Since 2006, Chicago has been taking steps to prepare itself for a warmer world.
Much of Chicago’s adaptation work is about transforming paved spaces. “Cities are hard spaces that trap water and heat,” said Janet L. Attarian, a director of streetscapes at the city’s Department of Transportation. “Alleys and streets account for 25 percent of groundcover, and closer to 40 percent when parking lots are included.”
The city’s 13,000 concrete alleyways were originally built without drainage and are a nightmare every time it rains. Storm water pours off the hard surfaces and routinely floods basements and renders low-lying roads and underpasses unusable.
To make matters worse, many of the pipes that handle storm overflow also handle raw sewage. After a very heavy rain, if overflow pipes become congested, sewage backs up into basements or is released with the rainwater into the Chicago River — an emergency response that has attracted the scrutiny of the Environmental Protection Agency.
As the region warms, Chicago is expecting more frequent and extreme storms. In the last three years, the city has had two intense storms classified as 100-year events.
So the work planned for a six-point intersection on the South Side with flooding and other issues is a prototype. The sidewalk in front of the high school on Cermak Road has been widened to include planting areas that are lower than the street surface. This not only encourages more pedestrian traffic, but also provides shade and landscaping. These will be filled with drought-resistant plants like butterfly weed and spartina grasses that sponge up excess water and help filter pollutants like de-icing salts. In some places, unabsorbed water will seep into storage tanks beneath the streets so it can be used later for watering plants or in new decorative fountains in front of the high school.
The bike lanes and parking spaces being added along the street are covered with permeable pavers, a weave of pavement that allows 80 percent of rainwater to filter through it to the ground below. Already 150 alleyways have been remade in this way.
The light-reflecting pavement is Chicago’s own mix and includes recycled tires. Rubbery additives help the asphalt expand in heat without buckling and to contract without cracking.
The new streets bring new challenges, of course. The permeable pavers have to be specially cleaned or they eventually become clogged with silt and lose effectiveness.
Still, the new construction is no more expensive than traditional costs, Ms. Attarian said. Transforming one alleyway costs about $150,000. But now, she said, “We can put a fire hose on it full blast and the water seeps right in.”