Bringing the shade back to our neighborhoods
A $6 million federal grant is aimed at cooling off Chattanooga’s urban heat islands.
A model of Chattanooga's tree canopy created with satellite imagery and artificial intelligence tools by Charlie Mix, GIS director for University of Tennessee at Chattanooga, 2023.
By William Newlin
Shade-providing trees cover nearly half the land within Chattanooga’s city limits. They’re concentrated in some of the obvious places — the sides of Lookout and Signal mountains and at Enterprise South Nature Park. But in downtown neighborhoods, from East Lake to East Chattanooga to the Westside, tree coverage is harder to find.
The result is heat islands: areas where streets and sidewalks can reach nearly 140 F in the summer. Charlie Mix, Geographical Information Systems (GIS) director for the University of Tennessee at Chattanooga (UTC) has mapped both the extent of Chattanooga’s forests and places where summer surface temperatures climb the highest across Chattanooga. His satellite data gathered over 2021-2023 showed a 3% reduction in urban canopy.
“ Every neighborhood we looked at saw a decrease in tree canopy,” Mix said.
The trend tracks with other research out of the UTC GIS lab, which found that while Chattanooga’s developed land area has more than doubled in the past four decades, tree canopy has declined 43%.
Now, the city is taking steps to make more shade. With a $6 million federal grant awarded to Chattanooga in 2023, the city, local nonprofit green|spaces and the Southeast Conservation Corps will plant around 5,000 trees over the next four years.
Despite development impacts, Chattanooga still has a larger canopy than other mid-size southern cities, said Pete Stewart, Chattanooga’s city forester. And the current planting effort is a step toward fostering more foliage, especially in tree-scarce areas.
“You see it here in Fort Wood,” Stewart said. “That's one of the few neighborhoods that has full canopy blocks. Even there, it's not many. That's something I think we should like plan for and shoot for in a lot of neighborhoods.”
‘A sense of place’
At the GIS teaching lab in the lower part of UTC’s multidisciplinary research building, colored maps of Chattanooga and the surrounding region wrap the walls. The effect is a slightly faded wallpaper, mostly green due to the abundant forests of lower Appalachia.
Mix uses satellite imagery and high-end artificial intelligence tools to make maps and crunch data for a range of research topics. He’s currently working with Stewart to implement the city’s major tree-planting grant, and his team’s mapping expertise is a key contribution.
“We're using GIS and remote sensing and deep learning and all these other buzzword technologies, you know, to basically make informed decisions of where those trees can be planted to really maximize that investment through the grant and by the city,” Mix said.
Using the surface temperature data gathered via NASA satellite, the GIS experts then layered additional data sorted geographically: poverty, car ownership rates, homes with and without air conditioning, and residences where young children and elderly residents live.
The result was a detailed map, filled with data indicating where people are most vulnerable to potentially harmful heat waves. Children and older adults have a greater heat risk. Lower car ownership translates to more time spent walking during hot summers.
Stewart and the other grant partners have used Mix’s heat risk index, along with environmental justice indexes from the EPA, to prioritize where new shade-providing trees will have the biggest benefit for residents' health. But Mix said the benefits of urban trees go beyond the “ecosystem services” of cooler air and better stormwater drainage.
"Trees give us that kind of solid sense of place and have been shown to give us kind of that strong connection to nature and those positive mental benefits that our forests provide,” he said.
Tracking every tree
In a huge brownfield behind East 11th Street, Parks & Outdoors project manager Courtney Alley stood tablet in hand, reviewing the unique IDs attached to a few dozen trees scheduled for planting.
The young trees — willow oaks, single-stem fringetrees, catalpas — had arrived by semi-truck that morning. Buried in parallel mounds of mulch, they shot out skyward at striking angles.
“This is just a small portion of the trees that are going to go in,” Alley said, gesturing to the two rows of leaning trees.
Anna Mathis, natural resource manager for Parks & Outdoors, oversees Alley and the department’s work on the grant. She said planting will continue into 2028, and their goal is a 90% tree survival rate over three years, a higher-than-typical number given threats to growing trees, such as drought.
The tree IDs are a game-changer in protection, Mathis said. Staff can follow plantings from the nursery through maturity, not only to manage pruning and watering needs, but also to track which species fare the best and, in the worst case, reasons why a tree died.
“I'm really excited about it because we haven't had this level of detail since I've been at the city almost nine years,” Mathis said. “ So these funds are really helping us with that.”
Grant partners also aim to remove 40 acres of invasive plants, train 30 workers on local, sustainable land management, and add native species along 16,000 feet of creek banks to reduce stormwater runoff and stream pollution.
Mathis knows it’ll take a while for the trees to take root and native plants to begin their soil repair work. But she expects this project to become a blueprint for future collaboration between the city and its partners to improve tree care and community outreach.
“A key component that we hope to see is that we’ll be able to stand up this for the long-term past the life of the grant,” Mathis said.
Contact William at william@chattamatters.com