Synoptic patterns of hourly extreme precipitation events over the Yangtze-Huaihe River Basin in China

The occurrence of disaster-producing hourly extreme precipitation events (HEPEs) is usually linked to certain atmospheric backgrounds. Using high-density automatic weather stations observations and ERA5 reanalysis, this study analyzed the synoptic patterns of HEPEs over the Yangtze-Huaihe River Basin with an objective classification method. Four primary atmospheric circulation patterns (accounted for over 71 % of HEPEs) are identified, including two mei-yu types differ in different temporal and spatial features, the deep trough type, and the post-mei-yu type. The two mei-yu types are responsible for nearly 50 % of all HEPEs with relatively large horizontal size, and the southwesterly low-level jets that influenced by the cyclone and Western North Pacific Subtropical High (WNPSH), are a representative feature of these two types during HEPEs. The deep trough type during HEPEs related to Northeast China Cold Vortex is characterized by a cold northerly flow collided with the warm southerly/southwesterly flows, resulting in a strong convergence. In contrast, the HEPEs in the post-mei-yu type exhibits an eastward WNPSH, with the convergence and updrafts over the study area are caused by the collision between the southerly cyclone flows and the northerly flows at low levels. During two mei-yu types and post-mei-yu type, the HEPEs (non-precipitation) showed a cyclone (an anticyclone) feature. Our findings demonstrate the significant impact of circulation types on HEPEs, highlighting the importance of understanding their characteristics and patterns, which would be helpful for disaster warning, forecasting, and management.