Anomalous Moisture Uptake Intensifying Summer Extreme Precipitation Linked to Atmospheric Rivers Over the Lower Yangtze River Basin

ABSTRACT The Lower Reaches of the Yangtze River Basin (LYRB) are highly vulnerable to summer extreme precipitation (EP). Understanding the long‐term intensification of such events has become a critical issue with both scientific and societal relevance. Although EP events can be categorised as either associated with atmospheric rivers (ARs) or not, the specific characteristics of AR‐associated EP (AR&EP) remain inadequately understood. By integrating gauge observations, Lagrangian modelling and moisture uptake diagnostics, this study investigates the drivers behind the intensification of high‐impact AR&EP events from the perspective of upstream evaporative moisture sources. Results show a significant intensification of AR&EP from 1991 to 2022. This trend is decoupled from changes in AR characteristics but aligns strongly with a concurrent increase in regional moisture uptake. Although remote oceans remain the ultimate moisture source for the LYRB, terrestrial regions contribute 94% of the total increase in moisture supply, far exceeding the oceanic contribution of 6%. Thus, the widespread increase in evaporative moisture uptake, rather than changes in AR dynamics, serves as the primary driver of the intensifying AR&EP events. These results highlight the crucial role of regional land–atmosphere interactions and are essential for predicting future hydrological risks and managing water resources under a changing climate in the LYRB.