Global warming has caused changes in the spatial and temporal distribution of water resources and affected the water environment. Land use change is mainly influenced by human activities, which is also one of the reasons for the water environment problems have become increasingly serious. The Yongding River basin is important water connotation area and ecological barrier in Beijing-Tianjin-Hebei region in China. The basin has been affected by human activities and climate change, there are problems such as significant reduction in runoff and serious water pollution. To study the effects of climate change and land use on runoff and water quality, this paper simulates runoff and water quality by the Hydrological Simulation Program FORTRAN(HSPF) model, then studied the changes of runoff and water quality under different land use and climate scenarios. The results show that: the HSPF model has good applicability in the Yongding River basin, the Relative Error (Re) of runoff and water quality simulation is within 10%, the Nash Coefficient (NSE) and Correlation Coefficient (R) are above 0.6. The simulation results of different land use scenarios show that the expansion of construction land has a facilitating effect on runoff and also leads to the increase of pollutant concentrations in river; forest and grassland inhibit the generation of runoff, while having a purifying effect on water quality. The simulation results of different climate scenarios show that the rainfall rising has a positive effect on runoff generation and water quality improvement and the temperature rising has a negative effect on runoff generation and water quality improvement. At the same time, the “evaporation paradox” also affects the runoff change. In the integrated scenario, simulation results show that the land use and climate change influence the changes in runoff and water quality, but the influence mechanism is not a simple superposition.

Since the Eastern Route of the South-to-North Water Diversion Project (SNWD-ERP) officially began operation, it was found that the concentrations of sulfate rapidly increased after water transfer from Jiangsu Province to Shandong Province, especially in Nansi Lake (NSL). The direct and original sources of sulfate in NSL and its surrounding inflowing rivers were investigated by analyzing the hydrochemical properties of the water bodies and sulfur and oxygen isotope compositions of dissolved sulfate during nondiversion and diversion water periods. During the diversion water period, the largest direct source of high SO42- concentrations in NSL was evaporite dissolution, accounting for 52.18% of the total contribution. In contrast, during the nondiversion water period, the maximum contribution of SO42- came from inflowing river inputs. To ensure the safety of the water supply of the SNWD-ERP, some measures must be taken to decrease the sulfate inputs from inflowing rivers, such as formulating strict discharge standards to reduce the direct discharge of sewage into the inflowing rivers around NSL.