Predominant Circulation Patterns Affecting Regional Persistent Extreme Heavy Rainfall over the Huaihe River Basin of China in July and Their Formation Mechanisms

Abstract Climatic anomalies become more uncertain because of global warming, altering the intensity and frequency of extreme events and making climate prediction more challenging. The Huaihe River basin in China is located in a climate-sensitive area with high population density but limited flood discharge capacity. Regional persistent extreme heavy rainfall (RPEHR) over the Huaihe River basin in July is more likely to trigger floods but has not been thoroughly explored. In this study, the 500-hPa atmospheric circulation affecting RPEHR is classified using K -means clustering, and associated formation mechanisms of the predominant circulation patterns are explored. Thirty seven RPEHR events occurred in July of 1961–2022, with three predominant patterns of the western North Pacific subtropical high (WNPSH) and atmospheric circulation in the mid- and high latitudes (M–h–Lat). The zonal synoptic-scale wave train in the M–h–Lat of the Northern Hemisphere and the East Asia–Pacific (EAP) teleconnection along the East Asian coast are critical in determining the onset of RPEHR. Enhanced southward invasion of negative vorticity advection guided by northerlies of a blocking high is the primary cause of WNPSH’s westward extension and northward lifting, while convective activities in the tropical western Pacific also contribute to that via a positive feedback mechanism. The skin temperature anomalies in the M–h–Lat and the enhanced meridional gradient of sea surface temperature in the tropical western Pacific are precursor signals for the northward lifting of the WNPSH. The results of this study will offer references for RPEHR prediction in climate-sensitive regions.