A 100-year floodplain, as defined by the Federal Emergency Management Agency (FEMA), is an area that has a 1 in 100 chance of flooding in any given year. Despite the name, it does not mean that such a flood happens only once every 100 years — rather, it represents a statistical probability of flood risk based on historical data, hydrologic modeling and environmental factors. In FEMA’s mapping system, the 100-year floodplain is officially called the Special Flood Hazard Area (SFHA). Properties located within this area are subject to federal flood insurance requirements if they have a federally backed mortgage; regulated by local building and zoning codes that must meet FEMA’s National Flood Insurance Program (NFIP) standards; and shown on Flood Insurance Rate Maps (FIRMs), which guide planning, development and emergency preparedness. It’s important to note that a 1% annual chance flood has about a 26% chance of occurring over a 30-year mortgage period, making the flood risk higher than many people assume, given the name.
