Changes in human-perceived temperature extremes and associated population exposure across China

Extreme temperature events are the primary factors contributing to human morbidity and mortality related to climate change. However, there is limited understanding of changes in past and future human-perceived temperature (HPT) extremes evaluated in a consistent manner. Building upon the traditional framework of using relative thresholds to define temperature extremes, we further introduce the absolute threshold constraint of human thermal comfort indices, which allows us to capture extreme HPT events that do have the potential to threaten human health. Based on daily observations and model outputs from the Coupled Model Intercomparison Project phase 6 (CMIP6), we investigate the climatology and long-term change in the frequency of summer heat extremes (conditions of high temperatures and humidity) and winter cold extremes (conditions of cold temperatures and winds) across China. The associated population exposure is also quantified. Results show a substantial increase in heat extremes along the coast of Southeast China and parts of Northwest China, as well as a significant decrease in cold extremes over northern China and the Tibetan Plateau from 1961 to 2014. CMIP6 models project that China will confront an elevating risk of extreme heat stress and a decreasing threat of extreme cold events in the future period. South China and Jianghuai are expected to experience the largest increases of population exposure to extreme heat days, and the greatest decreases of cold exposure are located in North China and Jianghuai. Our findings indicate that opposite conclusions regarding the trend in the frequency of HPT extremes might be drawn with and without the absolute threshold constraint of human thermal comfort indices, as well as the use of different absolute thresholds.