A US heat disaster? Intersection of social vulnerability and temperature extremes exacerbated by mid-century climate change and population shifts

Abstract Future impacts of climate change-driven increases in extreme heat exposure on population health will be driven both by the frequency and intensity of future heat, as well as changes in the size and vulnerability of affected communities. Given indications of spatial persistence of social vulnerability across the US, we explore the implications for heat exposures of the most vulnerable populations due to mid-century climate change. Population heat exposure is estimated by combining heat hazard with population growth projections. Specifically, median projected acute (95% maximum temperature), extreme (hot days, daily maximum heat index >40 °C), and chronic (cooling degree days) heat hazard are assessed in contemporary (1995–2014) and projected (2041–2060) epochs across 25+ climate models under three climate scenarios against 2020 social vulnerability index (SVI). By mid-century, increases in both chronic and extreme heat will be concentrated in the South region. Population is expected to grow faster in census tracts at the high and low extrema of the SVI. The intersection of these projected future trends suggests that the intensity and exacerbation of heat exposures due to climate change will not be evenly distributed across the population. Individuals who are most vulnerable today will face disproportionately larger heat exposures circa mid-century. Populations in high SVI areas will both increase in size and experience the largest increases in extreme heat exposure. Spatial aggregation masks fine scale changes. While cities and counties with concentrations of vulnerable populations will face rightward shifts in the tails of their temperature across the US, extreme and especially chronic population heat exposures will be concentrated in a swath stretching across southern US states. The magnitude of population heat exposure changes and their intersection with underlying vulnerability require action to focus adaptation resources on resilience to extreme heat.