In Phoenix, Arizona, the country’s hottest city, temperatures reach scorching heights of 118 degrees in June. And in 2020—the hottest year on record—53 days saw heat above 110 degrees. This extreme heat is dangerous, even deadly, and it places city officials in a precarious predicament: How can they protect their citizens when the temperature becomes untenable?
Phoenix Mayor Kate Gallego—co-chair of the Climate Mayors coalition—has made addressing heat-related issues a priority of her tenure, and her city has become a model for how cities can address climate change. In 2020, the Office of Sustainability and the Street Transportation Department began a year-long Cool Pavement Study in nine specific city neighborhoods. (“Pavement” here refers to streets and roads, not sidewalks.) The study’s goal was simple: Lower the temperature by repaving roads with an innovative new and sustainable material.
They based their pilot on Los Angeles’ Green New Deal-based Cool Streets program, which, in combination with an expanded tree canopy, is on track to lower temperatures by 1.7 degrees by 2025 and by 3 degrees by 2035 at a time when temperatures are otherwise on the rise.
Extreme heat is dangerous, even deadly, and it places city officials in a precarious predicament: How can they protect their citizens when the temperature becomes untenable?
In order to duplicate—and improve upon—L.A.’s outcomes, Phoenix allocated $3 million and enlisted scientists from Arizona State University to create a reflective, spray-on asphalt street coating that was applied to 36 miles of heat-resilient residential roads. By day, the coating reflects sunlight, preventing roads from getting as hot as they typically would. By night, the surface releases heat incrementally. What’s more, Phoenix’s asphalt is water-based, making it much easier to recycle.
In September 2021, the first results of Phoenix’s study were announced, elating scientists and city officials alike with a promising drop in temperature. Some key results included an average pavement surface temperature 10.5 to 12 degrees lower than traditional asphalt at noon and afternoon hours, with an overall lower surface temperature at all times of the day compared to normal asphalt. Ambient air temperature at night decreased around 0.5 degrees; and daytime temperatures, as reflected off the new surface, only felt 5.5 degrees hotter than the air; that is cooler than on traditional black asphalt streets in neighborhoods like these with little tree cover.
Up next: Philly?
The results from the Phoenix Cool Pavement Study are sparking a light at the end of a rather hot tunnel in Philadelphia, which is plagued by worsening hot zones, particularly in North, South, and West Philly. According to the Philadelphia Heat Vulnerability Index, lower-income neighborhoods like Strawberry Mansion tend to be hotter than higher-income enclaves such as Society Hill—by a whopping 22 degrees.
The EPA refers to the reason for hot urban centers as “the urban heat island effect,” attributed to a combination of limited or nonexistent natural cooling factors—such as trees, bodies of water or stretches of grass to deflect sunlight and, therefore, heat—and an increase in concentrated manmade materials, such as black asphalt, that absorb and release heat.
“The hottest neighborhoods have vast expanses of heat-trapping materials, like asphalt. They also lack trees and other forms of green space, often due to a legacy of environmental injustice against residents with lower incomes and communities of color,” says Saleem Chapman, Philadelphia’s first and current Chief Resilience Officer.
To combat this, Philly has designated cooling centers and uses empty SEPTA buses as mobile cooling spots to provide relief. Other efforts are more grassroots, like when the Hunting Park Neighborhood Advisory Committee used crowdfunding to purchase air conditioning units for those in need. Still, electricity-based fixes are temporary—and have long-term repercussions. Running more a/c only makes the city hotter overall and increases our carbon footprint. It’s also costly. Philadelphia’s energy burden hit such highs in 2020 that Mayor Kenney wrote a letter to the state to request stimulus dollars to pay for cooling assistance (and the funds were subsequently received).
Truly cooling off our city—and our planet—requires more permanent solutions, in more parts of the city. (This is, in large part, Chapman’s mission.) Already, Parks & Rec’s Philly Tree Plan is giving higher-heat exposure neighborhoods preferential consideration in planting trees, which cool the air and provide shade for houses for the long term.
Now Chapman hopes to follow Phoenix’s lead in cooling the pavements in lower-income neighborhoods as well, with a tentative plan to launch a local pilot this summer—if he can find the funds.
Both Phoenix and Philadelphia are founding members of the Cool Roadways Partnership, an initiative of the Global Cool Cities Alliance. This partnership means Chapman has been at the table since the beginning, working with L.A. and Phoenix—and enjoying a front-row view of their cool pavement pilot rollouts.
To bring the project to Philly, though, Chapman and his team of 14 have to tango with limited funds. Philadelphia’s Office of Sustainability has a total budget of $1.5 million—half of what Phoenix spent on the cool pavements pilot alone. This is, in part, a factor of Covid-related cost-cutting: Between 2020 and 2021, the city slashed the department’s allowance to purchase supplies, materials, and equipment by 94 percent, leaving only $1,000 for 2022, plus $675,966 to purchase services and set up what Chapman called a “scalable program.”
On the other hand, many miles of Philly roads are upgraded every year; and this year, federal infrastructure funds are providing additional opportunities for thinking innovatively about how that’s done. As a start, Philly could mimic Phoenix’s practice of implementing cool pavements in neighborhoods already due for street upgrades. As Heather Murphy of the Phoenix Street Transportation Department notes, “We were already going to treat every single one of these streets with some kind of seal coat anyway.”
Chapman says his office is working on a pilot with the Streets Department, whose workers would install the cool pavement. But any further details, including which neighborhoods will be included in a potential pilot, how much of the budget would be supplied by Streets, and when specifically all physical work will begin are still up in the air.
Chapman, though, is optimistic: “I feel more confident about this than perhaps we did a year ago.”
The Citizen is one of 20 news organizations producing Broke in Philly, a collaborative reporting project on solutions to poverty and the city’s push towards economic justice. Follow the project @brokeinphilly.
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Photo by Alan Levine