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Natural hazard risk in San Mateo County, California

Updated October 30, 2026. Based on FEMA, NOAA and OpenFEMA data. Published by Humblebee.

FEMA overall Risk Index rating: Relatively High (score 99.2 of 100)[5]

Expected annual loss (FEMA)
$740.0 million[1]
Federal disaster declarations since 1977
22[2]
NFIP flood claims paid, 1978 to 2026
$20.1 million[3]
Tornadoes recorded, 1950 to 2024
4[4]

FEMA's National Risk Index (version 1.20, December 2025) gives San Mateo County an overall rating of Relatively High compared with other US counties[5]. The hazards with the highest FEMA scores in this county are earthquake, landslide and inland flooding[6].

FEMA risk ratings for each hazard

Ratings and expected losses from the FEMA National Risk Index. Each rating compares this county with all US counties for that hazard, from Very Low to Very High. They are planning estimates, not predictions, and they do not describe any single property.

FEMA's National Risk Index estimates Expected Annual Loss from all 18 natural hazards at $740.0 million a year for San Mateo County[1]. This is FEMA's estimate of average yearly loss, not money anyone has paid[7]. FEMA's largest hazard-type estimates are earthquake at $497.3 million a year, then inland flooding at $212.3 million a year, then coastal flooding at $8.7 million a year[8]. FEMA rates social vulnerability Relatively Low[9] and community resilience Very High[10], both compared with other US counties. FEMA says the index does not predict how much damage a community will have in the next year[7].

Hazards sorted by FEMA hazard-type Risk Index score, highest first
HazardFEMA risk ratingExpected annual loss
EarthquakeRelatively High$497.3 million[11]
LandslideRelatively High$4.4 million[12]
Inland FloodingRelatively High$212.3 million[13]
DroughtRelatively High$2.3 million[14]
WildfireRelatively Moderate$2.2 million[15]
Coastal FloodingRelatively High$8.7 million[16]
Heat WaveRelatively Moderate$4.1 million[17]
TsunamiRelatively Moderate$7.2 million[18]
LightningRelatively Moderate$549,000[19]
TornadoRelatively Low$627,000[20]
Strong WindRelatively Low$222,000[21]
HailVery Low$43,000[22]
Winter WeatherVery Low$2,709[23]

Rated Not Applicable by FEMA for this county: avalanche, hurricane, ice storm, volcanic activity[24].

Social vulnerability and community resilience

FEMA uses these two ratings to scale expected losses into the Risk Index.

FEMA measureRatingScore
Social vulnerabilityRelatively Low20.5[9]
Community resilienceVery High97.5[10]

Flooding and flood insurance

FEMA rates inland flooding Relatively High and coastal flooding Relatively High for San Mateo County, compared with other US counties[13][16]. OpenFEMA lists 3,346 residential flood insurance contracts in force, a penetration rate of 1.8%[25]. Inside FEMA's mapped Special Flood Hazard Area, 30.9% of homes are insured[25]. OpenFEMA's NFIP claims data show 1,110 claims filed for losses from 1978 to 2026, and NFIP paid $20.1 million in total[3]. To learn about the flood zone of one address, use FEMA's Flood Map Service Center[26].

Measure Value
Inland Flooding, FEMA risk rating[13] Relatively High, $212.3 million expected loss a year
Coastal Flooding, FEMA risk rating[16] Relatively High, $8.7 million expected loss a year
NFIP residential flood policies in force (2026)[25] 3,346 of 182,415 homes
Homes in FEMA's mapped high-risk flood area (SFHA)[25] 7,052, of which 2,178 insured
NFIP flood claims, 1978 to 2026[3] 1,110 filed, $20.1 million paid

Is a specific address in a flood zone? Only FEMA's flood maps answer that, property by property[26]. This page describes the whole county.

Search an address on the FEMA Flood Map Service Center

Disaster declarations and tornado records

OpenFEMA lists 22 federal disaster declarations for natural hazards that include San Mateo County since 1977[2]. The most recent listed is DR-4699-CA for severe winter storms, straight-line winds, flooding, landslides and mudslides, declared 2023-04-03[27]. NOAA's tornado database records 4 tornadoes touching the county from 1950 to 2024, and the strongest were rated F1[4].

Federal disaster declarations for natural hazards that include San Mateo County, since 1977
Incident type Declarations
Severe Storm[2] 7
Flood[2] 7
Fire[2] 3
Drought[2] 1
Hurricane[2] 1
Coastal Storm[2] 1
Earthquake[2] 1
Freezing[2] 1
Most recent declarations
Declaration Incident Declared
DR-4699-CA[27] Severe Winter Storms, Straight-Line Winds, Flooding, Landslides, And Mudslides 2023-04-03
EM-3592-CA[27] Severe Winter Storms, Flooding, Landslides, And Mudslides 2023-03-10
DR-4683-CA[27] Severe Winter Storms, Flooding, Landslides, And Mudslides 2023-01-14
EM-3591-CA[27] Severe Winter Storms, Flooding, And Mudslides 2023-01-09
DR-4558-CA[27] Wildfires 2020-08-22

How to prepare

Steps from Ready.gov, FEMA's preparedness site, for the hazards with the highest FEMA ratings here. Follow instructions from local officials and the National Weather Service when a warning is issued.

Earthquakes

Before

  • Practice Drop, Cover, and Hold On with your family and coworkers.
  • Sign up for earthquake alerts that can warn you before shaking starts.
  • Make a plan with an out-of-state contact and a place to meet if you get separated.
  • Anchor heavy items such as bookcases, refrigerators and water heaters, and keep heavy things on low shelves.
  • Consider earthquake insurance. Standard homeowners policies do not cover earthquake damage.

During

  • Drop to your hands and knees, cover your head and neck, and hold on until the shaking stops.
  • Indoors, stay where you are and avoid doorways. Outdoors, move to an open area away from buildings and power lines.
  • If you are driving, pull over, stop and set the parking brake.

Source: Ready.gov, earthquakes

Floods

Before

  • Check your flood risk with FEMA's Flood Map Service Center, and remember that floods do not follow map lines.
  • Sign up for your community's warning system. NOAA Weather Radio also broadcasts alerts.
  • Buy flood insurance through the NFIP well before a disaster. Homeowners policies do not cover flooding, and a new policy typically takes up to 30 days to go into effect.
  • Make a household plan with evacuation routes, shelter locations and what to do in a flash flood.
  • Keep important documents in a waterproof container and make password-protected digital copies.

During

  • If you are told to evacuate, leave right away and never drive around barricades.
  • Do not walk, swim or drive through floodwater. Six inches of moving water can knock you down.
  • If you are trapped in a building, go to the highest level, but do not climb into a closed attic.

Source: Ready.gov, floods

Wildfires

Before

  • Sign up for community alerts and watch for air quality alerts.
  • Make sure everyone knows the evacuation plan, including for school, work and other places you go often.
  • Keep a fire-resistant zone of at least 30 feet around your home, clear of leaves and debris.
  • Use fire-resistant building materials and keep a hose long enough to reach every part of your property.
  • Pick a room you can seal off from outside air and keep a portable air cleaner ready.

During

  • Leave right away when authorities tell you to evacuate.
  • If you are trapped, call 9-1-1 with your location and turn on lights to help rescuers find you.
  • If you are not ordered to leave but there is smoke, stay in a safe indoor place or go to a community building with less smoke.

Source: Ready.gov, wildfires

Questions people ask

Is San Mateo County at risk of flooding?
FEMA rates inland flooding Relatively High and coastal flooding Relatively High compared with other US counties[13][16]. FEMA's Flood Map Service Center shows flood maps for a specific address[26].
Is San Mateo County at risk of earthquakes?
FEMA rates earthquake risk Relatively High compared with other US counties, with a score of 99.7 out of 100[11]. FEMA estimates earthquake Expected Annual Loss at $497.3 million a year[11].
Does San Mateo County get tornadoes?
NOAA's tornado database records 4 tornadoes touching the county from 1950 to 2024, and the most recent was on 2005-03-20[4]. FEMA rates tornado risk Relatively Low compared with other US counties[20].
How many disasters have been declared in San Mateo County?
OpenFEMA lists 22 federal disaster declarations for natural hazards that include the county since 1977[2].
Does San Mateo County have hurricane risk?
FEMA's National Risk Index rates hurricane Not Applicable for San Mateo County[24].

Facts and sources

  1. FEMA National Risk Index (version 1.20, December 2025): Expected Annual Loss from all 18 natural hazards in San Mateo County is $740.0 million a year (Expected Annual Loss rating Relatively High, score 99.4). Of this, buildings account for $573.2 million, injuries and deaths (converted to dollars by FEMA) for... FEMA National Risk Index
  2. OpenFEMA Disaster Declarations Summaries list 22 federal disaster declarations for natural hazards that include San Mateo County since 1977 (16 major disaster, 6 emergency or fire management). By incident type: severe storm 7, flood 7, fire 3, drought 1, hurricane 1, coastal storm 1, earthquake 1, freezing 1.... OpenFEMA Disaster Declarations
  3. HazardFacts tally of OpenFEMA NFIP Redacted Claims (losses from 1978 to 2026): 1,110 National Flood Insurance Program claims were filed for losses in San Mateo County, 714 of them with a payment, and NFIP paid $20.1 million in total (building, contents and increased cost of compliance, in dollars of the year paid).... OpenFEMA NFIP claims
  4. NOAA Storm Prediction Center tornado database (1950 to 2024): 4 recorded tornadoes touched San Mateo County. The strongest were rated F1 (most recent of them on 2005-03-20). 0 were rated F3/EF3 or stronger. The most recent recorded tornado was on 2005-03-20. Ratings used the Fujita scale until early 2007 and the... NOAA Storm Prediction Center
  5. FEMA National Risk Index (version 1.20, December 2025): the overall natural hazard Risk Index rating for San Mateo County is Relatively High, with a Risk Index score of 99.2 out of 100. The score is the county's percentile rank among all US counties. FEMA National Risk Index
  6. Among the 18 hazards in the FEMA National Risk Index (version 1.20, December 2025), the hazards with the highest hazard-type Risk Index scores for San Mateo County are earthquake (99.7, Relatively High), landslide (99.6, Relatively High), inland flooding (98.4, Relatively High). HazardFacts sorted FEMA's published... FEMA National Risk Index
  7. FEMA's National Risk Index FAQ (December 2025): Expected Annual Loss is FEMA's estimate of the average economic loss in dollars from natural hazards each year. The index is not meant to predict how much damage a community will have in the next year, and a hazard can still cause damage where a rating is low. Scores... FEMA National Risk Index documentation
  8. HazardFacts sorted FEMA's hazard-type Expected Annual Loss values for San Mateo County (National Risk Index v1.20): the largest are earthquake ($497.3 million a year), inland flooding ($212.3 million a year), coastal flooding ($8.7 million a year), out of $740.0 million a year from all 18 hazards. FEMA National Risk Index
  9. FEMA National Risk Index (version 1.20, December 2025): Social Vulnerability rating for San Mateo County is Relatively Low (score 20.5). FEMA describes social vulnerability as how susceptible social groups are to the harm natural hazards cause. FEMA National Risk Index
  10. FEMA National Risk Index (version 1.20, December 2025): Community Resilience rating for San Mateo County is Very High (score 97.5). FEMA describes community resilience as a community's ability to prepare for, withstand and recover from hazards. FEMA National Risk Index
  11. FEMA National Risk Index (version 1.20, December 2025), earthquake in San Mateo County: Risk Index rating Relatively High (score 99.7 of 100). Expected Annual Loss $497.3 million a year (rating Very High). FEMA's modeled annual frequency is 0.1373 events per year. FEMA National Risk Index
  12. FEMA National Risk Index (version 1.20, December 2025), landslide in San Mateo County: Risk Index rating Relatively High (score 99.6 of 100). Expected Annual Loss $4.4 million a year (rating Relatively High). FEMA National Risk Index
  13. FEMA National Risk Index (version 1.20, December 2025), inland flooding in San Mateo County: Risk Index rating Relatively High (score 98.4 of 100). Expected Annual Loss $212.3 million a year (rating Relatively High). Annualized frequency 1.39 event-days per year, from recorded occurrences over a period of record of... FEMA National Risk Index
  14. FEMA National Risk Index (version 1.20, December 2025), drought in San Mateo County: Risk Index rating Relatively High (score 92.0 of 100). Expected Annual Loss $2.3 million a year (rating Relatively High). Annualized frequency 37.99 event-days per year, from recorded occurrences over a period of record of 22 years. FEMA National Risk Index
  15. FEMA National Risk Index (version 1.20, December 2025), wildfire in San Mateo County: Risk Index rating Relatively Moderate (score 92.0 of 100). Expected Annual Loss $2.2 million a year (rating Relatively Moderate). FEMA's modeled annual frequency is 0.0016 events per year. FEMA National Risk Index
  16. FEMA National Risk Index (version 1.20, December 2025), coastal flooding in San Mateo County: Risk Index rating Relatively High (score 91.8 of 100). Expected Annual Loss $8.7 million a year (rating Relatively High). FEMA's modeled annual frequency is 0.9918 events per year. FEMA National Risk Index
  17. FEMA National Risk Index (version 1.20, December 2025), heat wave in San Mateo County: Risk Index rating Relatively Moderate (score 91.5 of 100). Expected Annual Loss $4.1 million a year (rating Relatively Moderate). Annualized frequency 4.46 event-days per year, from recorded occurrences over a period of record of... FEMA National Risk Index
  18. FEMA National Risk Index (version 1.20, December 2025), tsunami in San Mateo County: Risk Index rating Relatively Moderate (score 70.7 of 100). Expected Annual Loss $7.2 million a year (rating Relatively Moderate). FEMA National Risk Index
  19. FEMA National Risk Index (version 1.20, December 2025), lightning in San Mateo County: Risk Index rating Relatively Moderate (score 68.2 of 100). Expected Annual Loss $549,000 a year (rating Relatively Moderate). Annualized frequency 4.62 events per year, from recorded occurrences over a period of record of 24 years. FEMA National Risk Index
  20. FEMA National Risk Index (version 1.20, December 2025), tornado in San Mateo County: Risk Index rating Relatively Low (score 30.6 of 100). Expected Annual Loss $627,000 a year (rating Relatively Low). Annualized frequency 0.05 events per year, from recorded occurrences over a period of record of 38 years. FEMA National Risk Index
  21. FEMA National Risk Index (version 1.20, December 2025), strong wind in San Mateo County: Risk Index rating Relatively Low (score 20.5 of 100). Expected Annual Loss $222,000 a year (rating Relatively Low). Annualized frequency 0.03 events per year, from recorded occurrences over a period of record of 38 years. FEMA National Risk Index
  22. FEMA National Risk Index (version 1.20, December 2025), hail in San Mateo County: Risk Index rating Very Low (score 11.3 of 100). Expected Annual Loss $43,000 a year (rating Very Low). Annualized frequency 0.02 events per year, from recorded occurrences over a period of record of 37 years. FEMA National Risk Index
  23. FEMA National Risk Index (version 1.20, December 2025), winter weather in San Mateo County: Risk Index rating Very Low (score 3.3 of 100). Expected Annual Loss $2,709 a year (rating Very Low). Annualized frequency 0.61 events per year, from recorded occurrences over a period of record of 18 years. FEMA National Risk Index
  24. FEMA National Risk Index (version 1.20, December 2025) rates these hazards Not Applicable for San Mateo County: avalanche, hurricane, ice storm, volcanic activity. FEMA uses Not Applicable when its source data has no historical record of the hazard in the community and the hazard is not considered geographically... FEMA National Risk Index documentation
  25. NFIP Residential Penetration Rates (OpenFEMA, as of 2026-08-03): 3,346 residential flood insurance contracts were in force in San Mateo County, out of 182,415 residential structures, a penetration rate of 1.8%. Inside FEMA's mapped Special Flood Hazard Area there were 7,052 residential structures and 2,178... OpenFEMA NFIP penetration rates
  26. FEMA's Flood Map Service Center is the official public source for flood maps (Flood Insurance Rate Maps) produced under the National Flood Insurance Program. Flood zones apply to specific properties: look up an address there or ask the local floodplain manager. County-level ratings do not tell you the flood zone of... FEMA Flood Map Service Center
  27. Most recent federal disaster declarations for natural hazards (table on this page). OpenFEMA Disaster Declarations

FEMA's National Risk Index compares each county with all other US counties. Ratings are relative (Very Low to Very High), not a measure of safety. Never call a place safe, unsafe, good or bad to live in. Risk Index and Expected Annual Loss values are FEMA estimates for planning. They do not predict next year's losses and do not apply to a single property. Flood zones are set by FEMA flood maps for specific properties. County ratings and flood insurance counts do not tell anyone whether an address is in a flood zone. Disaster declaration, NFIP and tornado counts are records of the past for this county only. Do not compare with other counties unless a fact does.

Federal Emergency Management Agency (FEMA), National Risk Index Dataset: National Risk Index Counties, v1.20 (December 2025). Retrieved from fema.maps.arcgis.com on October 30, 2026. 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). This product uses the FEMA OpenFEMA API, but is not endorsed by FEMA.