Flood hazards are dynamic and can change frequently as a result of a variety of factors, including weather
patterns, erosion, and new development. Because flood risks can change over time, and water flow and drainage patterns can be altered dramatically by surface erosion, land use, and natural forces, FEMA works with communities to identify areas where such changes occur and determines the best approach for updating the flood hazard information shown on the Flood Insurance Rate Maps (FIRM) for that area.
Flood zone designations and other flood hazard information may be established or revised when new
and more accurate information becomes available because of a FEMA-funded restudy or because the
community makes the information available to FEMA.
The frequency that Flood Insurance Rate Maps are updated is influenced by several factors, including the extent of new development and the completion of flood control projects.
Each FEMA-funded flood risk project and associated Flood Insurance Rate Maps update is tailored to the needs and capabilities of each affected community and may involve different steps, products and services.
When FEMA doesn’t have the money to do a new flood risk study, it relies on scientific and technical data and documentation provided by communities to reflect changes that might have occurred.