Comparing Approximated Heat Stress Measures Across the United States

Climate change is escalating the threat of heat stress to global public health, with the majority of humans today facing increasingly severe and prolonged heat waves. Accurate weather data reflecting the complexity of measuring heat stress is crucial for reducing the impact of extreme heat on health worldwide. Previous studies have employed Heat Index (HI) and Wet Bulb Globe Temperature (WBGT) metrics to understand extreme heat exposure, forming the basis for heat stress guidelines. However, systematic comparisons of meteorological and climate data sets used for these metrics and the related parameters, like air temperature, humidity, wind speed, and solar radiation crucial for human thermoregulation, are lacking. We compared three heat measures (HI_max, WBGT_Bernard, and WBGT_Liljegren) approximated from gridded weather data sets (ERA5-Land, PRISM, Daymet) with ground-based data, revealing strong agreement from HI and WBGT_Bernard (R² 0.76–0.95, RMSE 1.69–6.64°C). Discrepancies varied by Köppen-Geiger climates (e.g., Adjusted R² HI_max 0.88–0.95, WBGT_Bernard 0.79–0.97, and WBGT_Liljegren 0.80–0.96), and metrological input variables (Adjusted R² T_max 0.86–0.94, T_min 0.91–0.94, Wind 0.33, Solar_max 0.38, Solar_avg 0.38, relative humidity 0.51–0.74). Gridded data sets can offer reliable heat exposure assessment, but further research and local networks are vital to reduce measurement errors to fully enhance our understanding of how heat stress measures link to health outcomes.