Natural Hazard Glossary

Definitions of terms used in hazard risk assessment, FEMA flood maps, seismic data, and wildfire risk.

FEMA — Federal Emergency Management Agency

The US government agency responsible for coordinating disaster response and mitigation. FEMA administers the National Flood Insurance Program (NFIP) and produces Flood Insurance Rate Maps (FIRMs).

NFIP — National Flood Insurance Program

Federal program that provides flood insurance to property owners, renters, and businesses in participating communities. FEMA administers the NFIP and sets flood zone designations based on FIRM maps.

FIRM — Flood Insurance Rate Map

Official FEMA map showing a community's flood zones, base flood elevations, and floodways. Used to determine flood insurance requirements and premiums. Also called a flood map.

SFHA — Special Flood Hazard Area

Land that FEMA has determined faces a 1% or greater annual chance of flooding. Includes Zones A, AE, AO, AH, V, and VE. Federal law requires flood insurance for most properties with federally-backed mortgages in SFHA zones.

Zone AE — AE Flood Zone

1% annual chance flood zone (commonly called the "100-year floodplain"). The most common high-risk SFHA designation. Mandatory flood insurance required for federally-backed mortgages.

Zone VE / V — Coastal High-Velocity Zone

Coastal flood zone subject to high-velocity wave action (wave heights of 3+ feet). Highest risk SFHA designation. Strict building requirements and mandatory flood insurance.

Zone X — Minimal Flood Hazard Zone

Area outside the 500-year floodplain with minimal flood risk. No mandatory flood insurance requirement, though voluntary coverage is available and recommended.

Zone X (Shaded) — 500-Year Floodplain

Area with 0.2% annual chance of flooding — between the 100-year and 500-year floodplains. Moderate risk; flood insurance not mandatory but recommended.

100-Year Flood — 1% Annual Chance Flood

A flood event with a 1% probability of occurring in any given year — not a flood that only occurs once per century. Over a 30-year period, there is approximately a 26% chance of experiencing a "100-year flood."

LOMA — Letter of Map Amendment

An official FEMA document that amends an existing FIRM to remove a structure or parcel from a SFHA if it was incorrectly mapped. Property owners can apply for a LOMA if they have a survey showing their land is above the base flood elevation.

BFE — Base Flood Elevation

The elevation to which floodwater is anticipated to rise during a 1% annual chance flood event. Used to determine flood insurance rates and required building elevations in SFHA zones.

USGS — US Geological Survey

Federal scientific agency that monitors and reports on natural hazards including earthquakes, landslides, volcanic activity, and floods. USGS operates the National Earthquake Information Center (NEIC) and the seismic monitoring network.

Moment Magnitude (Mw) — Earthquake Magnitude Scale

The standard scale used by seismologists to measure earthquake size. More accurate than the original Richter scale for large earthquakes. Each whole number increase represents ~31.6x more energy released.

Richter Scale — Local Magnitude Scale (ML)

Original earthquake magnitude scale developed by Charles Richter in 1935 for California earthquakes. Still commonly referenced in public discourse, but seismologists now use Moment Magnitude for most reporting.

USFS — US Forest Service

Federal agency that manages national forests and produces the Wildfire Hazard Potential (WHP) dataset used to measure long-term fire risk across the US.

WHP — Wildfire Hazard Potential

A USFS index measuring the relative likelihood and intensity of wildfire that would be difficult to control. Ranges from 1 (very low) to 100 (very high). Integrates fuel conditions, topography, and historical fire weather data.

WUI — Wildland-Urban Interface

Zone where developed land (homes, businesses) borders undeveloped wildland vegetation. WUI areas face the highest wildfire risk for structures, as fire can spread from wildland fuels into developed areas.

NEIC — National Earthquake Information Center

Part of USGS — monitors global seismic activity 24/7 and publishes earthquake data including magnitude, depth, and location through the USGS Earthquake Hazards Program API.