ReportJuly 14, 2021

Hot Zones: Urban Heat Islands

Urban heat islands are metropolitan places that are hotter than their outlying areas, with the impacts felt most during summer months. About 85% of the U.S. population lives in metropolitan areas. Paved roads, parking lots, and buildings absorb and retain heat during the day and radiate that heat back into the surrounding air. Neighborhoods in a highly-developed city can experience mid-afternoon temperatures that are 15°F to 20°F hotter than nearby tree-lined communities or rural areas with fewer people and buildings.

Climate change is making extreme heat events worse and more frequent, with summer temperatures stretching into the shoulder seasons of spring and fall. Heat events adversely affect health and quality of life—and this is especially acute in urban communities. Higher cooling demand strains the electric grid and raises electric bills. And heat-related impacts fall unequally, with historically underserved populations facing greater health threats.

This report will look at the factors that contribute to the heat island effect, and our analysis will show how they vary in places across the United States. We’ll discuss some of the impacts of higher temperatures on human health and the built environment. We’ll also take a look at how communities are adapting to these new normals and consider solutions for lessening some of the intensity of the urban heat island.

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