Study on Critical Rainfall for Flash Flood Disasters in Small Watersheds of the Three Gorges Reservoir Area: A Case Study of Futian Small Watershed in Wushan County of Chongqing

Abstract. Taking the Futian Small Watershed in Wushan, within the Three Gorges Reservoir area, as the research object, this study utilized hourly rainfall data from 2010 to 2023 collected at the Futian Small Watershed and nearby rainfall stations, historical disaster information on mountain flood disaster processes, digital elevation models, land use data, and other relevant information. Statistical analysis methods such as the single-station critical rainfall method, regional critical rainfall method, probability distribution method, and the hydrodynamic model FloodArea, were employed to simulate and calculate the critical rainfall amounts leading to disasters. Results indicate that the trends of critical rainfall amounts leading to disasters calculated by various methods are generally consistent. However, at different time scales, the critical rainfall amounts calculated by different methods exhibit variations. The FloodArea simulation yields the smallest critical rainfall amounts for 1-hour, 2-hour, 24-hour durations; the single-station critical rainfall method provides the smallest values for 5-hour, 6-hour, and 12-hour durations; the regional critical rainfall method gives the smallest results for 3-hour, 4-hour durations. Statistical methods can swiftly and efficiently establish critical rainfall amounts leading to disasters at different time scales, the FloodArea model can more precisely depict the precipitation-runoff processes of mountain flood disasters. Therefore, by integrating statistical methods with hydrological model simulations to leverage their respective strengths, we can more accurately determine the critical rainfall amounts leading to mountain flood disasters.