Methodology & data sources
Transparency is the core of our E-E-A-T: this page documents where our data comes from, how often it is refreshed, and the formulas behind every calculation.
Data sources
| Source | Refresh cadence | License |
|---|---|---|
| OpenFEMA Disaster Declarations Summaries v2 | monthly | U.S. public domain (FEMA / OpenFEMA) |
| USGS Earthquake Hazards Program (FDSN event service) | monthly | U.S. public domain (USGS) |
How the figures are produced
Disaster figures come from the OpenFEMA Disaster Declarations Summaries v2 API.
We download the full table (tens of thousands of records), then aggregate it locally per state.
A key detail: FEMA returns one row per affected county per declaration, so a
single declaration appears in many rows. To avoid inflating counts, we deduplicate on the unique
femaDeclarationString — every count on the site is therefore of
distinct declarations, not county-rows (we report the raw county-row total
separately for transparency). From the distinct declarations we compute, for each state, the
total, the breakdown by incident type, the breakdown by declaration program type (DR / EM / FM),
the count by decade, and the most recent declarations.
Earthquake figures come from the USGS FDSN event service. We query magnitude 6.0+ events since 1900 within a US bounding box, keep the strongest, and attribute each to a state by matching the state name in the USGS event description. Smaller earthquakes and events whose description names no state are not attributed.
Reference tables (the Saffir-Simpson hurricane scale and FEMA flood-zone codes) are transcribed from the official NOAA/National Hurricane Center and FEMA sources cited on each page.
Refresh
The data is a committed snapshot, refreshed manually (no automated jobs). The "data as of" date shown across the site reflects when the snapshot was last built.
Limitations
- Counts are raw federal declarations, not adjusted for population or land area, so large states rank highest.
- Earlier decades reflect a narrower federal declaration program, not only fewer disasters.
- Earthquake state-attribution is text-based; a "0" earthquake count means no M6.0+ event named that state in the catalog — not that the state has no seismic risk.
- Where the data shows zero of something, we say so; we never fabricate a figure the source does not contain.
HazardMap is not affiliated with or endorsed by FEMA, USGS or NOAA. Figures are factual public-data summaries for general information only — not safety, emergency, or insurance advice. Always verify against the primary source. See our disclaimer.