Objectives To assess long-term trends in outdoor heat and wildfire smoke exposure at 410 correctional facilities in California from 2000–2023.

Methods We used ERA5-Land data to calculate daily wet-bulb globe temperature (WBGT) and identified days exceeding the NIOSH 28°C threshold. Wildfire smoke exposure was estimated using NOAA’s Hazard Mapping System (HMS). Temporal trends in daily heat and smoke exposure were modeled using linear regression for each facility.

Results Smoke-affected days rose statewide from 4.9% (2006–2010) to 12.5% (2019–2023), with Northern California experiencing the highest burden and steepest increases. Days above 28°C WBGT increased from 27.3% to 29.8% statewide, with the Central Valley and desert regions showing the highest current burden and coastal areas experiencing the steepest increases. Coastal facilities show emerging heat risks, and some regions—especially the Central Valley and Sierra foothills—face dual exposure to both hazards.

Conclusions Correctional officers and incarcerated workers face rising environmental risks, with regional variation in exposure. Facilities with concurrent heat and smoke burdens must balance cooling and filtration needs. Resilience planning and occupational protections must evolve to meet facility- and region-specific challenges.

The authors have declared no competing interest.

This study was funded by the California Fifth Climate Change Assessment Core Climate Research Program.

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Select data produced in the present study are available upon reasonable request to the authors.