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