The Heat Divide: Mapping America’s Unequal Burden of Heat

BU Study Maps Climate Change, Demographics, and Disaster Risk, Providing Actionable Insights

By Maeve Smillie and Maureen Stanton

By mid-century, the U.S. will be a much hotter place. Heatwaves will last longer, summer temperatures will soar, and the number of dangerously hot days will rise sharply—especially in the US South. But not everyone will feel the heat in the same way.

A BU-led study published in Environmental Research: Health reveals that the communities least equipped to handle rising temperatures will face the greatest increases in extreme heat exposure. And that’s not just because of climate change—it’s also because of where people live, how fast populations are growing, and their social vulnerability as measured by poverty levels, housing quality, age, race, and other factors. Think of elderly residents in poorly insulated homes, low-income families who can’t afford air conditioning, or urban neighborhoods with little shade and few cooling centers. These are the communities on the frontlines where heat will hit hardest.

“As the planet heats up, those least able to cope will suffer the most,” says lead author Zachary Popp, research data analyst at Center for Climate and Health, School of Public Health (SPH) at Boston University. “With public health resources already declining, it’s critical to address the health risks of extreme heat now to reduce the growing toll of extreme heat.”

The study applied statistical and geospatial methods to pinpoint specific areas where future heat exposure will be both most intense and most dangerous due to the residents’ limited ability to respond. With this approach, the researchers aim to go beyond broad generalizations and ultimately empower local governments to prioritize resources where they’re needed most. Study co-authors include Ian Sue Wing, CAS professor of earth & environment; Kevin J. Lane,  SPH professor of environmental health; and Gregory A. Wellenius,  SPH professor of environmental health and director of the Center for Climate and Health.

A New Way of Seeing Risk

In other related research, information is often studied in isolation. Climate scientists often project future heat extremes, while demographers track population change, and public health researchers map social inequities. The novel approach in this study brings together these three layers of data, delivering insights in a comprehensive and spatially precise way. 

“Our multidisciplinary approach applies data-driven methods to help shift the question from ‘How hot will it get?’ to ‘Which communities will be hardest hit—and how can we help these communities reduce these risks?’” says Wellenius. “This makes the science timely, directly useful, and actionable.” 

Projecting the Heat Burden

The study assessed the health-hazardous heat through multiple metrics: extreme hot days when the heat index exceeded 104 degrees, chronic heat through estimated air conditioning use, and acute heat through the 95th percentile high temperature (the temperature on the 20th hottest day of the year). To analyze rising temperatures, population changes, and social vulnerability collectively, the researchers examined 30+ global climate models and paired them with population projections. The study compared changes in heat and population to demographic and economic characteristics using the CDC Social Vulnerability Index. This index uses U.S. Census data to estimate how vulnerable each community is to disaster based on 15 social factors, including poverty, lack of vehicle access, and crowded housing. 

The study found that while the South and West – already hot- will see large absolute increases in heat, New England regions could see the largest relative increases, going from just a few hot days a year to many more. This geographical distinction is crucial for planning purposes. Southern states are generally better equipped for heat, with infrastructure designed for hot weather. In contrast, northeastern regions often lack adequate cooling resources, leaving residents particularly vulnerable to extreme heat.  

A key takeaway from the study is that population growth in already hot regions could make extreme heat even more dangerous. Areas in the Southeast and Southwest face rising heat indexes and often have vulnerable populations without access to air conditioning to cope with extreme heat. Cities experiencing rapid urbanization and migration trends may struggle to adapt, especially if local infrastructure is not equipped to handle prolonged extreme heat events. “Cities are especially of interest because of urban heat island effects – less tree cover, more buildings and dark pavement means higher temperatures and more health risks,” says Popp.

(Above is an example of one of the interactive visualization tools that shows how heat index days—combining temperature and humidity—are projected to rise in the 100 largest U.S. cities by 2050 under three global emissions scenarios. SSP585 represents the most extreme pathway. Explore more tools on the Center for Climate Health webpage here.)

Infrastructure as Intervention

The granular, localized nature of the research makes it particularly valuable for urban planners and public health officials. The specificity of the data would allow cities and states to prioritize allocation of resources to specific neighborhoods where temperature increases will hit vulnerable populations hardest.

To support these aims, the research provides specific, actionable insights that can help local governments target interventions where they’re most needed. The study emphasizes the importance of policies to invest in heat-reducing infrastructure to address the growing intersection of climate change and social vulnerability. Proactive adaptation measures, such as enhancing green spaces, improving emergency response systems, and protecting at-risk populations, extreme heat could help mitigate widespread public health crises. 

“Simply suggesting that people move away from increasingly hot areas isn’t realistic or fair to communities already facing both economic and environmental challenges,” says Popp. “Interventions like increasing green space, using reflective materials like white roofing, and improving access to air conditioning – especially in areas with vulnerable populations – can make a big difference.” 

Convergent Research Catalyzed by Hariri Institute

This work was supported by the Hariri Institute Focused Research Program, which aims to catalyze convergent research by offering seed funding for faculty-led teams to develop sustainable collaborations.

“The Hariri Institute’s Focused Research Program (FRP) was instrumental in advancing our project by helping connect us with experts from various disciplines, and providing essential resources and support,” says Wellenius. “This support enabled us to access the large-scale data processing capabilities necessary to efficiently analyze vast datasets and generate actionable insights to drive policy recommendations as well as the multidisciplinary expertise required to get the science right.”

“These are exactly the type of multidisciplinary projects that the Hariri FRPs are supposed to enable,” says Yannis Paschalidis, distinguished professor of engineering (ECE, SE, BME),  director of the Hariri Institute, and a member of the University’s Task Force on Convergent Research and Education. “In this case, it is notable that the program brought together researchers from the medical campus and the Charles River campus.”  

In the future, the research team hopes to introduce interactive visualizations to further illuminate the study as well as measuring these intersecting elements and their implications in other countries around the world. 

Citation: Zachary Popp et al. A US heat disaster? Intersection of social vulnerability and temperature extremes exacerbated by mid-century climate change and population shifts 2025 Environ. Res.: Health 3 025009 DOI 10.1088/2752-5309/adb902