Summer Drought Dynamics in the Sichuan Basin of China Driven by the Atmospheric Water Cycle

Abstract Frequent droughts in the Sichuan Basin (SCB) have caused severe socioeconomic impacts and significantly altered the regional water cycle. However, the connection between these droughts and the atmospheric water cycle remains unclear. Here, we applied two process‐based models—the Dynamic Recycling Model (DRM) and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model—to investigate the characteristics and mechanisms of atmospheric water cycles during SCB summer droughts from 1979 to 2022. The results show that the climatological mean precipitation recycling ratios for June, July, and August were 12.92%, 13.04%, and 12.63%, respectively, indicating the SCB's strong dependence on externally transported moisture. Most droughts are linked to deficits in external moisture transport. However, in the later stages of the most severe droughts (e.g., August 2006 and 2022), the drought evolves from preceding external moisture reduction into an internal‐moisture‐depletion regime. This shift is driven by extreme soil moisture depletion, which markedly intensifies land–atmosphere coupling and ultimately leads to the collapse of local moisture recycling. Moisture tracking further reveals that droughts with external deficits are associated with reduced oceanic inflow, while those with internal deficits exhibit reduced terrestrial moisture contributions despite sufficient oceanic supply, reflecting low efficiency in converting available moisture into rainfall. Large‐scale circulation systems, especially the Western Pacific Subtropical High and mid‐latitude westerlies, play a key role in shaping these drought‐related anomalies by regulating moisture transport and precipitation efficiency, while land–atmosphere coupling further amplifies these anomalies. These findings provide new insights into summer drought dynamics in the SCB and inform improved drought prediction under a changing climate.