Final Guidelines for Using Future-Conditions Hydrology

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Two of the key objectives of FEMA's Flood Map Modernization effort are to integrate communities, regional agencies, and States more fully into the mapping process and to reduce the potential for loss of life and property. The agency's decision to evaluate and implement the use of future-conditions hydrology is directly aligned with meeting those goals. The use of future-conditions hydrology should promote the implementation of better, more proactive mitigation measures; and is a clear indication of FEMA’s desire to be flexible with, and supportive of, those progressive communities that implement stricter land-use requirements than the minimum requirements for participating in the National Flood Insurance Program (NFIP).

A complete summary of the agency's evaluation of future-conditions hydrology is documented in the final version of a report entitled "Modernizing FEMA's Flood Hazard Mapping Program: Recommendations for Using Future Conditions Hydrology for the National Flood Insurance Program." As a result of that evaluation, FEMA decided the following:

  • The local community will determine the future-conditions land-use and hydrology.
  • If the community chooses to adopt a regulatory floodway based on future-conditions hydrology, the use of this floodway must be supported by local ordinances.
  • If the community requests that FEMA do so, FEMA will show the future-conditions 1-percent-annual-chance (100-year) floodplain on the Flood Insurance Rate Map (FIRM) and designate it as "Zone X (Future Base Flood)."
  • When possible, FEMA will show three floodplains on the map: existing-conditions 1-percent-annual-chance (100-year) floodplain, existing-conditions 0.2-percent-annual-chance (500-year) floodplain, and future-conditions 1-percent-annual-chance (100-year) floodplain.
  • FEMA will not show future-conditions 1-percent-annual-chance (100-year) flood elevations on the FIRM; however, FEMA will include them in the Flood Insurance Study (FIS) report.
  • When the future-conditions 1-percent-annual-chance (100-year) floodplain and the existing-conditions 0.2-percent-annual-chance (500-year) floodplain are so close together as to be confusing if both are shown on the FIRM, FEMA will show the future-conditions 1-percent-annual-chance (100-year) floodplain on the FIRM in lieu of the existing-conditions 0.2-percent-annual-chance (500-year) floodplain.
  • If existing-conditions 0.2-percent-annual-chance (500-year) floodplain information is not shown on the FIRM, FEMA will include that information in the FIS report.
  • FEMA will show the existing-conditions 0.2-percent-annual-chance (500-year) flood elevations on the Flood Profiles in the FIS report to meet the requirements of Executive Order No.11988 and to provide Federal agencies with information to evaluate the potential effects of any actions they may take in a floodplain.
  • If the community chooses to do so, FEMA will show the existing-conditions 0.2-percent-annual-chance (500-year) floodplain on the FIRM and include the future-conditions 1-percent-annual-chance (100-year) flood elevations only on the Flood Profiles in the FIS report. (FEMA recognizes that other combinations to display the flood hazard data also are possible and will work with the community to produce the most useful FIRM and FIS report possible.
  • FEMA will continue to require regulation of floodplain development based on the existing-conditions data, while local floodplain managers can regulate development based on the future-conditions data.
  • FEMA will continue to require flood insurance for structures shown in the existing-conditions 1-percent-annual-chance (100-year) floodplain: that is, the Special Flood Hazard Area.

These FEMA decisions were implemented through issuance of a Final Rule that was published in the Federal Register.

Please direct questions concerning the implementation of the use of future-conditions hydrology in a particular community to the floodplain administrator for that community or the appropriate FEMA Regional Office.

Resources related to the Final Guidelines for Using Future Conditions Hydrology can be downloaded through the link below. These resources and an array of other useful FEMA, NFIP, and Map Mod resources are now located in the FEMA Library.

Future-Conditions Hydrology Final Report

Future-Conditions Final Rule

Last Updated: 
07/24/2014 - 16:00
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