The southern Himalayas, characterized by its dense population and hot, humid summers, are confronted with some of the world’s most severe heat stress risks. This study uses the hourly ERA5 dataset (1979–2022) and CMIP6 projections (2005–2100) to evaluate past and future heat stress based on the Wet Bulb Globe Temperature (WBGT). This has significant implications for the management of occupational workloads in the southern Himalayas. Heat stress levels are classified into 6 categories (0 to 5) using WBGT threshold intervals of 23 °C, 25 °C, 28 °C, 30 °C, and 33 °C. With heat stress surpassing level 3 for almost half of the time, people are constrained to engage in less than moderate workloads to ensure their health remains uncompromised. Flow-analogous algorithm is employed to contextualize the unprecedented heat stress case in the summer of 2020 and the associated atmospheric circulation patterns from historical and future perspectives. The results show that over 80% of the time in 2020, heat stress levels were at 3 and 4. The identified circulation pattern explains 27.6% of the extreme intensity, and such an extreme would have been nearly impossible in pre-21st-century climate conditions under the identified pattern. Future projections under SSP2-4.5 and SSP5-8.5 scenarios indicate that heat stress similar to what was experienced in 2020 will likely become a common occurrence across the southern Himalayas. Under a similar circulation pattern, the heat stress levels by the end of the 21st century would be elevated by at least one category compared to the climatic baseline in over 70% of the region, leading to an additional 120.5 (420.1) million daily population exposed to the highest heat stress level under the SSP2-4.5 (SSP5-8.5) scenario.

喜马拉雅山脉南部人口稠密，夏季炎热潮湿，面临着世界上最严重的热应激风险。本研究使用每小时 ERA5 数据集（1979-2022）和 CMIP6 预测（2005-2100）根据湿球地球温度（WBGT）评估过去和未来的热应激。这对喜马拉雅山脉南部的职业工作量管理具有重大影响。使用 WBGT 阈值区间 23 °C、25 °C、28 °C、30 °C 和 33 °C，将热应激水平分为 6 类（0 至 5）。由于近一半的时间热应激超过 3 级，人们被迫从事低于中等的工作量，以确保他们的健康不受影响。采用流类比算法从历史和未来的角度来描述 2020 年夏季前所未有的热应激情况以及相关的大气环流模式。结果显示，2020 年超过 80% 的时间，热应激水平处于 3 和 4 级。确定的环流模式解释了 27.6% 的极端强度，而在 21 世纪之前的气候中，这种极端情况几乎是不可能发生的已识别模式下的条件。 SSP2-4.5 和 SSP5-8.5 情景下的未来预测表明，类似于 2020 年经历的热应激可能会在喜马拉雅山脉南部普遍发生。在类似的环流模式下，到 21 世纪末，该地区 70% 以上的地区的热应激水平将比气候基线提高至少一类，导致每天额外有 1.205 亿（4.201 亿）人口受到暴露。达到SSP2-4.5（SSP5-8.5）情景下的最高热应激水平。