Variation of Runoff and Sediment and Their Driving Factors of the Yellow River Mainstream in the Past 60 Years

Based on the time series data of runoff and sediment from 4 hydrological control sections including Toudaoguai,Tongguan,Huayuankou and Lijin,the variations of runoff and sediment of the Yellow River and their major driving factors from 1952 to 2011were analyzed quantitatively.Some conclusions were as follows:1)Both runoff and sediment showed apparently decreasing trends in the past 60 years,and the trends would continue for some time to come.There existed rich-poor transitions of runoff in all sections in 1968 and 1985,while different transitions of sediment happened at all sections except for the upstream one.The annual runoff variation of Tongguan and Huayuankou sections showed mutations in the later 1980s,the sediment discharge of all sections,otherwise,appeared mutations during 1985-1998.2)For the relationship between runoff and sediment,mutations emerged in 1968 and 1989 at Toudaoguai section,in 1979 and 1999 at Tongguan and Huayuankou sections,and in 1999 at Lijin section.3)Both of the runoff and sediment presented multi-scale periodic changes.The cycles of runoff were mainly about 3,9,25 years,and the cycles of sediment were mainly about 3~4 years and 9 years.Also,there were strong periodical responses existed between runoff and sediment and along the entire stream.4)The variation of runoff and sediment in the upper Yellow River was mainly driven by climate change,also by hydraulicprojects and water intake and consumption.Factors in the midstream could be mainly ascribed to soil erosion,hydraulic measures and soil and water conservation.In addition to the strong response to the variation of runoff and sediment in the upper and middle reaches of the Yellow River,factors of the lower reaches also included water intake and consumption.