Prioritizing areas for flood mitigation activities

The Chicago Metropolitan Agency for Planning (CMAP) developed urban and riverine flood susceptibility indexes (FSIs) to identify priority areas for flood mitigation activities.

Locations highlighted in the FSIs may be more susceptible to different types of flooding than other parts of the region. Streets and buildings in 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 correlate with reported flood damages.

While riverine flood risk is best identified through updated floodplain modeling efforts, urban flood risk areas 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 priorities across the region for mitigation activities and help inform flood susceptibility in communities that need technical analysis.

CMAP created two versions of the FSI to reflect the different causes and factors that contribute to urban and riverine flooding. The urban and riverine FSIs are spatially-depicted through raster grids and are available for the seven counties of northeastern Illinois.

Urban flood susceptibility index

Urban flood susceptibility index map

The urban FSI includes all developed areas of the region outside of Federal Emergency Management Agency’s (FEMA) 100-year floodplain and the Metropolitan Water Reclamation District 100-year inundation layer within Cook County.

Riverine flood susceptibility index

Riverine flood susceptibility map

The riverine FSI pertains to developed areas in the region within the FEMA 100-year floodplain or Metropolitan Water Reclamation District 100-year inundation layer within Cook County.

Use the flood susceptibility indexes

More information about the FSIs methodology, as well as the FSIs index rasters and flood-related factor data, are available for download on the CMAP Data Hub. Raw values for the FSIs are available upon request. CMAP is currently using the indexes to integrate stormwater management strategies into technical assistance projects. View the Guide to Flood Susceptibility and Stormwater Planning to learn how you can use the indexes in your planning activities.

Methodology

The FSIs were 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 FEMA, 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, many which experienced flooding from 2007 to 2017. CMAP developed the FSI with support from John D. and Catherine T. MacArthur Foundation.