Spatiotemporal characteristics of Universal Thermal Climate Index during five-year return period extreme heat events in the Beijing–Tianjin–Hebei region

Frequent extreme heat events exacerbated by global warming pose a significant threat to human health. However, the dynamic changes in human thermal comfort during such regional extremes remain understudied. This study investigates the spatiotemporal characteristics of the Universal Thermal Climate Index (UTCI) during 5-year return period extreme heat events across the Beijing–Tianjin–Hebei (BTH) region of China, utilizing 40 years of meteorological data from 174 stations. A non-stationary Generalized Extreme Value distribution model with a location parameter link function was identified as the optimal model (for 65.3% of stations) through the Akaike Information Criterion, capturing 16 regional extreme heat events. Results indicate that extreme heat thresholds rise with increasing return periods, with the highest thresholds concentrated around Beijing and Shijiazhuang. Air temperature and mean radiant temperature were found to be the dominant factors influencing UTCI, with daytime air temperature contributing 47.03% to 50.64% and nighttime mean radiant temperature contributing up to 48.55%. Spatially, “extreme heat stress” conditions, as defined by UTCI, were predominantly observed in the southeastern plains of Beijing and southern Hebei Province. Diurnally, UTCI peaked between 1200 and 1600 BT (Beijing time), generally returning to “no heat stress” levels across most areas between 0000 and 0600 BT. These findings provide crucial insights into the dynamics of human thermal comfort during extreme heat events in the BTH region, offering valuable scientific support for developing targeted heat mitigation and adaptation strategies. 本研究旨在探讨京津冀地区5年一遇极端高温事件期间通用热气候指数的时空特征, 弥补极端高温条件下人类热舒适度动态变化研究的不足.基于40年174站点数据, 采用非平稳广义极值(GEV)分布模型, 通过赤池信息准则选取最优模型, 识别出16次极端高温事件.结果表明, 极端高温阈值随重现期延长而升高, 北京,石家庄周边最高.气温和平均辐射温度是UTCI主导因素, 极端高温热应力主要分布于北京东南部平原及河北南部, UTCI在12至16时达峰值, 00至06时降至“无热应力”水平.本研究为高温应对提供科学支撑.