Urban flood susceptibility index (FSI) and input layers, northeastern Illinois (CMAP, 2026)

What is this data? In a continued effort to help the region tackle current and future flooding challenges, CMAP updated the region’s urban and riverine flood susceptibility indexes (FSIs). Originally published in 2017, the FSIs identify priority areas across the region for stormwater management and flood resilience planning activities. Areas ranked higher on the indexes’ susceptibility scale of 1-10 exhibit characteristics that may make them more likely to experience flooding than other parts of the region. The FSIs were updated in two significant ways to provide a more accurate and up-to-date understanding of urban flood susceptibility. Refining the methodology, including modifying the geographic extents and using statistical tests to select the flood-related factors used in the analyses. Updating the data, including adding more recent flood event data and updating and/or adding new flood-related factors. The urban FSI measures flood susceptibility in developed areas within both floodplain and non-floodplain areas, acknowledging that even developed areas within floodplains can experience urban flooding issues. On a 1-10 scale, with 10 being the most susceptible, areas in the urban index with heightened susceptibility are more likely to experience urban flooding, such as basement backups and water ponding in streets and yards. This zipped geodatabase contains both the urban FSI raster layer and the input layers* used to create it. These layers include a variety of environmental, geographic, and infrastructure characteristics that impact or contribute to flooding. The following input layers are included in the zipped geodatabase: • Age of development • Catchment runoff rate • Combined sewer service areas • Flow accumulation • Impervious cover • Low-lying areas near floodplains • Precipitation How can I access this data? Download the ZIP folder directly or click “Open” in the top right to begin the download process. Explore the FSIs through our interactive web map. The riverine FSI and its input layers are also available for download. *The potential future flooding input layer used in the urban FSI is not included in the geodatabase but is available upon request. Please contact Kate Evasic ([e-mail]) for more details.