CMAP has developed urban and riverine flood susceptibility indexes (FSI) to identify priority areas across the region for flood mitigation activities. Locations highlighted in the FSI may be more susceptible to riverine or urban flooding than other parts of the region. Streets and buildings within these areas could be more susceptible to overbank flooding, surface ponding, overland flow, water seepage, and basement backups due to the presence of flood-related physical conditions that are correlated with reported flood damages.

While riverine flood risk continues to best identified through updated floodplain modeling efforts, locations of urban flood risk remain largely unknown outside of individual modeling efforts done by municipalities. These indexes are not intended to replace those more technical efforts; instead, they are designed to identify larger scale priorities across the region for mitigation activities and help inform flood susceptibility in communities lacking more technical analysis.

The FSI was constructed using a statistical method based on the observed relationship between the distribution of reported flood locations and a variety of flood-related factors. With data assistance from Federal Emergency Management Agency, counties, and the City of Chicago, CMAP created an address-level database of documented flood locations to cross-reference with flooding-related factors. CMAP’s database consists of over 165,000 unique locations, with the majority of the reported locations experiencing flooding within the past ten years (2007-17).

CMAP created two versions of the FSI to reflect the different causes and factors that contribute to urban and riverine flooding. The riverine FSI pertains to developed areas of the region within the Federal Emergency Management Agency 100-year floodplain or Metropolitan Water Reclamation District 100-year inundation layer within Cook County, and the urban FSI includes all developed areas of the region outside of those 100-year zones. The urban and riverine FSIs are spatially-depicted through raster grids and are available for the seven counties of northeastern Illinois.

More information about the FSI methodology, as well as the FSI index rasters and flood-related factor data, are available for download on CMAP Data Hub. Raw values for the FSI are available upon request.

CMAP is currently using the index to integrate stormwater management strategies into CMAP Local Technical Assistance projects. See the Guide to Flood Susceptibility and Stormwater Planning for information on how to use the FSI in planning activities. CMAP developed the FSI with critical support from John D. and Catherine T. MacArthur Foundation.

Regional Urban Flood Susceptibility Index