Flood hazard · San Mateo County, CA
Flood hazard
To create the beginnings of a vulnerability assessment, this snapshot combines local vulnerability data with maps that depict the 100-year floodplain.
People at Risk
Rising populations in flood prone areas exacerbate flooding risk. Impacts can be greater to the elderly or those with a low income, as these citizens may not have the resources to adequately prepare or recover.
of San Mateo County’s land area is inside the FEMA 100-year floodplain.
Share of population at risk
Flooded Facilities Can't Provide Critical Services
First responders. Hospitals. Shelters. All play a central role in response and recovery. Incorporating vulnerability information into planning efforts save lives (fewer instances where critical services are made unavailable) and is cost effective (fewer damages to facilities).
of the critical facilities in San Mateo County falls within the FEMA 100-year floodplain.
Critical facilities, by type.
Critical facilities, by type: data table
| Category | Inside the floodplain | Outside the floodplain |
|---|---|---|
| Schools | 8 | 214 |
| Police stations | 0 | 21 |
| Fire stations | 5 | 56 |
| Medical facilities | 1 | 7 |
Homes at Risk
Flooding is costly for homeowners, no doubt. But the community also shares in the cost as lowered property values negatively affect tax revenues.
paid by the National Flood Insurance Program on 694 claims in San Mateo County since 1996.
NFIP payouts by five-year period.
NFIP payouts by five-year period: data table
| Category | Value |
|---|---|
| 1996–2000 | $3,846,237 |
| 2001–2005 | $2,254,480 |
| 2006–2010 | $498,563 |
| 2011–2015 | $1,339,276 |
| 2016–2020 | $942,446 |
| 2021–2025 | $9,350,987 |
Being Underwater Is Not a Good Business Plan
Flood-related losses of services, revenues, and salaries can hit a community hard.
of all 425,111 jobs in San Mateo County are in the FEMA 100-year floodplain.
A Better Future is a Greener Future
How do past development trends in your county compare to today’s approach? Development in flood-prone areas should be kept to a minimum. Creating more greenspace, which acts as a flooding buffer, lowers flood risk. Adding more impervious surfaces (even outside of the floodplain) can increase runoff and exacerbate flooding.
(12.5 square miles) of the designated 100-year floodplain are natural features.
Development added, 1996–2021, as a share of land developed by 2021
Data, methods and citation
- Snapshot
- 2026-09-24
- Methodology
- Version 1. What changed: https://seachangeatlas.org/county-profiles/about/changelog/#methodology-changelog
Recommended citation. California Sea Change Atlas. (2026, September 24). San Mateo County coastal county profile: Flood hazard. https://seachangeatlas.org/county-profiles/county/san-mateo/2026-09-24/flood-hazard/
| Source | Period covered | Retrieved |
|---|---|---|
| Census ACS 5-year estimates (2020–2024) https://www.census.gov/programs-surveys/acs/data.html | 2024 | 2026-09-24 |
| Census 2020 tabulation blocks (TIGERweb) https://tigerweb.geo.census.gov/arcgis/rest/services/Census2020/Tracts_Blocks/MapServer | 2020 | 2026-09-24 |
| FEMA National Flood Hazard Layer https://www.fema.gov/flood-maps/national-flood-hazard-layer | 2012-10-16 to 2019-04-05 | 2026-09-24 |
| USGS National Structures Dataset https://data.usgs.gov/datacatalog/data/USGS:db4fb1b6-1282-4e5b-9866-87a68912c5d1 | 2025-05-09 | 2026-09-24 |
| OpenFEMA NFIP claims https://www.fema.gov/openfema-data-page/nfip-redacted-claims-v3 | 2026-09-08 | 2026-09-24 |
| LEHD LODES8 workplace area characteristics https://lehd.ces.census.gov/data/lodes/LODES8/ca/wac/ | 2023 | 2026-09-24 |
| NOAA C-CAP regional land cover https://coast.noaa.gov/digitalcoast/data/ccapregional.html | 1996-01-01 to 2021-12-31 | 2026-10-21 |