Weather pattern classification of regional extreme precipitation events and their formation mechanisms in the Yangtze-Huai Region, China

Extreme precipitation is one of the most frequent and catastrophic extreme weather events in China. In the last few decades, the Yangtze-Huai Region (YHR) has experienced a number of regional extreme precipitation events (REPE) that cause serious damage to human society and natural environment. In order to better understand these events, this study identified the weather patterns responsible for REPE using spectral clustering method considering the multi-level and multi-scale characteristics of weather systems, and further investigated the circulation configurations, main formation conditions and water vapor process of REPE based on the daily precipitation data and reanalysis data from 1979 to 2018 in the YHR. The results showed that there were four weather patterns of REPE, namely low vortex shear weather pattern (Pattern 1), extratropical cyclone weather pattern (Pattern 2), surface cold front weather pattern (Pattern 3) and landfalling typhoon weather pattern (Pattern 4). The four patterns showed different features for the intensity, location and coverage of the western Pacific subtropical high and the South Asian high. For the four patterns, vertical upward motion extended from near the surface to 200 hPa, and three types of moist potential vorticity configurations were favorable for the occurrences of REPE over the YHR. Further analysis of water vapor processes showed that the water vapor flowed in via the west and south boundaries in Pattern 1–3 and the east boundary in Pattern 4. And transient water vapor transport played an important role during REPE in comparison to stationary components. Despite differences between these patterns, the precipitation conversion efficiency was significantly higher near the shear line and coastal areas, and the areas of high-value precipitation conversion efficiency did not correspond to the areas of high-value water vapor content, which needs further investigation in the future.