Comparison of methods for estimating Wet-Bulb Globe Temperature index from standard meteorological measurements

Environmental heat illness and injuries are a serious concern for the Army and Marines. Currently, the Wet-Bulb Globe Temperature (WBGT) index is used to evaluate heat injury risk. The index is a weighted average of dry-bulb temperature (Tdb), black globe temperature (Tbg), and natural wet-bulb temperature (Tnwb). The WBGT index would be more widely used if it could be determined using standard weather instruments. This study compares models developed by Liljegren at Argonne National Laboratory and by Matthew at the U.S. Army Institute of Environmental Medicine that calculate WBGT using standard meteorological measurements. Both models use air temperature (Ta), relative humidity, wind speed, and global solar radiation (RG) to calculate Tnwb and Tbg. The WBGT and meteorological data used for model validation were collected at Griffin, Georgia and Yuma Proving Ground (YPG), Arizona. Liljegren (YPG: R(2) = 0.709, p < 0.01; Griffin: R(2) = 0.854, p < 0.01) showed closer agreement between calculated and actual WBGT than Matthew (YPG: R(2) = 0.630, p < 0.01; Griffin: R(2) = 0.677, p < 0.01). Compared to actual WBGT heat categorization, the Matthew model tended to underpredict compared to Liljegren's classification. Results indicate Liljegren is an acceptable alternative to direct WBGT measurement, but verification under other environmental conditions is needed.