Temperature-Humidity-Wind index variability on the Qinghai-Tibet Plateau over the past half millennium

The Qinghai-Tibet Plateau has experienced rapid warming over the past six decades, resulting in more frequent extreme weather events with significant impacts on human health. This warming trend, along with improved infrastructure and transportation, has spurred a rise in summer tourism, boosting local economies yet exposing visitors and residents to high risks of public health. However, the relationship between the historical variability of THW index on the Qinghai-Tibet Plateau and human health under the combined influence of external forcing factors and internal climate variability remains unclear. In this study, we reconstructed the summer (June–August) Temperature–Humidity–Wind (THW) index, an indicator of apparent temperature and associated health impacts, across the western, southern, southeastern and northeastern Qinghai–Tibet Plateau over the past 500 years. Our results reveal that the post-1971 CE upward trend in the THW index for the southern, southeastern, and northeastern plateau regions is the most rapid of the past five centuries. Despite the accelerated warming, current THW values remain below the thresholds for heat-related health risks. Notably, the two coldest intervals during 1630–1660 and 1670–1700 CE exhibited marked drops in THW index, possibly lowering oxygen levels and exacerbating chronic mountain sickness, thereby reducing life expectancy. Solar activity shows a significant positive correlation with the THW index on multi-decadal timescales and affects the THW index by altering the radiation flux at the top of the Earth's atmosphere and amplifying it through the water vapor transport feedback mechanism of the ocean. However, the relationship between the Atlantic Multidecadal Oscillation (AMO) and the THW index shifted from negative to positive after the Industrial Revolution. This shift likely stems from the AMO-driven changes in the North Atlantic sea surface temperatures, which alters the Silk Road teleconnection wave train and leads to spatially inconsistent THW patterns. These findings highlight the critical influence of long-term climate variability on human health, underscoring the importance of Predicting future THW index trends by modeling to guide effective public health strategies during global warming.