Mapping the misery: Citizen scientists identifying SLC’s hottest places

Here’s how data could help cities prepare for a warmer future.

This story is part of The Salt Lake Tribune’s ongoing commitment to identify solutions to Utah’s biggest challenges through the work of the Innovation Lab.

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It was still dark out on a recent Saturday morning when Roxanne Christensen and Christopher Knoles parked their white Tesla next to a church off the corner of 900 West and North Temple.

At 5:45 a.m. they clipped a white box with a two foot-long antennae to the car’s passenger window.

Fifteen minutes later it was time to start their route. “And the science begins,” Christensen said as she made a right turn onto North Temple.

The couple was one of several teams driving around Salt Lake City in mid-July during the earliest, and still relatively cool, hours of the day as part of a project to map the hottest spots across the city.

(Christopher Knoles) Roxanne Christensen sits in her the vehicle with a heat monitor clipped to the passenger window. Christensen and Christopher Knoles drove around Salt Lake City collecting data as part of NOAA's urban heat mapping campaign this July.

Another pair would drive the same route in the afternoon and evening to gather a complete picture of heat in the city throughout the day.

The same weekend citizen-scientists spread out across the city taking temperatures, the temperatures recorded at the Salt Lake City International airport rose above 100 degrees. A road buckled and search and rescue teams had to pull heat-weary hikers off Mount Olympus. The Guardian reported about a third of Americans were under “heat warnings” this past week.

The excessive heat plaguing large swaths of the country this summer isn’t only unpleasant — it can be dangerous.

“A lot of Americans don’t know [heat] is the number one weather-related killer in the U.S.,” said Morgan Zabow, who manages the urban heat island mapping campaign and works as the community heat and health information coordinator for the National Oceanic and Atmospheric Administration (NOAA). When temperatures fail to drop at night and people don’t have a way to cool down, it gets even riskier.

But with proper education and planning, Zabow said, people can prevent many heat-related illnesses and deaths.

These heat mapping projects provide a way for cities to better understand and prepare for that excessive heat. Possibilities include planting and properly caring for more trees and other green spaces along high-rise apartments and parking lots and creating cooling centers in particularly hard-hit areas.

Understanding the heat island effect

The Tuesday evening before the mapping campaign, volunteers met in a pleasantly air-conditioned room at the Salt Lake Public Library’s Glendale branch.

Robert Wilson, a science teacher at Rowland Hall, a private school in Salt Lake City, delivered a brief lecture on what exactly the group, made up of some of his students and their parents as well as other residents, had signed up for.

Wilson partnered with Utah State University’s Climate Center and applied to participate in NOAA’s urban heat mapping program.

Through the program, cities are able to access monitors that can capture the “heat index” — a number that reflects how the human body experiences heat, Wilson explained.

“They provide the instruments, they help with logistics. They also do the initial receiving and processing of the data.”

Wilson, the USU Climate Center and Salt Lake City worked to find and train volunteers to drive through the city with monitors clipped to their car windows.

The science teacher became interested in heat mapping after taking walks through Salt Lake City and noticing the disparity in tree coverage. Places with fewer trees, more black asphalt and near freeways with hundreds of heat-emitting vehicles tend to be hottest. This phenomenon is known as the urban heat island effect.

Satellites logging temperatures using infrared already show that the West side of Salt Lake City, where the tree canopy is less developed, tends to get hotter. When Wilson looked at old redlining maps that historically carved up the city by race, ethnicity and income and combined those with existing heat data, there was a close connection.

“What neighborhoods experienced the hottest temperatures and the most prolonged heat?” he wondered. During heatwaves, Wilson said, “those are the people at greatest risk.”

(Rick Egan | The Salt Lake Tribune) People take advantage of the shade, as a dog cools off in the creek at Memory Grove, on Saturday, July 15, 2023.

The data volunteers collected is more granular and will hopefully provide clear answers to these questions. “I knew the first thing we needed to do to address this question of heat waves was to get some baseline information on heat in neighborhoods during the summertime,” Wilson said. Unlike existing data, the sensors used this past weekend measured both air temperature and humidity — providing a snapshot of what the human body feels on different streets across Salt Lake City.

How cities can use data to adapt

The heat mapping project began in 2017, explained Zabow with NOAA.

While certain results are not that surprising (areas without many trees tend to be hotter), cities have discovered certain hotspots.

Last summer, Las Vegas took part and learned that bus routes ran along the hottest neighborhoods, Zabow said. The city leveraged that data to quickly secure a federal grant to add shading over bus stops.

Additionally, Honolulu and Cincinnati launched massive tree planting campaigns after participating in the heat mapping project, Zabow said.

Mapping heat in Seattle, Wash. in 2020 showed “the largest temperature difference between neighborhoods of all of the cities that we have collected,” Zabow said. “They found an over 25-degree Fahrenheit temperature difference.”

Heat maps can help cities like Seattle quickly identify the most dangerous neighborhoods and implement cooling strategies, Zabow said.

The following year (2021) a heat dome enveloped Seattle and one report estimated that 441 people died in one week.

In Salt Lake City, officials supported the data collection efforts and are eager to see the maps that result.

“We’re waiting to see the data and see how we can turn it into an efficient allocation of resources,” said Tony Gliot, director of Salt Lake City’s Urban Forestry division. “Long term, we can solve this with better design, with prioritizing the locations to grow canopy,” Gliot said. “Information like this can serve to guide policy.”

While there are major tree-planting efforts underway, Salt Lake City is losing more trees than ever before, Gliot said. Drought and failure to water trees have put stress on older growth. It also has made establishing new trees difficult.

(Francisco Kjolseth | The Salt Lake Tribune) Tony Gliot, director of Salt Lake City's Urban Forestry division, a member of gets an assist from third graders at Meadowlark Elementary as they plant the 1,000th tree of the year on the city's west side on Wednesday, Oct. 26, 2022. Mapping the hottest areas of Salt Lake City may help leaders prioritize locations to plant more trees for heat relief, Gliot told The Tribune.

The data and public participation can also serve as a simple reminder that as more people turn to “strip-ripping” and xeriscaping their landscapes with ornamental rocks and gravel, trees still need regular water.

Getting people to water trees in public parking strips regularly can be a challenge. Alessandro Rigolon, an associate professor at the University of Utah’s city and metropolitan planning department, said that he would like to see the municipality take on that job.

“It’s something that reflects a view of street trees as ‘being nice to have,’ and not essential. If we saw them as essential, we would provide more public resources to take care of them,” Rigolon said.

He noted that citizens are not expected to fill the potholes on their streets. Rigolon said framing green space in general as essential infrastructure remains a challenge — although he pointed to the city’s proposed Green Loop linear park, which could provide a green belt around downtown, as an effective way to combat heat islands. Plus, it would make active transportation (i.e. biking and walking) more appealing during the summer.

Planting and maintaining trees is just one strategy. In Phoenix, where temperatures are regularly surpassing 110 degrees this month, a pilot project installing 100 miles of “cool pavement” is underway. The initial findings from Arizona State University found that cool pavement, which reflects heat away from the surface, can lower the subsurface temperature by 4.8 degrees.

(Rick Egan | The Salt Lake Tribune) Marla Hernandez relaxes in the shade at Jordan Park, on Saturday, July 15, 2023, the day that volunteers drove around Salt Lake City mapping hot spots. The data may inform policies that help cool down cities as temperatures continue to rise.

On Saturday morning, as Christensen and Knoles drove around the West side of the city, it was easy to guess which parts of the route might clock in at higher temperatures.

Their route took them through a parking lot full of idling semi-trucks, along well-canopied neighborhood roads and near Salt Lake City’s portion of the Jordan River Trail, where birds flocked in the distance.

Christensen works in marketing for a large architecture firm and Knoles in commercial construction. They are both acutely aware of their “built” environment — homes, apartment and office buildings, roads and parking lots.

The couple often thinks about the decisions that go into creating a neighborhood and worry about how livable this high-desert city will be as the world warms.

However, mapping heat in Salt Lake City, Christensen said, helped her find a little bit of hope.

Additional resources

  • To learn more about Salt Lake City’s tree planting and ways to help visit the Urban Forestry page here.

  • If you’re trying to avoid the heat The Salt Lake Tribune created a list of cooling centers across the state here.

  • For information on the urban heat islands, heat forecasts and other resources you can visit Heat.gov.