Analysis of the runoff variation of the Yellow River to the sea and its influencing factors

The runoff of the Yellow River to the sea is an important component of water cycle,which involves the entire basin,and its temporal and spatial changes are comprehensive reflection of climate and human activities in the basin.Based on the measured runoff data(1963-2009) from the Lijin hydrographic station at the Yellow River estuary,the evolutionary characteristics of runoff into the sea in the past 50 years were analyzed using stochastic hydrology methods.Combining average monthly precipitation and temperature data obtained from 78 weather stations in seven runoff source areas and water withdrawal and water conservancy projects,we explored the influence of climate change and human activities in different runoff source areas on the runoff to the sea. The measured runoff to the sea showed a significant decreasing trend in the evolution of the past 50 years,and four hopping points were identified in the runoff sequence,and the natural runoff to the sea saw the same trend and had only one hopping point.The precipitation in the region above Tangnaihai,the temperature in Lanzhou-Longmen region and the precipitation and temperature in Longmen-Sanmenxia region were a principal factor affecting the change of natural runoff to the sea.Seasonal climatic factors had also influence on runoff to the sea,and summer precipitation and winter temperature were the important factors.The impact of human activities on runoff into the sea continued to increase after the 1970s.Different runoff source areas showed significant differences in water consumption,soil conservation and water conservancy projects.The contribution rates of different influencing factors to the measured runoff into the sea were different,and those of the water withdrawal,precipitation and temperature were 42.2%,39.2%,and 18.6%,respectively.