Depaving to cool and ease flooding in cities
It all started because Arif Khan wanted a garden. In 2007, he moved into a house in Portland, Oregon, with a backyard covered in asphalt. Well, that had to go! So some friends helped him tear it up, and soon after, they won a small grant to carry out a similar project in front of a local café.
“It was a one-off,” says Ted Labbe, co-founder of Depave, an organisation that removes concrete and asphalt in urban settings. “But it was so successful the next year we got solicited to do three projects, and then five the year after that. It just kept escalating.” In the 15 years since breaking ground on Khan’s backyard, Depave has completed 75 projects in schoolyards, churches and other community spaces across Portland.
In recent years, the Depave movement has spread across the United States and Canada as cities rethink the wisdom of all those heat-absorbing, impervious surfaces.
Depave’s newest chapter is in Chicago, where more than 60% of the city is covered in impervious surfaces, and when record rains fell in early July, more than 12,000 residents reported flooding in their basements.
Since launching in 2022, the founder of Depave Chicago, Mary Pat McGuire, a professor of architecture at the University of Illinois, and a group of volunteers have been holding listening sessions across the city to identify local needs. They’ve just finished drawing up plans for their pilot project: greening a public schoolyard in West Englewood, a low-income neighbourhood in southwest Chicago.
“They teach the Montessori method, which is very hands-on,” McGuire says. Depave consulted with sixth, seventh and eighth graders, along with teachers, parents and school board members to draw up a blueprint for the new schoolyard. It includes pollinator gardens, an outdoor classroom, log structures, bioswales and shady trees. “Green infrastructure isn’t clean, neat and tidy,” McGuire says. “We’re going to get messy.”
Paved roads and carparks take up about 30% of urban areas in the United States; in some cities, such as New York, it’s double that. Carparks alone cover more than 5% of developed land in the lower 48 states, according to the US Geological Survey.
“We’ve had a love affair with paving things for several generations,” notes Brendan Shane, climate director at the nonprofit Trust for Public Land (TPL). “We have too many unnatural paved surfaces and not enough natural surfaces, and that’s creating these urban heat islands [and] rapidly flooding neighbourhoods.”
Replacing asphalt with greenery has benefits beyond lowering temperatures and reducing flood risk. It also helps lower stress levels, reduces noise, means fewer traffic-related injuries and can even restore local biodiversity. It can also improve air quality: asphalt releases hazardous air pollutants into communities, especially in extreme heat and direct sunlight.
Other US cities are rethinking the streetscape. In Phoenix, Arizona, where asphalt can get so hot during heatwaves it can give third-degree burns, officials are painting surfaces with reflective grey paint. Nashville, which had deadly floods back in 2010, has transformed alleyways into blooming bee-filled rain gardens.
More than a decade ago, Chicago invested US$14 million in building what it dubbed the “greenest street in America”, a 3km stretch sporting rain gardens, permeable pavements and solar-powered street lights.
Last year, Arup, an engineering and architecture firm, released a study examining the “sponginess” — or ability to absorb rainfall — of several cities and making the case for cities to invest in nature-based solutions to prevent flooding. “But implementation is a major challenge due to lack of funding, outdated policies and codes and minimal cross-sector collaboration,” says Vincent Lee, a principal at Arup.
Many advocates say schoolyards are ideal sites for greening projects. Space to Grow, another Chicago organisation, has overhauled 34 schoolyards over the last decade, replacing asphalt with permeable sports fields, rain gardens and other porous surfaces. “Our schools are the centre of the community, and we want to make sure kids are excited to be in those spaces,” says Meg Kelly, Space to Grow’s director.
According to the group’s data, replacing asphalt with permeable sport fields, rain gardens and other porous surfaces has reduced ground temperatures by up to 12°C and captured more than 13 million litres of stormwater, alleviating neighbourhood flooding.
McGuire says she wants Depave Chicago to help neighbours avoid the next flood or find respite from the next heat wave, but she also wants to help Chicagoans envision a different future for their city. “It’s about changing attitudes towards concrete,” she argues. “We’ve been missing an opportunity to embrace nature in the city, and I’m just trying to get people to look at the world around them and dream of something different.”‘
ABOVE Members of Depave Portland begin asphalt removal at Whitman Elementary in November 2021
PHOTO Depave Portland