Impact of climate variability and human activity on streamflow decrease in the Miyun Reservoir catchment
Introduction
Streamflow of the Hai River basin in North China has dramatically decreased since the 1980s. The annual river discharge of Hai River over the period from 1980 to 2000 has been evidently lower than that from 1956 to 1979 (Ren et al., 2007). The stage of Miyun Reservoir (the largest reservoir in North China which serves as the main surface water supply for Beijing) has approached the dead water level during the last 20 years. The drainage area of Miyun Reservoir, a major part of the Chaobai River basin, is a sub-basin of the Hai River. Historical data showed that inflow into the Miyun Reservoir has decreased significantly from 1956 to 2005. It has been speculated that the decrease in inflow is attributable to the impacts of climate variability and human activity. The authors strive to evaluate quantitatively these impacts as a first step towards improving the management of water resources in Chaobai River catchment and Miyun Reservoir.
To date, a number of studies had reported decreasing trends of river discharge from the Yellow River (Yang et al., 2004, Zhang et al., 2009) and Yangtze River (Xu et al., 2008). Analysis of the impact of human activity and climate variations on changes in flow discharge had also been reported (Cong et al., 2009, Zheng et al., 2009, Ma et al., 2008). The methodologies used in these studies include the distributed hydrological model, the Budyko water balance model (Budyko, 1974), Fu’s water balance model (Fu, 1981), and the climate elasticity of streamflow (Schaake, 1990, Sankarasubramanian et al., 2001, Fu et al., 2007), among others. Ren et al. (2002) studied the impacts of human activity on river runoff in northern China by analyzing the amount of water stored in reservoirs and water intake from rivers, and showed that the impact of human activity on river discharge was more significant in arid or semi-arid areas than that in more humid areas. Other studies reported on the impact of groundwater pumping and return flow on river flow (Wang and Cai, 2009); impact of change in land use on storm-runoff generation (Niehoff et al., 2002); and impact of forest change on the summer streamflow in four experimental catchments (Iroumé et al., 2005). Specific to Miyun Reservoir and the catchment, there were studies on changes in hydrology and water resources (Sun et al., 2008, Pang, 2007), and impacts of climate variations and human activities on the runoff in Chaobai River basin (Wang et al., 2009).
This paper aims to estimate quantitatively the contribution of climate variability and human activity to the decrease of inflow into Miyun Reservoir from 1956 to 2005, based on selected technique of data analysis, as well as the distributed hydrological model and climate elasticity model. The findings of these analyses provide inter-comparison of water resources impact studies vis-à-vis climate variability and human activity.
Section snippets
Catchment and human activity in the study area
The Miyun Reservoir, built in 1960, is about 100 km north of Beijing. The total storage capacity is about 4.4 billion m3. It is located at the junction of the Chao River and the Bai River (Fig. 1). The drainage area is about 15,800 km2, occupying nearly 88% of the Chaobai River basin area. The drainage areas of Chao River and Bai River are 6700 km2 and 9100 km2, respectively.
There are three major reservoirs upstream of the Miyun Reservoir, as shown in Fig. 1. These reservoirs supply irrigation needs
Basic hypothesis
In this paper, climate variability refers primarily to the variation in precipitation and air temperature. The impact of human activity on the inflow into the Miyun Reservoir includes both direct and indirect impact. Direct impact refers to the water consumption in the upstream of Miyun Reservoir, and indirect impact refers to the effect of man-made changes in land use and vegetation covers. Based on Fig. 4, it is clear that the “direct abstraction of water” from upstream of the Miyun Reservoir
Data analysis and direct impact of human activity
In this study, Mann–Kendall nonparametric test (Maidment et al., 1993) and trend-free pre-whitening (TFPW) (Yue and Wang, 2002) were adopted to determine the significance of the trends in annual inflow, precipitation, and mean temperature. Inflow into Miyun Reservoir from 1956 to 2005 depicted a decreasing trend (by 0.36 × 108 m3/a, or 2.28 mm/a) at the 5% significant level (Fig. 2). The annual precipitation of the Miyun Reservoir catchment showed a decreasing trend (by 1.97 mm/a) at the 10%
Conclusion
Decrease in the discharge in many rivers in China has been reported in recent years, and that of the Miyun Reservoir catchment is but one of the most serious cases. This study attempts to quantify the impact of climate variation and human activity on the decrease of inflow into Miyun Reservoir, whereupon the direct impact of human activity is attributable to significant amount of water abstracted upstream of the Miyun Reservoir and indirect impact of man-made changes in land use, vegetation,
Acknowledgments
This research project was supported by the Ministry of Water Resources (Project No. 200801012) and the National Key Technology R&D Program (Project No. 2006BAB14B02-01) of China. Parts of the manuscript had been prepared by the lead author during her attachment at the DHI-NTU Centre, Nanyang Technological University, Singapore in 2008-2009, under China Scholarship Council (CSC) scholarship. Supports from all the parties are gratefully acknowledged.
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