Analysis of impact of human activities on stream flow and sediment discharge from Hekouzhen to Huayuankou in middle reaches of Yellow River

The runoff and sediment changes in the middle reaches of the Yellow River and the driving factors are the attention focus of the community. They are also an important basis for evaluation of ecological construction and ecosystem restoration on the Loess Plateau. The objectives of this work are to quantify the change trends of precipitation,streamflow and sediment discharge during 1950- 2008 and to statistically identify the change points or transition years in the changing trends. The results show that significant decreasing trends in the annual runoff and annual sediment discharge existed in the middle reaches of the Yellow River( P =0. 01). Change-point analyses further reveal that transition years existed and that abrupt decline in the runoff and sediment discharge began in 1985 and 1981 in this region( P = 0. 01),respectively. Double-mass curves of precipitation vs. runoff(sediment load) in the periods before and after the transition year show remarkable decreases in proportionality of runoff( sediment load) generation. Comparing with the period before the transition year,the cumulative runoff and cumulative sediment discharge reduced 17. 8% and 28%,respectively.Human activities contributed 70% of runoff reduction and 80% of sediment reduction. It is,therefore,concluded that the human activities played a major role in the runoff and sediment discharge reduction in the middle reaches of the Yellow River.