Analysis And Forecast Of Runoff-Sediment Variation In The Lower Yellow River Under The Changing Environment

The Yellow River is the mother river of the Chinese nation,and it plays an important role in the development of economic and social and the promotion of traditional culture.The lower Yellow River occupies an important position in the major national strategy of the Yellow River.In recent years,construction of water conservancy projects in main and tributaries,implementation of soil and water conservation measures,development of irrigation project from the Yellow River and other human activities has partly changed runoff-sediment characteristics.Therefore,it is necessary to study the anaylsis on runoff-sediment variation characteristics and forecast in the lower Yellow River under the changing environment.Based on the data of annual runoff and sediment yield from four hydrological stations of Huayuankou,Gaocun,Aishan and Lijin in the lower Yellow River from 1960 to 2016,the runoff-sediment variation characteristics in the lower Yellow River are synthetically analyzed by using multiple mathematical statistics methods.Firstly,then the rich-poor status and variation feature of annual runoff and sediment yield in the lower Yellow River was analyzed using the Markov method.Secondly,empirical mode decomposition and set pair analysis are used to analyze the structure of runoff-sediment relationship in different time scales.Then the variation characteristics of annual runoff and sediment yield in the lower Yellow River was analyzed using double mass curve method and moving correlation coefficient method.Next The variation of rich-poor encountering between annual runoff and sediment yield in the lower Yellow River under the changing environment was analyzed using copula functions.Finally,the error correction model based on cointegration theory was used to forecast annual sediment yield under the changing environment in the lower Yellow River.Results show that:During the study period,three fluctuation periods for annual runoff and sediment series in the Lower Yellow River were existed,and their residual functions are reduced significantly.The probability of rich-poor asynchronism of annual runoff with sediment yield increased gradually in longer fluctuation period.The lower the reach location,the smaller the asynchronism probability is.During the long-term variation of water and sediment yield,the probability of normal runoff and normal sediment yield is the highest.The relationship between runoff and sediment yield of Huayuankou,Gaocun and Aishan stations changed significantly around 1997,and that of Lijin station changed significantly around 2003.The sums of synchronous coincidence probabilities for annual runoff and sediment yield were bigger than the sums of asynchronous coincidence probabilities at Huayuankou,Gaocun and Aishan stations in the period before changing years.The sums of synchronous coincidence probabilities were less than the sums of asynchronous coincidence probabilities at Huayuankou and Gaocun stations in the period after changing years,while the sums of synchronous coincidence probabilities were still bigger than the sums of asynchronous coincidence probabilities at Aishan station.The sums of synchronous coincidence probabilities were always much bigger than the sums of asynchronous coincidence probabilities at Lijin station during the whole study period.The variable structure cointegration relationship exists between the annual runoff and sediment yield of the lower Yellow River.The variable structure error correction model is suitable in sediment yiled forecasting,and the simulation error are all less than 20%.The overall prediction effect is good.