South China is one of the most active regions of warm-season convection in East Asia, where heavy rainfall events are frequently observed during the post-flood season. In this period, precipitation is not only influenced by tropical cyclones, but also by a substantial number of non-typhoon mesoscale convective systems (MCSs), which can independently produce short-duration intense rainfall and associated flooding. Motivated by the important role of these systems in regional hydroclimate, this study focuses on the spatiotemporal characteristics and synoptic-scale environments of non-typhoon MCSs over South China during the post-flood season. 
Using a high-resolution gridded radar dataset and multi-source observational data, 123 non-typhoon MCSs from 2019 to 2022 are identified and analyzed. Results show that MCS activity is preferentially distributed over southern Guangxi and the Pearl River Delta (PRD), but the two regions exhibit distinct diurnal and environmental features. MCSs over southern Guangxi mainly occur from midnight to early morning and are associated with stronger southwesterly moisture transport, enhanced low-level convergence, deeper upward motion, and stronger moisture flux convergence. In contrast, MCSs over the PRD mainly occur from afternoon to evening and are characterized by weaker large-scale southwesterly flow, more localized convergence and ascent, locally enhanced convective instability, and smaller convective inhibition. The South Asian High and the western North Pacific subtropical high provide a favorable large-scale circulation background for moisture transport and convective development.
These results indicate that post-flood-season non-typhoon MCSs over South China exhibit marked regional dependence in both occurrence characteristics and environmental controls. The study provides observational evidence for understanding regional MCS development in coastal monsoon regions and offers a useful reference for warm-season heavy-rainfall forecasting.