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National Heat Vulnerability Index Reveals Neighborhoods at High Vulnerability to Heat

December 18, 2022
by Matt Kristoffersen

As the Earth’s climate warms, abnormal heat waves remain an increasingly dire health hazard. But not all neighborhoods are affected equally: Redlining, housing discrimination, and inequitable public infrastructure have all contributed to disparities in health outcomes from heat.

Policymakers and government officials now have a powerful tool to address these issues.

A team of researchers at the Yale School of Public Health has developed a metric to gauge heat vulnerability at the census-tract level and created a color-coded interactive map for public use.

The visual aid, presented in refined detail, can help officials identify areas that may need more public health and policy interventions to combat the adverse effects of heat stress, said Kai Chen, assistant professor of epidemiology (environmental health) and director of research for the Yale Center on Climate Change and Health.

“We want this tool to be used by the public so that we can raise awareness of how vulnerable their communities are and help them take appropriate action,” Chen said. “But also, we want this to be used by policymakers so that they can see the distribution within their state, or even nationally so that they can have certain communities in mind when they implement climate adaptation policies.”

The paper appears in the journal GeoHealth.

The team’s index-based analysis reveals new insights into the nature of heat-related health disparities, including its association with race. According to the analysis, which spanned more than 55,000 census tracts across the continental United States, non-white people of color composed more than three-quarters of the population of the nation’s most vulnerable tracts. Meanwhile, in the least vulnerable areas, only about one-quarter of the population were people of color.

The index draws a clear correlation between historically redlined neighborhoods and heat vulnerability today. Redlining was a discriminatory practice initially employed by the federal government during the 1930s when it attempted to rank the risk of issuing government-insured mortgages to homeowners. Federal officials used color-coded maps to classify perceived investment risk, with the riskiest areas – neighborhoods where property values were most likely to go down – marked in red. Most of the ‘redlined’ areas were neighborhoods where Black residents lived, thereby making it difficult for Black residents to access homeownership and government-backed lending programs. Efforts to address redlining culminated in the Fair Housing Act of 1968, which prohibits housing discrimination.

Chen explained the correlation this way:

“In the Upper East Side of New York City, for example, you may have a high temperature exposure, but in that area, there are a lot of means and economic ways to cope with the heat,” Chen said. “In Harlem, maybe there is a similar temperature exposure, but the neighborhood is socioeconomically disadvantaged. From our Heat Vulnerability Index, we can review at a very granular level these disparities within cities, so that people can access specific information as to which local neighborhoods are more vulnerable. Only when we know that information can we have targeted interventions and policies.”

By clarifying the inequities of adverse heat on vulnerable communities, this study exemplifies the impact we strive for in our research at Yale.

Yale Vice Provost for Research Michael Crair

The disparities transcended race, too. In general, urban areas showed a higher score — that is, higher vulnerability — than suburban and rural areas.

This may be due to the unique heat challenges that urban areas face, like a lack of tree cover and the heat island effect, which makes ambient temperatures rise compared to nearby natural landscapes, said Mitchell Manware, a second-year MPH student who led the study.

More research is needed to fully understand the factors which lead to these differences. Still, Manware said, the different scores within the index can help officials target areas for intervention.

“Not only are people in rural areas just as vulnerable to heat, but their vulnerabilities may differ,” Manware said. “People in rural areas may have more access to green space, which is a protective factor, but they may not have access to air conditioning, so their vulnerability is a different type of vulnerability, but that doesn’t mean that it’s less important.”

The Heat Vulnerability Index developed by the research team combines a variety of data points like race and ethnicity, diabetes prevalence, building density, evidence of historic redlining, and air temperature anomalies into a single score, from 10 to 26. The results are striking: New Haven’s Long Wharf neighborhood — an area considered by the federal government to be burdened by discrimination and climate injustice — received a score of 24, higher than 99.5 percent of all other census tracts in the nation. Meanwhile, East Rock, a relatively wealthy community in New Haven, received a score of 18.

Interestingly, many areas in the traditionally hottest areas of the United States — such as desert regions in Nevada, California, and Arizona — do not seem as vulnerable to adverse heat events compared with areas in more northern latitudes. The tip of Maine, for example, ranks in the top third in the nation for heat vulnerability.

While the desert may get hotter than New England, residents’ existing adaptations to heat — from air conditioners to lifestyle changes — make them generally sturdier against these kinds of adverse weather events compared to people living in colder climates, Chen said.

“When we look at heat effects, many only look at the heat exposure. That is, the temperature,” he explained. “But from the public health perspective, it is not only the exposure that eventually leads to all of these heat-related illnesses, but also all these other factors which can influence how vulnerable a community is to heat — not just degrees Fahrenheit.”

There are limitations to their index. More than 18,000 tracts could not receive a score because they lacked certain data points. Also, a nationwide assessment of homes that contain air conditioners, a critical tool to avoid heat-related illnesses, does not currently exist. And the metrics the researchers used for historic housing discrimination, like the screening tool from the White House Council on Environmental Quality, did not include race and ethnicity as a criterion, which may skew the final scores.

Still, the researchers hope that their online tool will help identify new areas for interventions and stimulate further research towards the interventions themselves.

“We thought that the Heat Vulnerability Index would be useful to policymakers to clearly identify the areas in their city, their town, their state that are most vulnerable to heat and where adaptation-related resources would be most beneficial,” Manware said.

The study was supported by a seed grant from the Yale Planetary Solutions Project and the High Tide Foundation.

“Our congratulations to the authors on this incisive study and on its publication,” said Michael Crair, Yale’s vice provost for research. “By clarifying the inequities of adverse heat on vulnerable communities, this study exemplifies the impact we strive for in our research at Yale. It also highlights the importance of early-stage, interdisciplinary research support of the type the Planetary Solutions Project seed-grant program provides. We hope to see more similarly inspired outcomes in the near future.”

Yale School of Public Health Professor Dr. Robert Dubrow (faculty director of the Yale Center on Climate Change and Health) and Assistant Professor Daniel Carrión (director of education for the Yale Center on Climate Change and Health) are co-authors on the paper along with doctoral student Yiqun Ma.

Submitted by Colin Poitras on December 19, 2022