Estimating hourly outdoor WBGT from routine meteorological observations for heat-stress assessment in tropical Singapore

Site-specific hourly WBGT information is needed for outdoor heat-stress assessment in hot-humid tropical environments, where heat exposure varies across station locations and work periods. Dedicated WBGT sensors, however, remain spatially limited, constraining routine station-scale assessment and retrospective exposure analysis. This study develops a locally calibrated, compact, physics-motivated formulation (fWBGT) for estimating hourly outdoor WBGT from routine automatic weather-station observations in tropical Singapore. The zero-iteration linear formulation uses a closed-form psychrometric wet-bulb surrogate ([Formula: see text]), global horizontal irradiance represented by [Formula: see text], dry-bulb temperature, and 2-m wind speed to retain radiation- and wind-aware predictors without iterative heat-balance calculations. It was calibrated using five years of hourly co-located data from Changi, Singapore (2020-2024; [Formula: see text]) and benchmarked against iterative, analytic, lookup-table, and multilayer perceptron (MLP) methods. fWBGT reproduced measured WBGT with RMSE = [Formula: see text]C, [Formula: see text], and approximately zero MBE. It was less accurate than the MLP (RMSE = [Formula: see text]C) but executed approximately 1,750 times faster than the iterative Liljegren model. The simplified WBGT lookup approach showed nighttime errors exceeding [Formula: see text]C. In 2025 temporal and spatial validation, fWBGT achieved daytime RMSE [Formula: see text]C and nighttime RMSE [Formula: see text]C. These results demonstrate that locally calibrated WBGT estimation provides an efficient methodology for station-scale heat-stress screening and exposure assessment in tropical microclimates. While the calibration-and-validation procedure is transferable, the Singapore-specific coefficients require local recalibration prior to application in other environments.