Trend and causation analysis of runoff variation in the upper reach of Chaobaihe River Basin in northern China during 1961-2005

Based on hydro-data and meteorological data of the upper Chaobaihe River Basin, characteristics and variation tendency of annual runoff during 1961-2005 of the basin were analyzed by time series contrasting method. The impacts of climate changes and human activities on the runoff variation were studied. The causes resulting in runoff variation were revealed. Results show that the interannual distribution of the runoff was extremely uneven and its variety was exquisite. The annual runoff in the basin declined markedly. The mean annual runoff in the 1990s was only 75.8% in proportion to that of the 1960s. The main conclusion is that the precipitation changes and temperature variations were not the main causes leading to the drastic decrease of the annual runoff, and the runoff reduction in the basin was affected greatly by human activities such as water resources utilization, land use, reservoirs construction and inter-basin water transfer.