Prolonged seasons of compound heat-humidity extremes amplify vulnerable population exposure in eastern ChinaOA

Compound heat–humidity extremes(CTHEs)pose escalating threats to human health,particularly for vulnerable populations(children and elderly)with limited physiological adaptability.This study reveals the expansion of CTHE-active seasons across eastern China from 1961 to 2022.Southern China(SC)and the Yangtze–Huaihe region(YH)exhibit earlier onsets and delayed terminations,prolonging hazardous CTHE seasons by one month post-2015 in SC.The prolonged CTHE-active seasons,coupled with population growth,have driven sharp increases in exposure across eastern China,with annual CTHE and hazardous CTHE exposure increasing by 106 million and 78 million person-days since the 2000s.Vulnerable groups constitute 39%of total exposure,with 11%(CTHEs)and 34%(hazardous CTHEs)attributable to season prolongation.Mechanistically,an intensified and westward-extended western North Pacific subtropical high enhances diabatic heating and moisture advection,driving prolonged CTHE-active seasons in SC and YH.These findings quantify climate–demographic synergies in heat–health risks,providing a scientific basis for climate-resilient health strategies targeting age-sensitive populations in eastern China’s warming and humidifying hotspots.