Urban Heat Island Inequalities by Sociodemographic Characteristics in Major U.S. cities

Abstract:

In 2017, more than three-quarters of the U.S. population lived in urban areas, a proportion growing over time. With the expansion of urban growth and land-use conversion to more dense built-up environments, urban heat stress poses a major public health issue. While previous research has established disparities in land surface temperature (LST), air temperature, heat stress as well as other environmental stressors for different income classes through case studies or limited multi-city analyses, large-scale evaluations have been non-existent. Scarce evidence exists to understand how if these patterns persist and across sociodemographic characteristics including age and race. To fill this gap, we adapt a conceptual framework based on income inequality analysis methods to compare differences in SUHI across race, income, and vulnerable age groups in all major U.S. cities with populations greater than 250,000. We apply this framework to a unique SUHI database we developed using satellite-derived LST data and census-tract level sociodemographic data from the American Community Survey. We find that people of color tend to live in census tracts with higher daytime SUHI than non-Hispanic whites in all but 6 of the 175 largest urban areas in the continental United States during summer daytime, when the SUHI intensity is highest. A similar pattern emerges for people living in households below the poverty line relative to those at more than two times the poverty line in all but five areas. Populations of color under the age of 5 are particularly vulnerable. In nearly half the urban areas the average person of color faces a higher summer daytime SUHI ‘exposure’ as the average person living below poverty, despite the fact that on average only 10 percent of people of color live below the poverty line. This last finding suggests that widespread inequalities in heat exposure by race and ethnicity may not be well explained by differences in income.