Projection for the occurrence dates of heat stress in North China

High humidity has been causing extreme heat stress during summer in North China, presenting threats to human life. Although future changes in the intensity and frequency of heat stress have been well recognized, it remains unclear whether the alterations in humidity resulting from increasing greenhouse gases (GHG) will change the occurrence date of heat stress in North China in the future. In this study, we identify three models, including CMCC-CM2-SR5, CMCC-ESM2, and TaiESM1, as the models that most reasonably simulate the dependence of the heat stress on the near-surface specific humidity and the occurrence date of the heat stress in North China. Based on these three models, we show that the increased specific humidity during the warm season, which is caused by rising GHG emissions, will extend the occurrence date of extreme heat stress from only July and August under the SSP1-2.6 scenario to June through September under SSP5-8.5 scenario. A more prevalent occurrence of the extreme heat stress during the warm season under SSP5-8.5 scenario will cause a three-to four-fold increase in the population exposure to the Severe heat stress (wet-bulb temperature > 27.5 °C) compared to the SSP1-2.6 scenario. The findings highlight that North China will suffer more prevalent and extreme heat stresses in the future due to the GHG-caused increasing humidity. The results are valuable for developing adaptation and mitigation strategies to minimize the impacts of the extreme heat stress in North China.