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To track inequality in cities, measure the heat

In Atlanta, volunteers with Bluetooth sensors are gathering data that could lead to greener neighborhoods.

By Adina Solomon

As Brionna Findley walked around Atlanta’s West End last August, she couldn’t help but sweat. The Spelman College student wasn’t used to heat like this: 92 degrees at 1:30 p.m. It was a full three degrees higher than her home in Hiram, Georgia, 25 miles away.

And it felt even hotter.

In Hiram, “I didn’t feel overpowered by the heat. It was manageable,” Findley says. “But in the city, I thought I was going to pass out. I was so dehydrated that day we had to end it early. That’s how hot it was. It was just too much.”

Findley saw these temperature differences firsthand when she collected data for UrbanHeatATL, a project that uses local volunteers to collect temperature data, neighborhood by neighborhood. Three times a week from May through August, Findley walked or biked with her Bluetooth sensor, traversing up to two miles every time.

UrbanHeatATL is a collaborative effort between Spelman, Georgia Tech, the city of Atlanta, and a group of community-based organizations. The goal is to map “heat islands” — the areas most affected by extreme heat changes and the resulting negative health impacts — and, ultimately, offer solutions.

Urban heat islands occur when cities experience warmer temperatures than their rural neighbors. The larger amounts of concrete and roads trap heat, while there are fewer trees to cool it down.

“They know which areas are hottest because they experience them every day.”

Museum of Science researcher David Sittenfeld, on community heat-mapping volunteers

But this heat island divide goes deeper than cities vs. rural areas. Some communities within a city experience even hotter temperatures because of their history. In the early 20th century, the federal government and companies “redlined” neighborhoods of color — systematically denying services such as home loans because of race. Though the discriminatory practice was formally outlawed in 1968, the effects linger. One of them is a lack of investment in parks and green spaces — the very elements that help cool down a neighborhood — among communities of color, which also tend to have more warehouses and industrial developments that are built from heat-trapping concrete.

As a result, many formerly redlined areas still have higher temperatures than their non-redlined neighbors, according to a study of 108 urban areas across the U.S.

For example, Atlanta’s English Avenue neighborhood is majority Black and has one of the lowest percentages of tree canopy in the city. Its first park, on Lindsay Street, didn’t open until 2015. “It really aligns with this narrative of what we have seen in other cities,” says Na’Taki Osborne Jelks, a professor of environmental and health sciences at Spelman and the academic co-lead for the project. Those formerly redlined neighborhoods “lack the critical natural infrastructure that serves as this buffer to extreme heat,” she says.

Atlanta isn’t the only city studying its heat. The National Oceanic and Atmospheric Administration has conducted national heat mapping for the past four years. This summer saw community volunteers in about 25 cities, including Albuquerque, New York City and San Francisco, collect temperatures for NOAA. Volunteers for a similar project, called Wicked Hot Boston, collected temperature data in Boston, Cambridge and Brookline, Massachusetts, in July 2019 on the hottest days of the summer. “It’s these heat-wave events, when the urban areas don’t cool down very much, that can be a real stressor for infrastructure and public health,” says David Sittenfeld, a researcher at the Museum of Science in Boston who worked on the project.

Atlanta’s heat-mapping project is different from the others in a few key ways. For one, it’s more comprehensive: Temperatures are recorded year-round and throughout the day, not just during the summer at specific hours. Most cities run one-off, daylong events where volunteers get together to record data. But Atlanta largely relies on volunteers to create their routes and collect temperatures themselves. This leads to a more diverse collection of data points, from all over the city and throughout different days and months.

“They know which areas are hottest because they experience them every day,” Sittenfeld says.

And when community members are involved in the scientific process from the start, advocates say, they have more of a voice when it comes to acting on those findings.

For UrbanHeatATL, Jelks and her co-organizers placed stationary sensors in key locations such as Southwest Atlanta, near transit stations in the city core and on the Spelman and Georgia Tech campuses, as well as locations in the suburbs. In addition, 80 Spelman and Tech students, plus 10 community residents, walk or bike through neighborhoods and take temperature measurements using Bluetooth-enabled sensors. They email researchers with their data, which is automatically uploaded into a database and used to conduct analysis.

Since the study launched in March 2021, volunteers have logged more than 280 hours collecting temperatures, and have sent researchers a million data points.

Maya Griffin, also a Spelman student, recorded data from May to August — first in Vine City, a historically Black neighborhood in urban Atlanta, and then in the suburb of Sandy Springs, where she moved later in the summer. Griffin says the heat affects Atlanta’s large population of homeless people.

“If you’re homeless in the inner city and you’re sleeping on the ground or wherever you can find, what is that heat doing to your body over time?” she wonders. “What medical issues could be affected by this long-time heat exposure?”

Sittenfeld says neighborhood-level data can help identify places that most need heat resilience strategies for the future — and demonstrate what’s working in less-impacted areas.

Possible heat mitigation steps include more investment in trees and parks, along with anti-displacement policies so that existing residents can afford to stay in place when “green” gentrification comes to their neighborhoods, Jelks says. Programs to help make homes more energy-efficient would lessen the financial burden of energy costs and make homes more protective of their inhabitants, she adds. In that sense, the project couldn’t come any sooner for Atlanta.

“There’s a lot more construction going on in Atlanta, a lot more things happening like building new stadiums, building new offices,” says Findley, the volunteer. “It’s going to get worse, and there has to be some point where someone looks at the data and makes a collection to get things done. And I wanted to be a part of that.”

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Adina Solomon is a writer based in Atlanta. She has written for The Washington PostThe GuardianNational Geographic, and others.


Illustration by Martín Elfman


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