Understand the differences between FEMA flood zones

Learn about the definitions of FEMA Flood Zones and the differences between them.

 

Federal Emergency Management Agency (FEMA) Flood Maps 

FEMA maps flood zones in communities across the US, identifying areas of varying flood risk on Flood Insurance Rate Maps (FIRMs). FEMA creates FIRMs to inform flood insurance pricing in the National Flood Insurance Program (NFIP) and to guide floodplain management regulations for NFIP-participating communities. 

 

Importance of FEMA Flood Zones

In developing zone maps, FEMA focuses primarily on identifying the 1-percent annual chance floodplain (also known as the 100-year floodplain, Special Flood Hazard Area, or SFHA). As a result, FEMA maps the areas with a 1% annual chance of flooding. The SFHA designation is important because it is the basis for floodplain management regulations for communities across the country and because it decides whether a home is required to have flood insurance or not.

FEMA’s high-risk flood zones – those that make up the SFHA – are those that begin with the letters “A” or “V.” Homeowners located in A or V zones are required to purchase flood insurance if they have a mortgage from a federally-backed or federally-regulated lender. FEMA’s low and moderate risk flood zones – those outside the SFHA – are those that begin with the letters “X,” “B,” or “C.” Flood insurance is not required within these zones. These zones could still have flood risk as historically more than 20% of NFIP claims are made by policyholders in a X, B, or C zone. Definitions for all FEMA flood zones are provided in the table below.

 

FEMA Flood Zones

A
Areas subject to inundation by the 1-percent-annual-chance flood event generally determined using approximate methodologies. Because detailed hydraulic analyses have not been performed, no Base Flood Elevations (BFEs), or flood depths are shown. Mandatory flood insurance purchase requirements and floodplain management standards apply.

AE, A1-A30
Areas subject to inundation by the 1-percent-annual-chance flood event determined by detailed methods. Base Flood Elevations (BFEs) are shown. Mandatory flood insurance purchase requirements and floodplain management standards apply.

AH
Areas subject to inundation by 1-percent-annual-chance shallow flooding, typically areas of ponding, where average depths where average depths are between one and three feet. Base Flood Elevations (BFEs) derived from detailed hydraulic analyses are shown in this zone. Mandatory flood insurance purchase requirements and floodplain management standards apply.

AO
Areas subject to inundation by 1-percent-annual-chance shallow flooding, usually sheet flow on sloping terrain, where average depths are between one and three feet. Average flood depths derived from detailed hydraulic analyses are shown in this zone. Mandatory flood insurance purchase requirements and floodplain management standards apply.

AR
Areas that result from the decertification of a previously accredited flood protection system that is determined to be in the process of being restored to provide base flood protection. Mandatory flood insurance purchase requirements and floodplain management standards apply.

A99
Areas subject to inundation by the 1-percent-annual-chance flood event, but will ultimately be protected upon completion of an under-construction Federal flood protection system. These are areas of special flood hazard where enough progress has been made on the construction of a protection system, such as dikes, dams, and levees, to consider it complete for insurance rating purposes. Zone A99 may only be used when the flood protection system has reached specified statutory progress toward completion. No Base Flood Elevations (BFEs) or depths are shown. Mandatory flood insurance purchase requirements and floodplain management standards apply.

V
Areas along coasts are subject to inundation by the 1-percent-annual-chance flood event with additional hazards associated with storm-induced waves. Because detailed hydraulic analyses have not been performed, no Base Flood Elevations (BFEs) or flood depths are shown. Mandatory flood insurance purchase requirements and floodplain management standards apply.

VE, V1-V30
Areas subject to inundation by the 1-percent-annual-chance flood event with additional hazards due to storm-induced velocity wave action. Base Flood Elevations (BFEs) derived from detailed hydraulic analyses are shown. Mandatory flood insurance purchase requirements and floodplain management standards apply.

D
Areas with possible but undetermined flood risk. No analysis of flood hazards has been conducted in these areas.

X (shaded), B
Areas of moderate flood hazard between limits of the 1-percent-annual-chance floodplain and the 0.2-percent-annual-chance floodplain. Note: zone B is being replaced with shaded zone X on new FIRMs.

X (unshaded), C
Areas of minimal flood hazards outside 0.2-percent-annual-chance floodplain. Note: zone C is being replaced with unshaded zone X on new FIRMs.


Limitations of FEMA Maps
 

While FEMA maps can provide useful information about flood risk, they do not provide a complete picture of flood risk for individual homes. FIRMs are using historical flow data from river and tidal gauges but do not account for current or future environmental changes. They also only show whether a property is in the 100-year floodplain, the 500-year floodplain, or neither, which can be perceived that flood risk suddenly changes at these boundaries even though risk can vary significantly within them. They can also often be outdated. For example, under federal law, FEMA is required to assess the need to revise and update flood maps every 5 years, but Congress does not provide sufficient funding for the agency to do so. As a result, 75% of FIRMs are out of date, with 11% dating back to the 1970’s and 1980’s.  

 

Flood Factor

In contrast to FEMA maps, Flood Factor provides access to flood risk information at an individual property level and incorporates future environmental changes due to sea level rise or changes in precipitation. It also provides a wider range of risk assessment to give a complete view of a property’s flood risk.

 

Learn more

Learn about the benefits of having flood insurance

Learn about flood risk disclosures and which states have them

Understand the differences between FEMA and Flood Factor 

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