Disproportionate Exposure to Urban Heat Island Across 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 densely built environments, urban heat stress poses a major public health issue. Case studies of individual cities suggest that heat exposure, like other environmental stressors, may be unequally distributed across income groups. There is little evidence, however, as to whether such disparities are pervasive at the national level. Here, we combine US-specific surface urban heat island (SUHI) data, a proxy for isolating the urban contribution to additional heat exposure in built environments, with census tract-level demographic data from the American Community Survey to answer these questions for summer days, when heat expo-sure is likely to be at a maximum. We find that the average person of color lives in a census tract with higher summer daytime SUHI intensity than non-Hispanic whites in all but 6 of the 175 largest urbanized areas in the continental United States. 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 nearly half the urbanized areas, the average person of color faces a higher summer daytime SUHI then 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 alone.

Keywords: Urban Heat Island, Environmental Justice, Inequality, U.S. Cities