Comments? Click here.

Reduce flood risk to protect people and assets

Reduce flood risk to protect people and assets

The significant economic, social, infrastructural, and environmental challenges posed by flooding impair communities' efforts to achieve local and regional goals. Chronic flooding damage can make communities less desirable, as does the flood-related deterioration of building facades, streets and sidewalks, and other infrastructure and property. CNT found that wet basements can decrease property values by 10 to 25 percent and are cited as a primary reason for not purchasing a home.[1] According to FEMA, nearly 40 percent of small businesses never reopen after a flooding disaster.[2] Increasing floodwaters also strain our natural and open spaces as streambanks erode, pollutants and invasive species degrade habitat, and groundwater recharge is reduced.


Flooded streets reduce mobility and increase maintenance costs for repair and reconstruction. In addition to the direct costs of delay and reduced access, road and transit closures can cause a cascade of indirect impacts that impair economic productivity, safety, emergency services, bicycling, and walking.[3] When flooding does occur, it does not affect all populations or communities equally. Exposure to flooding risks appears to be greater in populations and communities already facing socioeconomic, demographic, and health challenges and barriers.[4]


[GRAPHIC TO COME: An illustrated graphic explaining the differences between urban and riverine flooding.]


While flooding is a natural occurrence, continued urbanization and climate change are leading to more flooding. Development of impervious cover prevents the infiltration of rainwater and generates stormwater runoff, while climate change results in more frequent and intense storm events. Increased stormwater runoff can overwhelm local drainage systems and lead to urban flooding, such as ponding water in streets and yards, basement seepage, and sewer backups. Stormwater eventually flows to rivers and streams and can cause riverine flooding as water flows over riverbanks and into the floodplain. Buildings and roads in floodplains are at greater risk of flooding and can lead to flooding downstream as the natural function of the floodplain is reduced.


From the extensive network of preserved habitat, open space, and wetlands to the engineered detention basins, sewer systems, and Tunnel and Reservoir Plan, the Chicago region has made significant investments in green and gray infrastructure. However, development in significant portions of the region predated modern stormwater management standards, and even current infrastructure design specifications rely on old data[5] and do not account for a changing climate.[6] Some neighborhoods experience flooding after less than two inches of rain -- small storms that, over time, result in significant harm to property and quality of life.


ON TO 2050 reaffirms GO TO 2040’s recommendation to integrate planning with water resource management. The region can advance stormwater and floodplain management in various ways that include protecting and enhancing the stormwater services currently provided by natural areas and open spaces; avoiding investments in areas where environmental conditions -- from floodplains to low-lying areas -- pose high risk of urban and riverine flooding; and minimizing stormwater runoff volumes through development regulations and design standards. Integrating stormwater management into larger planning can help coordinate investments and leverage limited resources to address flooding while achieving other community goals. CMAP has developed the Regional Urban Flooding Susceptibility Index[7] to help prioritize areas for planning and mitigation investment, particularly in locations with municipal capacity constraints that make it difficult to address these challenges.

The following subsection describes strategies and actions to implement this recommendation.

Identify and communicate flooding risk

Extreme precipitation events in the central U.S. increased as much as 40 percent between 1979 and 2009 compared to the previous 30 years (1948-1978).[8] Yet many of the region’s infrastructure standards and floodplain maps are based on older precipitation data. Reducing the region’s exposure to flooding and optimizing long-term investments so that they account for future conditions requires a more current and comprehensive understanding of where and when urban and riverine flooding could occur. Watershed plans, stormwater models, and other studies help the region identify the most effective stormwater solutions, and coordination of these tools can help address problems across jurisdictional boundaries. In the absence of detailed models, the Regional Urban Flooding Susceptibility Index can help convey the potential risk of urban flooding. Residents and business owners making important investment decisions often lack information about flood risk. Ironically, though established to provide affordable flood insurance, repair damaged homes and businesses, and promote floodplain management, the National Flood Insurance Program (NFIP) has the unintended effect of perpetuating development in flood-prone areas. This is particularly true in locations without strong floodplain management regulations that discourage redevelopment. The NFIP does not adequately communicate the level of risk, set premiums to reflect the full risk of loss, or provide options for low income property owners.


ISWS should regularly update precipitation data and explore options to account for future climate scenarios.

FEMA, IDNR, and county stormwater agencies should update floodplain maps to reflect current development conditions as well as current and future precipitation.

County stormwater agencies and municipalities should continue advancing watershed and sewer modeling efforts to identify and increase awareness of areas of riverine and urban flooding risk.

Local governments should collect flooding data and communicate risk and possible solutions to residents and businesses, with particular attention to residents who may be more vulnerable to the impacts of flooding.

CMAP and partners should continue to develop planning tools to understand and plan for urban flooding risk.

The State and real estate community should implement efforts to ensure that the sale of property is informed by accurate flood risk information.

Congress should reform the NFIP to adequately identify and communicate risk.

Improve planning and development to reduce current and future flooding risk

Planning in advance of potential flooding can reduce risks to health and safety as well as costs and damages to private and public property and infrastructure. From hazard mitigation plans to development ordinance updates, many locally implemented best practices could be used broadly throughout the region and can help achieve multiple community benefits, such as increased green space, lower flood insurance premiums, and higher property values. Municipalities can locate development and critical facilities, such as treatment plants, hospitals, and civic institutions, away from floodplains and other floodprone areas. Restoring the natural function of floodplains and wetlands enhances the ecosystem services they provide.


In the Chicago region, all counties have established minimum standards for stormwater management, including limiting the amount of runoff that may be generated by new development or redevelopment. Continued advancements are needed to address urban flooding, incorporate current and projected precipitation data, and streamline volume reduction and green infrastructure techniques, among others.[9] Municipal development ordinances also contain provisions that significantly affect stormwater runoff and management, such as the amount of impervious cover, and building and street design requirements. Local governments can be proactive about addressing flooding challenges by going beyond county requirements to require stormwater best management practices on smaller parcels. Some municipalities in the region, such as Downers Grove, are leading the way in seeking to protect their existing neighborhoods from urban flooding by recognizing and preserving stormwater flow capacity in areas with local drainage problems.


Local governments should continue to update stormwater management ordinances and performance standards to reflect best practices, including green infrastructure solutions, and emerging information about climate change and development trends.

CMAP should convene county stormwater agencies and other partners to exchange information about regulatory updates that improve stormwater management.

CMAP and partners should explore the use of transfers, credits, and water quality and volume trading programs to achieve regional water resource goals.

IDNR and local governments should continue to improve floodplain management guidance, techniques, and compliance, and participate in the Community Rating System.

Local governments should update plans and development standards to improve stormwater and floodplain management.

CMAP, counties, and other partners should support continued pre-disaster planning efforts, including buyout programs, flood risk assessments, identification and protection of critical facilities, and stormwater planning, and identify opportunities for coordination.

Maintain and invest in gray and green infrastructure

Parts of the region are adequately protected from flood risk, but others have gray and green infrastructure systems that lack adequate capacity for even small storms. Green infrastructure has the potential to improve our flood control and stormwater system while achieving co-benefits unavailable with gray infrastructure solutions. Coordinating green and gray infrastructure solutions into public investments (e.g., streets, parks, schools, and public grounds and facilities) -- as well as encouraging retrofits of private property -- will be essential to improving the stormwater management capacity of our communities. This will allow the region to build a more distributed stormwater management system with greater resilience to disruptions or constraints.


Prioritizing investment in high need, high risk areas will be critical. Watershed plans, modeling efforts, and the Regional Urban Flooding Susceptibility Index, combined with information about vulnerable populations, can help inform regional and local priorities. In some situations, the best long-term solution is to return flood-prone land to open space through acquisition and stewardship, removing people and property from harm’s way. Federal resources that historically funded infrastructure improvements may be insufficient as increased sea levels, storm surges, and flooding across the country strain disaster assistance resources. Dedicated revenue streams, such as stormwater utility fees, can support maintenance and expansion of gray and green infrastructure based on a long-term vision.


Local governments should use the Regional Urban Flooding Susceptibility Index, along with other mapping, planning, and modeling efforts to prioritize flood mitigation investments.

Counties, municipalities, and other infrastructure managers should enhance maintenance and monitoring of gray and green infrastructure.

Local governments should develop stormwater utility fees to cover the full costs of stormwater management and improve flood control infrastructure.

Local governments and other land managers should protect and expand open spaces to enhance natural stormwater management while achieving resource management goals.

Local governments should pursue property acquisition and voluntary buyouts to help willing landowners vacate high flood risk areas.

Congress should reform the National Flood Insurance Program to develop long-term solutions for properties that suffer repetitive losses.

Address flood vulnerability of critical transportation assets

Flooding affects the performance and maintenance of the region’s transportation network. Retrofitting locations at risk of flooding to handle current and projected rain events can help maintain regional and local mobility and ensure that investments are built to last. The RTA, IDOT, and county transportation agencies are working to identify and plan for areas of the existing transportation system that are vulnerable to flooding. In other states, DOTs and regional planning agencies are conducting vulnerability assessments and improving system resilience with projects recommended in long-range transportation plans.[10] Local governments also need to address flooding vulnerability of their streets and update capital improvement plans and corresponding design standards. As precipitation data and floodplain maps are updated, local and regional vulnerability assessments should be revised periodically to reflect changing conditions. Avoiding construction of new streets and highways in current flood-prone areas is also critical and must be evaluated with future climate conditions in mind.


CMAP and transportation implementers should conduct studies to determine the flood vulnerability of transportation infrastructure and design projects to accommodate the projected precipitation during its designed lifespan.

CMAP and partners should conduct a regional climate vulnerability assessment of the transportation system to inform long-range transportation planning and programming.

CMAP should develop a regional pavement flooding reporting system to help plan for flood events.

Improve stormwater management in transportation projects

As the intensity and frequency of storm events increases with climate change, the region will need strategies to better integrate stormwater management into transportation planning and design. Best practices often include drainage improvements that increase detention capacity or promote infiltration, as well as a series of protective measures to reduce exposure to flood waters. Recently, the FAST Act expanded the scope of statewide and metropolitan transportation planning processes to reduce or mitigate stormwater impacts of surface transportation.[11] This provision could enhance how stormwater management is addressed in overall planning efforts as well as individual surface transportation projects. Recent updates to the Surface Transportation Program (STP) program now incentivize the use of green infrastructure to manage stormwater.[12]


Currently, highway and street design and reconstruction requirements do not reflect county-specific stormwater management goals or practices. Instead, they follow state design guidelines, which can limit the ability to implement green infrastructure and other innovative solutions or tailor design to local context and needs. Public rights of way often present good opportunities for green infrastructure. Many of our existing streets experience flooding due to development patterns in the surrounding area, particularly in communities developed prior to modern stormwater management standards. Street flooding could be addressed through infrastructure retrofits in surrounding neighborhoods instead of within constrained rights of way. Projects that comprehensively address stormwater management solutions can improve the performance of our transportation system while also reducing flooding damages in nearby neighborhoods.


Local governments should support continued efforts to better integrate stormwater management into land use and transportation planning projects.

IDOT should update statewide design standards to reflect green infrastructure techniques and precipitation trends, designing transportation infrastructure for the climate of its designed lifespan.

Transporation agencies should construct and maintain projects that can sufficiently manage current and future storm events.

IDOT should support CMAP’s stormwater management planning efforts to reduce flooding vulnerability of the transportation system.

Counties and municipalities should update development ordinances and reconstruction practices to improve stormwater management and promote green infrastructure techniques in new and reconstructed streets.



[1] Center for Neighborhood Technology, 2014, “The Prevalence and Cost of Urban Flooding: A Case Study of Cook County, IL,”

[2] Federal Emergency Management Agency, 2016, “Make Your Business Resilient,”

[3] Schwartz, H. G., M. Meyer, C. J. Burbank, M. Kuby, C. Oster, J. Posey, E. J. Russo, and A. Rypinski, 2014: Ch. 5: Transportation. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese­ (T.C.) Richmond, and G. W. Yohe­, Eds., U.S. Global Change Research Program, 130-149. doi:10.7930/J06Q1V53.

[4] Lowe, Dianne, Kristie L. Ebi, and Bertil Forsberg. 2013, “Factors Increasing Vulnerability to Health Effects before, during, and after Floods,” International Journal of Public Health, 10, 7015-7067; doi:10.3390/ijerph10127015.

[5] Winters, B. A., J. R. Angel, J.R., Ballerine, C., Byard, J., Flegel, A., Gambill, D., Jenkins, E., McConkey, S., Markus, M., Bender, B.A., O’Toole, M.J., 2015, “Report for the Urban Flooding Awareness Act,” Illinois Department of Natural Resources Springfield, IL:

[6] Markus, M., Angel, J., Byard, G., Zhang, C., McConkey, S., Cai, X., Notaro, and Ashfaq, M., 2018, “Communicating the Impacts of Projected Climate Change on Heavy Rainfall using a Weighted Ensemble Approach,” Journal of Hydrologic Engineering, 23(4).

[7] CMAP, 2018, “Regional Flood Susceptibility Index,”

[8] Groisman, P.Y., Knight, R.W. & Karl, T.R., 2012, “Changes in intense precipitation over the central United States,” Journal of Hydrometeorology, 13, 47-66.

[9] CMAP, 2018, “ON TO 2050 Stormwater and Flooding strategy paper,”

[10] U.S. Department of Transportation, Federal Highway Administration, 2018, “Vulnerability Assessment and Adaptation Framework, 3rd Edition,” FHWA-HEP-18-020,

[11] 23 U.S.C. 135 (d)(I) and 23 CFR 450.306 (b)(9)

[12] Memorandum of Agreement between the City of Chicago and the CMAP Council of Mayors regarding the distribution and active program management of locally programmed surface transportation block grant funds under the Fixing America’s Surface Transportation Act, October 11, 2017,

To Top


Return to Draft Plan Home