Expanding Irrigation Intensifies the Humid Heat Stress in China: Evidence From Observations and Modeling

Abstract China is the world's second‐largest agricultural irrigation country, with profound influences on the escalating heat stress. This study combines historical weather records and 10‐year regional climate simulations, in conjunction with optimized irrigation algorithm, to disentangle the dual impacts of irrigation on heat stress in China. Application of province‐specific soil moisture thresholds generates improved simulation of irrigation water amount and a lower model error by 30%. The substantial cooling and moistening effects by irrigation are revealed by weather records and optimized irrigation‐climate simulations, that is, −0.13°C/decade (−0.01°C to −0.72°C) for daily maximum air temperature and +1.80%/decade (0.02%–3.96%) for relative humidity. Despite alleviating the extreme high‐temperature events, agricultural irrigation intensifies the occurrence (0.93 days yr −1 ) and population exposure (0.46 million person‐days yr −1 ) of humid heat. This study suggests that irrigation may not serve as an optimal land management adaptation strategy to mitigate the growing humid heat under climate change.