Methodology & Data Sources

Data Sources

PlainHazard aggregates data from three official U.S. government sources:

• FEMA OpenFEMA API, Disaster Declarations Summaries v2: Official record of all federally declared disasters including major disaster declarations (DR), emergency declarations (EM), and fire management assistance declarations (FMAG). Data includes disaster type, declaration dates, and affected areas at the county level.
• NOAA NCEI Storm Events Database: The National Centers for Environmental Information database of severe weather and natural hazard events. Our data covers 2015–2025 and includes event counts, fatalities, injuries, and property/crop damage estimates for 50+ event types.
• FEMA National Risk Index (NRI): FEMA's county-level expected-annual-loss and risk-rating dataset, used on the homepage hazard-loss summary and in the interactive risk-score tool described below.

Processing Pipeline

1. Retrieve FEMA disaster declaration records from the OpenFEMA API
2. Download NOAA Storm Events CSV bulk data files from NCEI for years 2015–2025
3. Aggregate FEMA records by state and county: total declarations, declaration types, and most common disaster types
4. Aggregate NOAA records by state and county: event counts by type, total fatalities, total injuries, and property/crop damage in nominal dollars
5. Organize the FEMA and NOAA datasets side by side in state and county profile pages, the two ARE kept separate there, not merged into a single number, because they measure different things (see below)
6. Load into our geographically indexed database

Why FEMA and NOAA Stay Separate on Profile Pages

FEMA and NOAA measure different things. FEMA declarations capture disaster-level events that triggered a presidential or agency response. NOAA Storm Events capture individual weather events including many that never result in a federal declaration. Combining them into a single number on a state or county PROFILE page would conflate these different measurement frameworks, so profile pages show both datasets side by side, not merged, so readers can assess historical exposure from multiple angles.

Separately, our Risk Score tool DOES compute an explicit, transparently-weighted composite (FEMA declaration frequency 30 pts + NOAA storm density 25 pts + property/crop damage 25 pts + hazard diversity 20 pts, each benchmarked against national medians) as a single opt-in summary number for that specific tool, this is a distinct, separately-labeled feature from the state/county profile pages described above, not a claim that the underlying datasets are "merged" everywhere on the site.

Damage Figures

Property and crop damage figures are reported in nominal dollars as provided by NOAA, they are not inflation-adjusted. Fatality and injury counts include both direct and indirect causes as classified by NOAA.

Data Vintage and Update Frequency

The federal disaster declaration program itself dates to 1953, but PlainHazard's FEMA dataset (via the OpenFEMA API) begins in 1973, the earliest year in this database. New FEMA records are incorporated after they are available from the source and our pipeline is re-run. NOAA Storm Events data on PlainHazard covers 2015 through 2025, providing a decade of detailed severe weather event records. NOAA says Storm Data and Storm Events reports are generally available 90 to 120 days after an event, following reporting and verification. PlainHazard refreshes its database when a new source release is available and has been processed.

Coverage

• FEMA declarations: All federally declared disasters from 1973 to present (the earliest year with complete digitized OpenFEMA records; the declaration program itself dates to 1953), covering all 50 states, U.S. territories, and tribal nations
• NOAA Storm Events: 2015–2025, covering 50+ event types including tornadoes, hurricanes, floods, winter storms, wildfires, droughts, and hail events
• Geographic resolution: State and county level for both datasets
• Metrics: Event counts, fatalities, injuries, and property/crop damage estimates

Accuracy Commitment

PlainHazard preserves FEMA and NOAA source figures within their stated scopes, while clearly labeling its own aggregates, rankings, and comparisons. The two datasets remain separate on state and county profiles because FEMA declarations and NOAA Storm Events measure different phenomena. The optional Risk Score tool is separately labeled as a PlainHazard calculation, not an agency rating. When data is incomplete or unavailable for a specific county or time period, this is shown transparently.

Limitations

• Historical hazard frequency does not predict future risk. Climate patterns are changing, and past event frequency may not reflect future exposure for any given location.
• NOAA storm event damage estimates are preliminary and subject to revision. Not all events have complete damage data, particularly for events where property damage was difficult to assess or unreported.
• NOAA Storm Events counts are influenced by how many people are present to observe and report a storm, not purely by how often severe weather occurs. Densely populated areas tend to show more recorded events for a given hazard than sparsely populated ones with genuinely similar meteorological exposure, because there are more people, spotters, and media outlets to notice and log an event. Treat state and county event counts as a record of what was documented, not a precise measure of true storm frequency.
• FEMA declarations reflect political and administrative processes as well as physical severity, a state governor must request a declaration, and approval involves assessment of state and local capacity alongside disaster impact.
• County-level aggregation may mask variation within large counties. Urban and rural areas within the same county may face very different hazard exposures.
• Do not use this data as the sole basis for personal safety decisions, emergency planning, or insurance purchasing. Consult local emergency management agencies for community-specific risk assessments.
• PlainHazard is not affiliated with FEMA, NOAA, or any government agency.

Contact

Questions about our methodology? Contact us.