EPA Climate Change Indicators – Change in River Flooding

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This indicator examines changes in the size and frequency of inland river flood events in the United States. Indicator data are acquired from the EPA’s Climate Change Indicators in the United States, Fourth Edition, published in 2016.

FEMA Disaster Declarations, Flood, 1958-2018

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This layer displays the total number of federal disaster and emergency declarations for flood events by county for through June, 2018. For this analysis, flood events include the following designated events: Mud/Landslide; Dam/Levee Break; and Flood.
For more layers from this series, browse the Map Room data and navigate to Environment>Emergency Management.

FEMA Flood Hazard Zones, 2019

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The Flood Hazard Zones are extracted from the National Flood Hazard Layer, which is a database that contains FEMA’s flood hazard map data.

Army Corps Enbankments

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This layer displays United States Army Core of Engineers surveyed Embankments. The USACE defines an Embankment as the area of a floodplain from which flood water is excluded by the levee system. For more information about USACE data, visit the National Levee Database here .

Army Corps Floodwalls

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This layer displays United States Army Core of Engineers surveyed Floodwalls. The USACE defines an Floodwall as a structure erected to protect areas from high river stages. For more information about USACE data, visit the National Levee Database here .

Army Corps Leveed Areas

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This layer displays United States Army Core of Engineers surveyed Leveed Areas. The USACE defines a Levee Areas as the area of a floodplain from which flood water is excluded by the levee system. For more information about USACE data, visit the National Levee Database here .

FEMA Flood Hazard Zones

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The Flood Hazard Zones are extracted from the National Flood Hazard Layer, which is a database that contains FEMA’s flood hazard map data. The database contains flood hazard information and supporting data used to develop the information. The primary flood hazard classification is indicated in the Flood Hazard Zones layer.

Flood zones are geographic areas that FEMA has defined according to varying levels of flood risk and type of flooding. For complete information about different flood zone designations, please visit the Definitions of FEMA Flood Zones web page.

Flood Hazard Zone Descriptions:
  Floodway: The stream channel and that portion of the adjacent floodplain which must remain open to permit passage of the base flood.
  1% Annual Chance Flood Zone: The 100-year or base floodplain.
  0.2% Annual Chance Flood Zone: Area of moderate flood hazard, usually the area between the limits of the 100-year and 500-year floodplains, but also shallow flooding areas (< 1 foot) or flood zones for small drainage areas (< 1 square mile).
  Area with Reduced Risk Due to Levee: Areas protected by levees from the 100-year flood.
  1% Annual Chance Future Considerations: The 100-year floodplain based on anticipated future land-use conditions.
  Area of Undetermined Hazard: Area of undetermined but possible flood hazard, typically occurring in counties with partial flood studies.

This information was acquired by state-level release February, 2020. Data release dates by state range from December 07, 2016 (Vermont) to February 12, 2020 (Utah).

Flooding Frequency (Dominant Condition)

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Flooding Frequency, based on soil characteristics, has been updated to the October 2019 NRCS SSURGO data release. Note there is a change to the legend used to depict the data in this update.

FEMA Flood Hazard Zones

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The Flood Hazard Zones are extracted from the National Flood Hazard Layer, which is a database that contains FEMA’s flood hazard map data. The database contains flood hazard information and supporting data used to develop the information. The primary flood hazard classification is indicated in the Flood Hazard Zones layer.

Flood zones are geographic areas that FEMA has defined according to varying levels of flood risk and type of flooding. For complete information about different flood zone designations, please visit the Definitions of FEMA Flood Zones web page.

Flood Hazard Zone Descriptions:
  Floodway: The stream channel and that portion of the adjacent floodplain which must remain open to permit passage of the base flood.
  1% Annual Chance Flood Zone: The 100-year or base floodplain.
  0.2% Annual Chance Flood Zone: Area of moderate flood hazard, usually the area between the limits of the 100-year and 500-year floodplains, but also shallow flooding areas (< 1 foot) or flood zones for small drainage areas (< 1 square mile).
  Area with Reduced Risk Due to Levee: Areas protected by levees from the 100-year flood.
  1% Annual Chance Future Considerations: The 100-year floodplain based on anticipated future land-use conditions.
  Area of Undetermined Hazard: Area of undetermined but possible flood hazard, typically occurring in counties with partial flood studies.

This information was acquired by state-level release February, 2020. Data release dates by state range from December 07, 2016 (Vermont) to February 12, 2020 (Utah).