San Mateo County, California: Natural Disaster Risk and History
San Mateo County, California has a Relatively High natural-hazard risk rating in FEMA's National Risk Index (v1.20, December 2025): a score of 99.2 out of 100, higher than about 99% of US counties, with earthquakes, landslides and inland (river and flash) flooding scoring highest of its 18 hazards and $740 million a year in expected losses.
OpenFEMA lists 22 federal disaster declarations that included San Mateo County since 1977, not counting 2 for COVID-19; the latest is DR-4699-CA (Severe Winter Storms, Straight-Line Winds, Flooding, Landslides, and Mudslides, declared 3 April 2023). NOAA's Storm Prediction Center recorded 4 tornadoes touching San Mateo County from 1950 to 2025.
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Population 763,661 Buildings worth $174 billion Area 748 sq mi Risk rank in California 12 of 58 FIPS 06081
All 18 hazards, highest risk first
FEMA National Risk Index| Hazard | Risk rating | Score | Expected loss a year | How often | Events in record |
|---|---|---|---|---|---|
| Earthquake | Relatively High | 99.7 | $497 million | about once every 7.3 years | — |
| Landslide | Relatively High | 99.7 | $4.4 million | about 3.9 a year | — |
| Inland flooding | Relatively High | 98.4 | $212 million | about 1.4 a year | 39 |
| Drought | Relatively High | 92.1 | $2.3 million | about 38 a year | 987 |
| Wildfire | Relatively Moderate | 92.0 | $2.2 million | about once every 641 years | — |
| Coastal flooding | Relatively High | 91.8 | $8.7 million | about once a year | — |
| Heat wave | Relatively Moderate | 91.6 | $4.1 million | about 4.5 a year | 38 |
| Tsunami | Relatively Moderate | 70.8 | $7.2 million | about once every 2.9 years | 73 |
| Lightning | Relatively Moderate | 68.2 | $548,920 | about 4.6 a year | 37,458 strikes |
| Tornado | Relatively Low | 30.6 | $627,473 | about once every 21 years | 3 |
| Strong wind | Relatively Low | 20.6 | $222,247 | about once every 37 years | 1 |
| Hail | Very Low | 11.4 | $43,216 | about once every 42 years | 0.9 |
| Winter weather | Very Low | 3.4 | $2,709 | about once every 1.6 years | 7 |
| Cold wave | No Rating | 0.0 | — | — | 0 |
| Avalanche | Not Applicable | — | — | — | — |
| Hurricane | Not Applicable | — | — | — | — |
| Ice storm | Not Applicable | — | — | — | — |
| Volcanic activity | Not Applicable | — | — | — | — |
Score: FEMA's percentile among US counties that face the hazard (higher = more risk). Expected loss: FEMA's modelled average yearly loss to buildings, people (as a statistical value) and crops. How often: FEMA's annualised frequency of the hazard in the county; for some hazards it counts event-days, so it is a rough guide, not a forecast. "Not Applicable" means FEMA does not model that hazard here.
Federal disaster declarations 22
Most common: Severe Storm 7, Flood 7, Fire 3, Hurricane 1.
| Decade | Declarations | Incident types |
|---|---|---|
| 1970s | 1 | Drought |
| 1980s | 4 | Flood ×2, Earthquake, Coastal Storm |
| 1990s | 5 | Severe Storm ×4, Freezing |
| 2000s | 3 | Severe Storm ×2, Hurricane |
| 2010s | 3 | Flood ×2, Fire |
| 2020s | 6 | Flood ×3, Fire ×2, Severe Storm |
The last 10
Widest declarations that included San Mateo County
- Hurricane Katrina Evacuation (2005, EM-3248-CA): 58 California counties designated.
- Severe Winter Storms, Flooding Landslides, Mud Flow (1995, DR-1046-CA): 57 California counties designated.
- Severe Storms, Flooding, Mud and Landslides (1997, DR-1155-CA): 48 California counties designated.
Named storms in its declarations: Hurricane Katrina (2005).
Not counted above: 2 COVID-19 ("Biological") declarations — in 2020 every US county was included. California also had 30 statewide declarations with no county list.
Tornado record since 1950 4
| Tornadoes touching the county | 4 |
|---|---|
| Strongest-rated | (E)F1 ×2 |
| Peak month | March (2) |
| Deadliest | — |
| Longest path | 20 Mar 2005, F1, 3 mi path |
| Most recent | 20 Mar 2005, F1, 3 mi path |
| Deaths / injuries on those paths | 0 / 0 |
| Rating | (E)F0 | (E)F1 | (E)F2 | (E)F3 | (E)F4 | (E)F5 | Unrated |
|---|---|---|---|---|---|---|---|
| Count | 2 | 2 | 0 | 0 | 0 | 0 | 0 |
| Decade | 1950s | 1960s | 1970s | 1980s | 1990s | 2000s | 2010s | 2020s |
|---|---|---|---|---|---|---|---|---|
| Count | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 |
Deaths and injuries are for each tornado's whole path, which can run beyond this county. F-scale ratings before February 2007, Enhanced Fujita (EF) after.
How San Mateo County compares with its 5 nearest counties
| County | Distance | Overall risk | Score | Top hazard |
|---|---|---|---|---|
| San Mateo County (this page) | — | Relatively High | 99.2 | Earthquake |
| San Francisco County | 38 km | Very High | 99.5 | Earthquake |
| Alameda County | 46 km | Very High | 99.8 | Earthquake |
| Santa Cruz County | 50 km | Relatively High | 97.8 | Drought |
| Santa Clara County | 60 km | Very High | 99.7 | Earthquake |
| Contra Costa County | 66 km | Very High | 99.5 | Earthquake |
Nearest by distance between county centres. Every county in California, ranked.
Vulnerability and resilience
| Social vulnerability | Relatively Low 20.5 |
|---|---|
| Community resilience | Very High 97.6 |
| Community risk factor | 0.88 |
| Expected annual loss, all hazards | $740 million |
FEMA scales expected losses up where social vulnerability is high (people who may find it harder to prepare, evacuate or recover) and down where community resilience is high. A factor above 1 raises the risk score. For social vulnerability a high rating is worse; for resilience a high rating is better.
Prepare for San Mateo County's main hazards
- Right now: National Weather Service alerts for California · all official warnings on Global Incident Tracker.
- Earthquake: Earthquakes today · Earthquake safety guide
- Landslide: Landslides recorded
- Inland flooding: Flood safety: why shallow water kills · Floods recorded
- Your property's flood zone: FEMA Flood Map Service Center ↗ — this page cannot tell you that.
- Official preparedness guidance: Ready.gov ↗ and your county emergency management office.
What this page shows, and what it misses
FEMA's National Risk Index rates a whole county against every other US county; it is a planning-level estimate for nationwide comparison, not a flood-zone map and not a substitute for a local risk assessment or the risk to one home. Declarations are presidential disaster, emergency and fire management declarations that named this county; state declarations and SBA or USDA designations are not included. Tornadoes are counted when the county is one of up to four listed on the track; 670 tornadoes that crossed a state line carry no county list in NOAA's file and are left out.
Federal Emergency Management Agency (FEMA), National Risk Index Dataset: National Risk Index Counties - v1.20.0 (December 2025). Retrieved from https://services.arcgis.com/XG15cJAlne2vxtgt/ArcGIS/rest/services/National_Risk_Index_Counties/FeatureServer/0/query on November 2, 2026, 1:20 PM EST. This product uses the Federal Emergency Management Agency’s National Risk Index dataset API or downloadable datasets but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).
Federal Emergency Management Agency (FEMA), OpenFEMA Dataset: Disaster Declarations Summaries - v2, retrieved from https://www.fema.gov/api/open/v2/DisasterDeclarationsSummaries on November 2, 2026, 1:21 PM EST. This product uses the Federal Emergency Management Agency's OpenFEMA API, but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).
Tornado records: NOAA/NWS Storm Prediction Center, Severe Weather Database, tornadoes 1950–2025 (https://www.spc.noaa.gov/wcm/data/1950-2025_actual_tornadoes.csv, downloaded 2 November 2026). Public domain; not endorsed by NOAA. Compiled by Global Incident Tracker.
Questions about San Mateo County
What natural disasters is San Mateo County, California most at risk from?
San Mateo County, California has a Relatively High natural-hazard risk rating in FEMA's National Risk Index (v1.20, December 2025): a score of 99.2 out of 100, higher than about 99% of US counties, with earthquakes, landslides and inland (river and flash) flooding scoring highest of its 18 hazards and $740 million a year in expected losses.
How many federal disaster declarations has San Mateo County had?
OpenFEMA lists 22 federal disaster declarations that included San Mateo County since 1977, not counting 2 for COVID-19; the latest is DR-4699-CA (Severe Winter Storms, Straight-Line Winds, Flooding, Landslides, and Mudslides, declared 3 April 2023). Another 30 California declarations were made statewide without a county list.
How many tornadoes have hit San Mateo County?
NOAA's Storm Prediction Center recorded 4 tornadoes touching San Mateo County from 1950 to 2025.
Is the National Risk Index a flood zone map?
No. The National Risk Index is a planning-level estimate for a whole county, built for nationwide comparison. It does not tell you the flood zone or the risk of a single property: for that, look up the address on FEMA's Flood Map Service Center (msc.fema.gov) and ask your local floodplain manager.