Development of a Heat Vulnerability Index for the Southeastern United States

Epidemiological studies have demonstrated the adverse health effects of extreme heat, and have revealed population characteristics that increase vulnerability to heat-related illness (HRI). The rising prevalence of extreme heat events across the United States highlights the need to understand variations in community HRI vulnerability and identify high-risk locations. While spatial variations in heat vulnerability have been demonstrated in particular US regions and urban areas, an analysis for the Southeastern US and any large-scale county-level analyses are missing. In this study, county-level socioeconomic, demographic, and health-related heat-vulnerability variables were used to create a heat vulnerability index (HVI) for the Southeastern US. First, vulnerability variables with known effects on HRI were selected from the American Community Survey, US Census, and Behavioral Risk Factor Surveillance System. Principal component analysis with varimax rotation was used to reduce the variables to four components, loosely representing socioeconomic, age/disability, living conditions, and health-related axes of heat vulnerability, and explaining 76 percent of the variance in the original variables. Each of 736 counties was assigned a score along each component, whose sum gave each county’s total HVI value. Preliminary validation of the HVI demonstrated generally higher annual heat-related mortality in regions with higher HVI. Subsequent analysis of extreme heat data for three regions of North Carolina identified threshold temperatures at which heat-related emergency department visits increase. Using these thresholds and daily heat data, a preliminary modified HVI combining vulnerability and temperature was developed for North Carolina, allowing for potential identification of vulnerable areas during specific extreme heat events. Further analysis includes incorporating atmospheric humidity measures to better understand relationships between extreme heat, vulnerability, and health in moist climates. Mapping this HVI allows for identification of high-vulnerability areas in the Southeastern U.S., and for targeting of necessary policy interventions.