Quantifying natural and anthropogenic impacts on streamflow and sediment load reduction in the upper to middle Yellow River Basin

Study Region: Upper to Middle Yellow River Basin (UMYRB). Study Focus: Climate, land use, and landscape engineering measures are the main drivers affecting watershed hydrology, yet disentangling their respective contributions over large and complex regions is a great challenge. We combine process modeling techniques and hydrological observations to investigate the temporal changes of streamflow and sediment in the UMYRB during 1971-2016 and the imprints of climate change and anthropogenic activities. New hydrological insights for the region: Long-term statistical analysis shows that streamflow and sediment decreased over time across the basin with an increasing magnitude of reduction from upstream to midstream. Streamflow of UMYRB and sediment in the upstream area have decreased by 37.59 % and 71.86 %, respectively, since their change-point years. Analytical modeling results in the UMYRB demonstrate that 77.30 % of the streamflow reduction was attributed to landscape engineering measures, 16 % to climate change and the remaining 6.70 % to land use change. For sediment reduction, landscape engineering measures appeared to be the sole decisive factor for the upstream (over 126 %), while climate and land use changes positively affected sediment yield. Our study highlights the importance of considering the impacts of multiple factors when evaluating hydrological changes in large basins, and the method we adopted can be valuable elsewhere. Developing process-based methods to quantify the hydrological effects of engineering measures is still a research priority moving forward.