Coexposure to extreme heat, wildfire burn zones, and wildfire smoke in the Western US from 2006 to 2020.

Climate change drives three heat-related hazards: extreme heat (EH), wildfire burn zones (WFBZs), and wildfire smoke (WFS). Using daily census tract-level data from 2006 to 2020, we investigated when, where, and whom these hazards coexposed in 11 Western US states. Among 18,106 tracts, at least one hazard occurred an average of 32 days (581,867 tract-days) annually. EH-WFS coexposure increased over the study period and was the most frequent coexposure (annual average of 38,218 tract-days). EH-WFS-affected regions varied year to year. WFBZ-involved coexposures were spatially confined and did not increase over time. On average, the most tract-days of EH-WFBZ-WFS coexposure took place in California, Arizona, and Oregon. Among census tracts most exposed to EH-WFBZ-WFS, populations disproportionately consisted of people of older age, with disabilities, and living in poverty. American Indian and Alaska Native individuals disproportionately faced all coexposures. As climate change accelerates, tracking coexposure to multiple hazards can help target resources to protect health.