Wet Bulb Globe Temperature: Indicating Extreme Heat Risk on a Global Grid

The Wet Bulb Globe Temperature (WBGT) is an international standard heat index used by the health, industrial, sports, and climate sectors to assess thermal comfort during heat extremes. Observations of its components, the globe and the wet bulb temperature (WBT), are however sparse. Therefore WBGT is difficult to derive, making it common to rely on approximations, such as the ones developed by Liljegren et al. (2008, https://doi.org/10.1080/15459620802310770, ${WBGT}_{Liljegren}$ ) and by the American College of Sports Medicine ( ${WBGT}_{ACSM87}$ ). In this study, a global data set is created by implementing an updated WBGT method using ECMWF ERA5 gridded meteorological variables and is evaluated against existing WBGT methods. The new method, ${WBGT}_{Brimicombe}$ , uses globe temperature calculated using mean radiant temperature and is found to be accurate in comparison to ${WBGT}_{Liljegren}$ across three heatwave case studies. In addition, it is found that ${WBGT}_{ACSM87}$ is not an adequate approximation of WBGT. Our new method is a candidate for a global forecasting early warning system.