FIRMs and DFIRMs

Flood Insurance Rate Maps are developed by FEMA or a FEMA contractor by conducting engineering studies referred to as Flood Insurance Studies in a flood prone community.  Using historic, meteorologic, hydrologic, and hydraulic data, flood elevations are developed for the 100-year and 500-year flood.  A 100-year flood has a 1 percent chance of being equaled or exceeded during any given year (a 500-year flood has a 0.2 percent chance).  This type of flood is referred to as the base flood and is a regulatory standard used by federal agencies and most states to administer floodplain managment programs.  The 100-year flood is also used by the NFIP as the basis for insurance requirements nationwide. Any area within the base flood limits is referred to by FEMA as a Special Flood Hazard Area.

FIRMs are distributed by FEMA to private citizens, insurance agents and brokers, community officials, lending institutions, and federal agencies.  Private citizens and insurance agents use the FIRM to locate properties and buildings in relation to their corresponding flood insurance risk zone.  Community officials use the FIRMs  to administer floodplain management regulations and reduce flood damage.  Lending institutions and federal agencies use the Flood Maps to locate properties and buildings and determine if flood insurance is required when making loans or providing grants for the purchase or construction of buildings.  Flood insurance is required to receive any loans or grants intended for the purchase or construction of any property or building within the 100-year floodplain.

Existing FIRMs are produced using manual cartographic methods and are distributed only through paper copies.  FEMA is now in the process of using new digital technology to convert the existing FIRMs to new digital versions called Digital Flood Insurance Rate Maps.  DFIRMs will be a vast improvement over their paper counterparts in that they will be much easier to produce, store, and distribute.  Eventually, FEMA intends to allow easy access to DFIRMs through the internet, where anybody could search for the DFIRM panel in their area of interest, view or download the data, and print out a copy for themselves.  DFIRMs are also easier to update when new data becomes available (such as the digital aerial photos recently taken by the LCRA).  Only the portion of the data that is out of date needs to be changed.  Additionally, DFIRMs enable FEMA to store information that is not shown on the actual map product, but which is critical to the development of the floodplains, with the map product.  Examples of this kind of information are elevation data (contours are not displayed on FIRMs or DFIRMs) and digital versions of the text from the Flood Insurance Study report which includes the technical information and calculations used to developed the 100-year and 500-year flood elevations.