Trends and Causes of Runoff Changes in Mountainous Areas of the Baiyangdian Lake Basin during the Period 1959-2008
白洋淀流域1959年至2008年山区径流量变化规律及其动因分析

Baiyangdian is an important water control of the Daqing river basin, which is critical to flood protection and irrigation. Wetlands of the Baiyangdian Lake basin play a significant role in regulating local climate and maintaining ecological integrity across the Hebei Plain. The average annual discharge of the Baiyangdian Lake basin is 22.3 billon m3 per year and the average runoff depth is 71.5 mm, 75% of which is generated from the mountains area. Therefore, investigating the variation in runoff from the mountainous area of the Baiyangdian Lake basin and unraveling its causes are of significance for water resources management in the basin. In this study, a long-term trend of characteristics and variations of runoff in the basin was examined using runoff data observed at three hydrometric stations, i.e. Fuping, Zhongtangmei, and Zijingguan. Impacts of climate change and human activities on the runoff variation were studied using land use/cover data for five periods, i.e., 1970, 1980, 1990, 2000, and 2008 and historical climate records at the Baoding meteorological station. Discharge trends and abruptions in the Baiyangdian Lake basin were analyzed based on monthly discharge data using the Mann-Kendall statistical method. Major results are 1) annual runoff of the basin remained fairly invariant before the 1970s. A decreasing trend was detected in the annual discharge since the 1990s and the trend was significant, showing an accelerating rate after the 1990s. From then on, it experienced a continuous low-flow period. The environment within the study basin is facing a range of serious problems that may influence the sustainable development of the basin. The problem of water shortage was highlighted more than before. 2) For the entire study period 1959-2008, the coefficient of variation (Cvy) value at each station showed a decreasing trend, implying a decreasing trend in the uneven distribution during the year. 3) Non-uniformity of runoff in the study basin declined markedly during the period 1959-2008. 4) Both increased temperature and decreased precipitation detected from the historical climate data could be contributed in large part to the decreased runoff. It can be inferred that rainfall increased in dry season and decreased in wet season is one of the reason leading to an increased uniformity of the mountainous area of the basin. Meanwhile, expansion of industrial, agricultural, and mining land which may cause the increment of water withdrawal could be another potential cause for decreases in runoff. Furthermore, establishment of water conservancy projects is also a major cause for runoff reduction. In the future, an accurate quantitative assessment of the impact of human activities and climate change on water resources of the Baiyangdian River basin is required.