On a hot summer’s day, the neighborhood of Gilpin quickly becomes one of the most sweltering parts of Richmond.

There are few trees along the sidewalks to shield people from the sun’s relentless glare. More than 2,000 residents, mostly Black, live in low-income public housing that lacks central air conditioning. Many front yards are paved with concrete, which absorbs and traps heat. The ZIP code has among the highest rates of heat-related ambulance calls in the city.

There are places like Gilpin all across the United States. In cities like Baltimore, Dallas, Denver, Miami, Portland and New York, neighborhoods that are poorer and have more residents of color can be 5 to 20 degrees Fahrenheit hotter in summer than wealthier, whiter parts of the same city.

And there’s growing evidence that this is no coincidence. In the 20th century, local and federal officials, usually white, enacted policies that reinforced racial segregation in cities and diverted investment away from minority neighborhoods in ways that created large disparities in the urban heat environment.

The consequences are being felt today.

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Across more than 100 cities, a recent study found, formerly redlined neighborhoods are today 5 degrees hotter in summer, on average, than areas once favored for housing loans, with some cities seeing differences as large as 12 degrees. Redlined neighborhoods, which remain lower-income and more likely to have Black or Hispanic residents, consistently have far fewer trees and parks that help cool the air. They also have more paved surfaces, such as asphalt lots or nearby highways, that absorb and radiate heat.

“It’s uncanny how often we see this pattern,” said Vivek Shandas, a professor of urban studies and planning at Portland State University and a co-author of the study. “It tells us we really need to better understand what was going on in the past to create these land-use patterns.”