Calibrating the UTCI scale for hot and humid climates through comprehensive year-round field surveys to improve the adaptability

Abstract

The Universal Thermal Climate Index (UTCI), a recent advancement in outdoor thermal comfort modeling, requires calibration for hot-humid climates, as its original scale may not suit all climate conditions. This study conducted a comprehensive survey in Taichung City, central Taiwan, to develop a UTCI scale tailored for subtropical regions. Recognizing the limitations of symmetrical results in traditional regression methods, this study applied logistic regression to capture asymmetries in thermal sensation. This approach revealed that individuals in hot-humid regions tolerate warmth better than cold, leading to a calibrated UTCI scale. Our findings indicate that the revised UTCI scale for Taiwan displays higher ranges across thermal stress categories than the original scale, with the “no thermal stress” range extending from 21.6 to 30.9 °C UTCI. This adjusted scale is also higher than those for Mediterranean cities like Athens and Tehran, underscoring the influence of local climates and regional differences in thermal perception. Overall, our novel and more precise approach to evaluating thermal comfort addresses the limitations of the original scale for subtropical climates. Linear regression confirms a warming trend with potential impacts on local thermal stress, providing valuable insights for urban planning in hot-humid regions.