San Mateo County, California Natural Disaster Risk
FEMA National Risk Index assessment · CA
HighComposite Risk Score
National percentile: 99th
San Mateo County faces high composite natural disaster risk (NRI Risk Index score 99.2, 99th national percentile), driven primarily by earthquake and landslide exposure. Expected annual loss across all 18 hazard types is $740M.
Source: FEMA National Risk Index v1.20 · Updated December 2025
Risk Overview
San Mateo County carries a high composite natural disaster risk, with a National Risk Index score of 99.2 out of 100 — placing it in the 99th national percentile and in the upper tier of natural-disaster risk nationally. The score blends Expected Annual Loss, Social Vulnerability, and Community Resilience across all 18 FEMA hazard types.
The county's risk is driven primarily by earthquake (ground shaking from sudden movement along geologic faults) at High risk — $497M in expected annual loss and about 0.14 events per year; landslide (downhill movement of rock, soil, and debris on unstable slopes) at High risk — $4M in expected annual loss and about 3.94 events per year; and riverine flood (rivers and streams overflowing their banks after heavy rain or snowmelt) at High risk — $212M in expected annual loss and about 1.39 events per year. Across all hazards, FEMA estimates $740M in expected annual loss for a population of 764K.
Beyond physical exposure, San Mateo County has a low social vulnerability rating (how susceptible the population is to harm) and a very high community resilience rating (its capacity to prepare for and recover from disasters). A less vulnerable population paired with strong resilience helps the community absorb and recover from events.
The federal record bears this out: San Mateo County has received 24 federal disaster declarations since 1977, including 7 for severe storm events and 7 for flood events. The most recent was Severe Winter Storms, Straight-Line Winds, Flooding, Landslides, and Mudslides (severe storm), declared in April 2023.
Among 58 California counties, San Mateo County ranks #12 for overall natural disaster risk.
Top Hazards
All 18 Hazard Risks
| Earthquake | High | 0.14 / yr | $497M |
| Landslide | High | 3.94 / yr | $4M |
| Riverine Flood | High | 1.39 / yr | $212M |
| Drought | High | 37.99 / yr | $2M |
| Wildfire | Medium | 0.00 / yr | $2M |
| Coastal Flood | High | 0.99 / yr | $9M |
| Heat Wave | Medium | 4.46 / yr | $4M |
| Tsunami | Medium | 0.34 / yr | $7M |
| Lightning | Medium | 4.62 / yr | $549K |
| Tornado | Low | 0.05 / yr | $627K |
| Strong Wind | Low | 0.03 / yr | $222K |
| Hail | Very Low | 0.02 / yr | $43K |
| Winter Weather | Very Low | 0.61 / yr | $3K |
| Avalanche | Very Low | 0.00 / yr | $0 |
| Cold Wave | Very Low | 0.00 / yr | $0 |
| Hurricane | Very Low | 0.00 / yr | $0 |
| Ice Storm | Very Low | 0.00 / yr | $0 |
| Volcanic Activity | Very Low | 0.00 / yr | $0 |
Disaster History
San Mateo County has received 24 federal disaster declarations since 1977, most recently Severe Winter Storms, Straight-Line Winds, Flooding, Landslides, and Mudslides in April 2023. Most frequent causes: Severe Storm (7), Flood (7), Fire (3).
| Declared | Type | Disaster |
|---|---|---|
| April 2023 | Severe Storm | Severe Winter Storms, Straight-Line Winds, Flooding, Landslides, and Mudslides |
| March 2023 | Flood | Severe Winter Storms, Flooding, Landslides, and Mudslides |
| January 2023 | Flood | Severe Winter Storms, Flooding, Landslides, and Mudslides |
| January 2023 | Flood | Severe Winter Storms, Flooding, and Mudslides |
| August 2020 | Fire | Wildfires |
| August 2020 | Fire | Czu Lightning Fire Complex |
| March 2020 | Biological | Covid-19 Pandemic |
| March 2020 | Biological | Covid-19 |
| April 2017 | Flood | Severe Winter Storms, Flooding, and Mudslides |
| March 2017 | Flood | Severe Winter Storms, Flooding, and Mudslides |
Showing the 10 most recent of 24 declarations.
Source: FEMA Disaster Declarations Summaries (OpenFEMA).
Frequently Asked Questions
What is the overall natural disaster risk for San Mateo County?
San Mateo County has a composite FEMA National Risk Index score of 99.2 out of 100, placing it in the High category and the 99th national percentile. This combines Expected Annual Loss, Social Vulnerability, and Community Resilience across 18 hazard types.
What are the top natural hazards in San Mateo County?
The three highest-rated hazards are Earthquake (High, $497M EAL), Landslide (High, $4M EAL), Riverine Flood (High, $212M EAL). These account for most of the county's expected annual losses.
How does San Mateo County compare to other California counties?
San Mateo County ranks #12 of 58 California counties for overall natural disaster risk, with a high rating.
How many federally declared disasters has San Mateo County had?
FEMA records 24 federal disaster declarations for San Mateo County since 1977, most often 7 for severe storm events and 7 for flood events. The most recent was Severe Winter Storms, Straight-Line Winds, Flooding, Landslides, and Mudslides, declared in April 2023.
What does Expected Annual Loss (EAL) mean?
EAL is FEMA's estimate of average annual dollar losses from natural hazards, calculated from historical event data and exposure models. San Mateo County's $740M EAL is a statistical average, not a guarantee for any specific year or address.