The FEMA National Risk Index (NRI) is one of the most comprehensive natural hazard risk assessments available for the United States. Released by the Federal Emergency Management Agency, it provides county-level risk scores for 18 different natural hazard types — from earthquakes and hurricanes to heat waves and ice storms.
But what do these scores actually mean? How are they calculated? And how should homeowners, renters, and communities use them? This guide breaks down everything you need to know about the FEMA NRI and how RiskByCounty translates it into actionable information.
What Is the FEMA National Risk Index?
The NRI is a free, publicly available online tool that maps and scores natural hazard risk for every county and Census tract in the United States. It was developed by FEMA in partnership with various federal agencies and academic institutions.
The NRI does not predict when disasters will happen. Instead, it quantifies relative risk — how a county's exposure, vulnerability, and expected losses compare to all other counties nationwide. A county with a "Very High" risk rating faces more natural hazard risk than 99.5% of US counties.
The 18 Natural Hazard Types
The NRI evaluates risk from 18 natural hazard types:
- Avalanche — rapid flow of snow down a slope
- Coastal Flooding — flooding along ocean and Great Lakes shorelines
- Cold Wave — extreme cold temperature events
- Drought — prolonged dry conditions affecting water supply and agriculture
- Earthquake — ground shaking from seismic activity
- Hail — severe thunderstorm hail events
- Heat Wave — extreme heat events exceeding local thresholds
- Hurricane — tropical cyclones with sustained winds of 74+ mph
- Ice Storm — freezing rain events creating dangerous ice accumulation
- Landslide — downslope movement of rock, soil, or debris
- Lightning — cloud-to-ground lightning strike events
- Riverine Flooding — overflow of rivers and streams onto surrounding areas
- Strong Wind — non-tornadic, non-hurricane wind events
- Tornado — violently rotating columns of air
- Tsunami — ocean waves generated by underwater earthquakes or landslides
- Volcanic Activity — volcanic eruptions and related hazards
- Wildfire — uncontrolled fires in wildland or wildland-urban interface areas
- Winter Weather — snow, sleet, and freezing rain events
How NRI Risk Scores Are Calculated
The NRI composite risk score for each county is calculated using three components:
- Expected Annual Loss (EAL): The average dollar value of damage expected per year from natural hazards. This includes building damage, agricultural loss, and a "population equivalence" value for injuries and fatalities.
- Social Vulnerability: How susceptible the community is to adverse effects from hazards, based on Census demographic data. Factors include poverty rate, minority population percentage, age distribution, disability rates, and housing characteristics.
- Community Resilience: The ability of a community to prepare for, absorb, and recover from disasters. Higher resilience reduces the effective impact. Measured by connectivity, health access, housing quality, and economic factors.
Note
The NRI formula is: Risk = Expected Annual Loss x Social Vulnerability / Community Resilience. This means a county with high expected losses AND high social vulnerability AND low resilience receives the highest risk score.
Understanding Risk Ratings
FEMA assigns five risk ratings based on where a county falls in the national distribution. Out of 3,144 counties scored in our database:
| Rating | Percentile | What It Means |
|---|---|---|
| Very High | 99.5+ | Highest risk in the nation — more than 99.5% of all counties |
| Relatively High | 94.3 - 99.4 | Significantly above-average risk |
| Relatively Moderate | 81.0 - 94.2 | Above-average risk, but not extreme |
| Relatively Low | 42.8 - 80.9 | Below-average risk |
| Very Low | 0 - 42.7 | Minimal risk compared to national distribution |
What the NRI Does Not Tell You
The NRI is a powerful tool, but it has important limitations:
- It does not predict specific events. A "Very High" tornado risk county will not necessarily experience a tornado this year. The score reflects long-term historical patterns and modeled exposure.
- It uses county-level averages. Risk can vary dramatically within a single county — a floodplain property faces much higher flood risk than a hilltop home in the same county.
- It does not replace flood maps or insurance rate maps. For property-specific risk assessment, use FEMA flood maps and consult insurance professionals.
- Climate change projections are limited. The NRI is primarily based on historical data. Future risk from climate-driven changes (sea level rise, increased wildfire frequency) may not be fully captured.
How RiskByCounty Uses NRI Data
RiskByCounty takes the raw FEMA NRI data and makes it accessible through a simple interface. We convert NRI composite scores to percentile ranks on a 0-100 scale, extract the five most impactful individual hazard scores (flood, wildfire, tornado, earthquake, hurricane), and present them alongside contextual information for every county.
Our goal is to make this data useful for everyday decisions — whether you are buying a home, shopping for insurance, or creating an emergency preparedness plan. The NRI data is free and public, but navigating FEMA's own tool requires technical expertise. RiskByCounty simplifies the experience without sacrificing accuracy.
Methodology
All data on RiskByCounty comes from the FEMA National Risk Index. Composite and individual hazard scores are converted to percentile ranks on a 0-100 scale. Risk ratings follow FEMA's official percentile thresholds. County pages display the five most impactful hazard types (flood, wildfire, tornado, earthquake, hurricane) alongside the composite risk score. For the full NRI methodology, visit hazards.fema.gov/nri.
Data source: FEMA National Risk Index (NRI). Risk scores use percentile-rank methodology on a 0-100 scale. All figures are relative rankings and do not represent absolute predictions of natural disaster occurrence.