May 16, 2023 - News

Houston is one of the worst cities for urban heat islands

Air pollution absorbed by trees
Data: Climate Central analysis of U.S. Forest Service data; Map: Simran Parwani/Axios

Houston is among the worst cities in the country for intense heat islands because of a lack of tree canopies, Axios' Ayurella Horn-Muller and Simran Parwani report.

Driving the news: A new Climate Central analysis reveals which localities nationwide benefit most from the boons of urban forests.

Why it matters: Urban tree coverage helps reduce the impacts of extreme heat, prevents stormwater runoff, mitigates air pollution exposure, and can even sequester carbon, per the analysis.

  • Urban heat islands are created when developers replace natural landscapes with "dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat," per the U.S. Environmental Protection Agency.
  • A tree's leaves can absorb pollutants like ozone and nitrogen dioxide, the report noted.

What they found: The U.S. cities with the most air pollution absorbed by trees are Presque Isle, Maine; Eugene, Ore.; Eureka, Calif.; Bangor, Maine; and Duluth, Minn., according to Climate Central data shared with Axios.

  • By contrast, the cities with the most intense urban heat islands are Houston, New Orleans, Newark, New York City and San Francisco.

Zoom in: Only about 18% of Houston is currently covered by tree canopy, with a roughly 14% "tree cover discrepancy" between high- and low-income neighborhoods, the Houston Chronicle reports.

What they're saying: The City of Houston is working to meet an "ambitious" goal of 4.6 million trees planted by 2030, Jaime González, Community and Equitable Conservation Programs director for the Nature Conservancy's Texas chapter, tells Axios.

  • González's team in April partnered with the Texas A&M Forest Service to map available planting zones in Gulfton — a "nature-deprived" neighborhood in southwest Houston that's home to a largely immigrant and lower-income community. They estimated 804 trees should be placed there to increase tree canopy cover.
  • "You just walk around the neighborhood, there are long, long stretches where there are no trees and it's just hot pavement," says González. (In 2020, parts of Gulfton were 17 degrees hotter in the afternoon than the city's coolest neighborhood, per the Washington Post.)

Meanwhile, Houston's Alief neighborhood — where there's only 11% tree canopy — will get 1,200 new trees in the coming years.

Yes, but: "Tree for tree, [urban] trees are potentially doing a lot. But it's not going to offset the fossil fuels which are also concentrated in cities," says Lucy Hutyra, professor of earth and environment at Boston University.

  • From planting to maintenance, she notes the costliness of urban trees, as well as cities' different growing environments, which produces varying ecosystem services and benefits.

The bottom line: "Trees are part of the solution," Hutyra tells Axios. "But they are not the whole solution."

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