Heat waves cause more illness and death in U.S. cities with fewer trees

In the United States, urban neighborhoods with primarily white residents tend to have more trees than neighborhoods whose residents are predominantly people of color. A new analysis has now linked this inequity to a disparity in heat-related illness and death, researchers report April 8 in npj Urban Sustainability. 

Neighborhoods with predominantly people of color have 11 percent less tree cover on average than majority white neighborhoods, and air temperatures are about 0.2 degrees Celsius higher during summer, urban ecologist Rob McDonald of The Nature Conservancy and colleagues found. Trees already prevent 442 excess deaths and about 85,000 doctor visits annually in these neighborhoods. In majority white neighborhoods, trees save around 200 more lives and prevent 30,000 more doctor visits.

Though the results aren’t surprising, the quality of analysis is “really high,” says urban ecologist Steward Pickett of the Carey Institute of Ecosystem Studies in Millbrook, N.Y.

McDonald’s team compared 2020 U.S. census data for 5,723 urban areas across the country with data on tree cover and heat-related mortality and morbidity for those areas. The census data included 180 million people — about half the U.S. population — and the number of people living in majority white and majority nonwhite neighborhoods was a roughly even split.

Trees provide a cooling benefit during extreme heat waves, particularly when shade is cast over concrete or asphalt (SN: 10/24/23). Planting more trees in areas that need it could save hundreds of lives, says McDonald, who is based in Basel, Switzerland.

At the most ambitious level, planting 1.2 billion trees across the country could prevent about 460 additional heat-related deaths and about 81,000 additional doctor visits annually, the team projects. But even a five percent increase in preexisting canopy cover could make a substantial difference in cities such as Philadelphia or New York City, McDonald says. Both cities currently have millions of trees. “The places that are most suffering from tree inequality are also the best opportunities for new [trees].”

Pickett has previously shown that plans for green infrastructure often exclude the communities that could benefit most from them (SN: 2/6/23). Inclusivity in planning would help ensure that such communities have a say in the process, he says, and are prepared to maintain both new and old trees.