Data & methodology

Source

All risk scores and ratings on this site come directly from FEMA's National Risk Index (NRI), version 1.20.0, released December 2025. The NRI is a publicly available dataset published by FEMA at hazards.fema.gov/nri, covering expected annual losses, social vulnerability, and community resilience for natural hazards across the United States. SkyGround republishes the county-level table from that release without modification to the underlying figures.

What the scores mean

Each hazard (and the composite "Overall risk index") has a Score from 0–100 and a corresponding Rating. The score is a percentile: it reflects how a county's Risk Index value compares to every other county and county-equivalent in the country, not an absolute probability of a disaster occurring. The Risk Index value for each hazard is derived from three components:

Expected Annual Loss (EAL) — the modeled average loss in buildings, population, and agriculture each year from that hazard.
Social Vulnerability — community characteristics (from the CDC/ATSDR Social Vulnerability Index) that affect a community's ability to prepare for and recover from hazard events.
Community Resilience — a county's capacity to prepare for, adapt to, and recover from hazard events.

Ratings group the 0–100 score into five bands: Very Low, Relatively Low, Relatively Moderate, Relatively High, and Very High. Counties with a hazard that is not applicable in that area, or for which FEMA did not have enough data to compute a score, are shown as "Not Applicable" or "Insufficient Data" rather than a numeric score.

Hazards covered

Each county page on SkyGround shows six of the eighteen hazards in the NRI dataset: wildfire, inland flooding, coastal flooding, earthquake, heat wave, and tornado. These were selected as the hazards most commonly searched and most broadly applicable across the country. The full NRI release also includes hazards such as hurricane, drought, hail, landslide, tsunami, and volcanic activity, which are not currently shown here.

Coverage

SkyGround includes a page for every record in the NRI county table — 3,232 in total, covering all US counties and county-equivalents (including Louisiana parishes, Alaska boroughs and census areas, Virginia independent cities, Connecticut planning regions, and municipios of Puerto Rico and the US Virgin Islands).

Federal disaster declaration history

Alongside FEMA's modeled risk scores, each county page shows a summary of actual federal disaster declarations affecting that county, sourced from OpenFEMA's Disaster Declarations Summaries dataset. This is administrative data — it reflects which counties were included in a federal disaster declaration (and for what incident type), not a measure of modeled risk. A county can have a high modeled risk score with few declarations (if a disaster hasn't occurred recently) or a long declaration history with a lower current risk score (if conditions have changed). Statewide-only declarations (not tied to a specific county) are excluded from these counts. This dataset is refreshed periodically, independent of the NRI release cycle.

Recorded storm events

The hazard breakdown table also shows a count of recorded events from NOAA's Storm Events Database for each hazard, covering 2016–2025. This is ground-level observational data — actual recorded events — rather than a modeled score. Two limitations to be aware of:

NOAA does not track earthquakes (that hazard is shown without an event count).
Some hazard reports are filed against NWS forecast zones rather than counties. Only county-level (CZ_TYPE = C) records are counted here, so these figures undercount total activity in areas where zone-based reporting is common — most notably wildfire and heat events in parts of the western US.

Geomagnetic latitude

Each county page also shows an approximate geomagnetic latitude, which determines how far a geomagnetic storm has to reach before aurora and related space weather effects (e.g., HF radio disruption, GIC on power infrastructure) become significant at that location. This connects the county-level pages to the live space weather page.

Geomagnetic latitude is calculated from each county's geographic centroid (from the US Census Bureau's county gazetteer file) using a simple dipole approximation of Earth's magnetic field, based on an approximate geomagnetic pole position for the current epoch (~80.7°N, 72.7°W). Checked against published corrected geomagnetic coordinates for a sample of US cities, this approximation is typically accurate to within about 1 degree across the continental US (up to roughly 2–3 degrees for Alaska, Hawaii, and the Caribbean/Pacific territories) — close enough to match NOAA's own published aurora-visibility guidance, but not precise enough for engineering-grade geomagnetically induced current (GIC) analysis, which requires higher-order field models (e.g., IGRF/AACGM) and local ground conductivity data.

The aurora visibility threshold shown on each county page (the lowest planetary K-index at which aurora typically becomes visible on the horizon) is derived from the same Kp–to–geomagnetic-latitude table shown on the space weather page. Because the table's latitude bands are roughly 2 degrees apart and the underlying estimate carries about ±1 degree of uncertainty, a county's threshold can occasionally be off by one Kp level — treat it as a general guideline, not a guarantee. Historic extreme storms have also occasionally produced aurora at unusually low latitudes.

Identifiers

Each county page lists its 5-digit FIPS code (state + county code), which can be used to join SkyGround's ratings with other datasets that use standard Census/FIPS geographic identifiers.

Limitations

Scores are relative rankings among US counties for the current NRI release, not predictions of whether or when a disaster will occur.
The underlying models are based on historical hazard occurrence and loss data and do not incorporate forward-looking climate projections.
County-level scores can mask significant variation within large or geographically diverse counties.
"Insufficient Data" and "Not Applicable" ratings reflect gaps or non-applicability in FEMA's source data, not a "no risk" determination.

Updates

FEMA periodically releases new versions of the National Risk Index. SkyGround is currently built from the December 2025 (v1.20.0) release and will be updated when a newer release becomes available.

Citing this data

When citing the underlying hazard data, please cite FEMA's National Risk Index directly (e.g., "FEMA National Risk Index, v1.20.0, December 2025, hazards.fema.gov/nri"). If referencing a specific county page on this site, you may additionally link to that page as the presentation source.