Precipitation water conversion rate variations and driving mechanisms in the Yangtze-Huang-Huai-Hai river basin over the past 60 years

Precipitation water conversion rate (PWCR) is a key indicator of the efficiency with which atmospheric vertically integrated water vapor content (IWV) is converted into precipitation. This study investigates the long-term variations and driving mechanisms of PWCR in the Yangtze-Huanghe-Huaihe-Haihe River (YHHH) basin, China, from 1956 to 2024. The results show that PWCR decreased significantly at a rate of −1.19%·dec −1 , while IWV increased by 2.83 mm·dec −1 and precipitation decreased by −18.95 mm·dec −1 . These opposite trends indicate that increasing atmospheric moisture did not translate into enhanced precipitation conversion. Seasonal analysis further reveals distinct mechanisms in summer and winter. In summer, PWCR is mainly controlled by precipitation changes jointly regulated by relative humidity (RH) and temperature. Higher RH favors precipitation formation, whereas warming may reduce conversion efficiency by increasing atmospheric moisture-holding capacity. In winter, PWCR is primarily governed by RH-mediated precipitation processes. Overall, the decline in PWCR reflects a weakening efficiency of atmospheric water vapor conversion under a warming and drying background. These findings improve understanding of water vapor–precipitation transformation in large monsoon-influenced basins and provide useful evidence for hydrological modeling and climate adaptation.