factors
Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Dam and Levee Failure
Population and Life
Safety Medium
Populations exposed to this hazard are likely to experience some adverse impacts, such as injuries requiring acute
medical care.
2 6
Underserved/Equity Medium
Underserved populations exposed to the hazard are likely to experience some adverse/disproportionate impacts, such as injuries requiring acute medical care.
2 6
Property Damage High
More than $5 Million in property damages is expected from a single major hazard event, or damages are expected to occur to 15% or more of the property value within the jurisdiction. 3 6
Economic High Where the total economic impact is likely to be greater than $10 Million. 3 3
2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 101 Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Environmental High
Environmental impact from a single major hazard event is likely to be significant, requiring extensive outside resources and support; and/or repair, clean-up, restoration, and/or preservation work.
3 3
Essential Operations High
Impact greater than 72 hours on the ability of the jurisdiction to meet the essential day-to-day operational demands and needs of the community from a single major hazard event. 3 3
Future Development Medium Future development trends will increase the impact/consequence of this hazard, but not significantly. 2 2 Climate Change Medium Climate Change trends will increase the risk of this hazard and its impacts, but not significantly. 2 2

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Chapter 4: Hazard Identification and Risk Assessment 102

4.6.2.8. FEMA NRI Expected Annual Loss Estimates
The FEMA NRI does not assess dam and levee failure events.

4.6.2.9. FEMA Dam and Levee Failure Risk Index Score
The FEMA NRI does not assess dam and levee failure. Table 4-51 represents the Dam and Levee Failure Total Risk Score for Contra Costa County, based on the Risk Assessment Methodology, as defined in this Plan. For further details on how the probability, extent, vulnerability, and impact factors were calculated, please refer to Table 4-47 through Table 4-50. Additional details on how the Total Risk Score was calculated can be found in the Risk Assessment Methodology in Section 4.3 of this Plan.

Table 4-51. Dam and Levee Failure Total Risk Score
Hazard
Event
Probability Consequence Total Risk
Probability
Factor Extent Vulnerability Impact Consequence
Score
Total Risk
Score*
Dam and Levee Failure 1 18 6 31 55 30
Consequence: Sum of all weighted factors.

Extent: Sum of the weighted Extent factors.

Vulnerability: Sum of the weighted Vulnerability factors.

Impact: Sum of the weighted Impact factors.

The Total Risk Score is a measure of Probability and Consequence.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 103

4.6.3. Drought

4.6.3.1. Description
Drought can be difficult to define. Some definitions are an idea or concept which can be important in establishing drought policy, and others can be operational. Operational drought definitions describe how drought functions or operates in a way that can be measured. The National Integrated Drought Information System (NIDIS) defines drought as the deficiency of precipitation over an extended period of time (usually a season or more), resulting in a water shortage. 109 The National Weather Service (NWS)
defines drought as a deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizeable area. 110

Drought is part of the climate cycle, and it is an underestimated slow -moving hazard that can cause as much damage as other faster -moving hazards (e.g., hurricanes, flooding). Drought can impact agriculture, public health, transportation, ecosystems, wildfire, and water quality. In order to assist with drought classification and monitoring, scientists have defined five (5) types of droughts, listed on Table 4-52. 111
Table 4-52. Types of Drought
Type Description
Meteorological Occurs when dry weather patterns dominate the area.

Hydrological Occurs when low water supply becomes evident in the water system Agricultural Occurs when crops become affected by drought.

Socioeconomic Occurs when the supply and demand of various commodities is affected by drought.

Ecological Occurs when natural ecosystems are affected by drought.

A drought’s severity depends on numerous factors, including duration, intensity, and geographic extent, as well as regional water supply demands by humans and vegetation. Drought differs from other natural hazards in three (3) ways.

• The onset and end of a drought are difficult to determine due to the slow accumulation and lingering effects of an event after its apparent end.
• T he lack of an exact and universally accepted definition adds to the confusion about its existence and severity.
• I n contrast with other natural hazards, the impact of drought is less obvious and may spread over a larger geographic area. These characteristics have hindered many governments' preparation of drought contingency or mitigation plans.

109 National Integrated Drought Information System. (2023). What is a Drought? Drought Basics. Retrieved from https://www.drought.gov/what-is-drought/drought-basics. 110 National Oceanic and Atmospheric Administration, National Weather Service. (2009). National Weather Service Glossary. Retrieved from https://w1.weather.gov/glossary/. 111 National Integrated Drought Information System. (2023). What is a Drought? Drought Basics. Retrieved from https://www.drought.gov/what-is-drought/drought-basics. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 104

4.6.3.2. Hazard Location
A drought can occur anywhere in the Contra Costa County region and affect the entire planning area.

Due to the dynamic nature of droughts, drought conditions are experienced differently based on where someone lives and their sources of water. For example, ranchers grazing livestock on non-irrigated rangeland and rural residents relying on private wells for groundwater can quickly be impacted by dr y conditions. On the other hand, large urban water agencies with multiple water resources are able to manage for several dry years. However, if drought conditions in the area continue for an extended period of time, everyone will experience the effects.
112

4.6.3.3. Hazard Extent/Intensity
Many drought indices have been developed; however, the Palmer Drought Severity Index (PDSI) is the most prominent index of meteorological drought utilized in the United States for drought monitoring. PDSI uses readily available temperature and precipitation data to estimate relative dryness to indicate the prolonged and abnormal moisture deficiency or excess. As an important climatological tool, the PDSI assists in evaluating the scope, severity, and frequency of prolonged periods of abnormally dry or wet weather. Furthermore, it can be utilized to identify disaster areas and indicate the availability of irrigation water supplies, reservoir levels, range conditions, amount of stock water and potential intensity of wildfires.
113, 114

The PDSI is a standardized measure that compares moisture deficiency and excess on a numerical scale that usually ranges from positive five (5) to a negative five (5). Positive values mean there is an excess in moisture supplies and conversely, negative values indicate moisture demands in excess of supplies.

Table 4-53 displays the PDSI categories and Figure 4-9 illustrates the drought conditions in the contiguous United States as measured by the PDSI for the month of March 2024.

Table 4-53. Palmer Drought Severity Index
Palmer Drought
Severity Index Category
- 4.00 and below Extreme Drought
- 3.00 to - 3.99 Severe Drought
- 2.00 to - 2.99 Moderate Drought
- 1.99 to + 1.99 Mid-Range
+ 2.00 to + 2.99 Moderately Moist
+ 3.00 to + 3.99 Very Moist
+ 4.00 and above Extremely Moist

112 California Department of Water Resources. (n.d.). California Water Watch. Retrieved from https://cww.water.ca.gov/droughtindicator.
113 National Weather Service, Climate Prediction Center. (2005). Drought Indices: Explanation. Retrieved from https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/cdus/palmer_drought/wpdanote.shtml. 114 National Center for Atmospheric Research. (n.d.). Climate Data Guide: Palmer Drought Severity Index (PDSI). Retrieved from https://climatedataguide.ucar.edu/climate-data/palmer-drought-severity-index-pdsi. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 105 Figure 4-9. Palmer Drought Severity Index Map (March 2024)

The U.S. Drought Monitor (USDM) is a collaboration between the National Drought Mitigation Center (NDMC), United Stated Department of Agriculture, and NOAA. They also rate drought nationwide by intensity utilizing a D0 (Abnormally Dry) to D4 (Exceptional Drought) scale, shown in Table 4-54. 115 The
map updates weekly to show the location and intensity of drought across the country . 116 Figure 4-10 illustrates the USDM map for the State of California which shows where drought conditions are occurring and its severity.
117

115 National Drought Mitigation Center. (n.d.). What is USDM. Retrieved from https://droughtmonitor.unl.edu/About/WhatistheUSDM.aspx. 116 National Integrated Drought Information System. (2023). U.S. Drought Monitor (USDM). Retrieved from https://www.drought.gov/data-maps-tools/us-drought-monitor. 117 U.S. Drought Monitor. (2023). California. Retrieved from https://droughtmonitor.unl.edu/Maps/MapArchive.aspx.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 106 Table 4-54. U.S. Drought Monitor Classification
Category Description Possible Impacts PDSI Range
D0 Abnormally Dry
Used for areas showing dryness, but not yet in drought, or for areas recovering from drought.

Going into drought:
• Short-term dryness slowing planting, growth of crops or pastures.

Coming out of drought:
• Some lingering water deficits.
• Pastures or crops not fully recovered.
-1.0 to -1.9
D1 Moderate
Drought
• Some damage to crops and pastures.
• Streams, reservoirs, or wells are low, and some water shortages are developing or imminent.
• Voluntary water use restrictions requested.
-2.0 to -2.9
D2 Severe
Drought
• Crop or pasture losses are likely.
• Water shortages are common.
• Water restrictions imposed.
-3.0 to -3.9
D3 Extreme
Drought
• Major crop/pasture losses.
• Widespread water shortages or restrictions. -4.0 to -4.9 D4 Exceptional
Drought
• Exceptional and widespread crop/pasture losses.
• Shortages of water in reservoirs, streams, and wells are creating water emergencies.
-5.0 or less

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 107 Figure 4-10. California U.S. Drought Monitor (April 9, 2024)

4.6.3.4. Warning Time
Droughts develop gradually over long periods of time which can make it complicated to recognize when a drought will occur. However, understanding how large-scale climate patterns (e.g., El Niño–Southern Oscillation (ENSO)) affect the potential of drought in an area can help forecast when drought conditions will occur. DWR maintains the California Water Watch website which offers current local, at the regional and neighborhood level, and statewide water conditions. The website includes information on precipitation, temperature, reservoirs, streamflow, groundwater, snowpack, soil moisture, and vegetation conditions, and California drought updates. In California, drought is based on impacts to water users and observing and monitoring water availability can help have a better understanding of when and where drought can occur. DWR’s California Water Watch can be accessed via the following link cww.water.ca.gov
.

4.6.3.5. Probability and Frequency
Meteorological drought can begin and end rapidly while hydrological drought develops a lot slower and takes a lot longer to recover. Due to the significant differences in the types of droughts, different indices have been developed to measure and monitor droughts in the various sectors. The U.S. Drought Monitor depicts drought integrated across all time scales and differentiates between agricultural and hydrological impacts.
118 Meanwhile, NOAA utilizes the PDSI to measure drought conditions (Table 4-53).

118 National Oceanic and Atmospheric Administration. (n.d.). Did You Know? Index (Definition of Drought).

Retrieved from https://www.ncei.noaa.gov/access/monitoring/dyk/drought-definition.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 108 Estimating drought probability and frequency continues to be difficult, regardless of the improvements in science and technology. According to the 2023 California State Hazard Mitigation Plan, the normal occurrence droughts and documentation of past events and losses determine that the probability for drought events throughout the State will continue.
119
Probability of Future Hazard Events
The drought annualized frequency value represents the average number of recorded drought hazard occurrences, in event days, per year over the period of record ( 22 years). Table 4-55 outlines the annualized frequency for drought, based on FEMA NRI data, for Contra Costa County.

Table 4-55. Drought Annualized Frequency for Contra Costa County (FEMA National Risk Index)
Location Events on Record
(2000 – 2021) Annualized Frequency
Contra Costa County 1,386 52 events per year (in days)
Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year.

4.6.3.6. Past Events
Droughts reoccur every few years. Unlike other hazards (e.g., floods and earthquakes), droughts are not easily defined as “events”. Contra Costa County has experienced multiple droughts between 2000 and 2023, as illustrated in Figure 4-11. Contra Costa County has experienced severe drought from August 2008 through October 2009 and severe to exceptional drought from November 2013 through January 2017 and again from April 2021 through January 2023. A Presidentially Disaster Declaration for drought has never been declared in the State of California.

Figure 4-11. U.S. Drought Monitor for Contra Costa County 120

119 California Governor’s Office of Emergency Services. (2023). California State Hazard Mitigation Plan. Retrieved from https://www.caloes.ca.gov/wp-content/uploads/Hazard-Mitigation/Documents/2023-California- SHMP_Volume-1_11.10.2023.pdf.
120 U.S Drought Monitor. (2023). Time Series (Contra Costa County, CA). Retrieved from https://droughtmonitor.unl.edu/DmData/TimeSeries.aspx.

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Chapter 4: Hazard Identification and Risk Assessment 109 California hydrologic data shows multi -year droughts from 1912 to 1913, 1918 to 1920, 1922 to 1924, and 1928 to 1934. Since then, prolonged periods of drought continued to occur in California, all of which impacted Contra Costa County to some degree, are listed in Table 4-56.

Table 4-56. Drought Past Events
Date Event Summary
2021 – 2022
Water Year 2022 (October 1, 2021, through September 30, 2022) was the third driest year on record. Although it did not record the highest temperatures or lowest precipitation amounts, it preceded Water Year 2021.

The years 2020 through 2022 were the driest on record for the State of California. For maximum temperature, August 2020 came in second to 1967. For September, the maximum temperature ranked sixth warmest. On August 16, Death Valley recorded a temperature of 130 ºF. Five (5) of the State’s largest six (6) fires in history were ignited in August and September. The 2021 water year was the second driest on record, with extreme heat and lack of precipitation. By the end of 2021, all 58 counties in California were placed under a drought emergency proclamation (State of California 2022d). The drought continued through April 2022; the snowpack of the Sierra Nevada was at 38% of its statewide average (Becker 2022). The State experienced $1.2 Billion in crop damage as a result of this drought period.
2012 – 2016
California’s last drought set several records for the State. The period from 2012 to 2014 ranked as the driest three (3) consecutive years for statewide precipitation.

Calendar year 2014 set new climate records for statewide average temperatures and 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. The State has detailed executive orders and regulations concerning water conservation and management. Total impacts of the drought have not yet been determined.
2007 – 2009
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 – 1992
California received precipitation well below average levels for four (4) 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% 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 – 1977
This was the worst drought in the State’s history at the time. 1976 was the fourth driest year on record followed by 1977, the driest period on record in California. The cumulative impact led to widespread water shortages and severe water conservation measures throughout the State. Only 37% 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 an Emergency Declaration (EM-3023- CA) on January 20, 1977, for all 58 California counties.

4.6.3.7. Vulnerability and Impacts
Life Safety and Health: All residents within Contra Costa County would be vulnerable and impacted by a drought. Drought can affect people’s health and safety, including health problems related to low water flows, poor water quality, or dust. Other possible impacts include recreational risks; effects on air quality; 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 110 diminished living conditions related to energy, air quality, and hygiene; compromised food and nutrition; and increased incidence of illness and disease. Droughts can also lead to reduced local firefighting capabilities. However, the underserved and at risk population faces unique vulnerabilities and impacts to drought. These groups include, but are not limited to, outdoors workers and undocumented individuals. 121

• Outdoor Workers: Includes, but are not limited to, construction workers, agriculture workers, and recreation. Drought can reduce water availability for agricultural operations, parks, and recreation areas, which can indirectly harm outdoor workers. Agricultural operations and Delta recreational opportunities can be halted, which may cause outdoor workers to lose jobs. Additionally, drought events are accompanied by extreme heat which outdoor workers are extremely vulnerable to.

Outdoor workers are disproportionately impacted by extreme heat because they are required to be outside and risk heat related illnesses (e.g., heat cramps, heat exhaustion, heat stroke) .

Furthermore, outdoor work may also be halted during high temperatures, which can cause significant economic hardships.
• Undocumented Individuals: Includes people who do not have formal permission to live in the United States (i.e., do not have citizenship, permanent residency, visas, or other similar status).

Most of this population has outdoor occupations or work in a highly unregulated environment which leaves them susceptible to harm from extreme heat conditions that accompany drought events. Outdoor work may also be halted during high temperatures and droughts, which can cause significant economic hardships. Undocumented agricultural workers may face economic hardship if crops, vineyards, or rangeland are damaged by drought conditions. Furthermore, agricultural workers who are undocumented are more likely to be let go when farms experience economic hardship. There are no official counts of how many undocumented individuals live in Contra Costa County, but in 2019 there was an estimate of 63,000. 122
• Individuals with Chronic Illnesses: Includes those that have long term or permanent health conditions that can be exacerbated by drought conditions (e.g., cardiovascular disease, respiratory conditions, mental illness). This population is most vulnerable to the health impacts of droughts. During droughts, air quality can decrease as a result of wildfires and dust which produce air particulates that irritate the lungs and bronchial passages exacerbating chronic respiratory conditions. Additionally, drought conditions can also increase the incidence of illness and disease (e.g., mosquito-borne diseases, anxiety, depression, and other adverse mental health outcomes).
123

East Contra Costa County is more susceptible to the effects of drought due to extensive agricultural areas which impact the County’s economy. Additionally, these conditions can also impact low income populations, as food and water prices increase, or agricultural workers who rely on agriculture for their livelihood.

Table 4-61 outlines the vulnerability of the total population exposed to drought. Table 4-62 outlines the drought impacts to population and life safety, underserved/equity population, and essential operations, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

121 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
122 Migration Policy Institute. (2019). Profile of the Unauthorized Population: Contra Costa County, CA. Retrieved from https://www.migrationpolicy.org/data/unauthorized-immigrant-population/county/6013. 123 National Integrated Drought Information System. (n.d.). Drought.gov, By Sector: Public Health. Retrieved from https://www.drought.gov/sectors/public-health.
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Chapter 4: Hazard Identification and Risk Assessment 111 Property Damage and Critical Infrastructure: No structures will be directly affected by drought conditions, though some structures may become vulnerable to wildfires, which are more likely following years of drought. 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. Additionally, buildings and infrastructure do not need to be physically damaged to trigger a loss of service. For example, extreme heat, which accompanies drought, makes the machinery of the power grid run less efficiently and simultaneously increases demand to meet greater cooling needs. This combination raises the risk of grid overloading and causing brownouts or blackouts.

Similarly, drought conditions harm water delivery services but do not cause physical damage to pipes or water treatment plants.

Table 4-61 outlines the total property value exposed to drought and how the changes in development in the past five (5) years, have affected the vulnerability of the community to drought. Table 4-62 outlines the drought impact on total property damage, potential future development, and the economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Environment: 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 a longer time or may even become permanent. In Contra Costa County, the following ecosystems and natural resources are vulnerable to droughts:
124

• Aquatic: Aquatic habitat (i.e., streams, reservoirs, ponds, and sloughs or channels) are impacted by droughts. This ecosystem includes the Delta and shoreline areas that are submerged by water.

In Contra Costa County, the three (3) large reservoirs include San Pablo Reservoir, Briones Reservoir, and Los Vaqueros Reservoir. Aquatic wildlife species include various duck species, California red-legged frog, western pond turtle, and juvenile and spawning adult Chinook salmon.

A drought can lower water levels and water quality and raise water temperatures in aquatic habitants. Subsequently these conditions can cause algal blooms in the Delta areas, harm salmonoid populations, and cause other systemwide failures. Aquatic species can also be harmed by lower dissolved oxygen levels and increase algae growth in the Delta. • Riparian Woodland and Shrub: Riparian woodland and shrub ecosystems consist of Valley foothill riparian, undetermined shrub, and riverine habitat. These areas are scattered throughout Contra Costa County and have numerous wildlife species (e.g., gray fox, striped skunk, broad- handed mole, mule deer, dusky-footed woodrat, yellow warbler, northern flicker, white tailed kite, and Cooper’s hawk ). Drought conditions can cause smaller streams to run dry, which can subsequently harm the plants and animal habitat within the ecosystem. Additionally, trees may not have adequate water during drought periods, which can lead to pests and diseases destroying important habitat for the Gray fox, Cooper's hawk, and mule deer. Soil erosion can also occur on the banks of streams.
• Wetland: Wetland ecosystems, located adjacent to the San Francisco Bay and Delta, include permanent wetland, seasonal wetland, fresh emergent wetland, alkali wetland, and marshes.

Drought conditions can directly affect the wetland ecosystems by reducing water quantity and quality, contributing to algal blooms, low streamflow, higher temperatures, and increased erosion

124 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
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Chapter 4: Hazard Identification and Risk Assessment 112 in the Delta and inland wetland habitats. As a result, wildlife that depends on these ecosystems (e.g., California red-legged frog and western pond turtle) can be harmed. Wildlife within these ecosystems includes g reat blue heron, great egret, wood duck, green -winged teal, mallard, California red-legged frog, western pond turtle, garter snakes, western spadefoot toad, western toad, California tiger salamander, tri-colored blackbird, and vernal pool fairy shrimp.

Additionally, agriculture may be directly harmed from drought conditions due to an increase in soil salinity, topsoil erosion, and reduced water supply which can limit crop production and in turn result in a loss of income for agriculture owners. Agricultural operations are primarily located in eastern Contra Costa County, between the Mt. Diablo State Park and the Delta, and the economy in this area can be especially harmed by limited water for agricultural production. For example, in 2017, Contra Costa County farms and orchards produced approximately $95 Million in agriculture products. These impacts can result in reduced income for farmers and agribusiness, increased prices for food and lumber, unemployment, reduced tax revenues, increased crime, migration, and foreclosures on bank loans to farmers and businesses.

Rangeland is primarily located on grassland habitats, which can lose topsoil and productivity due to the drier conditions created by droughts. This can reduce the available foraging habitat for livestock and cause economic hardship for rangeland owners. Rangeland, primary located in the eastern Contra Costa County, are lands where many livestock species (e.g., cattle) are raised. In 2017, rangeland produced approximately $26 Million in livestock products. Furthermore, the Sacramento-San Joaquin River Delta, primarily encompasses the northern and easternmost borders of Contra Costa County and provides opportunities for boating, fishing, transportation, and a water source for the County. Drought conditions can reduce the streamflow of the Delta, reducing the water quality which can decrease commercial fishing, agricultural production, and recreation opportunities. Additionally, changes in water conditions can kill certain fish species and drought conditions can increase the salinity of the Delta which will affect the water supply for agricultural irrigation.
125

Table 4-62 outlines drought impacts on the environment and the economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Changes in Development and Impact of Future Development: There have been no significant changes in development that have affected the risks associated with drought. Future increases in population that result in greater water consumption may exacerbate the impacts of drought. Growth over the past decade has considerably increased. Between 2010 and 2022, as outlined in Table 3-3 , the population in Contra Costa County grew 10.6% , from 1,046,025 to 1,156,966 residents. The Bay Area Association of Governments ( ABAG) growth forecasts predict a steady increase in households through 2050. From 2015 to 2050, ABAG projects that the County’s number of households will grow by 44%. 126
This increase in population can add an additional strain to the water supply and power grid when drought conditions are present.

Table 4-61 outlines how the changes in development in the past five (5) years have affected vulnerability of the community to droughts. Table 4-62 outlines the drought impacts on potential future development, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

125 Ibid.
126 Bay Area Association of Government. (2020). Plan Bay Area 2050 Final Blueprint Growth Pattern. Retrieved from https://planbayarea.org/digital-library/plan-bay-area-2050-final-blueprint-growth-pattern. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 113 Effects of Climate Change in Severity of Impacts: In California and western United States, observations of climate change have shown an increase in frequency of drought and an increase in consecutive dry days. Climate change will not result in less frequency and intensity of precipitation in the County, while average annual temperatures may increase by as much as 2.0° F within 25 years. Table 4-57 indicates the 25-year climate projections in Contra Costa County. 127
Table 4-57. 25-Year Climate Projections for Contra Costa County Higher Emissions (RCP8.5)
Contra Costa County is expected to experience a 43% increase in extremely hot days and a 7% increase in days with heavy precipitation within 25 years.

By 2049, Contra Costa County is expected to experience 11 more days that reach above 95°F (from 23 days to 33 days per year).

Lower Emissions (RCP4.5)
Contra Costa County is expected to experience a 29% increase in extremely hot days and an 8% increase in days with heavy precipitation within 25 years.

By 2049, Contra Costa County is expected to experience seven (7) more days that reach above 95°F (from 22 days to 29 days per year).

Climate change is already profoundly impacting California's water resources, as evidenced by changes in snowpack, sea level, and river flows. These changes are expected to continue, and more precipitation will likely fall as rain instead of snow, decreasing snowpack levels. This potential change in weather patterns will add additional challenges to water supply reliability. 128

The California Department of Water Resources states climate change is responsible for the decrease in the Sierra snowpack levels which provides as much as a third of California's water supply by accumulating snow during wet winters and releasing it slowly during the spring and summer when the need is the greatest. Warmer temperatures will cause snow to melt faster and earlier, making it m ore difficult to store and use. By the end of this century, the Sierra snowpack is projected to experience a 48% to 65% loss from the historical April 1
st average. This loss of snowpack means less water will be available for water users in the State.129

Climate change is also expected to result in more variable weather patterns throughout the State. More variability can lead to longer and more severe droughts. In addition, rising sea levels will continue to threaten the Sacramento-San Joaquin Delta, the heart of the California water supply system and the source of water for 25 million Californians and millions of acres of prime farmland. 130 Table 4-58 outlines
the drought associated climate indicators for Contra Costa County projected through the end of the century.
131

127 Northeast Regional Climate Center. (n.d.). Neighborhoods at Risk: Climate Projections. Retrieved from https://nar.headwaterseconomics.org/.
128 California Department of Water Resources. (n.d.). Climate Change Basics. Retrieved from https://water.ca.gov/Water-Basics/Climate-Change-Basics. 129 California Department of Water Resources. (n.d.). Climate Change and Water. Retrieved from https://water.ca.gov/Programs/All-Programs/Climate-Change-Program/Climate-Change-and-Water. 130 Ibid.
131 Climate Mapping for Resilience and Adaptation. (n.d.). Climate Mapping for Resilience and Adaptation Assessment Tool. Retrieved from https://livingatlas.arcgis.com/assessment-tool/explore/details. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 114 Table 4-58. Future Climate Indicators for Contra Costa County Indicators
Modeled
History
(1976 – 2005)
Early Century
(2015 – 2044)
Mid Century
(2035 – 2064)
Late Century
(2070 – 2099)
Lower
Emissions
Higher
Emissions
Lower
Emissions
Higher
Emissions
Lower
Emissions
Higher
Emissions
Min – Max Min – Max Min – Max Min – Max Min – Max Min – Max Min – Max Precipitation
Average annual total
precipitation
19 inches 19 inches 20 inches 20 inches 20 inches 20 inches 21 inches 17 – 21 16 – 25 17 – 24 17 – 26 16 – 25 16 – 25 14 – 27 Days per year with
precipitation
(Wet Days)
84 days 82 days 82 days 80 days 80 days 80 days 77 days 80 – 88 74 – 91 74 – 91 68 – 91 69 – 98 70 – 90 58 – 94 Days per year with no
precipitation
(Dry Days)
281 days 283 days 283 days 285 days 285 days 285 days 288 days 277 – 285 275 – 291 274 – 291 275 – 298 267 – 296 275 – 296 271 – 307 Maximum number of
consecutive dry days
95 days 97 days 98 days 97 days 99 days 98 days 102 days 85 – 113 84 – 113 88 – 110 83 – 118 82 – 117 90 – 121 76 - 139 Temperature Thresholds
Annual days with
maximum temperature
greater than 90°F
36 days 55 days 57 days 62 days 68 days 70 days 90 days 36 – 43 47 – 63 51 – 65 51 – 74 55 – 84 57 – 91 72 – 124 Annual days with
maximum temperature
greater than 100°F
5 days 10 day 11 days 13 days 16 days 17 days 29 days
4 – 6 7 – 14 8 – 16 9 – 22 9 – 28 10 – 22 19 – 57

Table 4-62 outlines the climate change impacts to drought in Contra Costa County, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

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Chapter 4: Hazard Identification and Risk Assessment 115 Table 4-59. Probability of Occurrence
Hazard Event Probability of Occurrence Probability
Factor
Weighted
Factor
Drought Medium Significant hazard event is likely to occur within 25 years. 2 N/A Table 4-60. Extent Factors
Hazard Event Extent Factor Extent Extent
Factor
Weighted
Factor
Drought
Extent/Intensity High Historical and/or probabilistic models/studies for this hazard indicate the possibility of a high-intensity incident. 3 9 Catastrophic High Catastrophic hazard event is likely to occur at least once in 10 years. 3 9
Table 4-61. Vulnerability Factors
Hazard Event Vulnerability Factor Vulnerability Vulnerability Factor
Weighted
Factor
Drought
Population Exposure High 30% or more of the population is exposed to the hazard. 3 9 Property Exposure Low 9% or less of the total assessed property value is exposed to a hazard. 1 2
Changes in
Development Low
Changes in development have increased the
vulnerability/exposure of the community to the hazard by 4% or less.
1 1
Table 4-62. Impact Factors
Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Drought
Population and Life
Safety Low Populations exposed to this hazard are likely to experience minimal adverse impacts, such as ambulatory injuries. 1 3 Underserved/Equity Medium
Underserved populations exposed to the hazard are likely to experience some adverse/disproportionate impacts, such as injuries requiring acute medical care.
2 6
Property Damage Low
Less than $500,000 in property damages is expected from a single major hazard event or less than 5% of the property value within the jurisdiction.
1 2
Economic Medium Total economic impact is likely to be greater than $500,000, but less than or equal to $10 Million. 2 2
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Chapter 4: Hazard Identification and Risk Assessment 116 Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Environmental Low
Environmental impact from a single major hazard event is likely to be minimal, requiring little to no outside resources and support, and/or minimal repair, clean-up, restoration, or preservation work.
1 1
Essential Operations Low
Impact less than 24 hours on the ability of the jurisdiction to meet the essential day-to-day operational demands and
needs of the community from a single major hazard event. 1 1
Future Development Medium Future development trends will increase the impact/consequence of this hazard, but not significantly. 2 2 Climate Change High Climate Change trends will significantly increase the risk of this hazard and its impacts. 3 3

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Chapter 4: Hazard Identification and Risk Assessment 117

4.6.3.8. FEMA NRI Expected Annual Loss Estimates
A drought NRI EAL score, and rating represent a community's relative level of expected agriculture loss each year due to droughts when compared to the rest of the United States. The EAL score is positively associated with a community’s risk; therefore, a higher EAL score results in a higher Risk Index score.

Table 4-63 outlines the drought EAL for Contra Costa County.

Table 4-63. Drought Expected Annual Loss (FEMA National Risk Index) Jurisdiction Population
Equivalence
Building
Value
Agriculture
Value
Total
Expected
Annual
Loss
Expected
Annual
Loss
Score
Rating
Contra Costa
County n/a n/a $10.8 Million $10.8 Million 99.4 Very High Expected annual loss scores are calculated utilizing an equation that combines values for exposure, annualized frequency, and historic loss ratios (Expected Annual Loss = Exposure x Annualized Frequency x Historic Loss Ratio).

4.6.3.9. FEMA Drought Risk Index Score
The drought Risk Index score and rating represent a community's relative risk for droughts when compared to the rest of the United States. Table 4-64 illustrates the drought Risk Index rating and score for Contra Costa County.

Table 4-64. Drought Risk Index (FEMA National Risk Index) Jurisdiction Rating Score
Contra Costa County Very High 99.3
Risk Index scores are calculated using an equation that combines scores for Expected Annual Loss due to natural hazards, Social Vulnerability and Community Resilience (Expected Annual Loss x Social Vulnerability / Community Resilience = Risk Index).

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Chapter 4: Hazard Identification and Risk Assessment 118 Table 4-65 represents the Drought Failure Total Risk Score for Contra Costa County, based on the Risk Assessment Methodology, as defined in this Plan. For further details on how the probability, extent, vulnerability, and impact factors were calculated, please refer to Table 4-59 through Table 4-62.

Additional details on how the Total Risk Score was calculated can be found in the Risk Assessment Methodology in Section 4.3 of this Plan.

Table 4-65. Drought Total Risk Score
Hazard
Event
Probability Consequence Total Risk
Probability
Factor Extent Vulnerability Impact Consequence
Score
Total Risk
Score*
Drought 2 18 12 20 50 50
Consequence: Sum of all weighted factors.

Extent: Sum of the weighted Extent factors.

Vulnerability: Sum of the weighted Vulnerability factors.

Impact: Sum of the weighted Impact factors.

The Total Risk Score is a measure of Probability and Consequence.

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Chapter 4: Hazard Identification and Risk Assessment 119

4.6.4. Earthquake

4.6.4.1. Description
Earthquakes are rapid shaking of the earth caused by the release of energy stored in rocks. The United States Geological Survey (USGS) defines an earthquake as the sudden slip on a fault and the resulting ground shaking and radiated seismic energy caused by the slip, or by volcanic or magmatic activity, or other sudden stress changes in the earth. Ground shaking is a term utilized to describe the vibration of the ground during an earthquake. Other than the initial ground shaking, additional earthquake hazar ds include building collapses, displacement or cracking of the earth’s surface, landslides, liquefaction, tsunamis, seiches, flooding as a result of damage to dams or levees, and fires from ruptured gas lines, downed power lines and other sources.
132 Landslides, tsunamis, and flooding will be addressed separately in this Plan. Earthquakes cause both vertical and horizontal ground shaking which varies both in amplitude (the amount of displacement of the seismic waves) and frequency (the number of seismic waves per unit time), usually lasting less than 30 seconds. 133

Buildings with foundations resting on unconsolidated landfill and other unstable soil, and trailers or homes not tied to their foundations are at risk because they can be shaken off their mountings during an earthquake. When an earthquake occurs in a populated area, it may cause deaths, injuries, and extensive property damage.

Regulatory Environment
The Alquist-Priolo Earthquake Fault Zoning Act was signed into California Law on December 22, 1972, to mitigate the hazard of surface faulting to structures for human occupancy. The Act was a direct result of the significant damage to homes and businesses that occurred in the 1971 San Fernando Earthquake.

It enforces the following to increase earthquake safety: 134

• Directs the California Geological Survey (CGS) to create maps of known fault zones. • Requires the sale of any home located within the fault zone designated on the maps to disclose that the property lies adjacent to a known fault.
• Prohibits new construction of homes within these zones unless geologic studies are performed to prove that the fault will not pose a hazard to new structures proposed in these zones.

The State provides extensive regulations on earthquake-related issues. A key area for regulation is the California Building Standards Commission (CBSC). It is authorized by California Building Standards Law to administer the development, adoption, approval, publication, and implementation of California's building codes.

The California Building Standards Code, Title 24, serves as the basis for the design and construction of buildings in California. Improved safety, sustainability, maintaining consistency, new technology, construction methods, and reliability are paramount to the development of building codes. California’s building codes are published in their entirety every three (3) years. Intervening Code Adoption Cycles produce supplement pages halfway (18 months) into each triennial period. Amendments to California’s

132 U.S Geological Survey. (n.d.). Earthquake Hazards Program Glossary. Retrieved from https://www.usgs.gov/glossary/earthquake-hazards-program. 133 U.S Geological Survey. (n.d.). What are the Effects of Earthquakes. Retrieved from https://www.usgs.gov/programs/earthquake-hazards/what-are-effects-earthquakes. 134 Structural Engineers Association of Northern California. (1972). Events/Alquist-Priolo Earthquake Fault Zoning Act. Retrieved from https://legacy.seaonc.org/event/alquistprioloact/. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 120 building standards are subject to a lengthy and transparent public participation process throughout each code adoption cycle.

The California Seismic Safety Commission provides an array of regulatory and advisory information regarding seismic safety via the following link ssc.ca.gov .

4.6.4.2. Hazard Location
Contra Costa County is located in an area with high seismic activity with numerous local faults , as illustrated in Figure 4-12 which shows the active geologic faults in the San Francisco Bay region. 135 There are five (4) primary active faults that can produce significant earthquakes in the Contra Costa County area – Hayward Fault, Calaveras North Fault, Concord-Green Valley Fault, Mount Diablo Fault, and Greenville Fault. These faults are described in Table 4-66.

Table 4-66. Active Faults Within the Contra Costa County Area Fault Description
San Andreas Fault
The San Andreas Fault, the largest fault in California, is the major tectonic boundary between the Pacific and North American plates. The Pacific plate is moving northwest relative to North America, while the North American plate is moving southward. The fault is approximately 808 miles long and extends, at least, 16 miles deep. The San Andreas Fault has a maximum earthquake potential of 8.0.

Calaveras North
Fault
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 San Francisco Bay Area (USGS, 2003).

There is a 26% probability of a magnitude 6.7 or greater earthquake along the Calaveras Fault to occur in the next 30 years.

Concord-Green
Valley Fault
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-Marsh
Creek Fault
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.

135 United States Geological Survey. (n.d.). Map of Known Active Geologic Faults in the San Francisco Bay Region. Retrieved from https://www.usgs.gov/media/images/map-known-active-geologic-faults-san-francisco-bay- region.
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Chapter 4: Hazard Identification and Risk Assessment 121 Fault Description
Mount Diablo Thrust
Fault
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.

Figure 4-12. Faults Located in the San Francisco Bay Region

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Chapter 4: Hazard Identification and Risk Assessment 122 Figure 4-13 illustrates earthquake events greater than Magnitude 4.3 within 20 miles of Contra Costa County.

Figure 4-13. Earthquake History in Contra Costa County Area

4.6.4.3. Hazard Extent/Intensity
Earthquakes are measured both in terms of their inherent magnitude and in terms of their local intensity.

There are several standard measures of earthquakes, including the Richter Scale and the Modified Mercalli Intensity (MMI) scale. The Richter Scale measures the magnitude or amount of energy an earthquake releases. Magnitude is measured by seismographs. The MMI scale is an observed measurement of the earthquake’s intensity felt at the earth’s surface and it varies depending on the observer’s location at the earthquake’s epicenter. The MMI Scale is comprised of 12 increasing levels, designated by Roman numerals, that range from imperceptible shaking to catastrophic destruction.

Furthermore, the MMI can be used to map earthquake impacts. 136

Table 4-67 correlates the MMI Scale with the Richter Scale and effects of ground shaking.

136 Pacific Northwest Seismic Network. (n.d.). Magnitude/Intensity. Retrieved from https://pnsn.org/outreach/about-earthquakes/magnitude-intensity.

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Chapter 4: Hazard Identification and Risk Assessment 123 Table 4-67. Modified Mercalli Scale vs. Richter Scale

Earthquakes can trigger other types of ground failures, which could contribute to the damage. These include flow failures, landslides, and liquefaction. Liquefaction is not a type of ground failure; however, it is a physical process that occurs when shaking can mix groundwater and soil, liquefying and weakening the ground that supports buildings and severing utility lines. This is a problem in floodplains where the water table is relatively high, and the soil is more susceptible to liquefaction. 137

4.6.4.4. Warning Time
Earthquakes occur with little to no warning. Scientists cannot predict or forecast earthquakes. An earthquake early warning system uses earthquake science and technology of monitoring systems to alert devices and people when shaking waves generated by an earthquake are expected to arrive at a location.

Although it may not sound like a lot of time (compared to other natural hazards), seconds to tens of seconds of advance warning can allow people and systems to take action and protect life and property from destructive shaking.
138

In partnership with University of California Berkeley and USGS ShakeAlert, Cal OES developed the Earthquake Warning California system. The system uses ground-motion sensors to detect earthquakes that have already started and estimate their size, location, and impact. Once it detects a significant magnitude, the MyShake App (registration is required), Wireless Emergency Alerts, or Android Alerts

137 United States Geological Survey. (n.d.). What are the Effects of Earthquakes? Retrieved from:
https://www.usgs.gov/programs/earthquake-hazards/what-are-effects-earthquakes. 138 United States Geological Survey. (n.d.). What is the difference between earthquake early warning, earthquake forecasts, earthquake probabilities, and earthquake prediction? Retrieved from https://www.usgs.gov/faqs/what- difference-between-earthquake-early-warning-earthquake-forecasts-earthquake-probabilities.

Intensity Effects
Richter
Scale
(approximate)
I. Instrumental Not felt. 1 – 2
II. Just Perceptible Felt by only a few people, especially on upper floors of tall buildings. 3 III. Slight Felt by people lying down, seated on a hard surface, or in the upper stories of tall buildings. 3.5
IV. Perceptible Felt indoors by many, by few outside; dishes and windows rattle. 4 V. Rather Strong Generally felt by everyone; sleeping people may be awakened. 4.5 VI. Strong Trees sway, chandeliers swing, bells ring, some damage from falling object. 5
VII. Very Strong General alarm; walls and plaster crack. 5.5 VIII. Destructive Felt in moving vehicles; chimneys collapse; poorly constructed buildings seriously damaged. 6
IX. Ruinous Some houses collapse; pipes break. 6.5
X. Disastrous Obvious ground cracks; railroad tracks bent; some landslides on steep hillsides. 7
XI. Very Disastrous Few buildings survive; bridges damaged or destroyed; all services interrupted (electrical, water, sewage, railroad; severe landslides. 7.5 XII. Catastrophic Total destruction; objects thrown into the air; river courses and topography altered. 8
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Chapter 4: Hazard Identification and Risk Assessment 124 sends a warning to mobile phone users when shaking is about to occur in the user’s area. The speed of the alert varies depending on the individual’s distance from the origin of the earthquake. Therefore, if the individual is closer to the earthquake’s epicenter the warning will arrive faster than someone that is further away. Table 4-68 outlines the alerting thresholds for the Earthquake Warning California system. 139
Table 4-68. Earthquake Warning California Alerting Thresholds Warning System Threshold
Wireless Emergency Alerts
The Wireless Emergency Alerts are used in response to magnitude 5.0 or greater earthquakes and will alert people who will experience a shaking level of MMI IV (light) or greater.

MyShake App
The MyShake App is used in response to magnitude 4.5 or greater earthquakes and will alert people who will experience a shaking level of MMI III (weak) or greater.

Android Alerts
The Android Alerts are used in response to magnitude 4.5 or greater earthquakes and will alert people who will experience a shaking level of MMI III (weak) or greater.

4.6.4.5. Probability and Frequency
Earthquake probabilities are calculated by projecting earthquake rates based on earthquake history and fault slip rates and the result is expressed as the probability that an earthquake of a specified magnitude will occur on a fault or within an area.
140

According to USGS, there is 72% probability of at least one (1) earthquake before 2043 with a magnitude

6.7 or greater that could cause widespread damage in the San Francisco Bay area. 141 In 2017, the
Working Group on California Earthquake Probabilities (WGCEP) issued its third Uniform California Earthquake Rupture Forecast (UCERF3), which determined the likelihood of magnitude 6.7 and greater earthquakes by 2043. In the San Francisco Bay area, the probabilities are: 142

• 98% that an earthquake measuring magnitude 6.0 or greater. • 72% that an earthquake measuring magnitude 6.7 or greater. • 51% that an earthquake measuring magnitude 7.0 or greater. • 20% that an earthquake measuring magnitude 7.5 or greater.

Probability of Future Hazard Events
Table 4-69 lists the p robabilities, estimated by USGS, for earthquakes on major fault lines in the San Francisco Bay area where the Rodgers Creek and Hayward faults have high potential for experiencing major to great events. 143

139 California Governor’s Office of Emergency Services. (n.d.). Earthquake Warning California: Types of Alerts.

Retrieved from https://earthquake.ca.gov/get-alerts/.
140 California Department of Conservation. (n.d.). Earthquakes. Retrieved from https://www.conservation.ca.gov/cgs/earthquakes.
141 United States Geological Survey. (2016). Earthquake Outlook for the San Francisco Bay Region (2014 – 2043). Retrieved from https://pubs.usgs.gov/fs/2016/3020/fs20163020.pdf. 142 United States Geological Survey. (2015). UCERF3: A New Earthquake Forecast for California's Complex Fault System. Retrieved from https://pubs.usgs.gov/fs/2015/3009/pdf/fs2015-3009.pdf. 143 United States Geological Survey. (2016). Earthquake Outlook for the San Francisco Bay Region (2014 – 2043). Retrieved from https://pubs.usgs.gov/fs/2016/3020/fs20163020.pdf. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 125 Table 4-69. Earthquake Probabilities for the San Francisco Bay Area (2014 – 2043) Fault Probability of One (1) or More Magnitude 6.7 or
Greater Earthquake
Rodgers Creek Fault 33%
Hayward 33%
Calaveras 26%
San Andreas 22%
Hunting Creek 16%
Green Valley 16%
Concord 16%
Greenville 16%
Berryessa 16%
Maacama 8%
San Gregorio 6%

The USGS National Seismic Hazard Maps reflect the best and most current understanding of earthquake hazard in an area, the distribution of damaging earthquake shaking across the United States and compares earthquake shaking hazard areas with other areas across the United States. Figure 4-14 illustrates the most recent USGS National Seismic Hazard Map which represents the expected number of occurrences of damaging earthquake shaking in 10,000 years. A “damaging earthquake shaking” in this map is that of MMI level VI or higher.
144

144 United States Geological Survey, Earthquake Hazards Program. (2022). Introduction to the National Seismic Hazard Maps. Retrieved from https://www.usgs.gov/programs/earthquake-hazards/science/introduction-national- seismic-hazard-maps.
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Chapter 4: Hazard Identification and Risk Assessment 126 Figure 4-14. USGS National Seismic Hazard Map

The earthquake annualized frequency value represents the modeled frequency of an earthquake hazard occurrence per year. A higher annualized frequency value results in higher EAL and Risk Index scores.

Table 4-70 outlines the annualized frequency for earthquakes, based on FEMA NRI data, for Contra Costa County.

Table 4-70. Earthquake Annualized Frequency (FEMA National Risk Index) Location Events on Record
(2021 Dataset) Annualized Frequency
Contra Costa County N/A 0.970% chance per year
Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year.

4.6.4.6. Past Events
The San Francisco Bay area has experienced at least 22 earthquakes of magnitude 5.0 or greater since 1850. Table 4-71 lists the earthquakes of magnitude 5.0 or greater that have occurred in or within Contra Costa County.

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Chapter 4: Hazard Identification and Risk Assessment 127 Table 4-71. Earthquake Past Events Within or Near Contra Costa County (Magnitude 5.0 or Greater) 145
Date Magnitude Epicenter Location
August 24, 2014
(South Napa Earthquake) 6.0 South Napa
October 20, 2012
(King City Earthquake) 5.3 17.4 miles east-northeast of King City, California
October 31, 2007
(Alum Rock Earthquake) 5.5 3.7 miles north-northeast of East Foothills, California
August 12, 1998
(San Juan Bautista Earthquake) 5.1 6.2 miles southwest of Ridgemark, California April 18, 1990
(Northern California) 5.1

2.4 miles east of Interlaken, California

3.1 miles north-northwest of Aromas,
California
October 18, 1989
(Loma Prieta Earthquake) 6.9 Loma Prieta, California
August 8, 1989
(Santa Cruz County Earthquake) 5.4 2.5 miles east-southeast of Lexington Hills, California
June 27, 1989 5.3 5 miles east-southeast of Lexington Hills, California
June 13, 1988 5.3 3.7 miles east of East Foothills, California February 20, 1988 5.1 0.6 miles northeast of Tres Pinos, California March 31, 1986 5.7 9.3 miles northeast of East Foothills, California
January 26, 1986 5.5 1.9 miles east-northeast of Tres Pinos California
January 27, 1980 5.4 5.6 miles northeast of Livermore, California

4.6.4.7. Vulnerability and Impacts
Life Safety and Health: The entire population of the planning area is potentially exposed to direct and indirect impacts from earthquakes. Whether directly impacted or indirectly impacted, the entire population will have to deal with the consequences of earthquakes to some degree. Business interruption could keep people from working, road closures could isolate populations, and loss of functions of utilities could impact populations that suffered no direct damage from an event itself. A catastrophic earthquake would have significant impacts on the County since earthquake faults align with many County thoroughfares and population centers. West Contra Costa County is highly vulnerable to impacts from earthquakes along the Hayward Fault.

An earthquake impacts the life safety and health of the County by potentially causing injury or death to the population due to debris, failed infrastructure, and other hazards. The entire population of Contra Costa County falls within areas with the potential for either violent or extreme levels of ground shaking.

However, some populations within the planning area may be more vulnerable to an earthquake event than others. For example, those with mobility issues as well as the elderly may have challenges with evacuating or traveling to a shelter without assistance if they cannot stay in their homes.

145 United States Geological Survey. (2023). Search Earthquake Catalog. Retrieved from https://earthquake.usgs.gov/earthquakes/search/.
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Chapter 4: Hazard Identification and Risk Assessment 128 Approximately 11.4% of Contra Costa County population has a disability type (i.e., hearing, vision, cognitive, or ambulatory, self-care, and independent living difficulty). In Contra Costa County, the most prevalent type of disability is independent living difficulty (difficulty doing errands alone such as visiting a doctor’s office or shopping) followed by ambulatory difficulty (serious difficulty walking or climbing stairs).

As age increases, so does the percentage of each age group that has disability. For residents who are 75 years and over, 45.9% have a disability. The 65 to 74 years age group constitutes the second-highest number of disabilities with 22.9%. Disability and poverty are closely tied due to employment limitations.

Many senior-headed households have special needs due to their relatively low incomes, disabilities or limitations, and dependency needs. Specifically, many people aged 65 years and older live alone. In Contra Costa County, 201,136 residents are 65 years and older, representing 17.4% of the population and approximately 7.0% live below poverty level.
146,147

Table 4-72 summarizes the estimates for the disabled population by disability type, age, race, and ethnicity within Contra Costa County.
148
Table 4-72. Disability Characteristics (2022)
Disability Type Estimate Percent
Hearing Difficulty 35,029 3.0%
Vision Difficulty 23,653 2.1%
Cognitive Difficulty 52,048 4.8%
Ambulatory Difficulty 57,988 5.3%
Self-Care Difficulty 25,797 2.4%
Independent Living Difficulty 52,546 5.8%
Age Estimate Percent
Under 5 years 428 0.7%
5 to 17 years 8,463 4.5%
18 to 34 years 18,358 7.8%
35 to 64 years 39,323 8.4%
65 to 74 years 26,084 22.9%
75 years and over 38,792 45.9%

146 United States Census Bureau. (2022). S0101: Age and Sex (2022: ACS 1-Year Estimates Subject Tables).

Retrieved from https://data.census.gov/table/ACSST1Y2022.S0101?g=050XX00US06013. 147 United States Census Bureau. (2021). S1701: Poverty Status in the Past 12 Months (2021: ACS 1-Year Estimates Subject Tables). Retrieved from https://data.census.gov/table/ACSST1Y2021.S1701?t=Income and Poverty:Official Poverty Measure:Poverty&g=050XX00US06013. 148 United States Census Bureau. (2022). S1810: Disability Characteristics (2022: ACS 1-Year Estimates Subject Tables). Retrieved from https://data.census.gov/table/ACSST1Y2022.S1810?g=050XX00US06013,53037. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 129 Race and Ethnicity Estimate Percent
White (not Hispanic or Latino) 60,307 13.6%
Black or African American 14,735 14.8%
American Indian and Alaska Native 14,735 10.4%
Asian 17,988 8.1%
Native Hawaiian and Other Pacific Islander 1,085 18.3%
Two (2) or More Races 16,292 9.0%
Some Other Race Alone 16,486 10.1%
Hispanic or Latino 28,798 9.3%

The median age of Contra Costa County residents is 40 years old. The population has been steadily aging since 1970, when the median age was about 28 years old. Since 2010, the fastest growing age group has been seniors 65 and older as the Baby Boomer generation ages. The second fastest growth occurred in the 55 to 64 age group, which includes younger Baby Boomers and older members of Generation X.
149

The majority of the population in Contra Costa County is White (40.9%), with the next highest percent being Hispanic or Latino (27.0%) and Asian (19.3%). Additionally, 27.0% of the population in Contra Costa County is foreign-born.
150 Other than English, the most commonly spoken language in the County is Spanish (18.7%). The United States Census Bureau estimates that 14.5% of the County’s residents speak English “less than very well.”151 Table 4-73 summarizes the vulnerable and at-risk population for earthquakes.

Table 4-73. Vulnerability and At Risk Population
Category Estimate Percent
Population with Disability 131,448 11.4%
65 Years and Over 201,136 17.4%
75 to 84 Years Old 61,365 5.3%
85 Years and Over 24,486 2.1%
Language Other than English 416,505 38.0%
Spanish Spoken at Home 204,442 18.7%
Speak English “Less than very
well”152 158,965 38.2%

149 Contra Costa County. (2023). Contra Costa County 2045 General Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2024/02/Contra-Costa-County-General-Plan_Public- Review-Draft_Combined.pdf.
150 United States Census Bureau. (2022). DP02: Selected Social Characteristics in the United States (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP02?g=050XX00US06013. 151 United States Census Bureau. (2022). S1601: Language Spoken at Home (2022: ACS 1-Year Estimates Subject Tables). Retrieved from https://data.census.gov/table/ACSST1Y2022.S1601?g=050XX00US06013. 152 Ibid.
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Chapter 4: Hazard Identification and Risk Assessment 130 Category Estimate Percent
Occupied Housing Unit: Mobile
Home153 5,363 1.3%
Homeless Population154 2,372 0.2%

Table 4-78 outlines the vulnerability of the total population exposed to earthquakes. Table 4-79 outlines earthquake impacts to population and life safety, underserved/equity population, and essential operations, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Property Damage and Critical Infrastructure: According to Contra Costa County Assessor records, the total replacement value of buildings as of 2023 is $266.7 Billion. 155 Since all structures in the planning
area are susceptible to earthquake impacts to varying degrees, this represents the property exposure to seismic events. Most of the buildings are residential. The greater potential danger is the collapse of older residential units built from reinforced masonry. Of the 415,194 occupied housing units in Contra Costa County, approximately 50.0% of the housing structures were built before the 1970s, prior to the implementation of substantial improvements to building codes and construction practices. Understanding the distribution of housing structures by age helps identify older and potentially more vulnerable buildings.

Table 4-74 outlines information on the age of the housing units, categorized by the period when they were built.
156
Table 4-74. Physical Housing Characteristics in Contra Costa County Structure Built
(Year) Estimate Percent
(of occupied housing)
2020 or Later 5,099 1.2%
2010 to 2019 25,087 6.0%
2000 to 2009 52,348 12.6%
1980 to 1999 114,930 27.7%
1960 and 1979 120,531 29.0%
1940 and 1959 79,758 19.2%
1939 or Earlier 17,441 4.2%

All critical facilities in the planning area are exposed to earthquake hazards. Hazardous materials releases can occur during an earthquake from fixed facilities or transportation related incidents.

Transportation corridors can be disrupted during an earthquake, leading to the release of materials to the surrounding environment. Facilities holding hazardous materials are of particular concern because of

153 United States Census Bureau. (2022). S2504: Physical Housing Characteristics for Occupied Housing Units (2022: ACS 1-Year Estimates Subject Tables). Retrieved from https://data.census.gov/table/ACSST1Y2022.S2504?g=050XX00US06013. 154 Contra Costa Health. (2023). Health, Housing, and Homelessness Data Reports (Point-in-Time Count).

Retrieved from https://www.cchealth.org/services-and-programs/homeless-services/data. 155 Contra Costa County. (2023). 2023-2024 County Assessment Roll. Retrieved from https://www.contracosta.ca.gov/DocumentCenter/View/79697/2023-2024-BOS-Close-of-Assessment-Roll-Letter- and-Reports-to-the-CCC-Board-of-Supervisors?bidId=.
156 United States Census Bureau. (2022). S2504: Physical Housing Characteristics for Occupied Housing Units (2022: ACS 1-Year Estimates Subject tables). Retrieved from https://data.census.gov/table/ACSST1Y2022.S2504?g=050XX00US06013. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 131 possible isolation of neighborhoods surrounding them. During an earthquake, structures storing these materials could rupture and leak into the surrounding area or an adjacent waterway, having a disastrous effect on the environment.

The following major roads in the planning area intersect moderate to very high liquefiable soils and thus are exposed to earthquakes:

• Interstate 680
• Interstate 80
• State Highway 160
• State Highway 242
• State Highway 4
• State Highway 4 Bypass
• Road 20
• Eastshore Freeway
• Grove Shafter Freeway
• John T Knox Freeway
• Byron Highway
• Pittsburg Antioch Highway
• Port Chicago Highway
• Branch Parkway
• Chilpancingo Parkway
• Garin Parkway
• John Muir Parkway
• Marina Bay Parkway
• Mountaire Parkway
• Richmond Parkway
• Rossmoor Parkway
• Village Parkway
• Vineyards Parkway
• Vintage Parkway
• Waterworld Parkway
• Windemere Parkway

There are a total of 554 critical assets (i.e., schools, nursing homes, fire stations, police stations, and hospitals) throughout the County and 100% of these assets are susceptible to earthquake impacts to varying degrees. Table 4-75 provides a breakdown of critical assets that are located within Contra Costa County.

Table 4-75. Critical Assets Vulnerable to Earthquakes
Asset Estimate Percent
(of total assets)
Schools (public schools, private schools) 360 100.0%
Nursing Homes 78 100.0%
Fire Stations 81 100.0%
Police Stations 24 100.0%
Hospitals 11 100.0%

Table 4-78 outlines the total property value exposed to earthquakes and how the changes in development in the past five (5) years, have affected the vulnerability of the community to earthquakes.

Table 4-79 outlines earthquake impacts on total property damage, potential future development, and the economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 132 Building damage as a result of the magnitude 5.8 earthquake analysis was estimated using Hazus. In addition, annualized losses were calculated. Refer to the Hazus portion at the end of this section (Section

4.6.4.7).

Environment: Environmental problems as a result of an earthquake can be numerous and secondary hazards will likely have some of the most damaging effects on the environment. Earthquake induced landslides can significantly damage the surrounding habitat. It is also possible for streams to be rerouted after an earthquake. Rerouting can change the water quality, possibly damaging habitat and feeding areas.

Table 4-79 outlines earthquake impacts on the environment and the economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Changes in Development and Impact of Future Development: The County population has grown by

0.4% since completion of the previous Plan (in the last five (5) years) which slightly result in additional people at risk from an earthquake. Growth in structures has accompanied population growth, although the number of housing units has not matched the overall increase. Much of the population growth has occurred in eastern sections of the County which are less likely to be exposed to seismic hazards.

Changes in development have had minimal impact on vulnerability (between 5% and 9%) or expected losses due to earthquake. However, the Bay Area Association of Governments (ABAG) growth forecast predicts a steady increase in households through 2050. From 2015 to 2050, ABAG projects that the County’s number of households will grow by 44%.
157 This increase in development will significantly
increase the impact of an earthquake in the planning area.

Table 4-78 outlines how the changes in development in the past five (5) years have affected the vulnerability of the community to earthquakes. Table 4-79 outlines the earthquake impacts on potential future development, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Effects of Climate Change in Severity of Impacts: The exact nature and extent of this impact still needs to be studied and fully understood as it pertains to climate change. However, climate change can increase the risk of earthquake cascading hazards (e.g., landslides, tsunamis, flooding). The impacts of climate change for landslides, tsunamis, and flooding will be addressed separately in this Plan.

Table 4-79 outlines the climate change impacts to earthquakes in Contra Costa County, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

157 Bay Area Association of Government. (2020). Plan Bay Area 2050 Final Blueprint Growth Pattern. Retrieved from https://planbayarea.org/digital-library/plan-bay-area-2050-final-blueprint-growth-pattern. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 133 Table 4-76. Probability of Occurrence
Hazard Event Probability of Occurrence Probability
Factor
Weighted
Factor
Earthquake Medium Significant hazard event is likely to occur within 25 years. 2 N/A Table 4-77. Extent Factors
Hazard Event Extent Factor Extent Extent
Factor
Weighted
Factor
Earthquake
Extent/Intensity High Historical and/or probabilistic models/studies for this hazard indicate the possibility of a high-intensity incident. 3 9 Catastrophic High Catastrophic hazard event is likely to occur at least once in 10 years. 3 9
Table 4-78. Vulnerability Factors
Hazard Event Vulnerability Factor Vulnerability Vulnerability Factor
Weighted
Factor
Earthquake
Population Exposure High 30% or more of the population is exposed to the hazard. 3 9 Property Exposure High 25% or more of the total assessed property value is exposed to the hazard. 3 6
Changes in
Development Medium
Changes in development have increased the
vulnerability/exposure of the community to the hazard
between 5% and 9%.
2 2
Table 4-79. Impact Factors
Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Earthquake
Population and Life
Safety High
Populations exposed to this hazard are likely to experience significant adverse impacts, such as fatalities and severe injuries.
3 9
Underserved/Equity High
Underserved populations exposed to the hazard are likely to experience significant adverse/disproportionate impacts, such as fatalities and severe injuries.
3 9
Property Damage High
More than $5 Million in property damages is expected from a single major hazard event, or damages are expected to occur to 15% or more of the property value within the jurisdiction. 3 6
Economic High Where the total economic impact is likely to be greater than $10 Million. 3 3
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Chapter 4: Hazard Identification and Risk Assessment 134 Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Environmental High
Environmental impact from a single major hazard event is likely to be significant, requiring extensive outside resources and support; and/or repair, clean-up, restoration, and/or preservation work.
3 3
Essential Operations High
Impact greater than 72 hours on the ability of the jurisdiction to meet the essential day-to-day operational demands and needs of the community from a single major hazard event. 3 3
Future Development High Future development trends will significantly increase the impact/consequence of this hazard. 3 3
Climate Change No Impact Climate change trends will not increase the risk of the hazard and its impacts. 0 0

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Chapter 4: Hazard Identification and Risk Assessment 135 HAZUS
Scenario: Magnitude 5.8 Event
Building damage as a result of the magnitude 5.8 earthquake analysis was estimated using Hazus. In addition, annualized losses were calculated. Hazus estimates that there are 341,000 buildings in the region which have been an aggregated total replacement of $218.5 Million. Approximately 91.0% of the buildings are associated with residential housing. Table 4-80 provides a general distribution of the building value within Contra Costa County. In terms of building construction types found in the County, wood frame construction makes up 89.0% of the building inventory and the remaining 11.0% is distributed between the other general building types (i.e., steel, concrete, precast, reinforced masonry, unreinforced masonry, manufactured housing).

Table 4-80. Contra Costa County Population and Building Value Data Population Residential Building
Value
Non-Residential
Building Value Total
1,165,927 $158.1 Million $60.3 Million $218.5 Million

The total economic loss estimated for the earthquake is $17.345 Million, which includes building and lifeline related losses based on the region's available inventory. HAZUS estimates that about 47,683 buildings will be at least moderately damaged. This is over 14% of the buildings in the region. There are an estimated 1,094 buildings that will be damaged beyond repair. Table 4-81 summarizes the expected building damage by general occupancy within Contra Costa County.

Table 4-81. Expected Building Damage by Occupancy
Damage
Level None Slight Moderate Extensive Complete
Occupancy Count % Count % Count % Count % Count %
Agriculture 353 0.20 207 0.18 140 0.34 41 0.75 8 0.74
Commercial 7,411 4.21 4,763 4.05 4,189 10.18 1,379 25.40 249 22.78 Education 317 0.18 182 0.15 118 0.29 32 0.58 4 0.38
Government 2,265 1.29 1,249 1.06 1,080 2.62 368 6.77 62 5.68 Industrial 1,815 1.03 1,204 1.02 1,197 2.91 439 8.09 93 8.51 Other
Residential 13,172 7.48 9,568 8.13 4,763 11.57 1,360 25.05 261 23.86 Religion 543 0.31 333 0.28 251 0.61 84 1.54 16 1.43
Single Family 150,185 85.30 100,201 85.13 29,421 71.48 1,728 31.82 401 36.62 TOTAL 176,060 117,707 41,159 5,430 1,094

Table 4-82 summarizes the expected damage by general building type.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 136 Table 4-82. Expected Building Damage by Building Type
Building
Type
None Slight Moderate Extensive Complete
Count % Count % Count % Count % Count %
Wood 161,766 91.88 109,256 92.82 32,226 78.30 1,843 33.94 453 41.43 Steel 2,761 1.57 1,698 1.44 1,989 4.83 734 13.51 140 12.81 Concrete 3,133 1.78 2,090 1.78 1,612 3.92 601 11.07 101 9.20 Precast 1,840 1.04 1,223 1.04 1,415 3.44 524 9.64 83 7.63 Reinforced
Masonry 5,476 3.11 2,192 1.86 2,144 5.21 772 14.21 73 6.65 Unreinforced
Masonry 631 0.36 533 0.45 559 1.36 242 4.45 99 9.08
Manufactured
Housing 453 0.26 714 0.61 1,213 2.95 716 13.18 144 13.20 TOTAL 176,060 117,707 41,159 5,430 1,094

Hazus breaks critical facilities into two (2) groups – essential facilities (i.e., hospitals, medical clinics, schools, fire stations, police stations and emergency operations center) and high potential loss facilities (i.e., dams, levees, military installations, nuclear power plants and hazardous material sites). For essential facilities, there are 14 hospitals in the County with a total bed capacity of 1,804 beds. There are 384 schools, 78 fire stations, 35 police stations and two (2) emergency operation centers. With respect to high potential loss facilities, there are no dams identified within the inventory. The inventory also includes no hazardous material sites, no military installations and no nuclear power plants.

The Hazus model estimates the time to restore critical facilities to fully functional use. Before the flood event, Contra Costa County had 1, 804 hospital beds available for use. On the day of the flood event, Hazus estimates that 893 hospital beds (50.0%) are available for use by patients already in the hospital and those injured by the earthquake. After one (1) week, 71.0% of the beds will be back in service and

91.0% will be operational after 30 days. Table 4-83 summarizes the expected damage to essential facilities in Contra Costa County. 301 (58.7%) essential facilities are expected to have functionality greater than 50% one (1) day after the earthquake event.

Table 4-83. HAZUS Earthquake Expected Damage to Essential Facilities Facility Total
At Least
Moderate
(Greater than
50% damage)
Complete
(Greater than
50% damage)
With
Functionality
(Greater than
50% on day 1)
Hospitals 14 4 0 9
Schools 384 55 0 225
Emergency Operations Center 2 1 0 1
Police Stations 35 8 0 22
Fire Stations 78 8 0 53
TOTAL 513 76 0 301

Hazus divides the lifeline inventory between transportation and utility lifeline systems. There are seven (7) transportation systems (i.e., highways, highways, railways, light rail, bus, ports, ferry and airports) and 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 137 six (6) utility systems (i.e., potable water, wastewater, natural gas, crude and refined oil, electric power and communications). Hazus estimates that the total value of the lifeline inventory (transportation and utility) is over $28.9 Million which includes 344.9 miles of highways, 613 bridges, and 9,751.2 miles of pipeline (potable water, wastewater, natural gas, and oil). Table 4-84 summarizes the expected damage to utility systems in Contra Costa County. All utility systems are expected to have functionality greater than 50% on day seven (7) after the earthquake event.

Table 4-84. Expected Damage to Utility Systems
System Total
Number of Locations
With at Least
Moderate Damage
With Complete
Damage
With Functionality
Greater than 50%
After Day 1 After Day 7
Potable Water 6 5 0 0 6
Wastewater 14 1 0 0 14
Natural Gas 0 0 0 0 0
Oil Systems 11 1 0 0 11
Electrical Power 22 13 0 11 22
Communication 9 2 0 9 9

For the transportation systems, HAZUS calculates the direct repair cost for each component only. Table 4-85 provides damage estimate for the transportation systems.

Table 4-85. Expected Damage to the Transportation Systems System Component
Number of Locations
Locations /
Segments
With at
Least
Moderate
Damage
With
Complete
Damage
With Functionality
Greater than 50%
After Day 1 After Day 7
Highway
Segments 408 0 0 408 408
Bridges 613 1 0 612 613
Tunnels 5 0 0 5 5
Railways
Segments 97 0 0 97 97
Bridges 123 0 0 123 123
Tunnels 2 0 0 2 2
Facilities 10 0 0 10 10
Light Rail
Segments 1 0 0 1 1
Bridges 26 0 0 26 26
Tunnels 0 0 0 0 0
Facilities 3 0 0 3 3
Bus Facilities 0 0 0 0 0
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Chapter 4: Hazard Identification and Risk Assessment 138 System Component
Number of Locations
Locations /
Segments
With at
Least
Moderate
Damage
With
Complete
Damage
With Functionality
Greater than 50%
After Day 1 After Day 7
Ferry Facilities 4 0 0 4 4
Port Facilities 77 0 0 77 77
Airport
Facilities 3 0 0 3 3
Runways 6 0 0 6 6

Earthquakes also impact the economy, including loss of business function, damage to inventory (i.e., buildings, transportation, and utility systems), relocation costs, wage loss, and rental loss due to repair and replacement of buildings. Hazus estimates building-related economic losses, including income losses (i.e., wage, capital-related, rental, and relocation losses) and capital stock losses (i.e., structural, non-structural, content, and inventory losses).

Hazus estimates total building related losses were $14.894 Million where 14.0% of the losses were related to business interruption in Contra Costa County. The analysis concluded that the largest loss was sustained by the residential occupancies, which comprised 52% of the total loss. Table 4-86 summarizes the building related economic loss estimates.

Table 4-86. Building Related Economic Loss Estimates
(Millions of Dollars)
Area Single
Family
Other
Residential Commercial Industrial Others Total
Income
Losses
Wage 0.0 43.7 360.7 30.6 60.3 495.3
Capital-
Related 0.0 18.6 294.6 18.5 8.7 340.3
Rental 72.6 98.4 156.5 11.8 37.1 376.5
Relocation 263.7 67.0 258.4 48.2 177.0 814.2
TOTAL 336.3 227.7 1,070.1 109.0 283.0 2,026.2
Capital
Stock
Losses
Structural 670.4 175.6 467.1 227.9 216.2 1,575.2
Non-
Structural 3,616.5 1,188.9 1,460.1 747.6 789.9 7,803.0
Content 1,176.7 301.3 728.1 504.7 384.7 3,095.6
Inventory 0.0 0.0 117.1 84.4 10.3 211.8
TOTAL 5,463.7 1,665.8 2,772.3 1,564.6 1,401.1 12,867.5
SUBTOTAL 5,800.0 1,893.5 3,842.7 1,673.7 1,684.1 14,893.7

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 139 Table 4-87 provides a detailed breakdown in transportation system economic losses in Millions of dollars.

Table 4-87. HAZUS Earthquake Transportation System Economic Losses (Millions of Dollars)
System Component Inventory Value Economic Loss Loss Ratio (%) Highway
Segments 4,025.6 0.0 0.0
Bridges 5,593.8 97.2 1.74
Tunnels 92.1 2.2 2.37
TOTAL 9,711.5 99.4 -
Railways
Segments 4,328.5 0.0 0.0
Bridges 699.9 10.8 1.54
Tunnels 1.8 0.1 3.12
Facilities 26.6 5.4 20.40
TOTAL 5,056.7 16.3 -
Light Rail
Segments 263.2 0.0 0.0
Bridges 3.3 0.0 1.18
Tunnels 0.0 0.0 0.0
Facilities 17.1 3.3 18.94
TOTAL 283.6 3.3 -
Bus
Facilities 0.0 0.0 0.0
TOTAL 0.0 0.0 -
Ferry
Facilities 5.3 0.0 0.0
TOTAL 5.3 0.0 -
Port
Facilities 293.5 56.4 19.21
TOTAL 293.5 56.4 -
Airport
Facilities 24.0 5.3 22.14
Runways 40.5 0.0 0.0
TOTAL 64.5 5.3 -
SUBTOTAL 15,415.1 180.6 -

HAZUS estimates the number of households that are expected to be displaced from their homes due to the earthquake incident and the number of displaced individuals that will require accommodations in temporary public shelters. The model estimates 5,333 households will be displaced due to the earthquake. Of these, 2,628 people (out of a total population of 1,165,927) will seek temporary shelter in public shelters.

Hazus estimates the amount of debris that will be generated by the earthquake event. Debris estimates were divided into two (2) categories – brick/wood and reinforced concrete/steel. The distinction is made because of the different types of materials handling equipment required to handle debris. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 140 The analysis estimated that a total of 1,761 million tons of debris will be generated. Of the total amount,

37.0% is comprised of brick/wood and the remainder will be reinforced concrete/steel. If the debris tonnage is converted to an estimated number of truckloads, it will require 70,440 truckloads (25 tons/truck) to remove the debris.

4.6.4.8. FEMA NRI Expected Annual Loss
An earthquake NRI EAL score, and rating represent a community's relative level of expected building and population loss each year due to earthquakes when compared to the rest of the United States. The EAL score is positively associated to a community’s risk; therefore, a higher EAL score results in a higher Risk Index score. Table 4-88 outlines the earthquake EAL for Contra Costa County.

Table 4-88. Earthquake Expected Annual Loss (FEMA National Risk Index) Jurisdiction Population
Equivalence
Building
Value
Agriculture
Value
Total
Expected
Annual
Loss
Expected
Annual
Loss
Score
Rating
Contra Costa
County
$156.4
Million
$410.1
Million n/a $566.5
Million 99.8 Very High
Expected annual loss scores are calculated utilizing an equation that combines values for exposure, annualized frequency, and historic loss ratios (Expected Annual Loss = Exposure x Annualized Frequency x Historic Loss Ratio).

4.6.4.9. FEMA Earthquake Risk Index Score
The earthquake Risk Index score and rating represent a community's relative risk for earthquakes when compared to the rest of the United States. Table 4-89 illustrates the earthquake Risk Index rating and score for Contra Costa County.

Table 4-89. Earthquake Risk Index (FEMA National Risk Index) Jurisdiction Rating Score
Contra Costa County Very High 99.8
Risk Index scores are calculated using an equation that combines scores for Expected Annual Loss due to natural hazards, Social Vulnerability and Community Resilience (Expected Annual Loss x Social Vulnerability / Community Resilience = Risk Index).

2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 141 Table 4-90 represents the Earthquake Failure Total Risk Score for Contra Costa County, based on the Risk Assessment Methodology, as defined in this Plan. For further details on how the probability, extent, vulnerability, and impact factors were calculated, please refer to Table 4-76 through Table 4-79.

Additional details on how the Total Risk Score was calculated can be found in the Risk Assessment Methodology in Section 4.3 of this Plan.

Table 4-90. Earthquake Total Risk Score
Hazard
Event
Probability Consequence Total Risk
Probability
Factor Extent Vulnerability Impact Consequence
Score
Total Risk
Score*
Earthquake 2 18 17 36 71 68
Consequence: Sum of all weighted factors.

Extent: Sum of the weighted Extent factors.

Vulnerability: Sum of the weighted Vulnerability factors.

Impact: Sum of the weighted Impact factors.

The Total Risk Score is a measure of Probability and Consequence.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 142

4.6.5. Flood

4.6.5.1. Description
Floods are the most common and widespread of all weather-related natural disasters and result in more deaths each year than tornadoes, hurricanes, and lightning. A flood is defined as an overflowing of water onto dry land which occurs when the existing channel of a stream, river, canyon, or other watercourses cannot contain excess runoff from rainfall or snowmelt. Table 4-91 lists and describes the different types of flood. Flooding can be damaging, and it can happen with only a few inches of water or covering a house up to the rooftop. Additionally, floods can occur within a few minutes or over a long period of time, and last days, weeks, or longer.
158
Table 4-91. Flood Types 159
Type Description
River Flood
Occurs when water levels rise over the top of riverbanks due to excessive rain from tropical systems making landfall, persistent thunderstorms over the same area for extended periods of time, combined rainfall and snowmelt, or an ice jam.

Inland Flooding
Occurs when moderate precipitation accumulates over several days, intense precipitation falls over a short period, or a river overflow because of an ice or debris jam or dam or levee failure.

Flash Flood
Occurs during heavy or excessive rainfall in a short period of time, generally less than six (6) hours. Flash floods are usually characterized by raging torrents after heavy rains that rip through riverbeds, urban streets, or mountain canyons. They can occur within minutes or a few hours of excessive rainfall. They can also occur even if no rain has fallen, for instance after a levee or dam has failed, or after a sudden release of water by a debris or ice jam.

Coastal Floods
Caused by higher than average high tide and worsened by heavy rainfall and onshore winds (i.e., wind blowing landward from the ocean); the inundation of land areas along the coast.

Storm Surge
An abnormal rise in water level in coastal areas, over and above the regular astronomical tide, caused by forces generated from a severe storm's wind, waves, and low atmospheric pressure.

A floodplain is an area adjacent to a river, creek, or lake that is subject to recurring floods which can provide environmental and flood reduction benefits . 160 Floodplains may change over time from natural processes, changes in the characteristics of a watershed, or human activity (e.g., construction). River channels change as water moves downstream, acting on the channel banks and the bottom of the channel. Outside a channel curve, the banks are subject to erosion as the water scours against them.

On the inside of a channel curve, the banks receive deposits of sand and sediment transferred from the eroded sites. In areas where flow contains a high-sediment load, the course of a river or stream may shift dramatically during a single flood event.

Flooding in Contra Costa County is typically caused by high-intensity, short-duration (1 to 3 hours) storms concentrated on a stream reach with already saturated soil. Two (2) types of flooding are typical – flash

158 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Flood Basics. Retrieved from https://www.nssl.noaa.gov/education/svrwx101/floods/.
159 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Floods. Retrieved from https://www.nssl.noaa.gov/education/svrwx101/floods/types/. 160 Contra Costa County Public Works Department. (2020). Contra Costa County Floodplain Management Program. Retrieved from https://www.contracosta.ca.gov/DocumentCenter/View/8558/Floodplain-Pamphlet- January-2020-PDF?bidId=.
2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 143 floods and riverine flooding. Flash floods that occur suddenly after a brief, but intense downpour , move rapidly, end suddenly, and can occur in areas not generally associated with flooding (e.g., subdivisions not adjacent to a water body and areas serviced by underground drainage systems). Although the duration of these events is usually brief, the damage they cause can be severe. Flash floods cannot be forecast accurately. Riverine floods described in terms of their extent (including the horizontal area affected and the vertical depth of floodwater) and the related probability of occurrence (expressed as the percentage chance that a flood of a specific extent will occur in any given year).

4.6.5.2. Hazard Location
In California, 90% of the natural disasters are flood related. In Contra Costa County, flooding is predominantly confined within traditional riverine valleys. Locally, some natural or human-caused levees separate channels from floodplains and cause independent overland flow paths. Occasionally, railroads, highways, or canal embankments form barriers, resulting in ponding or diversion of the flow. Some localized flooding not associated with stream overflow can occur where there are no drainage facilities to control flows or when runoff volumes exceed the design capacity of drainage facilities. There are 87 creeks, channels, and bodies of water, listed in Table 4-92, that are considered principal flooding sources in the County. 161
Table 4-92. Contra Costa County Flooding Sources
Along Giant Road from Standard
Oil to Rheem Creek Ivy Drive Tributary Pinole Creek
Appian Creek Jonas Hill Creek Refugio Creek
Arroyo Del Hambre Creek Kirker Creek Reliez Creek
Brookside Road Tributary Lafayette Creek Rheem Creek Radeo Creek Carquinez Straight Laguna Creek Sand Creek
Cascade Creek Larch Creek San Francisco Bay
Cerrito Creek Las Trampas Creek San Pablo Bay
Clayton Valley Drain Lauterwasser Creek San Pablo Creek Corliss Drive Tributary Lawlor Creek San Ramon Creek
Deer Creek Line A, DA-40 San Ramon Creek Overflow
Ditch No. 2 Los Medanos Wasteway Sans Crainte Creek
Donner Creek Mangini Creek Sans Crainte Creek Tributary A Dutch Slough Markley Creek Shore Acres Creek
East Antioch Creek Marsh Creek South Branch Moraga Creek Each Branch Green Valley Creek Middle Branch West Antioch Creek South San Ramon Creek (overbank flooding)
East Branch Homestead Creek Miranda Creek South San Ramon Creek East Branch Refugio Creek Mitchell Creek St. Marys Road Tributary East Fork Grayson Creek Moraga Creek Stone Valley Creek

161 Federal Emergency Management Agency. (2017). Flood Insurance Study: Contra Costa County, California and Incorporated Areas. Retrieved from https://www.contracosta.ca.gov/DocumentCenter/View/77626/Volumes-I- V?bidId=.
2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 144 Eccleston Avenue Tributary Mount Diablo Creek Suisun Bay Farm Bureau Road Drain Mount Diablo Split Flow Sycamore Creek Galindo Creek Murderers Creek Tice Creek
Garrity Creek North Branch Reliez Creek Tice Creek Overflow Grayson Creek North Branch Stone Valley Creek Walnut Creek Green Valley Creek Orinda Village Overflow West Antioch Creek Grizzly Creek Overhill Creek West Branch Alamo Creek
Happy Valley Creek Overland Cross Section West Branch East Antioch Creek Hidden Valley Creek Pacheco Creek West Branch Refugio Creek Hillcrest Branch East Antioch
Creek Payton Slough Wildcat Creek
Homestead Creek Pine Creek Willow Creek

The Flood Insurance Rate Maps (FIRMs) show the flood zones, floodplain boundaries, and Base Floor Elevation (BFE) and are used for floodplain management, flood insurance ratings, and to determine flood insurance requirements. These maps show areas with a 1% chance of flooding each year, commonly known as the 100-year floodplains, and are shown as the Special Flood Hazard Areas (SFHA) in the FIRM maps. 162 The 500-year floodplains show areas with a 0.2% chance of flooding each year. Figure 4-15 illustrates the Contra Costa County SFHA, including each Flood Zone, and the 500-year floodplain.

162 Ibid.
2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 145 Figure 4-15. Contra Costa County Floodplain

4.6.5.3. Hazard Extent/Intensity
The magnitude of flooding that is used as the standard for floodplain management in the United States is a flood with a probability of occurrence of 1% in any given year. This flood is also known as the 100- year flood or base flood. The most readily availa ble source of information regarding the 100-year flood, as well as the 500-year flood (0.2 % probability of occurrence in any given year), is the FIRMs prepared by FEMA. These maps are used to support NFIP.

4.6.5.4. Warning Time
Flooding can be unexpected and leaves a small window of time for evacuation, if it is required. The National Weather Service San Francisco Bay Area Forecast Office is responsible for issuing flood advisories in Contra Costa County. Table 4-93 outlines the flood advisories issued by the NWS as conditions warrant.

2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 146 Table 4-93. NWS Flood Advisories
Type Definition
Flood Advisory
Issued when a flood event warrants notification but is less urgent than a warning.

Advisories are issued for conditions that could cause a significant inconvenience, and if caution is not exercised, could lead to situations that may threaten life and/or property.

Flood Watch
Issued to indicate current or developing conditions that are favorable for flooding. The occurrence is neither certain nor imminent. A watch is typically issued within several hours to days ahead of the onset of possible flooding. In situations where a river or stream is expected to be the main source of the flooding, forecast confidence may allow for a Flood Watch to be issued several days in advance.

Flood Warning
Issued to inform the public of flooding that poses a serious threat to life and/or property. A Flood Warning may be issued hours to days in advance of the onset of flooding based on forecast conditions. Floods occurring along a river usually contain river stage (level) forecasts.

Flash Flood Watch
Issued to indicate current or developing conditions that are favorable for flash flooding.

The occurrence is neither certain nor imminent. A watch is typically issued within several hours to days ahead of the onset of possible flash flooding.

Flash Flood Warning
Issued to inform the public, emergency management and other cooperating agencies that flash flooding is in progress, imminent, or highly likely. Flash Flood Warnings are urgent messages as dangerous flooding can develop very rapidly, with a serious threat to life and/or property. Flash Flood Warnings are usually issued minutes to hours in advance of the onset of flooding.

NWS issues Flash Flood Warnings Impact-Based Warnings for events that occur within approximately six (6) hours of heavy rainfall. The flash flood impact-based warnings fall into the three (3) categories listed in Table 4-94. 163
Table 4-94. NWS Flash Flood Impact Based Warnings
Type Definition
Base Used most of the time when flash flood impact is possible.

Considerable
Used rarely, when there are indications flash flooding capable of unusual severity or impact is imminent or ongoing and urgent action is needed to protect lives and property. Will trigger the Wireless Emergency Alert system.

Catastrophic
Used exceedingly rarely, when a flash flood threat to life and catastrophic damage is occurring or is imminent, and floodwaters have risen or will rise to levels rarely if ever seen. Will trigger the Wireless Emergency Alert system.

When a river reaches flood stage, NWS River Forecast Centers convey the magnitude of observed forecast flooding using flood severity categories based on property damage and public threat. The three (3) flood severity categories are listed in Table 4-95. 164

163 National Weather Service. (2019). Impact-Based Flash Flood Warning. Retrieved from https://www.weather.gov/media/wrn/FFW-IBW-factsheet.pdf. 164 National Oceanic and Atmospheric Administration, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Frequently Asked Questions About Floods. Retrieved from https://www.nssl.noaa.gov/education/svrwx101/floods/faq/. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 147 Table 4-95. NWS River Flood Severity Categories
Type Definition
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.

4.6.5.5. Probability and Frequency
The probability of occurrence for flooding in Contra Costa County is medium because significant occurrences of this hazard are likely to occur within 25 years. However, isolated and lower-impact events occur with recurrent regularity. The number of years between floods of any given severity significantly varies due to a naturally changing climate. According to USGS, the reoccurrence interval is based on the probability that the given event will be equaled or exceeded in any given year based on past occurrences.

The concept of reoccurrence intervals and probabilities is outlined in Table 4-96. 165
Table 4-96. Recurrence Intervals and Probabilities of Occurrences Recurrence Interval
(years)
Probability of Occurrence
In any Given Year
Percent Chance of
Occurrence in Any Given Year
100 1 in 100 1
50 1 in 50 2
25 1 in 25 4
10 1 in 10 10
5 1 in 5 20
2 1 in 2 50
Probability of Future Hazard Events
The FEMA NRI analyses flooding data as riverine flooding – when streams and rivers exceed the capacity of their natural or constructed channels to accommodate water flow and water overflows the banks, spilling out into adjacent low -lying, dry land.
166 The riverine flooding annualized frequency value
represents the average number of recorded riverine flooding hazard occurrences, in event days, per year over the period of record (24 years). Table 4-97 outlines the annualized frequency for riverine flooding, based on FEMA NRI data, for Contra Costa County.

Table 4-97. Riverine Flooding Annualized Frequency (FEMA National Risk Index) Location Events on Record
(1996 – 2019) Annualized Frequency
Contra Costa County 31 1.3 events per year
Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year.

165 United States Geological Surve, New Jersey Water Science Center. (n.d.). Floods: Recurrence Intervals and 100-Year Floods. Retrieved from https://www.usgs.gov/centers/new-jersey-water-science-center/floods- recurrence-intervals-and-100-year-floods#data.
166 Federal Emergency Management Agency. (n.d.). FEMA National Risk Index: Riverine Flooding. Retrieved from https://hazards.fema.gov/nri/riverine-flooding.
2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 148 Repetitive Loss and Severe Repetitive Loss Properties
FEMA defines a R epetitive Loss property as an NFIP -insured property meeting at least one (1) of the following paid loss criteria since 1978, regardless of any changes in ownership:

• Four (4) or more separate claims payments greater than $5,000 each (including building and contents payment).
• Two (2) or more separate flood insurance claims payments (building payments only), where the total of the payments is greater than the property’s current value.

Additionally, to receive a designation, at least two (2) of the claim payments must occur within 10 years of one another.
167

A Severe Repetitive Loss property is defined by FEMA as any NFIP-insured single-family or multi-family residential building meeting at least one (1) of the following paid loss criteria since 1978 or from building constructed after 1978, regardless of any changes in ownership:

• That has incurred flood-related damage for which four (4) or more separate claims payments have been made, with the amount of each claim (including building and contents payments) exceeding $5,000, and with the cumulative amount of such claims payments exceeding $20,000. • For which at least two (2) separate claims payments (building payments only) have been made under such coverage, with the cumulative amount of such claims exceeding the market value of the building.
168

Additionally, to receive designation, at least (2) of the claims must be within 10 years of each other .

Claims within 10 days of each other will be counted as one (1) claim.

Refer to Section 3.11 of this Plan for a list of Contra Costa County jurisdictions participating in the NFIP and CRS.

Table 4-98 summarizes FEMA Repetitive Loss and Severe Repetitive Loss properties for each of the participating jurisdictions in Contra Costa County.
169

167 Federal Emergency Management Agency, National Flood Insurance Program. (2023). A Policyholder’s Guide to Severe Repetitive Loss. Retrieved from https://agents.floodsmart.gov/sites/default/files/fema_nfip- policyholders-guide-severe-repetitive-loss_brochure_07-2023.pdf. 168 Federal Emergency Management Agency, National Flood Insurance Program. (2021). National Flood Insurance Program: Flood Insurance Manual. Retrieved from https://www.fema.gov/sites/default/files/documents/fema_nfip-all-flood-insurance-manual-apr-2021.pdf. 169 Federal Emergency Management Agency. (2024). OpenFEMA Dataset: NFIP Multiple Loss Properties - v1.

Retrieved from https://www.fema.gov/openfema-data-page/nfip-multiple-loss-properties-v1. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 149 Table 4-98. Contra Costa County Repetitive Loss and Severe Repetitive Loss Properties Jurisdiction
Total
Repetitive Loss
Properties
Total Severe
Repetitive Loss
Properties
Mitigated Repetitive
Loss and Severe
Repetitive Loss
Properties
Contra Costa County
22 (13 Single Family; 2 Two
(2)-Four (4) Unit Residential
Building; 1 More than Four
(4) Units Residential
Building; 3 Single-Family
Residential Building; 1
Residential Condo; 2 Non-
Residential Building)
2 (1 Single Family; 1 More
than Four (4) Units
Residential Building)
1 (1 Single Family)
City of Brentwood 0 0 0
City of Clayton 0 0 0
Town of Danville 0 0 0
City of El Cerrito
3 (2 Single Family; 1
Residential (2, 3, or 4 units)
Non-Condo Building)
0 0
City of Hercules 0 0 0
City of Lafayette
2 (1 Single Family; 1 More
than Four (4) Units
Residential Building)
0 0
City of Martinez
11 (4 Single Family; 3 Non-
Residential Building; 2 Two
(2)-Four (4) Unit Residential
Building; 1 Single Family
Residential Building; 1
Residential Non-Condo
Building)
1 (1 Single Family) 0
Town of Moraga 0 0 0
City of Oakley 0 0 0
City of Orinda
2 (1 Single Family Residential
Building; 1 Non-Residential
Building)
0 0
City of Pinole 0 0 0
City of Pleasant Hill 3
(3 Single Family) 0 1
(1 Single Family)
City of Richmond
5 (4 Single Family; 1 Non-
Residential Building)
1 (1 Single Family)
1 (1 Single Family)
City of San Pablo 7
(7 Single Family) 0 0
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Chapter 4: Hazard Identification and Risk Assessment 150 Jurisdiction
Total
Repetitive Loss
Properties
Total Severe
Repetitive Loss
Properties
Mitigated Repetitive
Loss and Severe
Repetitive Loss
Properties
City of San Ramon 1
(1 Single Family) 0 0
City of Walnut Creek 3
(3 Single Family)
1 (1 Single Family)
3 (1 Single Family; 2 Two (2)-
Four (4) Unit Residential
Building)
Occupancy Type: Single Family = Single family residence • Two (2)-Four (4) Unit Residential Building = Two (2)-four (4) unit residential building • More Than Four (4) Units Residential Building = Residential building with more than four (4) units • Non-Residential Building = Non-residential building • Non-Residential Business = Non-residential business • Single Family Residential Building = Single-family residential building with the exception of a mobile home or a single residential unit within a multi-unit building • Residential (2, 3, or 4 units) Non-Condo Building = Residential non-condo building with two (2), three (3), or four (4) units seeking insurance on all units • Residential (5 or more units) Non-Condo Building = Residential non-condo building with 5 or more units seeking insurance on all units • Residential Mobile/Manufactured Home = Residential mobile/manufactured home • Residential Condo Association = Residential condo association seeking coverage on a building with one (1) or more units • Single Residential Unit = Single residential unit within a multi-unit building • Non-Residential Mobile/manufactured Home = Non-residential mobile/manufactured home • Non-Residential Building = Non-residential building • Non-Residential Unit = Non-residential unit within a multi-unit building

4.6.5.6. Past Events
The National Center of Environmental Information (NCEI) has reported 58 flood events between 19 50 and 2023 in Contra Costa County. Additionally, there have been eight (8) flood disasters declared in Contra Costa County between 1950 and 2023. A notable event occurred between December 26, 2022, through January 17, 2023, a series of six (6) storm systems moved through the San Francisco Bay area resulting in widespread flooding, including river flooding. In Contra Costa County, the event resulted in a series of Flood Warnings and rainfall amounts ranged from 6.2 inches to 20.07 inches. 170 On January 9, 2023, a Major Disaster Declaration (DR-3591) was issued for this event.

Table 4-99 lists flood events that have occurred in the Contra Costa County between 1950 and 2023 according to NCEI.

Table 4-99. Flood Events (1950 – 2023)
Location
County /
Zone State Date Time Type Death Injury
Property
Damage
Crop
Damage
CAMEO ACRES Contra Costa
County CA 12/27/2022 06:00 Flood 0 0 0.01K 0.00K

SAN FRANCISCO

BAY SHORELINE
San Francisco
Bay Shoreline CA 1/12/2021 11:00 Coastal
Flood 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
San Francisco
Bay Shoreline CA 1/11/2021 10:30 Coastal
Flood 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
San Francisco
Bay Shoreline CA 12/14/2020 10:48 Coastal
Flood 0 0 0.00K 0.00K
SAN RAMON Contra Costa
County CA 1/16/2020 11:09 Flood 0 0 0.00K 0.00K
MARTINEZ Contra Costa
County CA 1/16/2020 09:31 Flood 0 0 0.00K 0.00K
PACHECO Contra Costa
County CA 12/7/2019 14:28 Flood 0 0 0.00K 0.00K
WALNUT CREEK Contra Costa
County CA 11/26/2019 20:15 Flood 0 0 0.00K 0.00K
ORINDA Contra Costa
County CA 3/6/2019 05:13 Flood 0 0 0.00K 0.00K

170 National Weather Service, San Francisco Bay Area, California Weather Forecast Office. (2023). A Parade of Storms Impact Bay Area. Retrieved from https://www.weather.gov/mtr/AtmosphericRivers_12_2022-01_2023. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 151 Location
County /
Zone State Date Time Type Death Injury
Property
Damage
Crop
Damage
LAS JUNTAS Contra Costa
County CA 3/6/2019 02:17 Flood 0 0 0.00K 0.00K
HOOKSTON Contra Costa
County CA 2/26/2019 04:35 Flood 0 0 0.00K 0.00K
OLEUM Contra Costa
County CA 2/14/2019 07:28 Flood 0 0 0.00K 0.00K
RICHMOND Contra Costa
County CA 2/14/2019 06:45 Flood 0 0 100.00K 0.00K
SAN PABLO Contra Costa
County CA 2/13/2019 10:35 Flood 0 0 0.00K 0.00K
VINEHILL Contra Costa
County CA 2/13/2019 08:00 Flood 0 0 0.00K 0.00K
MONSATO Contra Costa
County CA 2/9/2019 23:26 Flood 0 0 0.00K 0.00K
ORINDA Contra Costa
County CA 1/6/2019 16:05 Flood 0 0 0.00K 0.00K
WALNUT CREEK Contra Costa
County CA 11/23/2018 15:29 Flood 0 0 0.00K 0.00K
SELBY Contra Costa
County CA 4/7/2018 00:24 Flood 0 0 0.00K 0.00K
VINEHILL Contra Costa
County CA 3/1/2018 10:38 Flood 0 0 0.00K 0.00K
SELBY Contra Costa
County CA 3/1/2018 09:55 Flood 0 0 0.00K 0.00K
EAST RICHMOND Contra Costa
County CA 1/9/2018 01:30 Flood 0 0 0.00K 0.00K
WALNUT CREEK Contra Costa
County CA 1/9/2018 00:03 Flood 0 0 250.00K 0.00K
ALAMO Contra Costa
County CA 1/8/2018 14:33 Flood 0 0 0.50K 0.00K
WALNUT CREEK Contra Costa
County CA 1/8/2018 09:13 Flood 0 0 0.00K 0.00K
ORINDA Contra Costa
County CA 4/7/2017 22:02 Flood 0 0 0.00K 0.00K
NEROLY Contra Costa
County CA 1/8/2018 20:29 Flood 0 0 0.00K 0.00K
CLYDE Contra Costa
County CA 2/20/2017 20:29 Flood 0 0 0.00K 0.00K
BYRON Contra Costa
County CA 2/20/2017 20:29 Flood 0 0 0.00K 0.00K
ANTIOCH ARPT Contra Costa
County CA 2/20/2017 18:54 Flood 0 0 0.00K 0.00K
PACHECO Contra Costa
County CA 2/20/2017 17:49 Flood 0 0 0.00K 0.00K
TASSAJARA Contra Costa
County CA 2/20/2017 16:00 Flood 0 0 0.00K 0.00K
CLAYTON Contra Costa
County CA 2/20/2017 15:20 Flood 0 0 0.00K 0.00K
EAST RICHMOND Contra Costa
County CA 2/20/2017 07:47 Flood 0 0 0.00K 0.00K
PLEASANT HILL Contra Costa
County CA 2/20/2017 01:40 Flood 0 0 0.00K 0.00K
CLAYTON Contra Costa
County CA 1/10/2017 19:42 Flood 0 0 0.00K 0.00K
GREENBROOK Contra Costa
County CA 12/2/2012 08:56 Flood 0 0 0.50k 0.00K
ORINDA Contra Costa
County CA 12/2/2012 00:00 Flood 0 0 250.00K 0.00K
ORINDA VLG Contra Costa
County CA 1/19/2010 07:00 Flood 0 0 0.00K 0.00K
PITTSBURG Contra Costa
County CA 1/19/2010 06:00 Flood 0 0 0.00K 0.00K
LOS MEDANOS Contra Costa
County CA 1/19/2010 06:00 Flood 0 0 0.00K 0.00K
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Chapter 4: Hazard Identification and Risk Assessment 152 Location
County /
Zone State Date Time Type Death Injury
Property
Damage
Crop
Damage
LOS MEDANOS Contra Costa
County CA 10/13/2009 07:00 Flood 0 0 75.00K 0.00K
COUNTYWIDE Contra Costa
County CA 1/1/2006 00:00 Flood 0 0 22.00M 0.00K
COUNTYWIDE Contra Costa
County CA 12/31/2005 21:00 Flood 0 0 22.00M 0.00K
WALNUT CREEK Contra Costa
County CA 12/14/2002 09:00 Flood 0 0 0.00K 0.00K
ORINDA Contra Costa
County CA 2/13/2000 21:00 Flash Flood 0 0 100.00K 0.00K WALNUT CREEK Contra Costa
County CA 2/7/1998 13:00 Flash Flood 0 0 0.00K 0.00K
PITTSBURG Contra Costa
County CA 2/3/1998 00:00 Flash Flood 0 0 0.00K 0.00K
WALNUT CREEK Contra Costa
County CA 2/3/1998 00:00 Flash Flood 0 0 0.00K 0.00K
COUNTYWIDE Contra Costa
County CA 1/25/1997 05:35 Flash Flood 0 0 0.00K 0.00K
COUNTYWIDE Contra Costa
County CA 1/22/1997 14:15 Flash Flood 0 0 0.00K 0.00K
COUNTYWIDE Contra Costa
County CA 1/2/1997 16:00 Flash Flood 0 0 0.00K 0.00K
COUNTYWIDE Contra Costa
County CA 1/2/1997 11:45 Flash Flood 0 0 0.00K 0.00K
COUNTYWIDE Contra Costa
County CA 1/2/1997 05:52 Flash Flood 0 0 0.00K 0.00K
COUNTYWIDE Contra Costa
County CA 1/1/1997 10:40 Flash Flood 0 0 0.00K 0.00K
COUNTYWIDE Contra Costa
County CA 1/1/1997 09:00 Flash Flood 0 0 0.00K 0.00K
COUNTYWIDE Contra Costa
County CA 1/1/1997 07:18 Flash Flood 0 0 0.00K 0.00K
ORINDA Contra Costa
County CA 12/22/1996 00:00 Flood 0 0 0.00K 0.00K
TOTAL 0 0 44.43M 0.00K

4.6.5.7. Vulnerability and Impacts
Life Safety and Health: Most deaths during a flood occur when vehicles are driven into hazardous floodwater. Vehicles trying to drive through flooded areas or standing water can be swept away and potentially drown. Additionally, a number of hazards can be hidden below floodwater which is why it is imperative to avoid floodwater . Floodwater and standing water can make you vulnerable to infectious diseases, chemical hazards, and injuries.
171 Floods and their aftermath present numerous threats to public health and safety:

• Unsafe food: Floodwaters contain disease-causing bacteria, dirt, oil, human and animal waste, and farm and industrial chemicals. Their contact with food items, including food crops in agricultural lands, can make that food unsafe to eat. Refrigerated and frozen foods are affected during power outages caused by flooding. Foods in cardboard, plastic bags, jars, bottles, and paper packaging may be unhygienic with mold contamination. • Contaminated drinking and washing water, and poor sanitation: Flooding impairs clean water sources with pollutants. The pollutants also saturate in the groundwater. Flooded wastewater treatment plants can be overloaded, resulting in backflows of raw sewage. Private wells can be

171 Centers for Disease Control and Prevention. (2022). Flood Waters or Standing Waters. Retrieved from https://www.cdc.gov/healthywater/emergency/extreme-weather/floods-standingwater.html. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 153 contaminated by floodwater. Additionally, private sewage disposal systems can become a cause of infection if they overflow.
• Mosquitoes and animals: Floods provide new breeding grounds for mosquitoes in wet areas and stagnant pools. The public should dispose of dead animals that can carry viruses and diseases only in accordance with guidelines issued by local animal control authorities.

Leptospirosis—a bacterial disease associated predominantly with rats —often accompanies floods in developing countries, although the risk is low in industrialized regions unless cuts or wounds have direct contact with disease contaminated floodwaters or animals. • Mold and mildew: Excessive exposure to mold and mildew can cause flood victims , especially those with allergies and asthma, to contract upper respiratory diseases, triggering cold-like symptoms. Mold grows in as short a period as 24 to 48 hours in wet and damp areas of buildings and homes that have not been properly cleaned after flooding (e.g., water-infiltrated walls, floors, carpets, toilets and bathrooms). Very small mold spores can be easily inhaled by human bodies and, in large enough quantities, cause allergic reactions, asthma episodes, and other respiratory problems. Infants, children, seniors, and pregnant women are considered most vulnerable to mold-induced health problems.
• Carbon monoxide poisoning: In the event of power outages following floods, some people use alternative fuels for heating or cooking in enclosed or partly enclosed spaces, such as small gasoline engines, stoves, generators, lanterns, gas ranges, charcoal or wood. Built -up carbon monoxide from these sources can poison people and animals. • Hazards when reentering and cleaning flooded homes and buildings: Flooded buildings can pose significant health hazards to people entering them. Electrical power systems can become hazardous, and gas leaks can trigger fire and explosions. Flood debris (e.g., broken bottles, wood, stones and walls ) may cause injuries to those cleaning damaged buildings. Additionally, containers of hazardous chemicals may be buried under flood debris. Hazardous dust and mold can circulate through a building and be inhaled by those engaged in cleanup and restoration. • Mental stress and fatigue: People who live through a devastating flood can experience long term psychological impact. The expense and effort required to repair flood-damaged homes places severe financial and psychological burdens on the people affected. Post-flood recovery can cause anxiety, anger, depression, lethargy, hyperactivity, and sleeplessness. There is also a long-term concern among the affected that their homes could be flooded again in the future.

Everyone in Contra Costa County is vulnerable to flooding, but those within the SFHA (i.e., 100-year floodplain) are at a higher risk, followed by those within the 500-year floodplain. However, the underserved and at risk population face unique vulnerabilities and impacts as a result of flooding. These groups include, but are not limited to, households in poverty, low income households, population living in single access roads, people with limited English proficiency, individuals without access to lifelines, the elderly population (including those with access and functional needs), and undocumented individuals. 172

• Households in Poverty and Low Income Households: Households in poverty include those with an income at or below $24,300 for a household of four (4). In Contra Costa County, most households considered to live in poverty are located within the 100-year flood zone and households affected by coastal flooding are primarily located within North Richmond, Bay Point,

172 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
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Chapter 4: Hazard Identification and Risk Assessment 154 and the tracts and islands in the Delta. The low income population includes households with an income of 80% or less of the median income ($104,400) in Contra Costa County. This population tends to be less likely to evacuate in response to emergency incidents. Furthermore, households in poverty and low income households may have fewer financial resources to complete preparedness and recovery activities (i.e., fix flood damage) and the structures are not waterproofed or built above the current 100-year flood elevation. High concentration of this population is located within or near a flood zone or dam inundation area, mostly in the north and east portion of the County.
• Individuals Living on Single Access Roads: Includes the population living in areas with a single route in and out (i.e., accessible via one (1) roadway) of the neighborhood or area. This population is uniquely vulnerable to flooding if these roadways are blocked, damaged, and destroyed these individuals can become isolated from the community and emergency services . In Contra Costa County, several neighborhoods and communities in the Delta and in the hillside areas in the central and western side of the County are only accessible via one (1) roadway. • People with Limited English Proficiency: This group includes those that speak English “less than very well”, per the United States Census Bureau definition. In Conta Costa County, 158,965 people (38.2%) have limited English proficiency (i.e., speak English “less than very well”). This population are more likely to live in low income areas which are also most likely to be located within low lying areas. Flooding can cause significant damage to homes resulting in uninhabitable and unhealthy conditions to live in. Additionally, individuals with limited English proficiency may have limited access to information and resources designed to prevent or mitigate flooding risk due to language or cultural differences.
• Individuals Without Access to Lifelines: Includes individuals who do not have access to basic technology or services (e.g., transportation, modern communication). This population is vulnerable because not having access to these can create barriers to prepare and respond to emergency events (e.g., flooding) , may be unable to evacuate in a timely manner, and may become isolated if transit services are not operating. For example, this population may be unaware of an approaching weather event and may be unable to evacuate in a timely manner in the event an evacuation order is issued.
• Senior (65 years old and over): The elderly population (i.e., seniors), especially those with access and functional needs, may have physical limitations that make it harder to evacuate in the event of an emergency, such as flooding. Furthermore, the elderly population may lack access to social connections and community support that can assist in preparing for and responding to emergency events, evacuating, improving home resiliency, managing medical needs, and locating support servi ces. A high concentration of the elderly population lives in central Contra Costa County, Bethel Island, eastern part of Richmond, and several parts of Walnut Creek. • Undocumented Individuals: Includes people who do not have formal permission to live in the United States (i.e., do not have citizenship, permanent residency, visas, or other similar status).

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Chapter 4: Hazard Identification and Risk Assessment 155 Table 4-100 summarizes the vulnerable and at-risk population for flooding in Contra Costa County.

Table 4-100. Vulnerability and At Risk Population
Category Estimate Percent
Households in Poverty173 7,600 12.0%
Low Income Households174 25,340 41.0%
Spanish Spoken at Home175 204,442 18.7%
Speak English “Less than very
well”176 158,965 38.2%
Language Other than English177 416,505 38.0%
Foreign Born178 312,050 27.0%
Households Without Vehicle179 8,872 1.6%
65 Years and Over180 201,136 17.4%
Seniors (65 years and over) Living
Alone181 45,672 22.7%
Undocumented Individuals182 There are no official counts of how many undocumented individuals live in Contra Costa County, but in 2019 there was an estimate of 63,000.

Table 4-106 outlines the vulnerability of the total population exposed to floods, and Table 4-107 outlines the flood impacts to population and life safety, underserved/equity population, and essential operations, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Property Damage and Critical Infrastructure: In Contra Costa County, there is a range from the large, state-owned bridges that carry interstate freeways, to locally owned bridges that carry rural roads and pedestrians over small creeks. Countywide, there are over 400 bridges where approximately 80 are owned by the County and 160 are owned by Caltrans. There are 26 bridges that are within the 100-year flood zone and dam inundation areas. Some of these bridges are located in low lying areas that could become flooded during a heavy rainfall event. Additionally, flood control infrastructure (i.e., levees, dikes,

173 Ibid.
174 Ibid.
175 United States Census Bureau. (2022). S1601: Language Spoken at Home (2022: ACS 1-Year Estimates Subject Tables). Retrieved from https://data.census.gov/table/ACSST1Y2022.S1601?g=050XX00US06013. 176 Ibid.
177 Ibid.
178 United States Census Bureau. (2022). DP02: Selected Social Characteristics in the United States (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP02?g=050XX00US06013. 179 United States Census Bureau. (2022). S0801: Commuting Characteristics by Sex. Retrieved from https://data.census.gov/table/ACSST1Y2022.S0801?g=050XX00US06013. 180 United States Census Bureau. (2022). DP05: Demographics and Housing Estimates (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP05?g=050XX00US06013. 181 United States Census Bureau. (2022). DP02: Selected Social Characteristics in the United States (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP02?g=050XX00US06013. 182 Migration Policy Institute. (2019). Profile of the Unauthorized Population: Contra Costa County, CA. Retrieved from https://www.migrationpolicy.org/data/unauthorized-immigrant-population/county/6013. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 156 and drainage channels), meant to prevent the creeks, Delta, and other bodies of water from overflowing and causing floods can fail and cause flooding in these areas. Although the Contra Costa County Flood Control District is responsible for local flood control projects, many of these levees and drainage facilities in the Delta region of the County are privately owned and operated. Interstate 680 and 80, and State Route 4, along with many regional roadways, are within flooding zones. Flooding to these roadways and other local roadways can cause major disruptions to local and regional transportation, transit, and commuters.

There are three (3) standard rail lines that run through Contra Costa County which are operated by Union Pacific, Burlington Northern Santa Fe, and Richmond Pacific Railroad Corporation. These run along the western, northern, and eastern boundaries of the County, along Interstate 80, State Route 4, and Byron Highway. The aforementioned rail lines are used for freight trains; however, the Capitol Corridor commuter train runs along the Union Pacific railway. Additionally, the Bay Area Rapid Transit District (BART) operates its own separate rail lines used exclusively for public transit. Two (2) BART rail lines are located in the County – one beginning in Richmond and heading south toward Berkeley and another one in the central part of the County extending from the City of Orinda to the City of Antioch. The BART, Amtrak, and the freight lines are located within the flood areas in coastal and norther n Contra Costa County. Flooding can cause damage to the tracks and result in the system to completely shutting down.

There are 10 wastewater treatment plants in the County which treat wastewater for residents within cities and unincorporated County. Two (2) of these wastewater treatment plants are within the 100-year and 500-year floodplain. Furthermore, one (1) is located within a dam inundation area, including the West Contra Costa and Pinole-Hercules plants. Additionally, if the Delta levee fails the Mokelumne Aqueduct could be exposed to coastal flooding. The Contra Costa Canal and the Clifton Court Forebay are also within the coastal flooding area. In the event that these levees fail during a coastal flooding event, these water and wastewater infrastructure would also fail resulting in the contamination of freshwater, reducing the availability of drinking and agricultural water.

In Contra Costa County, there are approximately 61 industrial buildings within the coastal flooding areas, 68 are within the 500-year floodplain. Industrial buildings located outside the 100-year floodplain are unlikely to be waterproofed or flood resistant. If any of these structures are damaged due to flooding, it can increase the potential of a hazardous materials release. 183

There are a total of 554 critical assets (i.e., schools, nursing homes, fire stations, police stations, and hospitals) throughout the County, and 14 (2.5%) are located within the 100-y ear floodplain (i.e., SFHA) and 24 (4.3%) are located within the 500-year floodplain. Table 4-101 provides a breakdown of critical assets that are located within the floodplains in Contra Costa County.

Table 4-101. Critical Assets in the 100-Year and 500-Year Floodplains Asset Estimate Percent
(of total asset)
100-Year Floodplain
Schools (public schools, private schools) 5 1.4%
Nursing Homes 1 1.3%
Fire Stations 7 8.6%

183 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
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Chapter 4: Hazard Identification and Risk Assessment 157 Asset Estimate Percent
(of total asset)
Police Stations 1 4.2%
Hospitals 0 0.0%
500-Year Floodplain
Schools (public schools, private schools) 12 3.3%
Nursing Homes 4 5.1%
Fire Stations 7 8.6%
Police Stations 0 0.0%
Hospitals 1 9.1%

Locations that are directly flooded experience the greatest economic impact. In these areas, renovations of commercial buildings may be necessary, disrupting associated services. Significant damage may occur in agricultural areas, with the destruction of crops and other agricultural products. The tourism industry may be affected by major flood events, as popular vacation areas tend to overlap flood hazard zones. Also, flooding in major roadways can disrupt local and regional transportation and transit and if commuters in the Bay Area are unable to reach their jobs, large sections of the economy can be affected.

Additionally, flooding can cause damage to the rail and BART lines resulting in a shutdown which can disrupt regional transit networks that are essential to the economic activity of the County and region. Loss of power and communications may occur; and drinking water and wastewater treatment facilities may be temporarily out of operation.

Table 4-106 outlines the total property value exposed to floods and how the changes in development in the past five (5) years have affected the vulnerability of the community to floods. Table 4-107 outlines the flood impacts on total property damage, potential future development, and the economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Building damage as a result of a 100-year flood analysis was estimated using Hazus. In addition, annualized losses were calculated. Refer to the Hazus portion at the end of this section (Section 4.6.5.7).

Environment: The environment vulnerable to flood hazard is the same as the environment exposed to the hazard. 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. While the vulnerability assessment focuses on human vulnerability to flood events, the impact of human activities on flooding is also worth noting. Due to the negative impacts of floods, many structural and other measures have been devised to limit how far a floodplain can extend. However, floodplains have many natural and beneficial functions, and disruption of natural systems can have long-term consequences for entire regions.

In Contra Costa County, the wetland ecosystems, located adjacent to the San Francisco Bay and Delta, include permanent wetland, seasonal wetland, fresh emergent wetland, alkali wetland, and marshes.

Wildlife in these ecosystems includes great blue heron, great egret, wood duck, green-winged teal, mallard, California red-legged frog, western pond turtle, garter snakes, western spadefoot toad, western toad, California tiger salamander, tri -colored blackbird, and vernal pool fairy shrimp. It is forecast that coastal flooding will inundate most of the wetland and tidal marshes in Contra Costa County by 2070. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 158 The wildlife habitat, recreation, and flood protection that these ecosystems provide may not be able to be sustained.

Additionally, flooding can disrupt water and wastewater services, and failure of these treatment plants can result in sewer systems to backup which can potentially contaminate creeks, streams, and water systems with raw sewage. Contra Costa County currently has 10 wastewater treatment plants, some of which are located within the 100-year and 500-year floodpl ain. Furthermore, industrial buildings that sustain flood damage can result in a hazardous materials event which can contaminate soil, water, and aid. Contra Costa County has approximately 270 industrial buil dings, many of which are within flooding areas.
184

Table 4-107 outlines flood impacts on the environment, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Changes in Development and Impact of Future Development: There have been no significant changes in development that have affected the risks associated with flooding. Future increases in population within the SHFA may expose more of the population to floods. Growth over the past decade has considerably increased. Between 2010 and 2022, as outlined in Table 3-3, the population in Contra Costa County grew 10.6%, from 1,046,025 to 1,156,966 residents. The Bay Area Association of Governments (ABAG) growth forecasts predict a steady increase in households through 2050. From 2015 to 2050, ABAG projects that the County’s number of households will grow by 44%. 185 This increase
in population can add an additional strain to first responders in the event of an evacuation due to flooding.

Table 4-10 6 outlines how the changes in development in the past five (5) years have affected the vulnerability of the community to floods. Table 4-107 outlines the flood impacts on potential future development, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Effects of Climate Change in Severity of Impacts: As global average temperatures increase, evaporation increases adding moisture into the atmosphere which results in more precipitation. 186 In California and western United states, observations of climate change have shown sea level rise is expected to continue to increase flooding on coastal areas. Add itionally, scientists project that the frequency and intensity of heavy rainfall (e.g., atmospheric rivers), and associated floods in the County will increase. Although heavy precipitation does not necessarily result in flooding, the potential increases and in some location moderate amounts of precipitation can lead to serious damage. 187

Table 4-102 indicates the 25-year precipitation projections in Contra Costa County. 188 Table 4-103
outlines the flood associated climate indicators for Contra Costa County projected through the end of the century.
189

184 Ibid.
185 Bay Area Association of Government. (2020). Plan Bay Area 2050 Final Blueprint Growth Pattern. Retrieved from https://planbayarea.org/digital-library/plan-bay-area-2050-final-blueprint-growth-pattern. 186 Environmental Protection Agency. (n.d.). Climate Change Indicators: U.S. and Global Precipitation. Retrieved from https://www.epa.gov/climate-indicators/climate-change-indicators-us-and-global-precipitation. 187 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
188 Northeast Regional Climate Center. (n.d.). Neighborhoods at Risk: Climate Projections. Retrieved from https://nar.headwaterseconomics.org/.
189 Climate Mapping for Resilience and Adaptation. (n.d.). Climate Mapping for Resilience and Adaptation Assessment Tool. Retrieved from https://livingatlas.arcgis.com/assessment-tool/explore/details. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 159 Table 4-102. 25-Year Precipitation Projections for Contra Costa County Higher Emissions (RCP8.5)
By 2048, Contra Costa County is expected to have a 0.4 inches increase (from 19.6 inches to 20.1 inches) in average annual precipitation.

Lower Emissions (RCP4.5)
By 2048, Contra Costa County is expected to have a 0.15 inches increase (from 19.11 inches to 19.26 inches) in average annual precipitation.

Table 4-103. Future Climate Indicators for Contra Costa County Indicators
Modeled
History
(1976 – 2005)
Early Century
(2015 – 2044)
Mid Century
(2035 – 2064)
Late Century
(2070 – 2099)
Lower
Emissions
Higher
Emissions
Lower
Emissions
Higher
Emissions
Lower
Emissions
Higher
Emissions
Min – Max Min – Max Min – Max Min – Max Min – Max Min – Max Min – Max Precipitation
Average annual total
precipitation
19 inches 19 inches 20 inches 20 inches 20 inches 20 inches 21 inches 17 – 21 16 – 25 17 – 24 17 – 26 16 – 25 16 – 25 14 – 27 Days per year with
precipitation
(Wet Days)
84 days 82 days 82 days 80 days 80 days 80 days 77 days 80 – 88 74 – 91 74 – 91 68 – 91 69 – 98 70 – 90 58 – 94 Maximum period of
consecutive wet days
11 days 11 days 12 days 11 days 11 days 11 days 11 days 10 – 12 10 – 14 10 – 14 9 – 14 9 – 15 10 – 15 8 – 17
Temperature Thresholds
Annual days with total
precipitation greater
than 1 inch
2 days 3 days 3 days 3 days 3 days 3 days 4 days
2 – 3 2 – 4 2 – 4 2 – 5 2 – 5 2 – 5 2 – 7
Annual days with total
precipitation greater
than 2 inches
0 days 0 days 0 days 0 days 0 days 0 days 0 days
0 – 0 0 – 1 0 – 1 0 – 1 0 – 1 0 – 1 0 – 1
Annual days with total
precipitation greater
than 3 inches
0 days 0 days 0 days 0 days 0 days 0 days 0 days
0 – 0 0 – 0 0 – 0 0 – 0 0 – 0 0 – 0 0 – 0
Annual days that
exceed 99
th percentile
precipitation
4 days 5 days 5 days 5 days 5 days 5 days 6 days
3 – 7 3 – 8 3 – 8 3 – 8 3 – 9 3 – 9 4 – 11
Days with maximum
temperature below
32°F
0 days 0 days 0 days 0 days 0 days 0 days 0 days
0 – 0 0 – 0 0 – 0 0 – 0 0 – 0 0 – 0 0 – 0

Table 4-107 outlines the climate change impacts to floods in Contra Costa County, as outlined in the risk assessment methodology in Section 4.3 of this Plan.
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Chapter 4: Hazard Identification and Risk Assessment 160 Table 4-104. Probability of Occurrence
Hazard Event Probability of Occurrence Probability
Factor
Weighted
Factor
Urban/Flash Flooding Medium Significant hazard event is likely to occur within 25 years. 2 N/A Riverine/Creek Flooding Medium Significant hazard event is likely to occur within 25 years. 2 N/A Table 4-105. Extent Factors
Hazard Event Extent Factor Extent Extent
Factor
Weighted
Factor
Urban/Flash Flooding
Extent/Intensity High Historical and/or probabilistic models/studies for this hazard indicate the possibility of a high-intensity incident. 3 9 Catastrophic Medium Catastrophic hazard event is likely to occur at least once between 11 and 50 years. 2 6
Riverine/Creek Flooding
Extent/Intensity Medium Historical and/or probabilistic models/studies for this hazard indicate the possibility of a medium-intensity incident. 2 6 Catastrophic Medium Catastrophic hazard event is likely to occur at least once between 11 and 50 years. 2 6
Table 4-106. Vulnerability Factors
Hazard Event Vulnerability Factor Vulnerability Vulnerability Factor
Weighted
Factor
Urban/Flash Flooding
Population Exposure Medium 15% to 29% of the population (including underserved population) is exposed to the hazard. 2 6
Property Exposure Medium 10% to 24% of the total assessed property value is exposed to the hazard. 2 4
Changes in
Development Medium The changes in development have increased the vulnerability of the community to the hazard between 5% and 9%. 2 2
Riverine/Creek Flooding
Population Exposure Low 14% or less of the population is exposed to the hazard. 1 3 Property Exposure Low 9% or less of the total assessed property value is exposed to a hazard. 1 2
Changes in
Development Medium The changes in development have increased the vulnerability of the community to the hazard between 5% and 9%. 2 2

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Chapter 4: Hazard Identification and Risk Assessment 161 Table 4-107. Impact Factors
Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Urban/Flash Flooding
Population and Life
Safety Medium
Populations exposed to this hazard are likely to experience some adverse impacts, such as injuries requiring acute
medical care.
2 6
Underserved/Equity Medium
Underserved populations exposed to the hazard are likely to experience some adverse/disproportionate impacts, such as injuries requiring acute medical care.
2 6
Property Damage High
More than $5 Million in property damages is expected from a single major hazard event, or damages are expected to occur to 15% or more of the property value within the jurisdiction. 3 6
Economic Medium Total economic impact is likely to be greater than $500,000, but less than or equal to $10 Million. 2 2
Environmental Medium
Environmental impact from a single major hazard event is likely to be localized, requiring some outside resources and support; and/or repair, clean-up, restoration, or preservation work.
2 2
Essential Operations Medium
Impact between 24 and 72 hours on the ability of the
jurisdiction to meet the essential day-to-day operational demands and needs of the community from a single major
hazard event.
2 2
Future Development Medium Future development trends will increase the impact/consequence of this hazard, but not significantly. 2 2 Climate Change High Climate Change trends will significantly increase the risk of this hazard and its impacts. 3 3
Riverine/Creek Flooding
Population and Life
Safety Medium
Populations exposed to this hazard are likely to experience some adverse impacts, such as injuries requiring acute
medical care.
2 6
Underserved/Equity Low
Underserved populations exposed to the hazard are likely to experience minimal adverse/disproportionate impacts, such as ambulatory injuries.
1 3
Property Damage High
More than $5 Million in property damages is expected from a single major hazard event, or damages are expected to occur to 15% or more of the property value within the jurisdiction. 3 6
Economic Medium Total economic impact is likely to be greater than $500,000, but less than or equal to $10 Million. 2 2
Environmental Medium
Environmental impact from a single major hazard event is likely to be localized, requiring some outside resources and support; and/or repair, clean-up, restoration, or preservation work.
2 2
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Chapter 4: Hazard Identification and Risk Assessment 162 Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Essential Operations Medium
Impact between 24 and 72 hours on the ability of the
jurisdiction to meet the essential day-to-day operational demands and needs of the community from a single major
hazard event.
2 2
Future Development Medium Future development trends will increase the impact/consequence of this hazard, but not significantly. 2 2 Climate Change High Climate Change trends will significantly increase the risk of this hazard and its impacts. 3 3

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Chapter 4: Hazard Identification and Risk Assessment 163 HAZUS
Scenario: 100-Year Flood
Building damage as a result of a 100-year flood analysis was estimated using Hazus. In addition, annualized losses were calculated. Hazus estimates that there are 341,451 buildings in the region which have been an aggregated total replacement of $218.5 Million. Approximately 91.1 % of the buildings are associated with residential housing. Table 4-108 provides a general distribution of the building value within Contra Costa County. In terms of building construction types found in the County, wood frame construction makes up 89.0% of the building inventory and the remaining 11.0% is distributed between the other general building types (i.e., steel, concrete, precast, reinforced masonry, unreinforced masonry, manufactured housing).

Table 4-108. Contra Costa County Population and Building Value Data Population Residential Building
Value
Non-Residential
Building Value Total
1,165, 466 $158.1 Million $60.3 Million $218.5 Million

The total economic loss estimated for the flood is $9 .952 Million, representing 24.1% of the total replacement value of the scenario buildings. HAZUS estimates that about 8,489 buildings will be at least moderately damaged. This is over 62% of the total number of buildings in the scenario. There is an estimated 559 building that will be completely destroyed. Table 4-109 summarizes the expected damage by general occupancy for the buildings in Contra Costa County.

Table 4-109. 100-Year Flood Expected Building Damage by Occupancy Damage
Level 1 – 10 11 – 20 21 – 30 31 – 40 41 – 50 >50
Occupancy Count % Count % Count % Count % Count % Count % Agriculture 0 0 0 0 0 0 0 0 0 0 0 0
Commercial 223 36 370 59 27 4 6 1 0 0 0 0
Education 4 100 0 0 0 0 0 0 0 0 0 0
Government 45 55 37 44 0 0 1 1 0 0 0 0
Industrial 23 28 40 49 8 10 9 11 1 1 0 0
Religion 3 50 3 50 0 0 0 0 0 0 0 0
Residential 2,333 23 3,786 37 1,854 18 1,154 11 634 6 559 5 TOTAL 2,633 4,236 1,889 1,170 635 559

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Chapter 4: Hazard Identification and Risk Assessment 164 Table 4-110 summarizes the expected damage by general building type.

Table 4-110. Expected Building Damage by Building Type
Building
Type
1 – 10 11 – 20 21 – 30 31 – 40 41 – 50 >50
Count % Count % Count % Count % Count % Count %
Concrete 113 36 167 53 30 9 5 2 3 1 0 0
Manufactured
Housing 26 9 24 8 22 7 0 0 21 7 204 69
Masonry 83 31 141 53 35 13 5 2 3 1 0 0
Steel 49 33 81 54 14 9 3 2 2 1 0 0
Wood 2,312 23 3,774 38 1,756 18 1,143 11 603 6 355 4

For essential facilities, there are 14 hospitals in the County with a total bed capacity of 1,804 beds. There are 384 schools, 78 fire stations, 35 police stations and two (2) emergency operation centers. With respect to high potential loss facilities, there are no dams identified within the inventory. The inventory also includes no hazardous material sites, no military installations and no nuclear power plants.

The Hazus model estimates the time to restore critical facilities to fully functional use. Before the flood event, Contra Costa County had 1,804 hospital beds available for use. On the day of the flood event, Hazus estimates that 1,804 hospital beds (100%) are available. Table 4-111 summarizes the expected damage to essential facilities in Contra Costa County. None of the essential facilities listed are expected to be damaged due to the flood event.

Table 4-111. 100-Year Flood Expected Damage to Essential Facilities Facility Total At Least
Moderate
At Least
Substantial Loss of Use
Hospitals 14 0 0 0
Schools 384 0 0 0
Emergency Operations Center 2 0 0 0
Police Stations 35 0 0 0
Fire Stations 78 0 0 0
TOTAL 384 0 0 0

Flood events also impact the economy, including loss of business function, damage to inventory (i.e., buildings, transportation, and utility systems), relocation costs, wage loss, and rental loss due to repair and replacement of buildings. Hazus estimates building-related economic losses, including income losses (i.e., wage, capital-related, rental, and relocation losses) and capital stock losses (i.e., structural, non-structural, content, and inventory losses).

Hazus estimates total building related losses were $5.001 Million where 50.0% of the losses were related to business interruption in Contra Costa County. The analysis concluded that the largest loss was sustained by the residential occupancies, which comprised 52% of the total loss.

The total building related losses were $5.001 Million. 50% of the estimated losses were related to the business interruption of Contra Costa County. The residential occupancies made up 30.6% of the total 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 165 loss. Table 4-112 provides a summary of the losses associated with the building damage in Millions of dollars.

Table 4-112. 100-Year Flood Building Related Economic Loss Estimates (Millions of Dollars) Area Residential Commercial Industrial Others Total
Building
Loss
Building 1,481.3 352.1 101.3 96.3 2,030.9
Content 867.8 1,099.4 218.6 544.0 2,729.7
Inventory 0.0 195.2 31.4 14.0 240.7
TOTAL 2,349.1 1,646.7 351.3 654.3 5,001.3
Business
Interruptions
Income 39.6 778.0 7.4 193.4 1,018.6
Relocation 343.0 261.8 8.4 132.6 745.7
Rental
Income 221.8 169.8 2.1 27.4 421.0
Wage 93.2 880.7 12.8 1,778.7 2,765.4
TOTAL 697.5 2,090.3 30.6 2,132.3 4,950.6
SUBTOTAL 3,046.5 3,737.0 381.9 2,786.6 9,952.0

HAZUS estimates the number of households that are expected to be displaced from their homes due to the flood incident and associated potential evacuation, and the number of displaced individuals that will require accommodations in temporary public shelters. The model estimates that 23,642 households (70,926 people) will be displaced due to the flood. Displacement includes households evacuated from within or very near to the inundated area. Of these, 4,961 people (out of a total population of 1,165,466) will seek temporary shelter in public shelters.

Hazus estimates the amount of debris that will be generated by the flood event. Debris estimates were divided into three (3) categories – finishes (e.g., dry wall, insulation), structural (e.g., wood, brick), and foundations (e.g., concrete slab, concrete block, and rebar). The distinction is made because of the different types of materials handling equipment required to handle debris.

The analysis estimated that a total of 78,790 tons of debris will be generated. Of the total amount, 78.0% is comprised of finishes, 11.0% is structural, and 12.0% is foundation. If the debris tonnage is converted to an estimated number of truckloads, it will require 3,152 truckloads (25 tons/truck) to remove the debris.

4.6.5.8. FEMA NRI Expected Annual Loss Estimates
A riverine flooding NRI EAL score, and rating represent a community's relative level of expected building, population, and agriculture loss each year due to riverine flooding when compared to the rest of the United States. The EAL score is positively associated to a community’s risk; therefore, a higher EAL score results in a higher Risk Index score. Table 4-113 outlines the riverine flooding EAL for Contra Costa County.

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Chapter 4: Hazard Identification and Risk Assessment 166 Table 4-113. Riverine Flooding Expected Annual Loss (FEMA National Risk Index) Jurisdiction Population
Equivalence
Building
Value
Agriculture
Value
Total
Expected
Annual
Loss
Expected
Annual
Loss
Score
Rating
Contra Costa
County $4.0 Million $4.1 Million $291,636 $8.4 Million 96.3 Very High Expected annual loss scores are calculated utilizing an equation that combines values for exposure, annualized frequency, and historic loss ratios (Expected Annual Loss = Exposure x Annualized Frequency x Historic Loss Ratio).

4.6.5.9. FEMA Flooding Risk Index Scores
The riverine flooding Risk Index score and rating represent a community's relative risk for riverine flooding when compared to the rest of the United States. Table 4-114 illustrates the riverine flooding Risk Index rating and score for Contra Costa County.

Table 4-114. Riverine Flooding Risk Index (FEMA National Risk Index) Jurisdiction Rating Score
Contra Costa County Very High 96.2
Risk Index scores are calculated using an equation that combines scores for Expected Annual Loss due to natural hazards, Social Vulnerability and Community Resilience (Expected Annual Loss x Social Vulnerability / Community Resilience = Risk Index).

Table 4-115 represents the Flooding Total Risk Score for Contra Costa County, based on the Risk Assessment Methodology, as defined in this Plan. For further details on how the probability, extent, vulnerability, and impact factors were calculated, please refer to Table 4-104 through Table 4-107.

Additional details on how the Total Risk Score was calculated can be found in the Risk Assessment Methodology in Section 4.3 of this Plan.

Table 4-115. Flooding Total Risk Score
Hazard
Event
Probability Consequence Total Risk
Probability
Factor Extent Vulnerability Impact Consequence
Score
Total Risk
Score*
Urban/Flash Flooding 2 15 12 29 56 55
Riverine/Creek Flooding 2 12 7 29 48 48
Consequence: Sum of all weighted factors.

Extent: Sum of the weighted Extent factors.

Vulnerability: Sum of the weighted Vulnerability factors.

Impact: Sum of the weighted Impact factors.

The Total Risk Score is a measure of Probability and Consequence.

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Chapter 4: Hazard Identification and Risk Assessment 167

4.6.6. Landslide

4.6.6.1. Description
A landslide is the movement of a mass of rocks, debris, or earth down a slope. Landslides are a type of "mass wasting," which denotes any downslope movement of soil and rock under the direct influence of gravity. The landslide term is comprised of five (5) types of slope movement – falls, topples, slides, spreads, and flows – which are further subdivided by the type of geologic material (i.e., bedrock, debris, or earth).
190 Slope movement occurs when forces acting downslope exceed the strength of the earth’s material that compose the slope. The modes of slope movement are listed in Table 4-116. 191 Table 4-116. Types of Slope Movement
Type Description
Falls Masses of soil or rock that dislodge from steep slopes and free fall, bounce, or roll downslope.

Topples Move by the forward pivoting of a mass around an axis below the displaced mass.

Slides
Displaced masses of material along one (1) or more discrete planes. There are two (2) types of sliding – rational and translational.
• R otational sliding the slide plane is curved and the mass rotates backwards around an axis parallel to the slope.
• Translational sliding the failure surface is more or less planar and the mass moves parallel to the ground surface.

Lateral Spreads Move by horizontal extension and shear or tensile fractures and are commonly induced by liquefaction of material in an earthquake.

Flows Mobilize as a deforming, viscous mass without a discrete failure plane.

Complex Occurs when more than one (1) type of movement occurs sequentially during a failure.

Composite Occurs when more than one (1) type of movement does not occur sequentially during a failure.

Landslides are an important natural process because they shape the Earth’s landscape and contribute to the overall environmental quality of a region. However, when landslides impact people, property, or infrastructure it is considered a natural hazard. Landslides can occur in slopes already on the verge of movement by rainfall, snowmelt, changes in water level, stream erosion, changes in ground water, earthquake, volcanic activity, disturbance by human activities, or any combination of these factors. 192
The California Department of Conservation (CDC) classifies landslides into the six (6) categories listed in Table 4-117.

190 United States Geological Survey. (n.d.). What is a Landslide and What Causes One? Retrieved from https://www.usgs.gov/faqs/what-landslide-and-what-causes-one. 191 California Department of Conservation. (n.d.). Landslides. Retrieved from https://www.conservation.ca.gov/cgs/landslides.
192 United States Geological Survey. (n.d.). What is a Landslide and What Causes One? Retrieved from https://www.usgs.gov/faqs/what-landslide-and-what-causes-one. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 168 Table 4-117. Types of Common Landslide 193
Type Description
Earth Flows
The majority of the soil materials are fine-grained, cohesive silt and clay and occur in moderately steep slopes (10% to 30% grade). Earth flows are slow moving (centimeters or millimeters over a period of days or weeks) and are often triggered by periods of prolonged rainfall and sometimes do not occur until well after a rainfall event or the rainy season.

Debris Flows
The majority of the soil is coarse-grained (e.g., fine sand to boulder size particles) and non-cohesive and commonly begin as a slide of a shallow mass of soil and weathered rock. Debris flows tend to be small to an aerial extent and their deposits are relatively thin.

Debris Slide
The majority of the soil is coarse-grained, most common in unconsolidated sandy or gravelly units, but also are common in residual soils that form in-place weathering of relatively hard rock. Debris slides tend to occur on very steep slopes (60% to 70% grade) where the base of the slope is undercut with erosion. These move at rates between meters per day to meters per minute and are often triggered after a single heavy rainstorm or series of storms that deliver enough rain to trigger a debris slide.

Rockslides
Involves bedrock in which the rock that moves remains largely intact for at least a portion of the movement. Rockslides occur in a variety of sizes on a variety of gradients (35% to 70% grade) and have a range of triggering mechanism.

Rock Falls
Occurs when a mass of rock detaches from a steep slope by sliding, spreading, or toppling and descends mainly through the air by falling, bouncing, or rolling. Rock falls can be triggered by intense rain, earthquakes, and freeze-thaw wedging.

Additionally, earthquake shaking can induce underwater landslides (i.e., submarine landslides) which can cause tsunamis potentially resulting in damage to coastal areas.

4.6.6.2. Hazard Location
The best available predictor of where movement of slides and earth flows 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 and many 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 mass movement 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.

Landslide susceptibility maps describe the relative likelihood of future land sliding based solely on the intrinsic properties of a location or site. There are three (3) site factors that most determine susceptibility – prior failure, rock or soil strength, and steepness of slope. 194 Figure 4-16 illustrates landslide
susceptibility in Contra Costa County. Western Contra Costa County has a very high susceptibility to landslides. Meanwhile, central Contra Costa County susceptibility to landslide is medium and the eastern part of the County susceptibility is low.

193 California Department of Conservation. (n.d.). Landslides. Retrieved from https://www.conservation.ca.gov/cgs/landslides.
194 California Department of Conservation. (n.d.). Landslides. Retrieved from https://www.conservation.ca.gov/cgs/landslides.
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Chapter 4: Hazard Identification and Risk Assessment 169

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Chapter 4: Hazard Identification and Risk Assessment 170 Figure 4-16. Landslide Susceptibility in Contra Costa County

4.6.6.3. Hazard Extent/Intensity
In the United States, landslides cause billions of dollars in damages and kill between 25 and 50 people annually. Casualties are primarily caused by rockfalls, rockslides, and debris flows. Worldwide, landslides cause thousands of casualties and billions of dollars in damages. 195

Although there are no scales for the intensity or severity of landslides , understanding the likelihood of deep land sliding based on regional estimates of rock strength and steepness of slopes can help understand the extent and intensity of potential landslides. A statewide analysis of landslide susceptibility was conducted by the California Geological Survey using a combination of regional rock strength and slope data to create classes of susceptibility. The methodology used for the analysis assumed, in general, that landslide susceptibility is low on very low slopes in all rock materials, and that susceptibility increases with slope and in weak rocks. The analysis also factored in locations of past landslides. 196

4.6.6.4. Warning Time
Landslides can occur suddenly or slowly. The velocity of mass movement depends on slope angle, material, and water content. Some methods used to monitor mass movements can provide an idea of the type of movement and the amount of time prior to failure. It is also possible to determine what areas are at risk during general time periods. Assessing the geology, vegetation, and amount of predicted

195 United States Geological Survey. (2004). Landslide Types and Processes. Retrieved from https://pubs.usgs.gov/fs/2004/3072/pdf/fs2004-3072.pdf. 196 California Geological Survey. (2011). Susceptibility to Deep-Seated Landslides in California. Retrieved from https://www.conservation.ca.gov/cgs/documents/publications/map-sheets/MS_058.pdf.

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Chapter 4: Hazard Identification and Risk Assessment 171 precipitation for an area can help in these predictions. However, there is no practical warning system for individual landslides.

USGS provides a system of notification for potential landslides , listed in Table 4-118. Watches and warnings may be issued for discrete areas and include advice about contacting the area's local emergency management. Additionally, rainfall induced debris flows watches and warning are weather dependent and will closely track NWS advisories for flash flooding. 197
Table 4-118. USGS Landslide Advisories
Type Description
Landslide Advisory
A general statement about the potential of landslide activity in a given region relative to developing rainfall predictions. An advisory may include general statements about rainfall conditions that can lead to debris flow activity, and list precautions to be taken in the event of heavy rainfall.

Landslide Watch
Means that landslide activity will be possible but is not imminent. People in, or planning to travel through, a watch area should know landslide preparedness and stay informed about developing weather patterns.

Landslide Warning Indicate that landslide activity is presently occurring, and extreme caution should be taken.

4.6.6.5. Probability and Frequency
The probability of occurrence for landslides in Contra Costa County is high because significant occurrences of this hazard are likely to occur annually. Additionally, according to the 2023 California State Hazard Mitigation Plan, landslide probability of occurrence is notably high in the coastal regions of California where much of the State’s population, industry, and infrastructure is located.198 Probability of Future Hazard Events
The landslide annualized frequency value represents the average number of recorded landslide hazard occurrences in event days, per year over the period of record ( 11.8 years). Table 4-119 outlines the annualized frequency for landslides, based on FEMA NRI data, for Contra Costa County. While the FEMA NRI has an annual frequency of zero (0) landslide events in the County, studies and landslide data suggest that at least one (1) landslide event will occur every year.

Table 4-119. Landslide Annualized Frequency (FEMA National Risk Index) Location Events on Record
(2010 – 2021) Annualized Frequency
Contra Costa County 12 0.0 events per year
Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year.

4.6.6.6. Past Events
In Contra Costa County, landslides have occurred in conjunction with heavy rainfall events. Table 4-120 lists landslide events that affected Contra Costa County between 1980 and 2023. There are no records

197 United States Geological Survey. (n.d.). What is the Difference Between a Landslide Advisory, a Landslide Watch, and a Landslide Warning? Retrieved from https://www.usgs.gov/faqs/what-difference-between-landslide- advisory-landslide-watch-and-landslide-warning.
198 California Governor’s Office of Emergency Services. (2023). California State Hazard Mitigation Plan. Retrieved from https://www.caloes.ca.gov/wp-content/uploads/Hazard-Mitigation/Documents/2023-California- SHMP_Volume-1_11.10.2023.pdf.
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Chapter 4: Hazard Identification and Risk Assessment 172 in the County of fatalities attributed to landslides. However, deaths have occurred across the west coast as a result of slides and slope collapses.

Table 4-120. Significant Landslide Events
Date Event Type Location Description
December 27, 2022 –
January 31, 2023
Severe storms,
flooding,
landslides, and
mudslides
Contra Costa
County
(43 other counties
in the State)
An atmospheric river impacted the State of
California beginning on December 27, 2022,
producing torrential rainfall which resulted in
catastrophic landslides and mudslides
throughout Contra Costa County.

February 27, 2017 –
March 4, 2017 Mudslide
Near the City of
Concord and
City of
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.

January 3, 2017 –
January 12, 2017
Severe storms,
flooding, and
mudslides
Contra Costa
County
(33 other counties
in the State)
Trees and landslides covered roadways
throughout the Bay Area. (DR-4301)
March 13, 2016 Landslide Town of Moraga
A landslide forced two (2) homeowners to
evacuate their homes in the Town of
Moraga. A lower portion of the hill slid into
San Pablo Creek in January.
2011 Winter Storm Local
Central Contra Costa Sanitary District
reported landslides and damage to sewer
pipes.

December 17, 2005 –
January 3, 2006
Severe storms,
flooding,
mudslides, and
landslides
Contra Costa
County
(29 other counties
in the State)
A series of rainfall 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. In Contra Costa County, much of
the damage was in the following cities –
Walnut Creek, Richmond, San Pablo,
Martinez, and Orinda. Damaged facilities
included schools, park areas, and several
government agency structures. (DR-1628)
February 13, 2000 –
February 14, 2000 Flash Flood Countywide
Widespread rainfall occurred over 24 hours
with accumulations exceeding five (5)
inches. Several homes in Daly City had to
be evacuated due to mudslides and
consecutive years of above average rainfall.

February 2, 1998 –
April 30, 1998
Severe winter
storms and El
Niño rainstorm
San Francisco
Bay Area
Widespread flooding occurred that caused
landslides in Contra Costa County. (DR-
1203)
December 2, 1996 –
April 1, 1997
Severe storms,
flooding,
mudslides, and
landslides
Contra Costa
County
(46 other counties
in the State)
Minor landslide damage in Contra Costa
County was attributed to heavy rainfall and
saturated soils. (DR-1155)
February 13, 1995 –
April 19, 1995
Severe winter
storms, flooding,
landslides, and
mud flows
San Francisco
Bay Area
Minor landslide damage in Contra Costa
County was attributed to heavy rainfall and
saturated soils. (DR-1046)
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Chapter 4: Hazard Identification and Risk Assessment 173 Date Event Type Location Description
January 3, 1995 –
February 10, 1995
Severe winter
storms, flooding,
landslides, and
mud flows
San Francisco
Bay Area
Minor landslide damage in Contra Costa
County was attributed to heavy rainfall and
saturated soils. (DR-1044)
January 5, 1993 –
March 20, 1993
Severe winter
storm,
mudslides,
landslides, and
flooding
Contra Costa
County
(26 other counties
in the State)
Minor landslide damage in Contra Costa
County was attributed to heavy rainfall and
saturated soils. (DR-979)
January 21, 1983 –
March 30, 1983
Coastal storms,
floods, slides,
and tornadoes
Contra Costa
County
(35 other counties
in the State)
Heavy rainfall throughout coastal areas of
California caused landslides. (DR-677)
December 19, 1981 –
January 8, 1982
Severe storms,
flood, mudslides,
and high tide
San Francisco
Bay Area
Prolonged heavy rainfall and saturated soils
caused numerous slope failures and mud
flows on steep and unstable slopes
throughout the San Francisco Bay area. In
Contra Costa County, 335 homes were
damaged by landslides. (DR-651)
Sources: FEMA 2017; Hazard Mitigation Plan Annual Progress Report, California Geology 1982; USGS 1984, 1987, 1989 and 1998; and NOAA, 2017.

4.6.6.7. Vulnerability and Impacts
Life Safety and Health: In general, all of the population within landslide susceptibility areas are considered to be vulnerable, especially those within a high landslide susceptibility area (Class VIII – X).

As illustrated in Figure 4-16, the majority of the population in the western portion of Contra Costa County is within a high (Class VIII – X) landslide susceptibility area. Increasing population and the fact that many homes are built on property atop or below bluffs and on steep slopes subject to mass movement, increases the number of lives endangered by this hazard.

The underserved and at risk population faces unique vulnerabilities and impacts as a result of landslides.

These groups include, but are not limited to, households in poverty, the elderly population, undocumented individuals, and population living in single access roads. 199

• Household in Poverty: Includes those with an income at or below $24,300 for a household of four (4). This population may live in homes that are less structurally sound. In the event of a landslide, the foundation of these homes can be damaged or completely destroyed resulting in financial strain for these households. In Contra Costa County, a high concentration of households in poverty within high landslide susceptibility areas can be found in Rodeo, Crockett, Bay Point, and Port Costa.
• Senior (65 years old and over): The elderly population (i.e., seniors), especially those with access and functional needs, may have physical limitations that make it harder to evacuate in the event of an emergency, such as flooding. Furthermore, the elderly population may lack access to social connections and community support that can assist in preparing for and responding to emergency events, evacuating, improving home resiliency, managing medical needs, and

199 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
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Chapter 4: Hazard Identification and Risk Assessment 174 locating support services. Communities with high concentrations of seniors are primarily located on the hillsides in Contra Costa County, which are within high landslide susceptibility areas. • Undocumented Individuals: Includes people who do not have formal permission to live in the United States (i.e., do not have citizenship, permanent residency, visas, or other similar status).

This population is most likely to fall in the households in poverty and low income categories, which are considered to be at risk populations during a landslide event. • Individuals Living on Single Access Roads: Includes the population living in areas with a single route in and out (i.e., accessible via one (1) roadway) of the neighborhood or area. This population is uniquely vulnerable to landslides because if these roadways are blocked, damaged, and destroyed these individuals can become isolated from the community and emergency services.

In Contra Costa County, several neighborhoods and communities in the Delta and in the hillside areas of central and western Contra Costa County are only accessible via one roadway.

Table 4-121 summarizes the vulnerable and at-risk population for landslides in Contra Costa County.

Table 4-121. Vulnerability and At Risk Population
Category Estimate Percent
Households in Poverty200 7,600 12.0%
65 Years and Over201 201,136 17.4%
Seniors (65 years and over) Living
Alone202 45,672 22.7%
Undocumented Individuals203 There are no official counts of how many undocumented individuals live in Contra Costa County, but in 2019 there was an estimate of 63,000.

Table 4-126 outlines the vulnerability of the total population exposed to landslides, and Table 4-127 outlines the landslide impacts to population and life safety, underserved/equity population, and essential operations, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Property Damage and Critical Infrastructure: Although only a partial list of historical landslides in Contra Costa County is available, the available records suggest a significant vulnerability to this hazard.

The millions of dollars in damage C ountywide attributable to mass movement during those events affected private property and public infrastructure and facilities. 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%, 30%, and 50% of the replacement value of exposed structures. This allows emergency managers to select a range of economic impact based on an estimate of the percentage of damage to the general building stock. Damage in excess of 50% is considered to be substantial by most building codes and typically requires total reconstruction of the structure.

200 Ibid.
201 United States Census Bureau. (2022). DP05: Demographics and Housing Estimates (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP05?g=050XX00US06013. 202 United States Census Bureau. (2022). DP02: Selected Social Characteristics in the United States (2022: ACS 1-Year Estimates Data Profiles). Retrieved from
https://data.census.gov/table/ACSDP1Y2022.DP02?g=050XX00US06013. 203 Migration Policy Institute. (2019). Profile of the Unauthorized Population: Contra Costa County, CA. Retrieved from https://www.migrationpolicy.org/data/unauthorized-immigrant-population/county/6013. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 175 In Contra Costa County, there is a range from the large, state-owned bridges that carry interstate freeways, to locally owned bridges that carry rural roads and pedestrians over small creeks. Countywide, there are over 400 bridges where approximately 80 are owned by the County and 160 are owned by Caltrans. Landslides can cause severe damage to bridges which can cause them to become unstable and fail. State Route 4 and 24, Interstate 80 and 680, and 40 bridges are located within moderate to very high landslide susceptibility areas in Contra Costa County. Disruption to the fourth bore of the Caldecott Tunnel can substantially disrupt regional transportation and connections between the County and the rest of the Bay Area. Also, the following transportation assets are within moderate and high landslide susceptibility zones – North Concord/Martinez BART station, Martinez Amtrak station, Pittsburg/Bay Point BART station, and Lafayette BART station. A landslide disruption (e.g., damage to tracks or stations) could limit transit opportunities within the east and west County.

Electrical transmission and distribution lines are power lines that carry high voltage electricity between power plants and customers. T here are a number of transmission lines throughout the County and a number pass over hills and mountains within high landslide susceptibility areas in the eastern and western portion of the County. The electric infrastructure is extremely vulnerable to landslides as they can be damaged or destroyed. Also, these power lines are used to distribute electricity to other regions in the Bay Area, so, if multiple lines are disrupted due to a landslide it can cause widespread power outages.

Additionally, there are approximately 34 industrial structures within landslide prone areas within the County. In the event a landslide impacts these structures, holding tanks can be disturbed resulting in a chemical release and contamination of surrounding areas. 204

There are a total of 554 critical assets (i.e., schools, nursing homes, fire stations, police stations, and hospitals) throughout the County and 306 (55.2%) are located within a landslide susceptibility area. Table 4-43 provides a breakdown of critical assets that are located within a landslide susceptibility area in Contra Costa County.

Table 4-122. Critical Assets Vulnerable to Landslides
Asset Estimate Percent
(of total asset)
Schools (public schools, private schools) 173 48.1%
Nursing Homes 51 65.4%
Fire Stations 57 70.4%
Police Stations 17 70.8%
Hospitals 8 72.7%

Table 4-126 outlines the total property value exposed to landslides and how the changes in development in the past five (5) years have affected the vulnerability of the community to landslides. Table 4-127 outlines the landslide impacts on total property damage, potential future development, and the economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Environment: A landslide alters the landscape of an area. In addition to changes in topography, vegetation and wildlife habitats may be damaged or destroyed. Soil and sediment runoff will accumulate downslope, potentially blocking waterways and roadways and impairing the quality of streams and other

204 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
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Chapter 4: Hazard Identification and Risk Assessment 176 water bodies. Furthermore, landslides that fall into streams may impact fish and wildlife habitat, as well as affect water quality. Hillsides that provide wildlife habitat can be lost for prolonged periods . In central and western Contra Costa County, some aquatic habitats (i.e., streams, reservoirs, ponds, and sloughs or channels) are located within landslide prone areas. Streams can be blocked by a landslide which significantly affects fish and wildlife habitat because of additional debris that is being added into the habitat. Aquatic ecosystems in the County include the Delta and shoreline areas that are submerged by water, and the three (3) large reservoirs – San Pablo Reservoir, Briones Reservoir, and Los Vaqueros Reservoir. Aquatic wildlife species include various duck species, California red-legged frog, western pond turtle, and juvenile and spawning adult Chinook salmon. 205

Table 4-127 outlines landslide impacts on the environment and economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Changes in Development and Impact of Future Development: Changes in development have not significantly affected the risk from landslides and future development should have minimal impact on risk associated with landslides. Contra Costa County has implemented stricter zoning and building codes and policies for areas that are prone to landslides . For example, projects in areas of known landslide susceptibility require submittal of a geotechnical report and the County ensures effective mitigation measures are incorporated into the project’s design. The implementation of these policies will ensure that future development trends minimally increase impact/consequence of landslides within Contra Costa County.

Table 4-126 outlines how the changes in development in the past five (5) years have affected the vulnerability of the community to landslides. Table 4-127 outlines the landslide impacts on potential future development, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Effects of Climate Change in Severity of Impacts: Climate change does not directly cause more frequent or intense landslides. However, it is expected to increase the conditions that can lead to landslides, such as an increase in heavy storms that saturate the ground and make a landslide more likely. As global average temperatures increase; evaporation increases adding moisture into the atmosphere which results in more precipitation.
206 The frequency and intensity of heavy precipitation
events are projected to increase over the 21 st century.207 Although heavy precipitation does not necessarily result in landslides, landslides are predominantly a result of saturated soils, it is possible that increased intensity of rain events will result in a greater number of landslides annually and an increase in the severity of impacts. Increasing temperatures are expected to increase the occurrence and duration of droughts and the probability of wildfire, reducing the vegetation that helps to support slopes and slows down water. Overall, the impacts of climate change on drought, heavy rainfall, and wildfire will result in an increased probability for landslide occurrences. Table 4-123 indicates the 25-year climate projections in Contra Costa County.

205 Ibid.
206 Environmental Protection Agency. (n.d.). Climate Change Indicators: U.S. and Global Precipitation. Retrieved from https://www.epa.gov/climate-indicators/climate-change-indicators-us-and-global-precipitation. 207 U.S. Global Change Research Program. (2017). Climate Science Special Report: Fourth National Climate Assessment, Volume I (Chapter 7: Precipitation Change in the United States). Retrieved from https://science2017.globalchange.gov/chapter/7/.
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Chapter 4: Hazard Identification and Risk Assessment 177 Table 4-123. 25-Year Climate Projections for Contra Costa County 208 Higher Emissions (RCP8.5)
Contra Costa County is expected to experience a 43% increase in extremely hot days and a 7% increase in days with heavy precipitation within 25 years.

By 2048, Contra Costa County is expected to have a 0.4 inches increase (from 19.6 inches to 20.1 inches) in average annual precipitation.

By 2049, Contra Costa County is expected to experience 11 more days that reach above 95°F (from 23 days to 33 days per year).

Lower Emissions (RCP4.5)
Contra Costa County is expected to experience a 29% increase in extremely hot days and an 8% increase in days with heavy precipitation within 25 years.

By 2048, Contra Costa County is expected to have a 0.15 inches increase (from 19.11 inches to 19.26 inches) in average annual precipitation.

By 2049, Contra Costa County is expected to experience seven (7) more days that reach above 95°F (from 22 days to 29 days per year).

Table 4-127 outlines the climate change impacts to landslides in Contra Costa County, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

208 Northeast Regional Climate Center. (n.d.). Neighborhoods at Risk: Climate Projections. Retrieved from https://nar.headwaterseconomics.org/.
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Chapter 4: Hazard Identification and Risk Assessment 178 Table 4-124. Probability of Occurrence
Hazard Event Probability of Occurrence Probability
Factor
Weighted
Factor
Landslide High Significant hazard event is likely to occur annually. 3 N/A Table 4-125. Extent Factors
Hazard Event Extent Factor Extent Extent
Factor
Weighted
Factor
Landslide
Extent/Intensity Medium Historical and/or probabilistic models/studies for this hazard indicate the possibility of a medium-intensity incident. 2 6 Catastrophic Low Catastrophic hazard event is likely to occur at least once in 51 or more years. 1 3
Table 4-126. Vulnerability Factors
Hazard Event Vulnerability Factor Vulnerability Vulnerability Factor
Weighted
Factor
Landslide
Population Exposure Low 14% or less of the population is exposed to the hazard. 1 3 Property Exposure Low 9% or less of the total assessed property value is exposed to a hazard. 1 2
Changes in
Development Low
Changes in development have increased the
vulnerability/exposure of the community to the hazard by 4% or less.
1 1
Table 4-127. Impact Factors
Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Landslide
Population and Life
Safety Medium
Populations exposed to this hazard are likely to experience some adverse impacts, such as injuries requiring acute
medical care.
2 6
Underserved/Equity Low
Underserved populations exposed to the hazard are likely to experience minimal adverse/disproportionate impacts, such as ambulatory injuries.
1 3
Property Damage High
More than $5 Million in property damages is expected from a single major hazard event, or damages are expected to occur to 15% or more of the property value within the jurisdiction. 3 6
Economic Low Total economic impact is not likely to be greater than $100,000. 1 1
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Chapter 4: Hazard Identification and Risk Assessment 179 Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Environmental Low
Environmental impact from a single major hazard event is likely to be minimal, requiring little to no outside resources and support, and/or minimal repair, clean-up, restoration, or preservation work.
1 1
Essential Operations Medium
Impact between 24 and 72 hours on the ability of the
jurisdiction to meet the essential day-to-day operational demands and needs of the community from a single major
hazard event.
2 2
Future Development Low Future development trends will minimally increase impact/consequence of this hazard. 1 1
Climate Change Medium Climate Change trends will increase the risk of this hazard and its impacts, but not significantly. 2 2

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Chapter 4: Hazard Identification and Risk Assessment 180

4.6.6.8. FEMA NRI Expected Annual Loss Estimates
A landslide NRI EAL score, and rating represent a community's relative level of expected building and population loss each year due to landslides when compared to the rest of the United States. The EAL score is positively associated to a community’s risk; therefore, a higher EAL score results in a higher Risk Index score. Table 4-128 outlines the landslide EAL for Contra Costa County.

Table 4-128. Landslide Expected Annual Loss (FEMA National Risk Index) Jurisdiction Population
Equivalence
Building
Value
Agriculture
Value
Total
Expected
Annual
Loss
Expected
Annual
Loss
Score
Rating
Contra Costa
County $25,121 $207,224 n/a $232,345 94.6 Very High
Expected annual loss scores are calculated utilizing an equation that combines values for exposure, annualized frequency, and historic loss ratios (Expected Annual Loss = Exposure x Annualized Frequency x Historic Loss Ratio).

4.6.6.9. FEMA Landslide Risk Index Scores
The landslide Risk Index score and rating represent a community's relative risk for landslide when compared to the rest of the United States. Table 4-129 illustrates the landslide Risk Index rating and score for Contra Costa County.

Table 4-129. Landslide Risk Index (FEMA National Risk Index) Jurisdiction Rating Score
Contra Costa County Very High 93.7
Risk Index scores are calculated using an equation that combines scores for Expected Annual Loss due to natural hazards, Social Vulnerability and Community Resilience (Expected Annual Loss x Social Vulnerability / Community Resilience = Risk Index).

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Chapter 4: Hazard Identification and Risk Assessment 181 Table 4-130 represents the Landslide Total Risk Score for Contra Costa County, based on the Risk Assessment Methodology, as defined in this Plan. For further details on how the probability, extent, vulnerability, and impact factors were calculated, please refer to Table 4-124 through Table 4-127.

Additional details on how the Total Risk Score was calculated can be found in the Risk Assessment Methodology in Section 4.3 of this Plan.

Table 4-130. Landslide Total Risk Score
Hazard
Event
Probability Consequence Total Risk
Probability
Factor Extent Vulnerability Impact Consequence
Score
Total Risk
Score*
Landslide 3 9 6 22 37 55
Consequence: Sum of all weighted factors.

Extent: Sum of the weighted Extent factors.

Vulnerability: Sum of the weighted Vulnerability factors.

Impact: Sum of the weighted Impact factors.

The Total Risk Score is a measure of Probability and Consequence.

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Chapter 4: Hazard Identification and Risk Assessment 182

4.6.7. Sea Level Rise

4.6.7.1. Description
Sea level rise is the increase in the global mean sea level to the effects of climate change, a trend that is expected to continue. 209 Sea level has a significant role in flooding, coastal erosion, and storm hazards (e.g., coastal flooding).

Increasing global surface temperatures, melting glaciers and ice sheets, and thermal expansion are climate conditions causing sea level to rise globally. However, there are additional factors affecting global sea level change – subsidence and uplift. Vertical land motion (VLM) includes both subsidence and uplift and changes can add up over time. Subsidence may cause a relative rise in local sea levels, but this is highly dependent on localized factors. Likewise, uplift (the opposite of subsidence) may reduce sea level rise. Both instances of land fluctuation occur, on average, to the degree of a few millimeters per year. 210
Regardless of the cause of sea level rise, a higher average sea level means that hazards such as coastal flooding, flooding, and coastal erosion will have more severe impacts to the population, property, and infrastructure.
211

Sea level rise varies regionally along the United States coasts because of land and ocean height variations. In the next three (3) decades sea level rise is anticipated to be, on average, four (4) to eight (8) inches in western United States. Additionally, sea level rise is expected to create a profound shift in coastal flooding in the next 30 years by causing tide and storm surge heights to increase and move further inland. By 2050, damaging flooding is expected to occur, on average, 10 times more often than it does currently, and it can be intensified by other local factors. 212 Currently, the rate of sea level rise in
the San Francisco Bay area roughly matches the global average and expected to be higher than the global average based on half of NOAA’s average sea level rise scenarios. 213 Other sea level rise consequences include: 214

• Contra Costa County’s extensive coastal infrastructure (e.g., critical facilities, transportation networks, residential areas) vulnerability to inundation, erosion, and flooding will increase. • High water levels will become more frequent, increasing in extent, depth, and duration of temporary flooding, and expanding the area that is permanently inundated. Impacts will go beyond the coastal area.

209 National Geographic. (n.d.). Sea Level Rise. Retrieved from https://education.nationalgeographic.org/resource/sea-level-rise/. 210 National Aeronautics and Space Administration, Sea Level Change. (n.d.). Understanding Sea Level.

Retrieved from https://sealevel.nasa.gov/understanding-sea-level/regional-sea-level/subsidence. 211 National Oceanic and Atmospheric Administration, Climate.gov. (2022). Climate Change: Global Sea Level.

Retrieved from https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level. 212 National Oceanic and Atmospheric Administration, National Ocean Service. (2022). 2022 Sea Level Rise Technical Report. Retrieved from https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech- report.html.
213 San Francisco Baykeeper. (n.d.). Sea Level Rise Long California: Questions and Answers. Retrieved from https://baykeeper.org/shoreview/california-slr.html.
214 Contra Costa County Adapting to Rising Tides Project. (2017). Adapting to Rising Tides: Contra Costa County Assessment and Adaptation Project. Retrieved from https://www.adaptingtorisingtides.org/wp- content/uploads/2017/03/Contra-Costa-ART-Project-Report_Final.pdf. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 183 • The hazard poses substantial economic risks, as it threatens businesses, port facilities, and industries reliant on the San Francisco Bay area waterways, potentially resulting in loss of revenue, jobs, and decreased property values.
• Sea level rise can lead to the loss of critical coastal habitats, increased salinity in estuaries, and harm to native species, impacting the region's ecological balance.

4.6.7.2. Hazard Location
All coastal communities in the County are vulnerable to sea level rise. Areas with low lying shorelines such as the City of Richmond and the City of Concord are particularly at risk. Additionally, the extensive coastline along San Pablo and Suisun Bays, including unincorporated County and coastal cities – El Cerrito, San Pablo, Pinole, Hercules, Rodeo, Pittsburg, Antioch, and Martinez. Figures 4-17 and 4-18 depicts the Contra Costa County 2050 and 2100 sea level rise projections, respectively. 215 Figure 4-17. Expected Sea Level Rise 2050 Projection

215 Contra Costa County. (2023). Public Review Draft Contra Costa County 2045 General Plan – Health and Safety Element. Retrieved from https://envisioncontracosta2040.org/wp- content/uploads/2024/02/Chapter_9_Health-and-Safety-Element.pdf.

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Chapter 4: Hazard Identification and Risk Assessment 184 Figure 4-18. Expected Sea Level Rise 2100 Projection

4.6.7.3. Hazard Extent/Intensity
There are no intensity scales for measuring sea level rise. In 2018, the State of California updated the sea level rise projections for San Francisco, based on greenhouse gasses emissions scenarios used by the IPCC in the Fifth Assessment Report, called the Representative Concentration Pathways (RCP). The high emissions represent the RCP 8.5 scenario, and the low emissions represent the RCP 2.6 scenario.

Table 4-131 illustrate the recommended probabilistic projections for the height of sea level rise in the San Francisco area, as see in the Rising Seas Report. 216 Table 4-131. Projected Sea Level Rise for San Francisco Emissions Scenario Year
Likely Range
(feet)
66% probability sea level
rise is between…
1 in 200 Chance
(feet)

0.5% probability sea level
rise meets or exceeds…
High Emissions 2030 0.3 – 0.5 0.8
High Emissions 2040 0.5 – 0.8 1.3
High Emissions 2050 0.6 – 1.1 1.9
Low Emissions
2060

0.6 – 1.3 2.4
High Emissions 0.8 – 1.5 2.6

216 California Natural Resources Agency. (2018). State of California Sea level Rise Guidance (2018 Update).

Retrieved from https://www.opc.ca.gov/webmaster/ftp/pdf/agenda_items/20180314/Item3_Exhibit- A_OPC_SLR_Guidance-rd3.pdf.

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Chapter 4: Hazard Identification and Risk Assessment 185 Emissions Scenario Year
Likely Range
(feet)
66% probability sea level
rise is between…
1 in 200 Chance
(feet)

0.5% probability sea level
rise meets or exceeds…
Low Emissions
2070

0.8 – 1.5 3.1
High Emissions 1.0 – 1.9 3.5
Low Emissions
2080

0.9 – 1.8 3.9
High Emissions 1.2 – 2.4 4.5
Low Emissions
2090

1.0 – 2.1 4.7
High Emissions 1.4 – 2.9 5.6
Low Emissions
2100

1.0 – 2.4 5.7
High Emissions 1.6 – 3.4 6.9
Low Emissions
2110*

1.2 – 2.5 6.3
High Emissions 1.9 – 3.5 7.3
Low Emissions
2120

1.2 – 2.8 7.4
High Emissions 2.2 – 4.1 8.6
Low Emissions
2130

1.3 – 3.1 8.5
High Emissions 2.4 – 4.6 10.0
Low Emissions
2140

1.3 – 3.4 9.7
High Emissions 2.6 – 5.2 11.4
Low Emissions
2150

1.3 – 3.8 11.0
High Emissions 2.8 – 5.8 13.0
Most of the available climate model experiments do not extend beyond 2100. The resulting reduction in model availability causes a small dip in projections between 2100 and 2110, as well as a shift in uncertainty estimates (see Kopp et al. 2014).

Use of 2110 projections should be done with caution and with acknowledgement of increased uncertainty around these projections.

4.6.7.4. Warning Time
There is no warning time mechanism for sea level rise. However, probabilistic projections for sea level rise over various timescales have been developed. These projections are meant to help decision makers to better understand future sea level rise and when a particular level is expected to occur.

4.6.7.5. Probability and Frequency
The probability of occurrence for sea level rise in Contra Costa County is medium because along the Contra Costa County shoreline, sea levels are projected to rise up to about 2 feet (24 inches) by 2050 and 7 feet (84 inches) by 2100. However, it is possible that sea levels could rise faster than these projections, which has happened historically.

Probability of Future Hazard Events
The State of California Sea Level Rise Guidance 2018 update provides the probability of sea level rise meeting or exceeding a particular height for each decade between 2030 and 2150. The probability that sea level rise will meet or exceed a particular height in San Francisco for high emissions (RCP 8.5) is 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 186 listed on Table 4-132 and low emissions (RCP 2.6) is listed on Table 4-133. The areas shaded in gray have less than a 0.1% probability of occurrence. 217
Table 4-132. Probability that Sea level Rise Will Meet or Exceed a Particular Height in San Francisco (High Emissions – RCP 8.5)
1 Feet 2 Feet 3 Feet 4 Feet 5 Feet 6 Feet 7 Feet 8 Feet 9 Feet 10 Feet 2030 0.1%
2040 3.3%
2050 31% 0.4%
2060 65% 3% 0.2% 0.1%
2070 84% 13% 1.2% 0.2% 0.1%
2080 93% 34% 5% 0.9% 0.3% 0.1% 0.1%
2090 96% 55% 14% 3% 0.9% 0.3% 0.2% 0.1% 0.1%
2100 96% 70% 28% 8% 3% 1% 0.5% 0.3% 0.2% 0.1%
2150 100% 96% 79% 52% 28% 15% 8% 4% 3% 2%
Table 4-133. Probability that Sea level Rise Will Meet or Exceed a Particular Height in San Francisco (Low Emissions – RCP 2.6)
1 Feet 2 Feet 3 Feet 4 Feet 5 Feet 6 Feet 7 Feet 8 Feet 9 Feet 10 Feet 2060 43% 1.4% 0.2%
2070 62% 4% 0.6% 0.2% 0%
2080 74% 11% 2% 0.4% 0.2% 0.1%
2090 80% 20% 3% 1.0% 0.4% 0.2% 0.1% 0.1%
2100 84% 31% 7% 2% 0.8% 0.4% 0.2% 0.1% 0.1%
2150 93% 62% 31% 14% 7% 4% 2% 2% 1% 1%

The FEMA NRI analyses coastal flooding – when water inundates or covers normally dry coastal land as a result of high or rising tides or storm surges .
218 The coastal flooding annualized frequency value
represents the modeled frequency of coastal flooding occurrences, in events per year. Table 4-134 outlines the annualized frequency for coastal flooding, based on FEMA NRI data, for Contra Costa County.

Table 4-134. Coastal Flooding Annualized Frequency (FEMA National Risk Index) Location Events on Record Annualized Frequency
Contra Costa County n/a 1.5 events per year
Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year.

217 Ibid.
218 Federal Emergency Management Agency. (n.d.). FEMA National Risk Index: Coastal Flooding. Retrieved from https://hazards.fema.gov/nri/coastal-flooding.
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Chapter 4: Hazard Identification and Risk Assessment 187

4.6.7.6. Past Events
Changes in sea level have been occurring for at least the last 100 years and are projected to continue.

The rate of sea level rise is increasing, and this trend is projected to continue.

4.6.7.7. Vulnerability and Impacts
Life Safety and Health: The population in areas with low lying shorelines (e.g., City of Richmond, City of Concord) are particularly at risk. Additionally, the extensive coastline along San Pablo and Suisun Bays, including unincorporated County and coastal cities – El Cerrito, San Pablo, Pinole, Hercules, Rodeo, Pittsburg, Antioch, and Martinez.

The underserved and at risk population face unique vulnerabilities and impacts as a result of sea level rise. These groups include, but are not limited to, households in poverty, individuals experiencing homelessness, and the population living on single access roads.

• Household in Poverty: Includes those with an income at or below $24,300 for a household of four (4). This population is most likely to live in low lying areas and the structures may not be waterproofed or built above the 100-year flood elevation. In Contra Costa County, the households in poverty within Vine Hill, Bay Point, and North Richmond are vulnerable to sea level rise. • Individuals Experiencing Homelessness: Includes those who do not have a permanent home, including those who live in their vehicles or temporary shelters. This population is uniquely vulnerable to sea level rise because most of the homeless encampments are located along the coastal cities near and within coastal flood areas in the County. Therefore, sea level rise can damage or destroy these encampments and other homeless facilities located within the coastline resulting in additional hardship for this popul ation. In 2024, there are 2,843 people experiencing homelessness in Contra Costa County, an 18.5% increase from 2023. 219
• Individuals Living on Single Access Roads: Includes those living in areas with a single route in and out (i.e., accessible via one (1) roadway) of the neighborhood or area (e.g., Rodeo, Crockett, and Port Costa). This includes several communities in the Delta and in the hillside areas of central and western Contra Costa County. This population is uniquely vulnerable to sea level rise because as sea level continues to rise, these roadways may become permanently impassible.

These communities can become isolated from the community and emergency services in the long term. As illustrated in Figure 4-18, sea level rise is projected to significantly impact the Delta islands located in the eastern section of the County by 2100. 220

Table 4-135 summarizes the vulnerable and at-risk population for sea level rise in Contra Costa County.

Table 4-135. Vulnerability and At Risk Population
Category Estimate Percent
Households in Poverty221 7,600 12.0%

219 Contra Costa Health. (2024). Health, Housing, and Homelessness Data Reports (Point-in-Time Count).

Retrieved from https://www.cchealth.org/services-and-programs/homeless-services/data. 220 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
221 Ibid.
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Chapter 4: Hazard Identification and Risk Assessment 188 Category Estimate Percent
Low Income Households222 25,340 41.0%
Homeless Population223 2,372 0.2%

Table 4-139 outlines the vulnerability of the total population exposed to sea level rise, and Table 4-1 40 outlines the sea level rise impacts to population and life safety, underserved/equity population, and essential operations, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Property Damage and Critical Infrastructure: As sea level continues to rise, repeated disruptions by coastal flooding will aggravate existing impacts on infrastructure, initiate cascading impacts on the larger economy, and burden people. Saltwater intrusion into drinking water sources can result in the need for water utilities to increase treatment, relocate water intakes, or develop alternate sources of fresh water.

Saltwater intrusion, through surface water or groundwater sources, may diminish the availability or quality of source waters for drinking water utilities.

In Contra Costa County, the levees near North Richmond, Vine Hill, and the Delta can be damaged or overtopped due to an increase in coastal storm events and sea level rise is exacerbating the effects of these events. Interstate 80 and 680, and State Route 160 are within sea level rise inundation areas .

Flooding to these roadways and other local roadways can cause major disruptions to local and regional transportation, transit, and commuters.

The BART, Amtrak, and the freight lines are located within the flood areas in coastal and northern Contra Costa County. There are three (3) standard rail lines that run through the County which are operated by Union Pacific, Burlington Northern Santa Fe, and Richmond Pacific Railroad Corporation. These run along the western, northern, and eastern boundaries of the County, along Interstate 80, State Route 4, and Byron Highway. The aforementioned rail lines are used for freight trains; however, the Capitol Corridor commuter train runs along the Union Pacific railway. Additionally, the BART operates its own separate rail lines used exclusively for public transit. Two (2) BART rail lines are located in the County – one beginning in Richmond and heading south toward Berkeley and another one in the central part of the County extending from the City of Orinda to the City of Antioch. Furthermore, some of these rail lines serve as the first line of defense against coastal flooding for communities; these rail lines include Martinez and Antioch Amtrak stations, rail lines along Bay Point, Montalvin Manor, Rodeo, and Port Costa.

The Rodeo sewage treatment plant, West Contra Costa Wastewater, and the Mt. View Sanitary District are within low lying areas along the coastline. Wet weather flows into the treatment plants can be exacerbated with rising sea levels, preventing the system from functioning properly. Treatment plants can also fail if pumps and control panels are not waterproofed or are not salt-resistant. The Contra Costa Canal and Clifton Court Forebay are also within the coastal flooding area. These water and wastewater infrastructure systems are vulnerable to flooding and shoreline flooding which can be exacerbated by sea level rise. Also, there are approximately 44 industrial buildings in Contra Costa County that are located within sea level rise inundation areas. Most industrial and manufacturing centers, important economic drivers to the County, are located within sea level rise inundation areas along the bayfront and Delta in the western and northern portions of Contra Costa County. These center can be damaged by floods

222 Ibid.
223 Contra Costa Health. (2023). Health, Housing, and Homelessness Data Reports (Point-in-Time Count).

Retrieved from https://www.cchealth.org/services-and-programs/homeless-services/data. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 189 which could be exacerbated by sea level rise. These centers are located in the neighborhoods of North Richmond, Rodeo, Crockett, Bay Point, Pacheco, Clyde, and the City of Martinez. 224

There are a total of 554 critical assets (i.e., schools, nursing homes, fire stations, police stations, and hospitals) throughout the County and none are located within inundation areas for one ( 1) foot of sea level rise. Table 4-43 provides a breakdown of critical assets that are located within sea level rise inundation areas for one (1) foot in Contra Costa County.

Table 4-136. Critical Assets in Vulnerable to 1 Foot of Sea Level Rise Asset Estimate Percent
(of total asset)
Schools (public schools, private schools) 0 0.0%
Nursing Homes 0 0.0%
Fire Stations 0 0.0%
Police Stations 0 0.0%
Hospitals 0 0.0%

Table 4-139 outlines the vulnerability of the total property value exposed to a flood event, and the impact on total property damage in the event of a flood, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Environmental: Rising seas increase the risk of flooding, storm surge inundation, erosion and shoreline retreat, and wetland loss. Rising sea levels also threaten a significant portion of prime agricultural land in the County, as low lying areas could be subject to more frequent shoreline flooding and saltwater intrusion into groundwater basins could disrupt agricultural water supplies. Meanwhile, rising tides may increase groundwater levels, inundating contaminated soil and pushing toxins toward the surface. Given that some contaminated sites in Contra Costa County are located near the shoreline, rising groundwater may cause contaminated soil to leach into previously unaffected areas. Natural ecosystems in the Bay and Delta regions will be disrupted by the higher tide levels and intrusion of saltwater into freshwater systems. Historically, marshes have adapted to changes in sea level by building up sediment, increasing the height of the marsh to keep pace with the tide levels of San Francisco Bay, and by moving inland.

However, sea level rise is expected to outpace the rate of marsh-level rise and development near wetlands will likely prevent marsh migration. Without substantial intervention, most tidal marshes in Contra Costa County are expected to convert to another habitat type, a process called “downshifting,” which will lead to the establishment of different plant and animal species. Additionally, sea level rise may push saltwater into the Delta’s aquatic system which will decrease the water quality and harm aquatic species and organisms.

Some of the environmental assets that are vulnerable and can be impacted by sea level rise within the County are considered major economic drivers. Significant impacts to these assets can result in economic challenges to Contra Costa County and disruptions to these resources can impact the economy of populations that rely on these activities.
225

224 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
225 Ibid.
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Chapter 4: Hazard Identification and Risk Assessment 190 • Agriculture: Agriculture land in the eastern and Delta portions of the County are within sea level rise inundation areas and can face significant economic challenges if agriculture is not viable. Sea level rise can inundate farmland increasing the salinity in the water and soil damaging crops that do not grow in high salt conditions. Furthermore, sea level rise can cause saltwater intrusion which can decrease the water supplies for crop irrigation.
• Regional Parks: Regional shorelines and parks on the Bay and Delta could be permanently inundated due to sea level rise resulting in unusable parks which may not meet the demands of the public.
• The Delta: The Sacramento-San Joaquin River Delta spans from the City of Pittsburg in the west, Locke in the east, Sacramento to the North, and Tracy to the south. The Delta primarily encompasses the northern and easternmost borders of Contra Costa County and provides opportunities for boating, fishing, transportation, and a water source for the County. Sea level rise can continually or permanently inundate marinas, harbors, farmland, and other recreational facilities within the Delta. Furthermore, saltwater intrusion can disrupt water quality and fish/wildlife population.

Table 4-140 outlines sea level rise impacts on the environment and economy, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Changes in Development and Impact of Future Development: There have been no significant changes in development that have affected the risks associated with sea level rise. Future increases in population within the sea level inundation area and coastal communities will increase vulnerability and impacts to sea level rise. Growth over the past decade has considerably increased. Between 2010 and 2022, as outlined in Table 3-3, the population in Contra Costa County grew 10.6%, from 1,046,025 to 1,156,966 residents. The Bay Area Association of Governments (ABAG) growth forecasts predict a steady increase in households through 2050. From 2015 to 2050, ABAG projects that the County’s number of households will grow by 44%.
226 As sea level continues to rise, floodplain boundaries may expand further inland exposing areas that are not currently vulnerable to sea level rise. Additionally, the communities in Contra Costa County that are protected by levees may become more vulnerable because the levee will become increasingly vulnerable to overtopping due to increasing sea level.

Table 4-139 outlines how the changes in development in the past five (5) years have affected the vulnerability of the community to sea level rise. Table 4- 140 outlines the sea level rise impacts on potential future development, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

Effects of Climate Change in Severity of Impacts: The primary reasons for sea level rise are the added water from ice sheets and glaciers and the ocean water’s thermal expansion, both of which are a result of increasing global average temperatures.
227 Since 1880, the global average sea level has risen
between eight (8) to nine (9) inches and in 2022 the average sea level was four (4) inches above 1993 levels, a record high. Due to land processes (e.g., erosion, oil and groundwater pumping, subsidence), the rate of local sea level rise along the United States coastline is greater than the global average.

Furthermore, high tide flooding between 300% and 900% more frequent than 50 years ago. 228

226 Bay Area Association of Government. (2020). Plan Bay Area 2050 Final Blueprint Growth Pattern. Retrieved from https://planbayarea.org/digital-library/plan-bay-area-2050-final-blueprint-growth-pattern. 227 National Aeronautics and Space Administration. (2023). Sea Level. Retrieved from https://climate.nasa.gov/vital-signs/sea-level/.
228 Lindsey, R. (2022). Climate Change: Global Sea Level. Retrieved from https://www.climate.gov/news- features/understanding-climate/climate-change-global-sea-level. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 191 In California, observations of climate have shown that sea level rise is expected to continue to increase flooding and erosion of beaches, bluffs, and cliffs. Relative to the average sea levels between 1991 and 2009, sea levels in California may increase in most places by six (6) to 10 inches by 2030, 13 to 23 inches by 2050, and 41 to 83 inches by 2100. However, it is possible that sea level may increase faster than these projections. Studies show that eventually, sea levels may increase enough to permanently inundate low lying areas near the Bay shoreline and the Delta areas. 229

Table 4-140 outlines the climate change impacts to sea level rise in Contra Costa County, as outlined in the risk assessment methodology in Section 4.3 of this Plan.

229 Contra Costa County. (2023). Climate Action Plan (Public Review Draft). Retrieved from https://envisioncontracosta2040.org/wp-content/uploads/2023/10/CoCoCounty-2024CAP-PublicDRAFT-10-10- 23_Final.pdf.
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Chapter 4: Hazard Identification and Risk Assessment 192 Table 4-137. Probability of Occurrence
Hazard Event Probability of Occurrence Probability
Factor
Weighted
Factor
Sea Level Rise Medium Significant hazard event is likely to occur within 25 years. 2 N/A Table 4-138. Extent Factors
Hazard Event Extent Factor Extent Extent
Factor
Weighted
Factor
Sea Level Rise
Extent/Intensity Medium Historical and/or probabilistic models/studies for this hazard indicate the possibility of a medium-intensity incident. 2 6 Catastrophic Medium Catastrophic hazard event is likely to occur at least once between 11 and 50 years. 2 6
Table 4-139. Vulnerability Factors
Hazard Event Vulnerability Factor Vulnerability Vulnerability Factor
Weighted
Factor
Sea Level Rise
Population Exposure Low 14% or less of the population is exposed to the hazard. 1 3 Property Exposure Low 9% or less of the total assessed property value is exposed to a hazard. 1 2
Changes in
Development Low
Changes in development have increased the
vulnerability/exposure of the community to the hazard by 4% or less.
1 1
Table 4-140. Impact Factors
Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Sea Level Rise
Population and Life
Safety No Impact Populations exposed to this hazard are not likely to experience significant adverse impacts. 0 0
Underserved/Equity Low
Underserved populations exposed to the hazard are likely to experience minimal adverse/disproportionate impacts, such as ambulatory injuries.
1 3
Property Damage Medium
More than $500,000 but less than $5 Million in property damages is expected from a single major hazard event, or damages are expected to occur to more than 5% but less
than 15% of the property value within the jurisdiction. 2 4
Economic Medium Total economic impact is likely to be greater than $500,000, but less than or equal to $10 Million. 2 2
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Chapter 4: Hazard Identification and Risk Assessment 193 Hazard Event Impact Factor Impact Impact
Factor
Weighted
Factor
Environmental Medium
Environmental impact from a single major hazard event is likely to be localized, requiring some outside resources and support; and/or repair, clean-up, restoration, or preservation work.
2 2
Essential Operations Low
Impact less than 24 hours on the ability of the jurisdiction to meet the essential day-to-day operational demands and
needs of the community from a single major hazard event. 1 1
Future Development Medium Future development trends will increase the impact/consequence of this hazard, but not significantly. 2 2 Climate Change High Climate Change trends will significantly increase the risk of this hazard and its impacts. 3 3

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Chapter 4: Hazard Identification and Risk Assessment 194

4.6.7.8. FEMA NRI Expected Annual Loss Estimates
A coastal flooding NRI EAL score, and rating represent a community's relative level of expected building and population loss each year due to coastal flooding when compared to the rest of the United States.

The EAL score is positively associated to a community’s risk; therefore, a higher EAL score results in a higher Risk Index score. Table 4-141 outlines the coastal flooding EAL for Contra Costa County.

Table 4-141. Coastal Flooding Expected Annual Loss (FEMA National Risk Index) Jurisdiction Population
Equivalence
Building
Value
Agriculture
Value
Total
Expected
Annual
Loss
Expected
Annual
Loss
Score
Rating
Contra Costa
County $79.2 Billion $2.1 Billion N/A $81.3 Billion 56.8 Relatively Moderate
Expected annual loss scores are calculated utilizing an equation that combines values for exposure, annualized frequency, and historic loss ratios (Expected Annual Loss = Exposure x Annualized Frequency x Historic Loss Ratio).

4.6.7.9. FEMA Coastal Flooding Risk Index Scores
The coastal flooding Risk Index score and rating represent a community's relative risk for coastal flooding when compared to the rest of the United States. Table 4-142 illustrates the coastal flooding Risk Index rating and score for Contra Costa County.

Table 4-142. Coastal Flooding Risk Index (FEMA National Risk Index) Jurisdiction Rating Score
Contra Costa County Relatively Moderate 57.5
Risk Index scores are calculated using an equation that combines scores for Expected Annual Loss due to natural hazards, Social Vulnerability and Community Resilience (Expected Annual Loss x Social Vulnerability / Community Resilience = Risk Index).

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Chapter 4: Hazard Identification and Risk Assessment 195 Table 4-143 represents the Sea Level Rise Total Risk Score for Contra Costa County, based on the Risk Assessment Methodology, as defined in this Plan. For further details on how the probability, extent, vulnerability, and impact factors were calculated, please refer to Table 4-137 through Table 4-140.

Additional details on how the Total Risk Score was calculated can be found in the Risk Assessment Methodology in Section 4.3 of this Plan.

Table 4-143. Sea Level Rise Total Risk Score
Hazard
Event
Probability Consequence Total Risk
Probability
Factor Extent Vulnerability Impact Consequence
Score
Total Risk
Score*
Sea Level Rise 2 12 6 17 35 37
Consequence: Sum of all weighted factors.

Extent: Sum of the weighted Extent factors.

Vulnerability: Sum of the weighted Vulnerability factors.

Impact: Sum of the weighted Impact factors.

The Total Risk Score is a measure of Probability and Consequence.

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Chapter 4: Hazard Identification and Risk Assessment 196

4.6.8. Severe Weather

4.6.8.1. Description
For the purposes of this Plan, severe weather includes those hazards that are typically produced during severe thunderstorms (i.e., hail, strong winds, and tornado), heavy rainfall, and heat wave.

Severe Thunderstorms
A thunderstorm is a rain shower during which you hear thunder and since thunder includes lightning, then all thunderstorms include lightning. However, a thunderstorm is classified as severe when it contains one (1) or more of the following – hail one (1) inch or greater, winds gusting in excess of 58 mph, and/or a tornado.
230

Included below are the hazards that comprise a severe thunderstorm – hail, strong winds, tornado. Each hazard is examined independently, but it is recognized that these could occur simultaneously.

Hail
Hail is a form of precipitation that consists of solid ice that forms inside thunderstorm updrafts. During a thunderstorm, hail forms when raindrops are carried upward by the thunderstorm’s updrafts into extremely cold air and freeze. As the hailstones continue to be carried upward, they continue to collide with liquid water drops that freeze into the surface of the hailstone. Once the thunderstorm’s updraft can no longer hold the weight of the hailstone, which occurs when the updraft weakens or the hailstone is too heavy, then the hail falls. When a hailstone encounters different liquid water content conditions and temperatures within the thunderstorms, it causes hailstone to have layers of clear and cloudy ice. The speed at which hail falls primarily depends on four (4) characteristics – hail size, friction between the hailstone and surrounding air, local wind conditions (horizontal and vertical), and degree of melting of the hailstone. There is much uncertainty in the average speed hail falls; however, NOA A developed the estimates shown on Table 4-144.
231
Table 4-144. Hail Speed Estimates
Hail Size (inches) Fall Speed (mph)
Less than 1 9 – 25
1 – 1.75 20 – 40
2 – 4 44 – 72
4 or greater Over 100

230 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Thunderstorm Basics. Retrieved from https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/. 231 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Hail Basics. Retrieved from https://www.nssl.noaa.gov/education/svrwx101/hail/.
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Chapter 4: Hazard Identification and Risk Assessment 197 Strong Winds
Strong winds, also known as damaging winds, are classified as exceeding 58 mph and often originate from thunderstorms.
232 Most severe thunderstorm winds that cause damage at the ground are a result of outflow generated by the downdraft of a thunderstorm. Table 4-145 outlines the different types of strong winds. 233

In coastal regions a strong wind is called a gale. Gale winds are sustained surface winds between 34 and 47 knots (39 to 54 mph).

Table 4-145. Types of Strong Winds
Type Description
Straight-line Wind Term used to define any thunderstorm wind that is not associated with a rotation and is used mainly to differentiate from tornadic winds.

Downdraft A small-scale column of air that rapidly winds towards the ground.

Macroburst
An outward burst of strong winds at or near the surface with horizontal dimensions larger than 2.5 miles and occurs when a strong downdraft reaches the surface.

Macroburst winds may begin over a smaller area and then spread out over a wider area, sometimes producing damage similar to a tornado. Although usually associated with thunderstorms, macrobursts can occur with showers too weak to produce thunder.

Microburst
A small, concentrated downburst that produces an outward burst of strong winds at or near the surface. Microbursts are small (less than 2.5 miles across) and short-lived (five (5) to 10 minutes) with maximum windspeeds sometimes exceeding 100 mph.

There are two (2) 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
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 wind pushes up air above them, forming a shelf cloud or detached roll cloud.

Derecho
A widespread, long -lived windstorm that is associated with a band of rapidly moving showers or thunderstorms. A typical derecho consists of numerous downbursts and downburst clusters. By definition, if the wind damage swath extends more than 240 miles and includes wind gusts of at least 58 mph or greater along most of its length, then the event may be classified as a derecho.

Haboob A wall of dust that is pushed out along the ground from a thunderstorm downdraft at high speeds.
*A downburst is the general term used to broadly describe macro and microbursts.

Tornado
A tornado is a narrow, violently rotating column of air that extends from a thunderstorm to the ground. A tornado is hard to see unless it forms a condensation funnel made up of water droplets, dust, and debris.

Tornadoes are among the most violent phenomena of all atmospheric storms and atmospheric scientists continue to conduct research to better understand how tornadoes form. Tornadoes come from mainly

232 Federal Emergency Management Agency. (n.d.). Strong Wind. Retrieved from https://hazards.fema.gov/nri/strong-wind.
233 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Types of Damaging Winds. Retrieved from https://www.nssl.noaa.gov/education/svrwx101/wind/types/. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 198 two (2) types of thunderstorms – supercell and non-supercell. 234 Table 4-146 outlines the types of tornadoes. 235
Table 4-146. Types of Tornadoes
Type Description
Supercell
The most common and destructive tornadoes occur from supercells. A supercell is a rotating thunderstorm with a well-defined radar circulation called a mesocyclone.

Supercells can also produce damaging hail, severe non-tornadic winds, frequent lightning, and flash floods. The rotating updraft from a supercell is the key development for a tornado. One way a column of air can begin to rotate is from wind shear when winds at two (2) different levels above the ground blow at different speeds or in different directions. Once the updraft is rotating and fed with warm moist air flowing in the ground level, a tornado can form.

Non-Supercell
Nearly 20% of all tornadoes are associated with lines of strong thunderstorms called quasi-linear convective systems (QLCS). QLCS tornadoes frequently occur during the late night and early morning hours. These tornadoes, however, tend to be weaker and shorter-lived on average than those associated with supercell thunderstorms. NOAA’s National Severe Storms Laboratory (NSSL) researchers are looking for ways to detect QLCS tornadoes more effectively.

Another type of non-supercell tornado is a landspout. A landspout is a tornado with a narrow, rope-like condensation funnel that forms while the thunderstorm cloud is still growing and there is no rotating updraft - the spinning motion originates near the ground.

Heavy Rainfall
There is no single definition for heavy (or extreme) rainfall. However, meteorologists consider instances where the amount of precipitation (rain or snow) experienced in a location substantially exceeds normal amounts. The amount of precipitation needed to qualify as heavy rain varies with location and season.

Rainfall events share characteristics such as high moisture and an atmospheric disturbance (e.g., winter storm, atmospheric river) and when these conditions persist over an area the more rainfall an area will receive.
236 Heavy rainfall 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)
237.

Atmospheric River
A relatively common weather pattern that brings heavy rainfall and mountain snow to California is often referred to as an atmospheric river. About 30% to 50% of the annual precipitation in the west coast states occurs during a few atmospheric river events and approximately 80% of the levee breaches in the California’s Central Valley are associated with atmospheric rivers . 238 Atmospheric rivers are long, concentrated regions in the atmosphere that transport moist air from the tropics to higher latitudes . The combination of moist air and high wind speeds produce heavy precipitation upon landfall, especially over mountainous terrain. As atmospheric rivers move over land, conditions can be similar to a tropical cyclone

234 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Tornado Basics. Retrieved from https://www.nssl.noaa.gov/education/svrwx101/tornadoes/. 235 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Types of Tornadoes. Retrieved from https://www.nssl.noaa.gov/education/svrwx101/tornadoes/types/. 236 National Oceanic and Atmospheric Administration. (2018). Ask the Scientist: Extreme Rainfall, Why it Happens and How We Predict It. Retrieved from https://www.noaa.gov/stories/ask-scientist-extreme-rainfall-why-it- happens-and-how-we-predict-it.
237 United States Environmental Protection Agency. (2023). Climate Change Indicators: Heavy Precipitation.

Retrieved from https://www.epa.gov/climate-indicators/climate-change-indicators-heavy-precipitation. 238 Monroe, R. (2019). New Scale To Characterize Strength And Impacts Of Atmospheric River Storms. Retrieved from https://scripps.ucsd.edu/news/new-scale-characterize-strength-and-impacts-atmospheric-river-storms. 2024 Hazard Mitigation Plan
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Chapter 4: Hazard Identification and Risk Assessment 199 leading to flash flooding, mudslides, cyclone force winds, increased wave heights, and catastrophic damage to life and property. 239
Heat Wave / Extreme Heat
The definition of a heat wave varies based on different factors, such as location, weather conditions (e.g., temperature, humidity, cloud cover) and the time of year. 240 However, excessive/extreme heat can be
defined as a prolonged period of excessively hot weather, with temperatures above the average high.241 Heat alone does not make high temperatures a threat; both humidity and heat combined is what makes high temperatures a dangerous.
242 The Heat Index is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature (i.e., ambient temperature).

Figure 4-19 illustrates NWS’ Heat Index Chart. The NWS primarily uses Heat Index values to determine excessive heat events and issue the appropriate advisories. 243
Figure 4-19. National Weather Service Heat Index Chart

239 National Oceanic and Atmospheric Administration. (2023). Atmospheric Rivers: What are They and How Does NOAA Study Them? Retrieved from https://research.noaa.gov/2023/01/11/atmospheric-rivers-what-are-they-and- how-does-noaa-study-them/.
240 U.S. Environmental Protection Agency and the Centers for Disease Control and Prevention. (2016). Climate Change and Extreme Heat: What You Can Do to Prepared. Retrieved from https://www.epa.gov/sites/default/files/2016-10/documents/extreme-heat-guidebook.pdf. 241 Federal Emergency Management Agency. (n.d.). Extreme Heat | What. Retrieved from https://community.fema.gov/ProtectiveActions/s/article/Extreme-Heat-What. 242 National Oceanic and Atmospheric Administration. (2022). Heat Index. Retrieve from https://www.noaa.gov/jetstream/global/heat-index#.
243 National Weather Service. (n.d.). Heat Forecast Tools. Retrieved from https://www.weather.gov/safety/heat- index.

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Chapter 4: Hazard Identification and Risk Assessment 200

4.6.8.2. Hazard Location
Severe Thunderstorms (i.e., hail, strong winds, and tornado), heavy rainfall, atmospheric river, and heat waves can occur anywhere in Contra Costa County . Figure 4-20 illustrates hail events within five (5) miles of Contra Costa County that occurred between 1950 and 2023.

Figure 4-20. Contra Costa County Hail History (1950 – 2023)

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Chapter 4: Hazard Identification and Risk Assessment 201 Figure 4-21 illustrates strong wind events within five (5) miles of Contra Costa County that occurred between 1950 and 2023.

Figure 4-21. Contra Costa County Strong Wind History (1950 – 2023)

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Chapter 4: Hazard Identification and Risk Assessment 202 Figure 4-22 illustrates tornado events within five (5) miles of Contra Costa County that occurred between 1950 and 2023.

Figure 4-22. Contra Costa County Tornado History (1950 – 2023)

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Chapter 4: Hazard Identification and Risk Assessment 203

4.6.8.3. Hazard Extent/Intensity
Severe weather can be life threatening and can cause substantial damage to infrastructure and property.

The extent of damage caused by severe weather depends on the type of severe weather, strength, and location.

Figure 4-23 illustrates the severe thunderstorm outlook categories used by the NWS Storm Prediction Center (SPC) when issuing Severe Thunderstorm Outlooks.

Figure 4-23. SPC Severe Thunderstorm Outlook Categories

Hail can vary in shapes and sizes, and only the very large hailstones pose a serious risk to life safety.

NWS reports hail size by comparing the hailstone with traditional object to size conversion for assessment and translation of severe hail reports. Table 4-147 lists the traditional conversion of hail size descriptions.
244
Table 4-147. Converting Traditional Hail Size Descriptions Hail Size
(inches) Object Analog Reported

0.25 Pea

0.50 Mothball

0.75 Penny

0.88 Nickel

1.00 Quarter

1.50 Walnut, ping pong

244 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Hail Basics. Retrieved from https://www.nssl.noaa.gov/education/svrwx101/hail/.

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Chapter 4: Hazard Identification and Risk Assessment 204 Hail Size
(inches) Object Analog Reported

1.75 Golf ball

2.50 Tennis ball

2.75 Baseball

3.00 Teacup

4.00 Softball

4.50 Grapefruit

The Beaufort Wind Scale was developed to estimate and report wind speeds when a measuring apparatus is not available (e.g, open sea). It was invented in the 1805 by Sir Francis Beaufort of the British Navy as a way to interpret wind conditions at sea. Since then, the scale has been modified to include the effects on land. Table 4-148 outlines the 13 force classification that comprise the Beaufort Wind Scale.
245
Table 4-148. Beaufort Wind Scale
Force Wind
(knots) Classification Appearance of Wind Effects
On the Water On Land
0 < 1 Calm Sea surface smooth and mirror-
like. Calm, smoke rises vertically.
1 1 – 3 Light Air Scaly ripples and no foam crests. Smoke drift indicates wind direction and still wind vanes.
2 4 – 6 Light Breeze Small wavelets, crests glassy, and no breaking.

Wind felt on face, leaves rustle,
and vanes begin to move.
3 7 – 10 Gentle Breeze Large wavelets, crests begin to
break, and scattered whitecaps.

Leaves and small twigs constantly
moving, and light flags extended.
4 11 – 16 Moderate
Breeze
Small waves of one (1) to four (4)
feet becoming longer with
numerous whitecaps.

Dust, leaves, and loose paper
lifted, and small tree branches
move.
5 17 – 21 Fresh Breeze
Moderate waves of four (4) to
eight (8) feet taking longer form,
many whitecaps, and some spray.

Small trees and leaves begin to
sway.
6 22 – 27 Strong Breeze
Larger waves of eight (8) to 13
feet, whitecaps are common, and
more spray.

Larger tree branches moving and
whistling in wires.
7 28 – 33 Near Gale
Sea heaps up, waves are 13 to 19
feet, white foam streaks off
breakers.

Whole trees moving and
resistance felt walking against
wind.
8 34 – 40 Gale
Moderately high waves (18 to 25
feet) of greater length, edges of
crests begin to break into spindrift,
and foam blown in streaks.

Twigs breaking off trees and
generally impedes progress.
9 41 – 47 Strong Gale
High waves (23 to 32 feet), sea
begins to roll, dense streaks of
foam, and spray may reduce
visibility.

Slight structural damage occurs,
and slate blows off roofs.

245 National Weather Service. (n.d.). Beaufort Wind Scale. Retrieved from https://www.spc.noaa.gov/faq/tornado/beaufort.html.
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Chapter 4: Hazard Identification and Risk Assessment 205 Force Wind
(knots) Classification Appearance of Wind Effects
On the Water On Land
10 48 – 55 Storm
Very high waves (29 to 41 feet)
with overhanging crests, sea white
with densely blown foam, heavy
rolling, and lowered visibility.

Seldom experienced on land, trees
broken or uprooted, and
considerable structural damage.
11 56 – 63 Violent Storm
Exceptionally high waves (37 to 52
feet), foam patches cover sea, and
visibility more reduced.
--
12 > 63 Hurricane
Air filled with foam, waves over 45
feet, sea completely white with
driving spray, and visibility greatly
reduced.

See Saffir-Simpson Hurricane
Wind Scale.

Tornado rating, based on the Enhance Fujita Scale (EF Scale), is assigned after tornado-related damage is surveyed. The EF Scale is based on the estimated wind speeds and related damage. Table 4-149 outlines the EF Scale. When tornado damages are surveyed, they are compared to a list of Damage Indicators and Degrees of Damage which help to better estimate the range of wind speeds the tornado likely produced. The EF Scale was revised from the original Fujita Scale and became operational in February 2007.
246
Table 4-149. Enhanced Fujita Scale
EF Rating 3 Second Gust
(mph)
0 65 – 85
1 86 – 110
2 111 – 135
3 136 – 165
4 166 – 200
5 Over 200

The NWS HeatRisk Tool Prototype is a color numeric-based index that provides a forecast of the potential level of risk for heat-related impacts to occur in a 24-hour period. This serves as a supplementary tool for official NWS heat products and is meant to provide risk guidance for decision-makers and heat-vulnerable populations who require certain actions at levels that may be below the NWS heat product thresholds.

Table 4-150 outlines the NWS HeatRisk categories and risk of heat-related impacts. 247
Table 4-150. NWS HeatRisk Categories
Category Risk of Heat-Related Impacts
0 Green Little to no risk from expected heat.
1 Yellow Minor: This level of heat affects primarily those individuals extremely sensitive to heat, especially when outdoors without effective cooling and/or adequate hydration.

246 National Weather Service. (n.d.). The Enhance Fujita Scale (EF Scale). Retrieved from https://www.weather.gov/oun/efscale.
247 National Weather Service. (n.d.). NWS HeatRisk Prototype. Retrieved from https://www.wrh.noaa.gov/wrh/heatrisk/.
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Chapter 4: Hazard Identification and Risk Assessment 206 Category Risk of Heat-Related Impacts
2 Orange
Moderate: This level of heat affects most individuals sensitive to heat, especially those without effective cooling and/or adequate hydration. Impacts possible in some health systems and in heat-sensitive industries.
3 Red
Major: This level of heat affects anyone without effective cooling and/or adequate hydration. Impacts likely in some health systems, heat-sensitive industries, and infrastructure.
4 Magenta
Extreme: This level of rare and/or long-duration extreme heat with little to no overnight relief affects anyone without effective cooling and/or adequate hydration. Impacts likely in most health systems, heat-sensitive industries, and infrastructure.

The HeatRisk takes into consideration the following – how unusual the heat is for the time of the year, the duration of the heat including both daytime and nighttime temperatures, and those temperatures that pose an elevated risk of heat-related impacts based on data from the CDC.

The Atmospheric River Scale was developed in collaboration with the Center for Western Water and Weather Extremes at Scripps Institution of Oceanography at University of California San Diego and National Weather Service. The scale uses the amount of water vapor within the atmospheric river as its basis and a period of 24 to 48 hours as its standard measurement of duration. For example, if an atmospheric river remains over an area for over 48 hours the category is increased one and if it is less than 24 hours it is decreased by a category. The Atmospheric River Scale has five (5) categories outlined in Table 4-151. 248
Table 4-151. Atmospheric River Scale
Category Description
1 Weak Primarily beneficial.
2 Moderate Mostly beneficial, but also hazardous.
3 Strong Balance of beneficial and hazardous.
4 Extreme Mostly hazardous, but also beneficial.
5 Exceptional Primarily hazardous.

4.6.8.4. Warning Time
The NWS SPC is responsible for issuing severe thunderstorms and tornado advisories, as conditions warrant. Table 4-152 outlines the severe thunderstorms and tornado advisories. 249 Table 4-152. NWS Severe Weather Advisories
Type Description
Severe Thunderstorm
Watch
Issued by the NOAA SPC when conditions are favorable for the development of severe thunderstorms in and close to the watch area. The size of the watch can vary depending on the weather situation. Severe thunderstorm watches are usually issued for a duration of four (4) to eight (8) hours. They are normally issued well in advance of the actual occurrence of severe weather.

248 Monroe, R. (2019). New Scale To Characterize Strength And Impacts Of Atmospheric River Storms. Retrieved from https://scripps.ucsd.edu/news/new-scale-characterize-strength-and-impacts-atmospheric-river-storms. 249 National Weather Service. (n.d.). National Weather Service Glossary. Retrieved from https://w1.weather.gov/glossary/.
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Chapter 4: Hazard Identification and Risk Assessment 207 Type Description
Severe Thunderstorm
Warning
Issued by the local NWS Forecast Office when either a severe thunderstorm is indicated by radar, or a spotter reports a thunderstorm producing hail one (1) inch or larger in diameter and/or winds equal or exceed 58 mph. Severe thunderstorm warnings are usually issued for a duration of one (1) hour. They can be issued without a Severe Thunderstorm Watch being already in effect. Severe thunderstorms can produce tornadoes with little or no advance warning.

Tornado Watch
Issued by the SPC when conditions are favorable for the development of tornadoes in and close to the watch area. The size of the watch can vary depending on the weather situation. Tornado watches are usually issued for a duration of four (4) to eight (8) hours. They are normally issued well in advance of the actual occurrence of tornadoes.

Tornado Warning
Issued by the local NWS Forecast Office when either a tornado is indicated by radar or sighted by spotters. Tornado warnings are usually issued for a duration of around 30 minutes. They can be issued without a Tornado Watch being already in effect Gale Watch
Issued by the local NWS Forecast Office for locations along the water when one (1) or both of the following conditions is possible to begin within 36 hours and is not directly associated with a tropical cyclone – sustained winds of 34 to 47 knots (39 to 55 mph) or frequent gusts (duration of two (2) or more hours) between 34 to 47 knots (39 to 55 mph).

Gale Warning
Issued by the local NWS Forecast Office for locations along the water when one (1) or both of the following conditions is expected to begin within 36 hours and is not directly associated with a tropical cyclone – sustained winds of 34 to 47 knots (39 to 55 mph) or frequent gusts (duration of two (2) or more hours) between 34 to 47 knots (39 to 55 mph). At this point, the vessel needs to be secure at port.

Heavy rainfall can lead to flooding, which can be unexpected and leave a small window of time for evacuation if it is required. The NWS San Francisco Bay Area Forecast Office is responsible for issuing flood advisories and Flash Flood Warnings Impact-Based Warnings for events that occur within approximately six (6) hours of heavy rainfall in Contra Costa County. Refer to the Flood section of this Plan for more information on the warning time during a heavy rainfall event.

During an excessive heat event, the NWS San Francisco Bay Area Forecast Office issues excessive heat advisories, watches, and warnings. Table 4-153 outlines the heat- related products issued by the local NWS Forecast Office. NWS’ local offices collaborate with local agencies (e.g., emergency managers, public health professionals) to determine when an alert should be issued for the local area by establishing heat index thresholds for each advisory.

Table 4-153. NWS Excessive Heat Advisories
Type Definition
Excessive Heat Outlook
Issued when the potential exists for an excessive heat event in the next 3-7 days. An Outlook provides information to those who need considerable lead time to prepare for the event.

Heat Advisory
Issued within 12 hours of the onset of extremely dangerous heat conditions.

Generally, an advisory is issued when the heat index values are expected to reach 100°F or higher for at least two (2) days, and nighttime air temperatures will not drop below 75°F.

Excessive Heat Watch
Issued when conditions are favorable for an excessive heat event in the next 24 to 72 hours. Generally, a watch is issued when the risk of a heat wave has increased, but its occurrence and timing is still uncertain
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 208 Type Definition
Excessive Heat Warning
Issued within 12 hours of the onset of extremely dangerous heat conditions.

Generally, a warning is issued when the heat index values are expected to reach 105°F or higher for at least two (2) days and nighttime air temperatures will not drop below 75°F.

4.6.8.5. Probability and Frequency
The probability of occurrence for severe weather in Contra Costa County is high because significant severe weather events are likely to occur annually.

Probability of Future Hazard Events
The hail annualized frequency value represents the average number of recorded hail hazard occurrences, in event days, per year over the period of record (34 years). Table 4-154 outlines the annualized frequency for hail, based on FEMA NRI data, for Contra Costa County.

Table 4-154. Hail Annualized Frequency (FEMA National Risk Index) Location Events on Record
(1986 – 2021) Annualized Frequency
Contra Costa County 2 0.0 events per year
Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year.

The strong wind annualized frequency value represents the average number of recorded strong wind hazard occurrences, in event days, per year over the period of record (34 years). Table 4-155 outlines the annualized frequency for strong winds, based on FEMA NRI data, for Contra Costa County.

Table 4-155. Strong Wind Annualized Frequency (FEMA National Risk Index) Location Events on Record
(1986 – 2021) Annualized Frequency
Contra Costa County 2 0.0 events per year
Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year.

The tornado annualized frequency value represents the average number of recorded tornado hazard occurrences, in event days, per year over the period of record (72 years). Table 4-156 outlines the annualized frequency for tornadoes, based on FEMA NRI data, for Contra Costa County.

Table 4-156. Tornado Annualized Frequency (FEMA National Risk Index) Location Events on Record
(1950 – 2021) Annualized Frequency
Contra Costa County 5 0.1 events per year
Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year.

The heat wave annualized frequency value represents the average number of recorded heat wave hazard occurrences in event days, per year over the period of record (16 years). Table 4-157 outlines the annualized frequency for heat waves, based on FEMA NRI data, for Contra Costa County. 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 209 Table 4-157. Heat Wave Annualized Frequency (FEMA National Risk Index) Location Events on Record
(2005 – 2021) Annualized Frequency
Contra Costa County 27 1.8 events per year
Annualized frequency is defined as the expected frequency or probability of a hazard occurrence per year.

4.6.8.6. Past Events
NCEI has reported 95 severe thunderstorm events which include 92 high wind events (58 mph or greater) and five (5) tornado events between 1950 – 2023. There have been no hail events greater than one (1) inch reported by NCEI. Additionally, NCEI has reported 35 heavy rainfall events between 1950 and 2023 in Contra Costa County. Additionally, there have been eight (8) flood disasters, and six (6) severe storm disasters declared in Contra Costa County between 1950 and 2023. A notable event occurred between December 26, 2022, through January 17, 2023, a series of six (6) storm systems moved through the San Francisco Bay area resulting in widespread flooding, including river flooding. In Contra Costa County, the event resulted in a series of Flood Warnings and rainfall amounts ranged from 6.2 inches to 20.07 inches.
250 On January 9, 2023, a Major Disaster Declaration (DR-3591) was issued for this event.

Table 4-158 lists strong wind events, Table 4-159 lists tornado events, Table 4-160 lists heavy rainfall events, and Table 4-161 lists heat events that have occurred in the Contra Costa County between 1950 and 2023 according to NCEI.

Table 4-158. Strong Winds Events (1950 – 2023)
Location
County /
Zone State Date Time Type Death Injury
Property
Damage
Crop
Damage

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 3/28/2023 07:48 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS
(ZONE) East Bay Hills CA 3/28/2023 09:40 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 3/28/2023 10:10 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 3/21/2023 13:04 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 3/21/2023 14:29 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 3/14/2023 07:45 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS
(ZONE) East Bay Hills CA 3/14/2023 11:20 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS
(ZONE) East Bay Hills CA 3/9/2023 21:20 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/21/2023 13:33 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/21/2023 15:22 High Wind 0 0 0.00K 0.00K

250 National Weather Service, San Francisco Bay Area, California Weather Forecast Office. (2023). A Parade of Storms Impact Bay Area. Retrieved from https://www.weather.gov/mtr/AtmosphericRivers_12_2022-01_2023. 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 210 Location
County /
Zone State Date Time Type Death Injury
Property
Damage
Crop
Damage

EAST BAY HILLS
(ZONE) East Bay Hills CA 2/21/2023 16:30 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS
(ZONE) East Bay Hills CA 12/27/2022 01:50 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS
(ZONE) East Bay Hills CA 12/27/2022 03:10 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 12/7/2020 03:15 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 10/25/2020 23:50 High Wind 0 0 0.00K 0.00K
WALNUT HGTS Contra Costa
County CA 8/16/2020 02:50 Thunderstorm
Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 11/26/2019 19:18 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 11/26/2019 19:28 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 2/14/2019 01:28 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/14/2019 03:49 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 1/16/2019 1528 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 1/16/2019 16:21 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 1/16/2019 17:13 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 1/16/2019 17:28 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 1/16/2019 18:28 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 1/16/2019 18:38 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 1/9/2019 00:10 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 11/28/2018 23:45 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 10/7/2018 02:00 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 10/8/2017 21:15 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 2/20/2017 16:50 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/17/2017 09:07 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/17/2017 11:04 High Wind 0 0 0.00K 0.00K 2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 211 Location
County /
Zone State Date Time Type Death Injury
Property
Damage
Crop
Damage

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/9/2017 12:09 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 2/7/2017 04:50 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 2/7/2017 05:28 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 2/7/2017 09:30 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 1/22/2017 01:18 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 1/7/2017 07:00 High Wind 1 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/6/2015 11:10 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 2/6/2015 11:18 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 2/6/2015 13:00 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 2/6/2015 14:28 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 12/30/2014 16:00 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 12/11/2014 04:00 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 12/11/2014 07:18 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 12/11/2014 07:30 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 10/27/2013 19:45 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 10/27/2013 20:12 High Wind 0 0 25.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 10/27/2013 23:18 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 10/4/2013 01:45 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 5/1/2013 02:00 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 5/1/2013 07:17 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 4/8/2013 00:18 High Wind 0 0 0.00K 0.00K
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 212 Location
County /
Zone State Date Time Type Death Injury
Property
Damage
Crop
Damage

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 4/8/2013 02:12 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 11/28/2012 11:28 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 12/1/2011 01:45 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 3/19/2011 20:00 High Wind 0 0 100.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/15/2011 20:30 High Wind 0 0 150.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 1/20/2010 07:00 High Wind 0 1 245.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 1/19/2010 03:00 High Wind 0 0 40.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 1/19/2010 03:00 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 1/19/2010 04:00 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 11/28/2009 07:00 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 10/27/2009 11:00 High Wind 0 0 50.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 10/27/2009 21:00 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 10/13/2009 08:00 High Wind 0 0 2.500M 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 10/13/2009 08:00 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 10/13/2009 08:00 High Wind 0 0 20.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 4/14/2009 16:00 High Wind 0 0 80.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 2/15/2009 03:39 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 1/4/2008 90:00 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 1/4/2008 09:00 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 1/4/2008 09:00 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 1/4/2008 10:00 High Wind 0 0 0.00K 0.00K
2024 Hazard Mitigation Plan
Contra Costa County, California

Chapter 4: Hazard Identification and Risk Assessment 213 Location
County /
Zone State Date Time Type Death Injury
Property
Damage
Crop
Damage

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 1/4/2008 12:00 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 1/4/2008 12:00 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 12/27/2006 08:00 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 2/27/2006 10:00 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/27/2006 18:54 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 2/27/2006 19:00 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 12/31/2005 03:00 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 12/31/2005 07:46 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 12/18/2005 05:00 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 12/18/2005 07:57 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 12/18/2005 13:00 High Wind 0 0 0.00K 0.00K

EAST BAY

INTERIOR

VALLEYS (ZONE)
East Bay
Interior Valleys CA 12/1/2005 12:00 High Wind 0 0 0.00K 0.00K

SAN FRANCISCO

BAY SHORELINE
(ZONE)
San Francisco
Bay Shoreline CA 12/1/2005 12:28 High Wind 0 0 0.00K 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 12/1/2005 13:30 High Wind 0 0 0 0.00K

EAST BAY HILLS

AND THE DIABLO

RANGE (ZONE)
East Bay Hills
And The
Diablo Range
CA 12/1/2005 17:39 High Wind 0 0 0 0.00K
TOTAL 1 1 3.260M 0.00K
Table 4-159. Tornado Events (1950 – 2023)
Location
County /
Zone State Date Time Type Death Injury
Property
Damage
Crop
Damage
BRENTWOOD Contra Costa
County CA 1/23/2010 12:54 Tornado
(EF1) 0 0 25.00K 0.00K
RICHMOND Contra Costa
County CA 12/5/1998 19:30 Tornado (F0) 0 0 200.00K 0.00K BRENTWOOD Contra Costa
County CA 2/19/1998 12:30 Tornado (F0) 0 0 50.00K 0.00K

San Pablo City CouncilApril 7, 2025

San Pablo City Council
April 7, 2025