| In recent years, influenced by climate change and human activities, the flash flood triggered by extreme rainfall in mountainous area have occurred more frequently. Characterized by sudden onset and high destructive potential, these events pose significant challenges to China’s disaster prevention and mitigation. This study employs the spatiotemporal variable-source distributed hydrological model (SKY-HydroSAT), independently developed by the China Institute of Water Resources and Hydropower Research, to establish a distributed hydrological model considering reservoir regulation in the upper catchment of the Guilin City in the Lijiang River Basin. The model demonstrates good applicability, with absolute peak flow errors of 3.7% and 5.4% during the calibration and validation periods, respectively, and Nash-Sutcliffe efficiency (NSE) values of 0.87 and 0.83. Taking the "6·19" extreme flash flood event in 2024 as a case study, with the accurate modelling results (peak flow error 10.5%, NSE 0.94), the research investigates flood dynamics under reservoir influence. The analysis reveals that this event was triggered by a bimodal heavy rainfall pattern, with a three-day average rainfall of 442 mm across the watershed above Guilin and a maximum cumulative rainfall of 777 mm at Maolingjiao Station. Simulation results indicate the formation of combined infiltration-excess and saturation-excess runoff mechanisms, along with subsurface stormflow in major runoff-producing areas, leading to rapid runoff generation and posing severe challenges to midstream reservoirs and downstream flood safety. The coordinated regulation of 4 upstream reservoirs played a critical role in flood mitigation. Without regulation, the peak discharge at Guilin would have exceeded a 100-year return period event. After reservoir regulation, the peak flow was reduced to 6380 m3/s (approximately 30-year return period), significantly lowering downstream disaster losses. This study validates the applicability of the hydrological modeling approach in the Guilin region, demonstrating its capability to accurately characterize watershed runoff mechanisms and quantify the benefits of hydraulic engineering regulation. The proposed approach holds potential for extension to other mountainous area in China, providing scientific support for regional flood management decision-making. |