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Louisville Uses Trees to Fight Urban Heat

For the city's first director of sustainability, it's one tree at a time.

Maria Koetter squints into the sun and points toward the southeast, surveying Louisville from atop one of its tallest buildings.

 

“Look at that!” she says.

Sprawled before us are the elements that have shaped this city of 750,000. The Ohio River rolls muddy blue, straddled by bridges and dissected by barges that crawl through the watery thoroughfare that gave life to Louisville as a commercial center. Distant hills lush with fall foliage encircle the city, creating a basin that serves as Louisville’s foundation. Traffic rumbles in the distance on several of the major interstates that cross the city, and two coal-fired power plants belch out smoke in the horizon.

Closer in, a more stark landscape, largely stripped of nature, dominated by the man-made: The city center is marked by mid- and high-rise buildings and wide streets originally built for streetcars, but now functioning as six-lane arteries clogged with cars. Parking lots—dozens of privately-owned, half-empty parking lots—scar the city center. The occasional tree seems to pop out of the pavement and struggles to breathe.

“I think you could probably go to a tall building in many cities and see a boundary where you’re going from the dense urban core to a more residential area,” says Koetter, who is Louisville’s first director of sustainability. What Koetter is describing are the physical conditions that give rise to a phenomenon known as an urban heat island, where a city’s center experiences significantly hotter temperatures than its less-developed surroundings. Here’s how it works: During the hottest times of year, dark or paved areas—whether on roofs or on the ground—soak up and store heat. These surfaces continue to release this heat throughout the day and night, preventing the area from cooling down after sunset. Patchy urban tree canopies struggle to clean the air and keep temperatures down. The urban heat islands don’t cause air pollution, but make the effects of pollution worse.

 

Daniel Luzer is GOVERNING's news editor.
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