Flood Risk Glossary
Key terms and definitions related to flood risk assessment, FEMA programs, and the National Flood Insurance Program.
NFIP (National Flood Insurance Program)
A federal program administered by FEMA that provides flood insurance to property owners, renters, and businesses in participating communities. The NFIP was established by the National Flood Insurance Act of 1968 and covers over 5 million policies nationwide.
FEMA (Federal Emergency Management Agency)
The federal agency responsible for coordinating disaster response, recovery, and mitigation efforts. FEMA administers the NFIP, publishes flood maps, and maintains the disaster declarations database used in our flood risk scoring.
Flood Insurance Rate Map (FIRM)
An official map produced by FEMA that delineates flood hazard areas, risk zones, and base flood elevations for a community. FIRMs are used to determine flood insurance rates and regulatory requirements for new construction.
Flood Zone
A geographic area defined by FEMA according to varying levels of flood risk. High-risk zones (A and V zones) have a 1% or greater annual chance of flooding. Moderate-risk zones (B and X-shaded) fall between the 1% and 0.2% annual chance. Low-risk zones (C and X-unshaded) are above the 0.2% annual chance flood level.
Base Flood Elevation (BFE)
The computed elevation to which floodwater is anticipated to rise during a base flood (the 1% annual chance flood, also called the 100-year flood). BFE is shown on FEMA Flood Insurance Rate Maps and is used to set insurance rates and building requirements.
Special Flood Hazard Area (SFHA)
The area that would be inundated by a flood having a 1% chance of being equaled or exceeded in any given year (the 100-year flood). SFHAs are identified on FIRMs as zones beginning with the letters A or V. Properties in SFHAs with federally backed mortgages are required to carry flood insurance.
Repetitive Loss Property
A property insured under the NFIP that has had at least two paid flood claims of more than $1,000 each in any rolling 10-year period. These properties represent a disproportionate share of total NFIP claims payments and are a focus of FEMA mitigation efforts.
Claims Density
The number of NFIP flood insurance claims per capita or per housing unit in a given county. Claims density is the most heavily weighted factor (40%) in our composite flood risk score because it reflects actual, experienced flooding across a community.
Disaster Declaration
A formal statement by the President that a major disaster or emergency exists in a state or locality, making federal assistance available. Our scoring uses flood-related disaster declarations (FEMA Disaster Declarations Summaries dataset) as a measure of disaster frequency.
Flood Risk Score
A composite score from 0 to 100 that quantifies a county's overall flood risk. The score combines four normalized factors: NFIP claims density (40% weight), disaster declaration frequency (25%), claim severity measured by average payout (20%), and year-over-year trend (15%).
Letter Grade
A simplified representation of the flood risk score: A (0-20, lowest risk), B (21-40, below average risk), C (41-60, moderate risk), D (61-80, above average risk), and F (81-100, extreme risk). Grades provide a quick reference for comparing counties.
Community Rating System (CRS)
A voluntary FEMA program that rewards communities for floodplain management activities that exceed minimum NFIP requirements. Communities earn CRS credits that translate into flood insurance premium discounts of 5% to 45% for policyholders in that community.