SALT LAKE CITY (ABC4) — On a steamy July day last summer, Robert Wilson led more than 40 volunteers in a single-day project to take Salt Lake City’s temperature on the ground, all across the city.
Equipped with window-mounted sensors on their cars, Wilson and the volunteers repeatedly drove routes across Salt Lake, gathering data on how hot the city’s neighborhoods were during the morning, afternoon and evening.
Their efforts helped create hyper-detailed maps, showing that the city’s hottest spots — in downtown, along 1-15, and in westside neighborhoods — could be 15 degrees warmer than the coolests areas of the city at a given time.
“They revealed a significant difference in the temperatures of eastside neighborhoods versus westside neighborhoods,” said Wilson, Rowland Hall’s Upper School biology teacher and lead volunteer on the mapping project.
Funded by the National Oceanic and Atmospheric Administration (NOAA), the citizen science project was part of a campaign to visualize the urban heat island effect and help local leaders understand what neighborhoods face the biggest threat during heat waves.
Nationally, extreme heat kills more Americans every year than any other weather-related event, according to Morgan Zabow, community heat and health coordinator with NOAA.
“On average, over 1,200 Americans die each year from extreme heat,” she said, noting that climate change is causing heat waves to be more intense and arrive earlier in the season.
What is the urban heat island effect? According to scientists, dense concentrations of asphalt, concrete and other impermeable surfaces common in cityscapes can trap heat and radiate it outward, even overnight.
As shown in the heat maps for Salt Lake, temperatures on the higher-elevation and Wasatch-shaded eastside were generally cooler, except for the University of Utah campus, a signature heat island. Pockets of heat were also found along some of Salt Lake’s wide streets, which have little to no tree canopy.
When looking at the heat maps, Wilson noticed a strong resemblance to how Salt Lake was historically segregated through practices like redlining, wherein minority communities were confined to neighborhoods deemed “hazardous” and denied financial services.
“It’s striking how well the hot pockets correspond with the redlining pockets,” Wilson said, noting that he created a map showing the overlap.
Across the country, the urban heat island effect is often more pronounced in neighborhoods that were historically redlined or received less investment compared to their more affluent counterparts. According to Zabow, this lack of investment has corresponded to fewer trees and green spaces in these neighborhoods, which provide shade and a natural cooling effect.
Salt Lake Mayor Erin Mendanhall’s office told ABC4 that she is committed to planting more trees in the city, particularly on the west side. Since her first term, her administration has planted 1,000 trees each year west of State Street.
“We’re now on year five,” said Tony Gliot, the urban forestry director for Salt Lake City.
Recent planting took place on Earth Day, at the end of April, when more than 250 trees were planted at the Regional Athletic Complex in the city’s northwest, bordering I-215.
“That was our biggest single-day planting perhaps in our city’s history,” Gliot said.
It’s important to understand, he noted, that Salt Lake wasn’t carved out of a forest. Instead, the city’s urban tree canopy was built up over the decades to foster a more comfortable space in an environment that is naturally prone to high winds and scorching summer heat.
“From our perspective, everybody who lives or visits or works in this city should have access to shade and beauty that trees provide,” Gliot said. “There’s no reason the west side of the city can’t look like the east side of the city when it comes to tree canopy.”
According to Wilson, the city was an important partner in the heat mapping study. He hopes that the project he organized, alongside the Utah Climate Center and the Natural History Museum of Utah, will help decision-makers design naturally cooling infrastructure and educate Salt Lakers on the dangers of heat-related illnesses.
“In many cases, it’s easy to avoid heat risk by avoiding activity or making sure you’re hydrated,” he said. “You also might think about it as you plan how you design a garden or a home. You can be proactive about this.”
Wei Zhang, an assistant professor of climate science at Utah State University and the principal investigator on that heat map project, said that prior to this on-the-ground mapping initiative satellites could only guess at surface temperatures across Salt Lake.
Zhang has since done more research involving simulations of climate and urban canopy models to understand the role of trees and the cooling effect they provide in the American West.
“We find that adding green infrastructure can potentially reduce environmental heat locally and regionally,” he said.
