Understanding future changes of extremely pluvial winters over the Yangtze–Huai River Basin using CMIP6 projections

A significant wetting trend has been observed in the Yangtze–Huai River Basin (YHRB) during winter, suggesting an increasing risk of seasonal-scale extremely pluvial winters under global warming. Unlike previous studies focusing on daily precipitation extremes, this study investigates future changes in the total precipitation amount, frequency, and intensity of extremely pluvial winters in the YHRB under the SSP2-4.5 and SSP5-8.5 scenarios, based on simulations from 29 CMIP6 models. The total precipitation, frequency, and intensity of extremely pluvial winters are projected to increase substantially under both scenarios, with larger increases under SSP5-8.5 and for more severe events defined by the 95th percentile threshold. Under SSP2-4.5, for events defined by the 90th percentile threshold, the total precipitation may increase by about 50%–160%, the frequency by 20%–200%, and the intensity by 15%–35% relative to the historical period. The intensification of extremely pluvial winters is primarily associated with enhanced net moisture transport into the YHRB, driven by circulation changes and increased humidity gradients between Southwest China and the Indochina Peninsula. Projection uncertainty in the intensity of extremely pluvial winters mainly reflects the inter-model spread associated with differences in simulated circulation responses, moisture transport processes, and vertical motion changes. In contrast, the uncertainty in frequency projections remains considerable. These findings highlight an increasing risk of severe pluvial winters in the YHRB under continued warming and emphasize the importance of better constraining associated dynamic and thermodynamic processes in future climate projections.