The Chicago region experiences significant and repeated damages from flooding. Between 2007 and 2014, $2.319 billion in damages were paid out from public and private sources statewide, according to a 2015 Illinois Department of Natural Resources report that reviewed the cost and prevalence of urban flooding. The report also found that 90 percent of damage claims were for locations outside the mapped 100-year floodplain, highlighting the degree to which Illinois' floodplain maps have become out of date and no longer accurately reflect the risk that communities and developers must plan to address.

The increasingly negative effects of urban flooding outside the mapped floodplain are significant. Urban flooding happens when the local drainage system is overwhelmed, resulting in water ponding in streets and yards, entering buildings through foundations, and backing up from sewers into basements and streets. Yet many existing programs and strategies focus solely on riverine flooding, which occurs when water breaches river and streambanks, and not on more chronic urban flooding. Through ON TO 2050 and local planning work, CMAP is seeking to better understand urban flooding and improve the integration of urban and riverine flooding solutions into local plans. Land use and transportation decisions that increase impervious surfaces, such as parking lots, roofs, and roads, heavily influence stormwater volumes; the design of our streets and neighborhoods can prevent flooding as well as protect downstream areas.

This Policy Update reviews the effects of flooding in the region, potential strategies to reduce flooding damages being explored through the ON TO 2050 planning process, and current work by CMAP to better integrate stormwater management into local planning.   

Where flooding occurs in the region

To better understand the location and costs of flooding damages within the Chicago region, CMAP evaluated National Flood Insurance Program (NFIP) policies, claims, and payments; Federal Emergency Management Agency (FEMA) disaster relief Individual Assistance (IA) grants; and Small Business Administration loans from 2003 to 2015 by ZIP code. Combined, these programs provided the Chicago region with $907 million in flood relief between 2003 and 2015, as displayed in Figure 1. The majority of payouts come from FEMA IA grants (65 percent), most of which were for locations outside the 100-year and 500-year floodplains. The majority (63 percent) of NFIP claims (18 percent of payouts) were located within the 100-year floodplain. For more details on the insurance and assistance programs, as well as the limitations of these datasets, see CMAP's summary of the causes and impacts of flooding in this memo.

Flooding does not affect all populations equally. Exposure to flooding risks appears to be greater in populations and communities already facing vulnerability due to socioeconomic, demographic, and health factors. During flooding events, the elderly and residents with disabilities or illnesses are most vulnerable, particularly when power outages and transportation disruptions inhibit them from meeting daily needs, such as climate control and medical treatment. Low-income residents may struggle to pay for flood insurance, the clean-up costs and loss of personal belongings, as well as the repairs that could reduce their flood exposure in the future. Property damage from reoccurring flooding can contribute to larger scale disinvestment that is not fully captured in insurance claim or disaster relief data. In turn, local governments already facing constraints due to disinvestment may have a particularly difficult time responding during floods or taking preventative measures that reduce future risk.

Total flooding damage payments from public sources, 2003-15, Chicago region.

Note: CMAP evaluated National Flood Insurance Program (NFIP) payments, FEMA disaster relief Individual Assistance (IA) grants, and Small Business Administration (SBA) loans from 2003 to 2015 by ZIP code, normalized by 2010 households.  

Flooding and ON TO 2050

As part of ON TO 2050, CMAP is taking a closer look at stormwater and flooding. Preparing for infrequent, extreme events, such as those experienced by the region in summer 2017, will continue to present significant challenges. The more chronic problems faced by areas where neighborhood drainage systems struggle to handle even small storm events—with less than two inches of rain—are critical to improve everyday quality of life. Flood protection from smaller, more frequent storms is achievable for most communities, and reducing flooding damages over the long term is a regional priority.

Later this fall, CMAP will release the Stormwater and Flooding Strategy Paper, which will identify recent trends and recommendations to help the region respond to urban and riverine flooding. The paper will highlight strategies based on the principles of integrated water resource management. Many of these strategies will require participation from a variety of water management, land use, and transportation decision makers. CMAP is exploring the following strategies:   

Update precipitation and floodplain maps

Floodplain maps are the most commonly used tool to identify areas at risk of riverine flooding. While current efforts are underway to digitize floodplain maps and incorporate recently completed engineering studies, the region's floodplain maps rely on outdated rainfall data and lack information on recent development, which means the maps may not accurately reflect riverine flood risk. The data used in floodplain modeling and remapping relies on precipitation accounts from 1901 to 1983, failing to account for precipitation patterns experienced since 1983 or for the effects of a changing climate. CMAP supports adequate funding for FEMA, IDNR, and the Illinois State Water Survey (ISWS) to ensure that the region's floodplain maps reflect current precipitation and development conditions. To prepare for future climate conditions, these maps should be updated regularly and new approaches explored. CMAP can play a supportive role and work with partners to identify data needs.  

Continue advancing development designs and standards

In the Chicago region, all counties have established minimum standards for stormwater management, limiting the amount of stormwater runoff generated by new development or redevelopment. The County stormwater ordinances have led to dramatic improvements in how stormwater is handled, and CMAP recommends continued improvement to reflect new data and areas of concern, such as urban flooding, current and projected precipitation data, volume reduction and green infrastructure techniques, standards tailored to watershed and development conditions, and transfer of benefit programs (further described here.)

In addition to improving stormwater ordinances, municipal planning efforts can advance stormwater management in a variety of ways. At a broader scale, comprehensive plans should recognize and protect stormwater management services provided by existing natural areas and open spaces. Development regulations significantly affect stormwater runoff and management, such as the amount of site impervious cover, building design, and surface parking requirements. Conservation design principles that protect existing water resources and minimize the development footprint are particularly important for newly developing areas. Areas with existing development and redevelopment will need to focus on structural (i.e., rain gardens and sewer upgrades) and non-structural (i.e., preserving open space and minimizing disturbed areas) best management practices.   

Prioritize and coordinate mitigation activities and investments

Given the array of stormwater needs across the region, it can be difficult to determine where to focus efforts to address areas of greatest need. At the same time, improving stormwater management practices when implementing public and private investments in streets, buildings, and open spaces can cost effectively leverage limited resources to address flooding. CMAP has developed urban and riverine flooding susceptibility indexes to identify priority areas across the region for flooding mitigation activities. The regional flooding susceptibility indexes can help CMAP and partners focus stormwater planning efforts and investments, particularly in locations with lower capacity to address these challenges.

Current and future precipitation will continue to affect our transportation network. While modest flooding may only result in minor delays, severe flooding could cause larger damages that reduce our ability to use key portions of our transportation system and increase long-term maintenance costs. Partners including the Illinois Department of Transportation and Regional Transportation Authority have begun important vulnerability assessments to understand how flooding affects their components of the region's transportation system, and CMAP is working with the American Planning Association, and ISWS to develop an approach to examine a community's vulnerability to climate change impacts.   

Prepare for tomorrow's storms

Federal disaster assistance to local governments has been instrumental in paying for public investments that repair flooding damages or reduce exposure to future flooding. However, these national programs are struggling to provide the needed technical and financial assistance in the face of increasing costs and climate change. CMAP encourages the federal government to continue to fully fund FEMA and the NFIP program, which have been critical to planning for and recovering from flooding and other disasters. CMAP and partners should also support continued pre-disaster planning efforts and identify opportunities for more coordination to ensure that the region is effectively using available federal disaster assistance.  

Next steps

From structural improvements, such as the Metropolitan Water Reclamation District's Tunnel and Reservoir Plan, to coordination efforts such as the Calumet Stormwater Collaborative, the Chicago region is actively working to reduce urban and riverine flooding damages. With support from the John D. and Catherine T. MacArthur Foundation and the Cook County Community Development Block Grant-Disaster Relief program, CMAP developed a cost-effective approach to understand conditions that can lead to urban flooding and to integrate stormwater management strategies into CMAP Local Technical Assistance (LTA) projects. This approach has been deployed in LTA projects with South Holland, Franklin Park, Midlothian, Des Plaines, Richton Park, Berwyn, and unincorporated areas in Maine and Northfield Townships. CMAP is continuing to refine this approach and has provided the methodology and datasets to assist other communities and planners. FEMA and the National Academy of Sciences are conducting a national assessment on the extent and causes of urban flooding, influenced by prior work by the Center for Neighborhood Technology and IDNR, which will help inform the work of CMAP and partners. Once the Stormwater and Flooding Strategy Paper is complete, CMAP will incorporate key strategies into the ON TO 2050 Plan.