LUCC and its impact on run-off yield in the Bai River catchment-upstream of the Miyun Reservoir basin

The Miyun Reservoir is the most important drinking water source for Beijing-the capital of China with a population of more than 16 million. Since the 1980s, the inflow to the reservoir has been decreasing, which seriously threatens the security of water use in Beijing. Our goal was to analyze the impact of land use and cover change (LUCC) on run-off yield in the upstream of the Miyun Reservoir. In this study, the Soil andWater Assessment Tool (SWAT) was used to simulate the impacts of LUCC on the run-off yield in the Bai River catchment-upstream of the Miyun Reservoir basin in northern China. The investigation was conducted using two 6-year historical streamflow records: from 1986 to 1991 and from 2000 to 2005. A split sample procedure was used for model calibration and validation. The data from 1986 to 1988 and from 2000 to 2002 were used for calibration, while those from 1989 to 1991 and from 2003 to 2005 for validation. The SWAT calibration was based on monthly measured discharge at Zhangjiafen station at the catchment outlet from Bai River catchment. Additionally, the influence of LUCC on the surface run-off was distinguished from that of climate change on the surface runoff through SWAT scenarios modeling, the two-way analysis of variance (ANOVA), and the rainfall-run-off double-mass analysis in the Bai River catchment. We found that the SWAT model could be used successfully to accurately simulate run-off yield and different LUCC patterns affecting water quantity in this catchment. During calibraion for the two periods the simulated monthly run-off satisfactorily matched the observed values, with the Nash-Sutcliffe coefficient > 0.9 and 0.7 and a coefficient of determination of 0.9 and 0.65 at the outlet station (Zhangjiafen station), while during validation for the two periods the obtained values were 0.85, 0.65 and 0.9, 0.65, respectively. During the period of 1986-91, both the SWAT scenarios modeling and the analysis of the two-way ANOVA method showed that LUCC and climate change had some impact on run-off, and the impact of climate change was more significant than that of LUCC. Compared with the period during 1986-91, the run-off yield in the period during 2000-05 significantly decreased. The obtained results from the rainfall-run-off double-mass analysis indicate that since 1998 LUCC has had an increasing influence on the run-off, while the response of the run-off to rainfall has been decreasing. Since 1998, the LUCC has been a major driving force for run-off change in Bai River catchment.