Investigating climate change impacts on runoff and sediment transport processes in the midstream of the Yarlung Tsangpo river based on hydrological simulation

Runoff and sediment transport are critical concerns for water resource management and ecological security in the Tibetan Plateau. The midstream of the Yarlung Tsangpo River, a central habitat and cultural epicenter, was selected as the study area. Soil and Water Assessment Tool (SWAT), sensitivity analysis and redundancy analysis (RDA) were employed to investigate these processes. Results indicate annual runoff depth is 388.8 mm, with surface runoff, lateral flow, and groundwater components accounting for 47.2 %, 24.4 %, and 28.4 %, respectively. Estimated annual soil erosion, outlet sediment flux, and river channel sediment deposition rates are 7.11 x 108 t, 0.19 x 108 t and 6.92 x 108 t, respectively. Despite increases in runoff and its components, as well as soil erosion, and sediment deposition rates during 1983 to 2017, outlet sediment flux increased initially and decreased after implementation of Zangmu Reservoir in 2010. Soil erosion and sediment deposition exhibited significant spatial variations, with both being obviously higher in downstream areas compared to upstream regions. RDA reveals that precipitation was the primary factor explaining the variabilities in both runoff and sediment transport. In addition, the unfrozen area ratio influenced these processes by enhancing soil permeability and evaporation, thereby reducing runoff and sediment-carrying capacity. In contrast, glacier melt enhanced both runoff and sediment transport, with runoff and sediment flux sensitivity to temperature shifting from negative to positive as glacier area ratio increases. These findings provide valuable insights into the hydrological and sediment transport mechanisms in high mountain areas, offering a scientific foundation for integrated soil and water conservation strategies.