How Redlining Made City Neighborhoods Hotter

A growing body of research highlights the connection between systemic discrimination and the local climate

A map of the Loop and north side of Chicago, split up into small neighborhoods that are color-coded as red, yellow, blue or green
In one example of redlining, this Home Owners' Loan Corporation map depicts part of Chicago, Illinois and labels neighborhoods as "hazardous" (red) or "best" (green). Borrowers could be denied access to credit if their homes or businesses were located in "hazardous" neighborhoods, typically economically disadvantaged neighborhoods with large minority populations. Mapping Inequality: Redlining in New Deal America

Governments at the local and federal level in the United States have long played a role in segregating city blocks. For instance, in 1933 in the wake of the Great Depression, the federal government created the Home Owners’ Loan Corporation. The organization set out to map the perceived “riskiness” of lending in neighborhoods in 239 cities, marking them green for “best” or red for “hazardous” — a process known today as redlining. In doing so, these officials fortified structures that denied loans to lower-income, minority populations, which were typically deemed “hazardous,” and divert resources toward white neighborhoods, as Tracy Jan reported previously for the Washington Post.

Redlining was one in a series of governmental practices that effectively segregated city blocks by race and income level. As a 2018 study by the National Community Reinvestment Coalition found, these racist practices diverted resources away from poorer neighborhoods and deepened economic inequality, with consequences that continue to this day.

Now, a new and growing crop of research indicates that redlining practices in the 1930s also created a deadly disparity in temperature, report Brad Plumer and Nadja Popovich for the New York Times. One major study published in January in Climate found that, across 108 urban areas, redlined neighborhoods are on average 5 degrees Fahrenheit hotter in the summer than the neighborhoods that scored the highest on HOLC surveys decades ago. As a previous Times study found, temperatures in Baltimore, Washington D.C., Richmond, Portland and others can vary as much as 20 degrees Fahrenheit in the same city on the same scorching summer day, with historically white neighborhoods tending to be much cooler.

“Heat today is an indicator for what’s gone on in the past,” Vivek Shandas, a co-author of the study, tells National Geographic’s Alejandra Borunda. “You pull that string and so many things unravel, decade after decade.”

As Shandas explains, many factors can contribute to rising temperatures in formerly redlined neighborhoods. Busy freeways that cut through neighborhoods, large expanses of cement sidewalks and pavement that absorb and trap heat, and a lack of central air conditioning in lower-income buildings all make a difference.

Trees and plants also play a key role in cooling us down. As Meg Anderson reported for NPR this year, one study of 37 cities published in January found that formerly redlined neighborhoods have about half as many trees, on average, as the highest-rated predominately white neighborhoods. Per National Geographic, trees and plants provide much-needed shade, and cool down the air around them by a process called evapotranspiration.

The resulting temperature difference feels “like stepping into a parking lot from a park. You would feel that relatively quickly," Shandas told NPR earlier this year. “It was very surprising when we saw that it was a pattern that we were seeing consistently across the country.”

A few degrees’ difference in temperature can be the determining factor between life or death for some city residents, Catherine Harrison, a public health specialist, tells National Geographic. One 2011 study cited by the Times found that a single degree increase in temperature during a heat wave can increase the risk of dying by 2.5 percent.

As the Times reports, another study estimates that heat kills as many as 12,000 people per year in the United States. As heat waves blast the country with more intensity and frequency due to climate change, people living in the hottest neighborhoods in American cities are the most vulnerable. For instance, the Times found that formerly redlined zip codes in Richmond, Virginia have among the highest heat-related ambulance calls in the city.

Speaking with NPR earlier this year, Sarah Lillie Anderson, a senior manager of Tree Equity Programs at the nonprofit American Forests, noted that “the results of these studies confirm what we've been talking about for years.”

“Our cities, they're not like jungles where they developed just by natural selection on their own,” adds Anderson. “People designed these places, which means that they were designed for particular people, and that means that not everybody was held in mind when plans for cities and communities were made.”

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