Study Finds Trees Offset Nearly Half of Global Urban Heat Island Effect

Tree cover in cities provides an average cooling effect of 0.27 degrees Fahrenheit through shade and water vapor release, according to a study published in Nature Communications. Without trees, the urban heat island effect from pavement and buildings would raise average city temperatures by 0.56 degrees Fahrenheit.

The analysis covered nearly 9,000 large cities worldwide and divided each into segments of about 150 city blocks to isolate local cooling impacts.

Wealthier cities experience greater cooling from trees than poorer ones. Nearly 40 percent of cities in wealthy nations receive at least 0.45 degrees Fahrenheit of cooling, compared with just under 9 percent of cities in the poorest countries. Four cities with minimal tree cover—Dakar, Senegal; Jeddah, Saudi Arabia; Kuwait City; and Amman, Jordan—provide essentially no cooling benefit to more than 15 million residents.

Cities with the highest cooling include Berlin, Atlanta, Moscow, Washington, Seattle, and Sydney. Atlanta maintains tree canopy over 64 percent of its land area.

Rob McDonald, lead author and scientist at the Nature Conservancy, stated that cities could increase tree cover but face limits from water availability, land constraints, and suitable species. At most, additional planting would reduce future urban heating by 20 percent.

McDonald added that trees will not eliminate climate change driven by fossil fuel emissions. Thomas Crowther, an ecologist at the King Abdullah University of Science and Technology, noted that urban vegetation buffering effects will become vital as up to 75 percent of the global population moves to cities.