The Federal Emergency Management Agency (FEMA) produces Flood Insurance Rate maps and identifies Special Flood Hazard Areas as part of the National Flood Insurance Program's floodplain management. Special Flood Hazard Areas have regulations that include the mandatory purchase of flood insurance for holders of federally regulated mortgages. In addition, this layer can help planners and firms avoid areas of flood risk and also avoid additional cost to carry insurance for certain planned activities.Dataset SummaryPhenomenon Mapped: Flood Hazard AreasGeographic Extent: Contiguous United States, Alaska, Hawaii, Puerto Rico, Guam, US Virgin Islands, Northern Mariana Islands and American Samoa.Projection: Web Mercator Auxiliary SphereData Coordinate System: USA Contiguous Albers Equal Area Conic USGS version (contiguous US, Puerto Rico, US Virgin Islands), WGS 1984 Albers (Alaska), Hawaii Albers Equal Area Conic (Hawaii), Western Pacific Albers Equal Area Conic (Guam, Northern Mariana Islands, and American Samoa)Cell Sizes: 10 meters (default), 30 meters, and 90 metersUnits: NoneSource Type: ThematicPixel Type: Unsigned integerSource: Federal Emergency Management Agency (FEMA)Update Frequency: AnnualPublication Date: December 18, 2024This layer is derived from the December 18, 2024 version Flood Insurance Rate Map feature class S_FLD_HAZ_AR. The vector data were then flagged with an index of 88 classes, representing a unique combination of values displayed by three renderers. (In three resolutions the three renderers make nine processing templates.) Repair Geometry was run on the set of features, then the features were rasterized using the 88 class index at a resolutions of 10, 30, and 90 meters, using the Polygon to Raster tool and the "MAXIMUM_COMBINED_AREA" option. Not every part of the United States is covered by flood rate maps. This layer compiles all the flood insurance maps available at the time of publication. To make analysis easier, areas that were NOT mapped by FEMA for flood insurance rates no longer are served as NODATA but are filled in with a value of 250, representing any unmapped areas which appear in the US Census' boundary of the USA states and territories. The attribute table corresponding to value 250 will indicate that the area was not mapped.What can you do with this layer?This layer is suitable for both visualization and analysis across the ArcGIS system. This layer can be combined with your data and other layers from the ArcGIS Living Atlas of the World in ArcGIS Online and ArcGIS Pro to create powerful web maps that can be used alone or in a story map or other application.Because this layer is part of the ArcGIS Living Atlas of the World it is easy to add to your map:In ArcGIS Online, you can add this layer to a map by selecting Add then Browse Living Atlas Layers. A window will open. Type "flood hazard areas" in the search box and browse to the layer. Select the layer then click Add to Map.In ArcGIS Pro, open a map and select Add Data from the Map Tab. Select Data at the top of the drop down menu. The Add Data dialog box will open on the left side of the box, expand Portal if necessary, then select Living Atlas. Type "flood hazard areas" in the search box, browse to the layer then click OK.In ArcGIS Pro you can use the built-in raster functions to create custom extracts of the data. Imagery layers provide fast, powerful inputs to geoprocessing tools, models, or Python scripts in Pro.The ArcGIS Living Atlas of the World provides an easy way to explore many other beautiful and authoritative maps on hundreds of topics like this one.Processing TemplatesCartographic Renderer - The default. These are meaningful classes grouped by FEMA which group its own Flood Zone Type and Subtype fields. This renderer uses FEMA's own cartographic interpretations of its flood zone and zone subtype fields to help you identify and assess risk. Flood Zone Type Renderer - Specifically renders FEMA FLD_ZONE (flood zone) attribute, which distinguishes the original, broadest categories of flood zones. This renderer displays high level categories of flood zones, and is less nuanced than the Cartographic Renderer. For example, a fld_zone value of X can either have moderate or low risk depending on location. This renderer will simply render fld_zone X as its own color without identifying "500 year" flood zones within that category.Flood Insurance Requirement Renderer - Shows Special Flood Hazard Area (SFHA) true-false status. This may be helpful if you want to show just the places where flood insurance is required. A value of True means flood insurance is mandatory in a majority of the area covered by each 10m pixel.Each of these three renderers have templates at three different raster resolutions depending on your analysis needs. To include the layer in web maps to serve maps and queries, the 10 meter renderers are the preferred option. These are served with overviews and render at all resolutions. However, when doing analysis of larger areas, we now offer two coarser resolutions of 30 and 90 meters in processing templates for added convenience and time savings.Questions?Please leave a comment below if you have a question about this layer, and we will get back to you as soon as possible.

This resource describes a dataset of gridded depth at horizontal resolution of 3 meters, published November 15, 2017, downloaded from FEMA [1] and hosted in this archive at the University of Texas Advanced Computing Center (TACC) [2].. The raster dataset is contained within an Esri ArcGIS geodatabase. This product utilized Triangulated Irregular Network (TIN) interpolation, four quality assurance measures (identifying dips, spikes, duplication, and inaccurate/unrealistic measurements). High Water Marks were obtained from the Harris County Flood Control District (HCFCD), US Geological Survey (USGS), and other inspection data. Elevation data comprised a mosaic of 3 meter resampled elevations from 1M & 3M LiDAR, and IFSAR data. One section of the IfSAR data was found to be erroneous, and replaced with a blended 10 meter section. [This description was in correspondence January 22, 2018, from Mark English, GeoSpatial Risk Analyst, FEMA Region VIII, Mitigation Division.]

A preliminary version of these depths dated September 10, 2017 can be viewed in a FEMA web map [3]. This web map shows a forecasted depth grid, based on National Weather Service (NWS) Advanced Hydrologic Prediction Service (AHPS) forecasted water levels.

See FEMA's Natural Hazard Risk Assessment Program (NHRAP) ftp site [4] for additional HWM-based depth grids and inundation polygons: - Harris County AOIs and Inundation Boundaries [5] - Harris County Depth Grids [6] - Aransas, Nueces, and San Patricio Coastal Depth Grids and Boundaries [7] FEMA notes on these Modeled Preliminary Observations: o Based on observed Water Levels at stream gauges interpolated along rivers, downsampled to 5m resolution DEM o Depth grids updated with new observed peak crest as they become available o Will include High Water Mark information as it becomes available o Extents validated with remote sensing o Use for determining damage levels on specific structures

See also FEMA's journal of mitigation planning and actions related to Harvey [8].

References and related links: [1] FEMA_Depths_3m_v3.zip (39 gb ftp download) [https://data.femadata.com/Region8/Mitigation/Data_Share/] [2] TACC 39gb wget or ftp download [https://web.corral.tacc.utexas.edu/nfiedata/Harvey/flood_data/FEMA_Harvey_Depths_3m.gdb.zip] [3] FEMA map viewer for Hurricane Harvey resources (flood depths is bottom selection in layers list) [https://fema.maps.arcgis.com/apps/webappviewer/index.html?id=50f21538c7bf4e08b9faab430bc237c9] [4] FEMA NHRAP ftp [https://data.femadata.com/FIMA/NHRAP/Harvey/] [5] [https://data.femadata.com/FIMA/NHRAP/Harvey/Harris_AOIandBoundaries.zip] [6] [https://data.femadata.com/FIMA/NHRAP/Harvey/Harris_Mosaic_dgft.zip] [7] [https://data.femadata.com/FIMA/NHRAP/Harvey/Rockport_DG_unclipped.zip] [8] Hurricane Harvey Mitigation Portfolio - FEMA map journal [https://fema.maps.arcgis.com/apps/MapJournal/index.html?appid=70204cf2762d45409553fd9642700b7f]

The Composite Risk Index Plus Sea Level Rise is generated by multiplying the SACS Composite Exposure Index by the SACS Combined Hazard Plus Sea Level Rise. The Composite Exposure Index is created by summing three separate exposure indices which are weighted on a percentage basis: Population and Infrastructure Index 60%, Environmental Cultural and Habitat 30%, and Social Vulnerability 10% (For the US Virgin Islands, 65% Population and Infrastructure data and 35% Environmental, Cultural and Habitat due to a lack of CDC Social Vulnerability data for the USVI). For additional information on the input datasets and methodology for the exposure indices, please reference the NACCS report, Appendix C, page 103: https://www.nad.usace.army.mil/Portals/40/docs/NACCS/NACCS_Appendix_C.pdf.The SACS Combined Hazard Index Plus Sea Level Rise depicts the percentage annual chance of a specific flood hazard, with an additional 3 ft. of sea level rise added to the flood surface elevation. The three flooding hazards depicted are the 10% annual chance flooding event, the 1% annual chance flooding event, and Category 5 Hurricane Maximum of Maximums. The 10% annual chance flooding is derived via a statistical analysis of tide gauges within the SACS study area, utilizing methodology developed by the USACE Engineering and Research Development Center (https://hdl.handle.net/11681/7353 or https://www.jcronline.org/doi/abs/10.2112/JCOASTRES-D-15-00031.1). The 10% annual chance flooding event raster index grid cells are assigned a value of 0.1. The 1% annual chance flooding are aggregated from FEMA’s National Flood Hazard Layer (https://www.fema.gov/national-flood-hazard-layer-nfhl) and raster index grid cells are assigned a value of 0.01. The Category 5 Maximum of Maximums hazard is pulled from NOAA’s storm surge SLOSH inundation data. These data are assigned a value of 0.001 to reflect the low probability of a Category 5 event. Three feet of sea level rise were added to the 10% and 1% annual chance flooding events for this hazard grid.The Composite Risk Index Plus Sea Level Rise grid resolution is 30 meters.This Tier 1 dataset is available for download here:Tier 1 Risk Assessment Download

The Composite Risk Index is generated by multiplying the SACS Composite Exposure Index by the SACS Combined Hazard. The USACE South Atlantic Coastal Study’s (SACS) initial study product is the Tier 1 Risk Assessment. The main output of the Tier 1 Risk Assessment is the Composite Risk Index. In the SACS, risk is defined as the probability of a hazard, multiplied against the exposure of a specific element. The Composite Exposure Index is generated following the methodology for the Tier 1 Risk Assessment cited in the USACE North Atlantic Coastal Comprehensive Study (NACCS). The Tier 1 Composite Risk Index is derived from multiplying the SACS Composite Exposure Index by the SACS Combined Hazards Present index. The Composite Risk Index is depicted as a classified grid using the Jenks or Natural Breaks classification. The four classes are Low Potential Risk, Medium Potential Risk, Medium/High Potential Risk, and High Potential Risk. The resolution of the grid is 30 meters.The Composite Exposure Index is created by summing three separate exposure indices which are weighted on a percentage basis: Population and Infrastructure Index 60%, Environmental Cultural and Habitat 30%, and Social Vulnerability 10% (For the US Virgin Islands, 65% Population and Infrastructure data and 35% Environmental, Cultural and Habitat due to a lack of CDC Social Vulnerability data for the USVI). For additional information on the input datasets and methodology for the exposure indices, please reference the NACCS report, Appendix C, page 103: https://www.nad.usace.army.mil/Portals/40/docs/NACCS/NACCS_Appendix_C.pdf.The SACS Combined Hazard Index depicts the percentage annual chance of a specific flood hazard. The three flooding hazards depicted are the 10% annual chance flooding event, the 1% annual chance flooding event, and Category 5 Hurricane Maximum of Maximums. The 10% annual chance flooding is derived via a statistical analysis of tide gauges within the SACS study area, utilizing methodology developed by the USACE Engineering and Research Development Center (https://hdl.handle.net/11681/7353 or https://www.jcronline.org/doi/abs/10.2112/JCOASTRES-D-15-00031.1). The 10% annual chance flooding event raster index grid cells are assigned a value of 0.1. The 1% annual chance flooding are aggregated from FEMA’s National Flood Hazard Layer (https://www.fema.gov/national-flood-hazard-layer-nfhl) and raster index grid cells are assigned a value of 0.01. The Category 5 Maximum of Maximums hazard was pulled from NOAA’s storm surge SLOSH inundation data. These data are assigned a value of 0.001 to reflect the low probability of a Category 5 event.The Composite Risk Index grid resolution is 30 meters.This Tier 1 dataset is available for download here:Tier 1 Risk Assessment Download

The Composite Risk Index Plus Sea Level Rise is generated by multiplying the SACS Composite Exposure Index by the SACS Combined Hazard Plus Sea Level Rise. The Composite Exposure Index is generated following the methodology for the Tier 1 Risk Assessment cited in the USACE North Atlantic Coastal Comprehensive Study (NACCS). The Composite Exposure Index is created by summing three separate exposure indices which are weighted on a percentage basis: Population and Infrastructure Index 60%, Environmental Cultural and Habitat 30%, and Social Vulnerability 10%. For additional information on the input datasets and methodology for the exposure indices, please reference the NACCS report, Appendix C, page 103: https://www.nad.usace.army.mil/Portals/40/docs/NACCS/NACCS_Appendix_C.pdf.The SACS Combined Hazard Index Plus Sea Level Rise depicts the percentage annual chance of a specific flood hazard, with an additional 3 ft. of sea level rise added to the flood surface elevation. The three flooding hazards depicted are the 10% annual chance flooding event, the 1% annual chance flooding event, and Category 5 Hurricane Maximum of Maximums. The 10% annual chance flooding is derived via a statistical analysis of tide gauges within the SACS study area, utilizing methodology developed by the USACE Engineering and Research Development Center (https://hdl.handle.net/11681/7353 or https://www.jcronline.org/doi/abs/10.2112/JCOASTRES-D-15-00031.1). The 10% annual chance flooding event raster index grid cells are assigned a value of 0.1. The 1% annual chance flooding are aggregated from FEMA’s National Flood Hazard Layer (https://www.fema.gov/national-flood-hazard-layer-nfhl) and raster index grid cells are assigned a value of 0.01. The Category 5 Maximum of Maximums hazard is pulled from NOAA’s storm surge SLOSH inundation data. These data are assigned a value of 0.001 to reflect the low probability of a Category 5 event. Three feet of sea level rise were added to the 10% and 1% annual chance flooding events for this hazard grid.The Composite Risk Index Plus Sea Level Rise grid resolution is 30 meters.This Tier 1 dataset is available for download here:Tier 1 Risk Assessment Download