Multi-scale characteristics and synoptic pattern configuration of summer short-duration heavy rainfall in the Sichuan Basin

The Sichuan Basin is a key strategic area for promoting development in western China. During summer, short-duration heavy rainfall (SDHR) frequently triggers flood disasters in this region. This study analyzes the multi-scale characteristics of SDHR in the Sichuan Basin using hourly station precipitation data from 1980 to 2024. A spectral clustering method is applied to classify the dominant synoptic circulation patterns. And the correlation between the frequency of SDHR and local topographic factors under different synoptic patterns is also studied. The results are as follows. (1) Summer SDHR in the Sichuan Basin is primarily concentrated in the western part. In the western basin, SDHR peaks around 02:00 BT, while in the eastern basin, it peaks around 05:00 BT. On the sub-seasonal scale, most SDHR events occur in August, mainly over the western basin. Over the past 44 years, the frequency of summer SDHR shows a non-significant increasing trend. (2) Approximately 52.8% of summer SDHR events are associated with a synoptic pattern. This pattern features a northward-displaced South Asia High and western Pacific Subtropical High relative to the climatological mean, coupled with southerly moisture transport, and the local vertical velocity is the key dynamic factor. Under this pattern, SDHR is concentrated in the southwestern basin, occurs mainly from July to August, and shows a non-significant decreasing trend in frequency over the past 44 years. The occurrence of SDHR under this pattern is primarily related to the magnitude of the northerly wind component in the southwestern basin. (3) Another synoptic pattern controls 47.2% of summer SDHR events. It is characterized by a southward-displaced South Asia High and western Pacific Subtropical High relative to climatology, accompanied by southwesterly moisture transport, and the local divergence is the key dynamic factor. Under this pattern, SDHR occurs mainly on the southwestern basin edge, is concentrated in June, shows a non-significant increasing trend in frequency, and is mainly associated with the magnitude of the southerly wind component in the northwestern basin. SDHR under both synoptic patterns is negatively correlated with local altitude. The research results can provide important theoretical basis and weather classification reference for the extension period forecast and refined disaster risk early warning of short-term heavy precipitation in the Sichuan Basin.