Assessment of the Impacts of Rainfall Characteristics and Land Use Pattern on Runoff Accumulation in the Hulu River Basin, China

Climate change causes the river basin water cycle disorders, and rainfall characteristics frequently result in flood disasters. This study aims to simulate and assess the response behavior of basin floods under the influence of rainfall characteristics and land use changes in the Hulu River basin using a 2D hydrological and hydraulic GAST (GPU Accelerated Surface Water Flow and Transport Model). The peak flow rate and water depth during floods were examined by simulating the evolution process of basin floods and related hydraulic elements under the independent effects of various rainfall characteristics or land use and further simulating the response results of basin floods under the combined effects of rainfall characteristics and land use. The seven scenarios were set to quantify the degree of influence that land use and rainfall characteristics have on the basin flood process based on examining changes in land use and rainfall characteristics in the research area. The results from different rainfall characteristics scenarios depicted that as the rainfall return period is shorter, the peak flow rate is higher, and the peak flow rate is lower as the return period is prolonged. Under different rainfall characteristics, the peak flow rate in scenario R8 is 41.30%, 40.00%, and 34.51% higher than the uniform distribution of rainfall, while water depth is decreased by 0.55%, increased by 4.96% and 2.92% as compared to the uniform distribution of rainfall. While under different land use scenarios, it is observed that the change in land use has increased 2.7% in cultivated land and 1.1% in woodland. In addition, the interactive effect of different rainfall characteristics and land use it can be seen that the scenario with the greatest reduction in flood risk due to rainfall characteristics and land use is RL2-4, representing a 12.55% decrease in peak flow and a 37.69% decrease in peak water depth. In this scenario, the rainfall is heavier in the southeast and northwest regions and lighter in the northeast and southwest regions. The land use type is characterized by reforestation and the return of cultivated land to forests. The changes in rainfall distribution and the increase in grassland contribute to the decrease in flood threat. Future research in the erodible parts of the Hulu River basin, planning for water resources, and soil and water conservation can all benefit from the study's conclusions.