How the FEMA National Risk Index Works

Written by Dvir · Data: FEMA National Risk Index v1.20 · Updated July 19, 2026

Every number on this site traces back to a single public dataset: the FEMA National Risk Index (NRI). This page explains where that data comes from, how the scores are calculated, and — just as importantly — what they can and cannot tell you.

What the National Risk Index is

The NRI is a nationwide, county-level dataset published by the Federal Emergency Management Agency. It rates every US county and county-equivalent (parishes in Louisiana, boroughs and census areas in Alaska, independent cities in Virginia) on its relative risk from 18 natural hazards, from hurricanes and wildfires to avalanches and volcanic activity.

FEMA built the index with input from state and local governments, universities, and private-sector risk modelers, and updates it roughly once a year. This site currently publishes version 1.20, released December 2025. The data is public domain under OpenFEMA’s terms; FEMA requests attribution but does not endorse or sponsor this site.

The three ingredients of a risk score

A county’s composite Risk Index score (0–100) is not just “how often disasters happen there.” It combines three separately measured components:

Expected Annual Loss (EAL) is the core of the index. For each hazard, FEMA estimates the average dollar loss the county should expect per year, averaged over the long run. EAL is built from three factors: exposure (the value of buildings, population, and agriculture in harm’s way), annualized frequency (how often the hazard historically strikes), and historic loss ratio (what share of exposed value a typical event destroys). A county with enormous property value and rare-but-severe events can carry a higher EAL than a county hit constantly by small ones.

Social Vulnerability measures how susceptible the population is to harm when a disaster does strike. It draws on the CDC/ATSDR Social Vulnerability Index — factors like poverty, age, disability, housing type, and vehicle access. Two counties with identical expected losses can experience very different human outcomes; this component captures that.

Community Resilience measures a community’s capacity to prepare for, absorb, and recover from disasters, using indicators developed by the University of South Carolina’s HVRI program (governance, economic diversity, social capital, infrastructure).

The composite formula, conceptually: Risk = Expected Annual Loss × Social Vulnerability ÷ Community Resilience. High vulnerability amplifies a county’s risk score; high resilience dampens it.

Scores, percentiles, and ratings

The Risk Index is relative, not absolute. A score of 85 does not mean an 85% chance of anything — it means the county’s calculated risk is higher than roughly 85% of US counties. FEMA groups scores into five ratings: Very Low, Relatively Low (Low), Relatively Moderate (Medium), Relatively High (High), and Very High. On this site we show the score, the national percentile, and the rating together so the context is always visible.

Each of the 18 hazards also gets its own per-hazard score and rating, built the same way from that hazard’s EAL. A county can be Very High for one hazard and Very Low overall, or vice versa — the composite blends everything.

What this site adds on top

We publish the NRI data as-is — no re-weighting, no editorial adjustment of scores. What we add is context and navigability:

  • County pages show the composite score, all 18 hazard ratings, EAL, social vulnerability, and community resilience, plus each county’s federal disaster declaration history from FEMA’s separate Disaster Declarations Summaries dataset (1953–present).
  • State pages and rankings aggregate the same county data for comparison.
  • These guides are written and edited by a person (me — see the about page), not generated from the data.

Limitations you should know about

Risk is county-level, not address-specific. A county rated Very High for riverine flooding contains plenty of parcels that will never flood; a Low-rated county still has floodplains. For property decisions, pair this data with address-level tools — FEMA flood maps, state wildfire hazard maps, a local insurance agent.

EAL is a statistical average, not a forecast. A county with a $50M expected annual loss might see $0 in losses for a decade and then a $1B event. The average is meaningful for comparing places and pricing long-run risk, not for predicting any particular year.

The index looks backward and present-tense. Frequencies are estimated largely from historical records. Where climate change is shifting hazard behavior — wildfire seasons lengthening, rainfall intensifying — the historical record may understate future risk.

Boundaries and versions change. FEMA occasionally revises methodology between versions (v1.20, for example, renamed the riverine flooding hazard code from RFLD to IFLD). Scores are comparable within one version, not necessarily across versions.

Sources

Questions or corrections? Email [email protected].

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