An Investigation of Extreme Wet Bulb Globe Temperatures across the Contiguous United States

Wet Bulb Globe Temperature (WBGT) is a common measure of heat exposure used widely in athletics, the military, and occupational safety. Current guidelines that utilize WBGT, such as those recommended by the American College of Sports Medicine (ACMS), use fixed safety thresholds which neglect regional variations in acclimatization to heat. It is well established that exposure-response relationships to heat varies geographically, with lower minimum mortality and morbidity thresholds in regions with cooler climates. A modeled climatology of WBGT (1991-2005), consisting of data from around the contiguous United States, is used to identify geographic patterns of various warm season (May-September) WBGT percentile values. Our data indicate that in the southern region of the United States, WBGT values may exceed the ACMS recommendations for ceasing athletic activity (>32.3°C WBGT) at the 50th percentile while some areas in the Pacific Northwest, Upper Midwest, and New England may not meet this threshold until the 95th percentile or higher. This suggests that lower thresholds may be needed in areas that infrequently experience extreme heat. It is our intent that our results can help guide the development of local WBGT safety thresholds for use in regionally specific heat safety policies.