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

Abstract

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, normalWnormalBnormalGnormalTnormalLnormalinormallnormaljnormalenormalgnormalrnormalenormaln ${\mathrm{W}\mathrm{B}\mathrm{G}\mathrm{T}}_{\mathrm{L}\mathrm{i}\mathrm{l}\mathrm{j}\mathrm{e}\mathrm{g}\mathrm{r}\mathrm{e}\mathrm{n}}$) and by the American College of Sports Medicine (normalWnormalBnormalGnormalTnormalAnormalCnormalSnormalM87 ${\mathrm{W}\mathrm{B}\mathrm{G}\mathrm{T}}_{\mathrm{A}\mathrm{C}\mathrm{S}\mathrm{M}87}$). 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, normalWnormalBnormalGnormalTnormalBnormalrnormalinormalmnormalinormalcnormalonormalmnormalbnormale ${\mathrm{W}\mathrm{B}\mathrm{G}\mathrm{T}}_{\mathrm{B}\mathrm{r}\mathrm{i}\mathrm{m}\mathrm{i}\mathrm{c}\mathrm{o}\mathrm{m}\mathrm{b}\mathrm{e}}$, uses globe temperature calculated using mean radiant temperature and is found to be accurate in comparison to normalWnormalBnormalGnormalTnormalLnormalinormallnormaljnormalenormalgnormalrnormalenormaln ${\mathrm{W}\mathrm{B}\mathrm{G}\mathrm{T}}_{\mathrm{L}\mathrm{i}\mathrm{l}\mathrm{j}\mathrm{e}\mathrm{g}\mathrm{r}\mathrm{e}\mathrm{n}}$ across three heatwave case studies. In addition, it is found that normalWnormalBnormalGnormalTnormalAnormalCnormalSnormalM87 ${\mathrm{W}\mathrm{B}\mathrm{G}\mathrm{T}}_{\mathrm{A}\mathrm{C}\mathrm{S}\mathrm{M}87}$ is not an adequate approximation of WBGT. Our new method is a candidate for a global forecasting early warning system.

Post-Sunset Humid-Heat Maxima near the Southern Persian/Arabian Gulf

“…Even so, large humidity anomalies on hot-humid days keep WBGT in the 'light workload' category along the coast in the evening and through most of the night (Fig. 3) 30,31 , carrying the additional potential of sleep disruption for the entire population lacking access to arti cial cooling 32 . That the highest values of Tw and heat index at all hours, and of UTCI and WBGT at night, are located over the Gulf waters (Figs.…”

“…From ERA5 we also obtain wind direction and speed, planetary-boundary-layer height, and several radiation quantities needed to calculate mean radiant temperature: surface net short-wave, surface net long-wave, surface short-wave downwards, surface long-wave downwards, and total-sky direct. While Tw serves as our primary humidheat metric, for comparison purposes we assess the US National Weather Service heat index 43 , the Universal Thermal Climate Index (UTCI) 44 , and the wet-bulb globe temperature (WBGT) 30 .…”

The Land Wet‐Bulb Temperature Increases Faster Than the Sea Surface Temperature

“…The wet-bulb temperature T w is an implicit function of humidity (e a ), air temperature (T a ) and air pressure (P). Some researchers have used regression models to approximate T w from observations of e a , T a , and P (Brimicombe et al, 2023;Kong & Huber, 2022). Here we used a numerical method, similar to those presented by Krakauer et al (2020) and Davies-Jones (2008), to solve T w from the wet-bulb equation (Equation 4 below) at the daily timestep.…”

Comparing Approximated Heat Stress Measures Across the United States

“…To overcome the limitations of available in situ station data, researchers have developed various gridded weather data and reanalysis products, as well as several methods to calculate heat stress measures with these products (Bernard & Iheanacho, 2015 ; Brimicombe et al., 2023 ; Dimiceli et al., 2011 ; Liljegren et al., 2008 ; Spangler & Wellenius, 2021 ; Stull, 2011 ; Yaglou & Minaed, 1957 ). Among the various estimation methods for WBGT, the method proposed by Liliegren (WBGT Liljegren ) has been considered the most robust under outdoor conditions (Bernard & Iheanacho, 2015 ; Kong & Huber, 2022 ; Lemke et al., 2019 ; Patel et al., 2013 ).…”