Simulated Investigation on the Impact of Spatial–temporal Variability of Rainstorms on Flash Flood Discharge Process in Small Watershed

With the spatial–temporal variability of rainstorms becoming more diversified, it is urgent to summarize how the spatial–temporal variability of rainstorm affects the flash flood discharge process and to explore its internal mechanism. This work proposes a research framework based on the rainstorm spatial–temporal structure design method and the quantitative analysis of flash flood discharge process modeling. This framework generates rainstorm data with different spatial–temporal variability through the rainstorm spatial–temporal structure design method, and further simulates discharge process under different rainstorm scenarios through the hydrodynamic model. Based on the analysis of simulated results, the error correction coefficient is generated to improve the accuracy of simulation. In this study, the Baogaisi watershed was used for simulation. The results show that when the rainstorm center is at the upstream watershed, the peak discharge increases, and the flood peak time is advanced because of the transformation of gravitational potential energy into kinetic energy. When the rainstorm center is fixed at a position, the total flood volume and the peak discharge are about 2 ~ 10 times that of uniform spatial distributed scenario, the flood peak time can be advanced to 55 min. In the mobile rainstorm, the peak discharge and the total flood volume are significantly reduced and the flood peak time is lagged, the flood peak discharge can be reduced by up to 30% of the uniform spatial distributed scenario. Strengthening the understanding of the impact can help to improve the accuracy of discharge process simulation.