Effects of climate and land use changes on stream flow and sediment yield in Chaohe river basin

To explore the effects of climate and land use changes on water and sediment yield at multiple temporal scales in the watershed, the non-parametric Mann-Kendall test was used to identify the change trend and change points of annual precipitation, annual potential evapotranspiration (PET) and annual streamflow from 1961 to 2009 in the Chaohe watershed located in the upstream of Miyun Reservoir, Beijing, China. Water balance model was used to quantify the respective contribution of land use and climate changes to annual streamflow. Double mass cure was used to examine their effects on sediment yield reduction. The results indicated that there were no significant changes in annual precipitation and PET from 1961 to 2009. In contrast, the annual streamflow was significantly decreased from 1961 to 2009 with the change points occurred in 1999. Annual sediment yield significantly declined and the change point occurred in 2004. The land use/cover changes contributed 56.1% reduction in mean annual streamflow, while the rest was caused by climate variability. Land use changes contributed 98.05% of reduction for the declining of sediment yield. Land use changes were the main factor for the reduction of water resources and sediment yield. Developing the reasonable land use scenario for utilizing the water and soil resources, implementing the ecological restoration programs were the basic approaches for the adaptive watershed management strategies.