Abstract Farmworkers in California’s Imperial Valley face a disproportionate risk of heat stress from prolonged exposure to extreme temperatures. However, heat stress is more than just extreme temperature and depends on humidity, winds, and sun exposure. These conditions can be aggregated into the wet-bulb globe temperature (WBGT), a metric endorsed by the U.S. Occupational Safety and Health Administration (OSHA) for monitoring workplace heat. To better inform heat mitigation strategies, we construct a climatology of summertime WBGT in Imperial Valley for 30 years during 1991–2020. The climatology is constructed from a dynamical downscaling of ERA5 reanalysis to 1.5 km using the Weather Research and Forecasting (WRF) Model, using quantile mapping to bias correct WBGT inputs against regional weather station observations. We find that WBGT is the highest in urban areas, where summertime daily maxima average 34°C and in rural croplands below mean sea level. National Weather Service...