Editor’s Note: This is part of a series of dispatches from the Knight Science Journalism Program’s 2020-21 Project Fellows.
We know what a flooded city looks like. Parked cars bob in placid waters, first responders steer motorboats through streets, and marooned residents wait for help on their roofs. We have all seen videos of a hurricane’s gale force winds tearing metal from a shed. We can imagine the devastation after a wildfire or a tornado rips through town. But what about the silent, pernicious threat of extreme heat, which killed more Americans last year than all of those weather-related events combined? What does that look like?
I thought about that question as Kelly Turner, a University of California, Los Angeles urban environmental planning professor, presented computer-modeled heat maps of the Watts neighborhood at a community meeting held on Zoom last summer. Officially, Turner was there to share data on the neighborhood’s baseline temperature conditions, measured two Septembers ago with the help of local kids for a wider study of “micro-scale cooling strategies” — like planting trees and erecting shaded bus shelters — that California’s governor’s office is funding here and in other neighborhoods burdened by air pollution and urban heat.
The first set of baseline conditions were the neighborhood’s land surface temperatures, known as LSTs, which are ground temperatures recorded by satellites. Compared to other neighborhoods, Watts has a high overall LST, because there are fewer trees and grasses and more asphalt and concrete. It’s crisscrossed by railroad tracks and freight lines, and wide roads designed to haul cargo from a nearby port. But even within the neighborhood, some surfaces are hotter than others. According to Turner’s data, the hottest surface in Watts isn’t a parking lot or a road, but a school. She showed a heat map with a bright red splotch signaling a hot spot in the middle of the neighborhood. It was an AstroTurf play field at Markham Middle School, which was a scalding 134 degrees. That’s hot enough to burn bare skin in less than a minute of contact.
The second set of baseline conditions were the neighborhood’s mean radiant temperatures, or MRTs — calculations of the total thermal burden on a human body in a given location. MRT factors in air temperature, humidity, and wind speed, plus the things you don’t hear on the weather report, like the intensity of sunlight and all the heat reradiating from the ground, building walls, and other nearby surfaces. MRT records microscale conditions far better than air temperature does, and for that reason, it’s a better proxy for how people experience heat, step by step, block by block. In hot, dry environments like Watts, it’s the real “feels like” temperature.
By 3:00 p.m., the [mean radiant temperature] was almost 162 degrees — the result of all those hard, dark surfaces, holding in hours of sun and reradiating it back as heat.
Turner showed a map of these modeled MRTs surrounding Grape Street Elementary, another local school. This was heat vision, and the neighborhood was incandescent, all reds and oranges, submerging the roads, streets, and schools like magma. The school’s blacktop play yard looked nearly identical to the roads surrounding the nearby train tracks. At 10:00 a.m., the mean radiant temperature in both locations was around 152 degrees. It creeped up to 158 degrees at noon. And by 3:00 p.m., the MRT was almost 162 degrees — the result of all those hard, dark surfaces, holding in hours of sun and reradiating it back as heat.
“The play yard is essentially the same, thermally, as a major roadway,” Turner said. “The place where our children play is the same experience they would have as if they were playing on a parking lot or a highway.”
The good news, she said, is that thermal burdens are substantially reduced in shade, at all daytime hours. She pointed to cool, blue spots on the map, where bungalows had cast squat, north-facing shadows on sidewalks, or where tree canopies had blocked out the sun. At noon, the MRT in these shady spots was around 120 degrees — still hot, but much lower than a place in the sun. Three hours later, the modeled temperatures dipped to around 117 degrees — sweet relief from the afternoon sun.
The reason why shade is so effective, Turner said, is because it does “double work” to improve human thermal comfort. In the shade, people don’t absorb incoming, direct solar radiation from the sun, nor are they exposed to the outgoing, longwave radiation emitted by heated surfaces. For emphasis, she showed the temperatures modeled in an unshaded residential yard. The surface temperatures on soil were lower than those on asphalt, because moisture absorbs and evaporates heat. But the MRTs were about as high.
As Turner wrapped her presentation, the chat box lit up. Comments streamed in. People raised virtual hands. They were incensed by what they’d seen. The playgrounds are as hot as the railroad — really? Do the schools know this? Do the parents know this? Are you going to release this information to the public? Is anyone going to do something about it? A handful of neighborhood schools were slated for tree planting and asphalt replacement, but Grape Street and Markham weren’t among them.
A couple days later, I called Stephanie Ayala, a Watts resident and Markham graduate, to talk about that heat map. It hit hard, she said, because it confirmed what she’d already known — that Watts was too hot. She had her epiphany that summer — the hottest in California’s history — when she drove by her old middle school and saw the unshaded blacktop sizzling in the sun. She knew it was hot — but didn’t know it was that hot.
“And to think that it could get even hotter than it is already, and that it’s our youth that are going to be out there?” she asked. “It’s got me thinking — how can it be different? How can we help?”
The heat map helped her see what Watts needed — more trees and shade. Now, she wondered if her neighborhood would ever get it.
Sam Bloch is a contributing writer at The Counter, where he covers business, environment and culture. He has written for The New York Times, L.A. Weekly, Places Journal, Bloomberg CityLab, and Art in America, among other publications.
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