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This month, the greater Chicago area experienced a downpour that devastated homes on the West Side and in the town of Cicero by the city’s Southwest Side, flooding basements with up to three feet of murky water and causing shutdowns of both trains and Interstates.

More than 12,000 basement flooding cases were reported to the city from July 2 to July 18, surpassing the total number of basement flooding reports filed in all of 2021 and 2022 combined, according to an analysis of city flood reports by WBEZ; nearly nine inches of rain fell on July 2 alone.

Flooding is Chicago’s most pressing climate risk, significantly threatening both infrastructure and human health, and it is only expected to become a bigger threat due to climate change. Experts say more investments in water infrastructure and nature-based solutions are needed, along with targeted support for communities that face repetitive flooding.

As global temperatures rise, the intensity and variability of rainfall are expected to increase. Already, Illinois has seen a 12 to 15 percent increase in total annual precipitation and a 40 percent increase in the number of 2-inch rain days in the last 120 years, according to the Illinois State Climatologist Office. Research has shown that more extreme precipitation heightens the risks of waterborne diseases and other health risks and that socioeconomically disadvantaged communities are more likely to be in flood-prone areas and face greater infrastructure damage and health risks from flooding.

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Investments in so-called gray and green solutions are essential, and with millions available to support the effort, now is the time to do it, said Aaron Packman, professor of civil and environmental engineering at Northwestern University. The Inflation Reduction Act signed into law last year designates $2.6 billion for resilience solutions in coastal communities, including ones in the Great Lakes region.

Gray infrastructure in water management includes gutters, pipes and drains. The Metropolitan Water Reclamation District of Greater Chicago, which manages wastewater and stormwater in Cook County, built the Tunnel and Reservoir Plant system, which went online in 1980. It stores combined stormwater and sewage that would otherwise overflow from sewers into waterways in days of heavy rainfall, reducing water pollution in Lake Michigan and flooding. The system, also known as TARP, continues to be expanded with the aim of storing a total of 17.5 billion gallons of water when completed.

Experts say TARP is still working as it should, but that it isn’t enough to prevent flooding as intense precipitation is expected to continue to increase. It was built under and connected to Chicago’s and 51 suburbs’ combined sewer systems, most of which were built more than 100 years ago. Combined sewage systems convey both rainwater runoff and sewage into the same pipes.

“As our climate changes and we see heavier rain events in compressed periods of time, it is difficult for our sewer system to move the water efficiently,” the Mayor’s Office said in a statement following the floods this month.

The pipes are small and can’t convey large quantities of stormwater in enough time into the tunnels and reservoirs, sometimes resulting in overflows. “It’s sort of like you’re trying to fill your pool with a straw,” said Mariyana Spyropoulos, a Metropolitan Water Reclamation District of Greater Chicago commissioner. The tunnels and reservoirs are more likely to fill up more frequently as climate changes, she said.

“These systems were not designed for our current climate or the future climate,” said Packman, whose research focuses on hydrology. “The kind of frequent intense storms that we’re getting was not what this system was built to protect against, and that’s a big challenge.”

The Chicago Department of Water Management said it performs regular maintenance of the sewer system to ensure that it is efficiently conveying water to Metropolitan Water and Resources Management for flood control and processing, and that it is developing plans for a regional tunnel system that would expand capacity to move water to the reservoir system.

“Because impacts from climate change are worsening, our goals are a moving target,” the Chicago Department of Water Management said in a written statement to Inside Climate News.

The concrete landscape of the city also can worsen flooding as water runs off into streets and sewers instead of into the ground, a solution that green infrastructure can serve, said Mila Marshall, clean water advocate at Sierra Club Illinois.

Green infrastructure refers to planned natural features intended to divert some of the stormwater into the ground to prevent it from getting into the sewer. It can also provide other environmental, social and economic benefits to surrounding communities.

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Research is still ongoing about what kind of green infrastructure is most effective in certain parts of the city and for certain types of flooding, said Packman, who is currently studying nature-based solutions for stormwater management and flood prevention as part of a $25 million grant from the U.S. Department of Energy. More than a dozen academic and community partners in Chicago were awarded the grant to study climate change effects at local and regional scales. The goal of the funds, granted last year, is to inform communities on how to build resilience to the effects of climate change, including increased flood and heat risks.

The Chicago Metropolitan Agency for Planning, or CMAP, agrees with implementing multiple solutions at various scales to reduce the amount of stormwater going into the sewer. The agency serves the City of Chicago and surrounding suburbs.

“Tackling our flooding challenges is going to require a joint effort—we will have to think holistically and work regionally across communities, jurisdictions, and sectors,” CMAP said in a written comment to Inside Climate News. “It’s not just about what a community does on its own because water doesn’t obey political boundaries.”

Other adaptation measures at a household level include using pumps to prevent flooding in homes and reducing water use during heavy rain events to prevent adding wastewater to the already flooded system, but some families hardest hit by extreme rainfall sometimes cannot afford to pay out of pocket for those investments, said Marshall from Sierra Club Illinois.

Resources need to be targeted to communities most impacted by floods, and those communities should be involved in coming up with flood resilience solutions, said Joyce Coffee, president of Climate Resilience Consulting.

CMAP said it is working to update its Flood Susceptibility Index, a tool designed to identify large priority areas and inform stormwater mitigation and resilience planning efforts, with data from the last five to six years for a more accurate and up-to-date picture of the areas most vulnerable to flooding. The Chicago Department of Water Management said it reviews flood complaint data and conducts hydraulic analyses to determine where to prioritize sewer improvement projects throughout the city.

While data-informed research is essential, community groups and leaders must validate conditions on the grounds and collaborate to center community needs in planning and design, said CMAP.

“There is potential to unlock by working with communities most impacted,” said Packman. “We need to understand how these approaches can be blended together and what parts can be initiated successfully by communities.”

Aydali Campa covers environmental justice at Inside Climate News. She grew up on the U.S.-Mexico border in Arizona and taught third and fourth grade in Oklahoma City before pursuing a master’s degree in investigative journalism from Arizona State University. As a bilingual reporter with experience in multimedia, she has covered education, Covid-19 and transborder issues. Her previous work can be seen in The Wall Street Journal, The Arizona Republic and Arizona PBS.