Spatiotemporal variations of runoff and sediment flux in the Source Region of the Yellow River: Driving factor shifts and sub-regional attribution

With global climate change and intensifying human activities, the Source Region of the Yellow River (SRYR), as a critical water conservation zone of the Yellow River Basin, is crucial for water resource management and integrated upstream reservoir regulation. Nevertheless, the current understanding of the spatiotemporal variations is incomplete, particularly regarding the sub-regional attribution of climatic and non-climatic factors. Using runoff and sediment flux data from four hydrological stations in the SRYR from 1955 to 2021, combined with precipitation, evaporation, and land use data from 1970 to 2020, this study integrated the Mann-Kendall trend analysis, double mass curve method, and climate elasticity model to analyze the spatiotemporal evolution of runoff and sediment flux, and quantified the contribution rates of precipitation, evaporation, and non-climatic factors across different sub-regions. The results reveal that runoff exhibited no significant long-term trend but decreased by 8.5% since 1991, whereas sediment flux consistently declined. The downstream Maqu-Tangnaihai sub-region was the key sediment yield area (contributing 63.25%). Precipitation and evaporation increased significantly (Z = 3.90-6.77, p < 0.01) with distinct spatial heterogeneity: precipitation rose most in the Maqu-Tangnaihai sub-region, while evaporation increased most in the Huangheyan-Jimai sub-region. Runoff and sediment changes were synergistically driven by climatic and non-climatic factors, with the latter becoming dominant. Non-climatic factors contributed over 55.21% to runoff reduction (1970–2020) and accounted for 112.6-149.4% of sediment reduction in 2100.