Causes of inter-model uncertainty in projecting future summer extreme precipitation changes over eastern China

An ensemble of 12 CMIP6 models was used to project future changes in summer extreme precipitation over eastern China during 2036-2055 under the SSP2-4.5 scenario. Extreme precipitation was quantified using the total precipitation from days exceeding the 95^th percentile of wet-day precipitation (R95pTOT). Large inter-model uncertainty is evident over the Huabei region, substantially reducing the reliability of the multi-model ensemble (MME) projection there. To address this inter-model uncertainty, a pattern-based clustering analysis was applied to the MME projections, yielding three distinct and equally likely patterns (Clusters 1-3) of summer extreme precipitation change. Clusters 1 and 3 project increases in extreme precipitation over Huabei for 24.8 mm and 12.7 mm, whereas Cluster 2 indicates a decrease for -1.2 mm. An atmospheric moisture budget analysis reveals that the inter-cluster differences in extreme precipitation changes are primarily driven by dynamic effect associated with contrasting circulations. In Cluster 1, a strengthened and westward-shifted western North Pacific subtropical high (WNPSH) enhances southerly moisture transport, which is associated with cold SSTA over the central tropical Pacific. Cluster 3 exhibits a circulation pattern similar to that of Cluster 1, but with weaker intensity. In contrast, Cluster 2 is characterized by a weakened and eastward-shifted WNPSH at lower level, together with a southward-displaced East Asian subtropical westerly jet at upper level, resulting in less southerly moisture transport. In addition to differences in summer-mean circulation, atmospheric stability conditions over Huabei were compared across these clusters. Clusters 1 and 3 exhibit higher frequency of cases with large convective potential energy (CAPE), whereas Cluster 2 indicates more frequent occurrence of cases with large convective inhibition (CIN).