Recent flash floods highlight need to mitigate urban flooding

This summer has been a harsh reminder of the climate change impacts we face in northeastern Illinois. A summer that started with severe drought shifted to a storm on July 2 that dumped rain on Cook County — including more than eight inches in Berwyn, Cicero, and Chicago’s Austin neighborhood — and significant urban flooding. This storm is the type of intense flash flood event that we can expect to see more of in the future.

The amount of rainfall in Berwyn, Cicero, and Austin was between a 100-year (1-percent chance of happening) and 500-year (0.2-percent chance) flood. However, these probabilities are based on past data and do not account for the changing conditions we’re already seeing.

Garages with flood damage
Water ponds around backyard garages in Brookfield in May 2020.

What causes urban flooding?

Urban flooding happens when rainfall overwhelms the sewer system, causing water to pool in streets and yards, and to back up into basements.

Urban flooding is a widespread challenge in older and densely developed communities of our region. These communities were developed before modern stormwater regulations. A lack of adequate stormwater management capacity, paired with more impervious cover — rooftops, streets, and parking lots — means more rainwater runoff that has nowhere to go.

These same communities are more likely to have combined sewer systems that collect stormwater and sewage in the same pipes. Not only do combined sewer systems increase the risk of flooding during heavy rains, but they also exacerbate the damage and health impacts of basement sewer backups.

What can we do to mitigate urban flooding?

Through the Infrastructure Investment and Jobs Act and Inflation Reduction Act, more funding is available to mitigate flooding than ever before. But even with this historic influx of federal money, broad coordination is needed to tackle this shared problem. As the regional planning agency for northeastern Illinois, the Chicago Metropolitan Agency for Planning (CMAP) is helping local governments prioritize and coordinate investments in an equitable and inclusive way by providing valuable data and technical assistance.

Bioswale next to suburban road
A bioswale in Blue Island helps collect stormwater and let it soak into the ground. Bioswales are designed to collect stormwater from areas like streets and parking lots. They help the water soak into the ground instead of overwhelm sewer system.

Think holistically about infrastructure improvements

We must think beyond the parameters of traditional infrastructure projects. We need solutions that reduce the amount of stormwater runoff at every scale — watershed, community, block, property — and plans to maintain these investments over their service life. When adding sidewalks, improving roads, and protecting bike lanes, communities should upgrade sewer systems and expand green infrastructure to maximize benefits for mobility, flood control, and quality of life.

Equitably invest in flood mitigation projects

Flooding doesn’t affect communities equally — historically disinvested and underserved communities are disproportionately impacted by flooding. Systemic racism has forced these communities into areas with high flood risk, low tree canopy and park space, and high impervious cover, and deprived them of adequate resources for flood mitigation and recovery.

We need targeted investments that serve areas disproportionately impacted by flooding and underserved by past investments. Pairing information on flood risk with data on income, race and ethnicity, disability, health, housing, and other indicators can help identify communities that are most vulnerable to flooding and tailor resilience investments to improve the lives of the most vulnerable residents.

CMAP has been engaging decision makers and communities to understand the challenges and needs of those disproportionately impacted by flooding, and to identify equity approaches to inform investments. Later this year, the project will conclude with a guide to help CMAP, as well as municipal and county governments, incorporate equity into flood resilience investment planning, design, maintenance, and funding.

Collaborate with local community groups

We must ensure that communities are involved in decisions that affect them. By partnering with community groups, governments can better understand conditions on the ground and center community needs in planning and design. This will help communities buy into the project and lead to greater benefits.

When collaborating with community groups, it is important to compensate them for their time and expertise. Residents bring value to projects, offering knowledge of the community, serving on advisory committees, bringing ideas to neighbors to discuss, and much more.

Playground swingset and slides next to garden areas
The playground at Grissom Elementary School in Chicago’s Hegewisch neighborhood includes rain gardens with native plants and trees to help manage stormwater.

Use the latest data to understand current and future conditions

In 2017, CMAP developed the region’s first flood susceptibility index so partners throughout the region could prioritize flood mitigation activities together. CMAP’s data analysts are now working with local stakeholders to update the index with more recent flood events and bring in new data to improve its relevancy for decision makers. Once completed, CMAP will use the updated index to examine risk in communities that are disproportionately burdened by flooding.

CMAP is also studying the range of potential future impacts of extreme weather and climate change on our transportation systems. This assessment will inform a regional transportation resilience improvement plan which can unlock additional federal funding opportunities and, even more importantly, smarter, prioritized investments in communities. Local governments and industry stakeholders will be able to access and use these data and maps to make better investment decisions.

No single agency can fight climate change alone. Only by working together will we be able to stretch these new resources even further to build a more equitable and resilient future. Together, we can design a built environment that can adapt, respond, and withstand the climate crisis.