Digital Flood Insurance Rate Maps (DFIRMs)
In 1968, the United States Congress created the National Flood Insurance Program (NFIP) with the objective of reducing future flood damage and to provide protection for property owners from potential losses through the purchase of flood insurance. Currently, over 23,000 communities Nationwide participate in the NFIP. The Federal Emergency Management Agency (FEMA) produces digital flood maps called DFIRMs that show flood hazard areas within a community that are prone to flooding. The DFIRMs communicate the level of flood risk for the entire community by showing flood zones, the boundaries of regulatory floodways and floodplains, and flood heights (base floods elevations).
DFIRMs are generated based on engineering analyses using historic, meteorological, hydrologic, hydraulic, and topographic data, as well as open space conditions, flood control facilities, and urban and rural community development. These analyses are called Flood Insurance Studies (FIS) and they provide the technical engineering basis for determining lands that are subject to inundation by a flood that has a 1% or greater chance of occurring annually at any given time. This type of flood commonly is referred to as the 100-year flood or base flood. Lands that will be impacted by the 1% annual chance flood are referred to on the DFIRMs as ‘Special Flood Hazard Areas’.
A 100-year flood is not a flood that occurs every 100 years!
Some people believe that a 100-year flood occurs once every 100 years, but that is not factually correct. The term "100-year flood" is misleading. It is not the flood that will occur once every 100 years. Rather, it is the flood that has a 1% chance of being equaled or exceeded each year. Thus, the 100-year flood could occur more than once in a relatively short period of time or even within the same month. Interestingly, the 100-year flood has a 26% chance of occurring during a 30 year period, which also happens to be the length of many mortgages. People living outside of the 100-year floodplain are free of regulatory floodplain requirements, but are not risk-free. Flooding can still happen outside of the floodplain. Federally backed flood insurance is available to people living outside of the 100-year floodplain as well.
Because this term is misleading, FEMA no longer uses the term ‘100-year flood’ but rather, refers to it as the "1-percent-annual-chance flood." The "1-percent-annual-chance flood" is the term that is now used by most Federal and State agencies local communities as well as by the National Flood Insurance Program.
To learn more about the digital Flood Insurance Rate Maps, visit:
Click here to order a digital Flood Insurance Rate Map from FEMA’s Map Service Center (FEMA fees in effect), or make your own using FEMA's FIRMettes prompts.