Water And Sediment Evolution And Its Influencing Factors In The Huangfuchuan Basin Under Changing Environment

Under the influence of climate and human activities,the runoff and sediment load decrease sharply in the Yellow River(YR).Therefore,the study of water and sediment evolution and its influencing factors can help to grasp the time-varying characteristics of water and sediment and provide corresponding basis for the utilization of water and sediment in the basin.In this article,we investigated the Huangfuchuan basin,which located in main sediment yield area of the YR.The evolution of water and sediment under the changing situation and the mutual feedback mechanism of the meteorological-ecological-hydrological coupled system are analyzed based on the measured water and sediment data,meteorological data,ecological governance data.The main results of this study were:(1)The stationarity of the hydrological elements in the whole period(1954-2015)were destroyed under the influence of climate and human activities,1979 can be used to divide the base period(1954-1979)and variable period(1980-2015)in Huangfuchuan basin.(2)The analysis of the trend and periodicity of the annual hydrological sequence in the whole period,the base period and the changing period show,the runoff and sediment load in both entire period and variable periods showed a significant decreasing trend(p<0.001),the periodicity of runoff and sediment load is more consistent,and the cycle time of precipitation only coincides with the cycle time of runoff and sediment load when the time scale is small.(3)This paper quantifies the variation characteristics of hydrological elements in different time scales in different periods.The results show,the distribution of annual hydrological elements in the change period is lower than that in the base period,the discrete degree of sediment load in each period is greater than that of runoff than that of precipitation.The frequency of positive anomalies in precipitation in flood season during two periods were equal,while the frequency of positive anomalies in both runoff and sediment load decreased.The distribution during the year of runoff and sediment load are more concentrated overtime,while the precipitation is more stable.The concentrated period of precipitation,runoff and sediment load in the changing period were 6,3 and 4 days earlier than that in the base period(4)Based on the joint distribution model of runoff and sediment load,the occurrence probabilities of different rich and drought scenarios in the base period and the changing period are calculated.The results show that the combined scenarios of runoff and sediment load in the basin are mainly composed of water and sediment synchronization,which theoretical probability is 57.4%and 69.5%respectively in the base period and the changing period.Under the influence of climate and human activities,the synergetic relationship between water and sand in the changing period was stronger than that in the base period,with the theoretical probability of water and sediment synchronization in the base period is higher 12.1%than that in the changing period(5)The research analyzed two influential factors like climate and human activities of water and sediment in the basin,the typical period of water and sediment data of the basin was selected by combining with the data of human activities,then the correlation between the climate and runoff,the management measures and runoff,the climate and sediment load,the management measures and sediment load in the typical period were analyzed.The results showed the climate was warm and wet climate,cold and dry climate and warm and dry climate in whole period,the base period,the weak change period and the strong change period respectively,the overall trend of precipitation is not significantly reduced.Coupled with various factors,especially after the 1980s,under the influence of multiple factors such as the rapid growth of terraces,main check dams,and forest and grass construction,the water storage and sand fixation capacity of the watershed increased,resulting in a significant decrease in runoff and sediment transport,which in turn led to the correlation between precipitation and runoff gradually decreases,and this decrease also exists in the correlation between precipitation and sediment load.