A socio-spatial vulnerability model of the Urban Heat Island: exposure, sensitivity and health impacts of high temperatures

Urban Heat Islands in cities are increasing human vulnerability to rising temperatures already elevated due to global climate change. Vulnerability to extreme heat exists along a socio-spatially differentiated spectrum of exposure, sensitivity, and coping capacity that can mitigate or exacerbate the impacts of extreme heat. In this research, we assess the role of exposure and sensitivity in shaping human vulnerability to extreme heat by answering two research questions:1) How do exposure and sensitivity to extreme heat vary spatially according to socio-economic and built environment conditions in residential neighborhoods in an urbanized area, and 2) what are the effects of exposure and sensitivity to high temperatures on heat-related hospitalization rates in different types of neighborhoods? We construct and map a predictive index of sensitivity to heat health risks for neighborhoods in Maricopa County, Arizona, compare predicted neighborhood sensitivity to heat-related hospitalization rates, and estimate relative risk of hospitalizations for neighborhoods with different sensitivity profiles. Our results indicate that hospitalization rates increase exponentially beyond a threshold of 32 degrees C, and that for each 1 degree C > 32, there is a 21 percent increase in hospitalizations. Sensitivity to heat significantly affects heat-related hospitalizations: Compared with low-sensitivity groups, individuals living in neighborhoods with medium heat sensitivity are almost twice as likely to be hospitalized due to heat, while those in high sensitivity neighborhoods are almost four times as likely to be hospitalized. Two distinct sub-populations are found to be most sensitive to heat hazards: low-income, ethnic minorities in sparsely-vegetated urban core neighborhoods, and elderly people in retirement communities in the suburban fringe.