Drivers of drying on the Yongding River in Beijing

Summary. In recent decades, the Yongding River in Beijing has ceased to flow due to the impact of climate and anthropogenic factors, which has led to severe environmental degradation. The Beijing government is constructing new freshwater ecosystems on the Yongding River to improve environmental conditions for ecosystem services. Clarification is needed on the influence of precipitation and anthropogenic factors on streamflow decline in Beijing. A hydrological time-series analysis was conducted on recorded streamflow at Guanting Reservoir, Yanchi, and Sanjiadian to estimate the influence of precipitation variability on the drying of the Yongding River in Beijing. From 1980 to 2010, the mean annual rates of streamflow decline were 0.44 m³ s^-1 yr^-1 (Guanting), 0.42 m³ s^-1 yr^-1 (Yanchi), and 0.03 m³ s^-1 yr^-1 (Sanjiadian). The most probable abrupt change-point for annual streamflow was 1999 at Guanting Reservoir and Yanchi, and was 2000 at Sanjiadian. Between the pre-change (1980-1999) and post-change (2000-2010) periods, mean annual streamflow decreased by 68.56% (Guanting), 66.92% (Yanchi), and 96.78% (Sanjiadian). A multiple regression analysis using annual precipitation and streamflow at Guanting, Yanchi, and Sanjiadian showed an insignificant relationship between local precipitation and streamflow in both periods. Next we assessed the potential impact of upstream human activities on downstream flow using: (1) correlation statistics between upstream flow and downstream flow, (2) water abstracted above Sanjiadian, and (3) upstream socioeconomic data. The results suggest upstream human activities are important drivers on downstream flow decline, which could possibly explain the weak relationship between precipitation and streamflow. Further analysis is needed to clarify the influence of upstream water consumption on Guanting Reservoir to advise management on the new freshwater ecosystems along the Yongding River.