A team of scientists has used an advanced computer modeling technique to measure the extent to which non-white and lower-income residents of U.S. cities are exposed to higher summertime temperatures and greater heat stress. The new research provides a more direct measurement of heat exposure than earlier findings that relied on satellite measurements, and it can help with efforts to better protect vulnerable populations from increasingly severe heat waves.

The study, led by scientists at the Pacific Northwest National Laboratory with a co-author at the National Center for Atmospheric Research (NCAR), shows that residents who live in predominantly Black neighborhoods are exposed to air that is 0.28 degrees Celsius (about 0.5 degrees Fahrenheit) warmer than the city average. In contrast, white urban residents are likely to live in neighborhoods where air temperature is cooler than the city average by 0.22 degrees Celsius (0.4 degrees Fahrenheit).

Lower-income residents in general face higher temperatures, but the relationship between heat stress and race-based residential segregation is more pronounced.

Although the difference of a few-tenths of a degree may not sound significant, the authors note the impacts can be adverse, especially since poorer populations frequently lack resources such as household air conditioning to cope during extreme heat events.

The reasons for the racial and economic disparities have to do with urban development. Segregated housing patterns, often beginning with government redlining policies instituted in the 1930s, tended to cluster Black residents in dense neighborhoods with few trees and parks that provide a cooling influence.

The research team found that the overwhelming majority of U.S. urban residents — some 94%, or about 228 million people — live in cities where the poor are disproportionately burdened by peak heat stress in the summer. But they also found that inequities in heat stress exposure, although stark, are actually somewhat less than previous estimates based on satellite measurements.

Whereas satellites measure temperature at the ground, the research team relied on an NCAR-based database that draws on advanced computer models to estimate the temperature and humidity of ambient air in the urban environment, which is more closely related with heat stress and associated health impacts.

This new database captures heat stress in U.S. cities since 1981 at a resolution of 1 kilometer (about 0.6 miles), showing variations in heat and humidity in different neighborhoods. This resolution, along with the information on humidity, gives researchers an important new tool as they work to learn more about urban heat and human health.

“The new database provides a more direct estimate of human exposure to heat stress, which is increasingly important as heat waves become more intense,” said NCAR scientist Andrew Newman, who co-authored the study. “In this case, we've been able to confirm that there are pervasive inequities for heat exposure across urban areas in the U.S. This has important ramifications for public health and can inform efforts to help vulnerable populations.”

The study, published in the journal One Earth, was supported by the U.S. Department of Energy’s Office of Science and the National Institutes of Health, and by the U.S. National Science Foundation, which is NCAR’s sponsor. For more, see the Pacific Northwest National Laboratory news release.

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