A Climatology of Gridded Wet-Bulb Globe Temperature for the Southeastern United States

Abstract A gridded wet-bulb globe temperature (WBGT) climatology for the southeastern United States is presented, emphasizing athlete and worker safety thresholds. Hourly WBGT estimates are derived from the land component of the fifth generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5-Land) and validated using U.S. Climate Reference Network estimates from 1991 to 2020. Validation statistics indicate that, despite a nighttime warm bias across the region, ERA5-Land WBGT estimates are commensurate with estimates derived using in situ data. Across the southeastern United States, evergreen forests and moisture-rich locations such as rivers, lakes, and wetlands typically experience higher WBGT values than drier locations, with high-elevation (≥1000 m) areas experiencing the lowest WBGT values. The locations with the most days and the most hours per year with outdoor activity restrictions for athletes and workers shift as WBGT increases, with peak locations transitioning from southern Texas and southern Florida in May to northern Louisiana, southern Arkansas, and eastern Texas by August. An areal analysis of the most dangerous conditions shows a gradual expansion across the southeast, driven primarily by increases in Texas. There was no discernible spatial shift in the location of black flag conditions aside from interannual variability. The results characterize the spatiotemporal extent of heat exposure, provide a basis for delineating regions at risk for unsafe conditions, and support education and mitigation strategies by healthcare professionals, athletic administrators, and local officials.