Attribution Of Water And Sediment Regime Change And Its Response To Land Use In The Middle And Lower Reaches Of The Yellow River

The rapid social and economic development further intensifies human activities in the Yellow River Basin,leading to significant changes in the water and sediment situation in the basin,the intensification of land use transformation,and the gradual deepening of ecological landscape fragmentation,resulting in a series of prominent problems.Therefore,exploring the law of water and sediment evolution and its attribution,and analyzing its response to land use landscape pattern in the Yellow River Basin not only has important theoretical significance for achieving sustainable and high-quality development of water resources in the Yellow River basin,but also provides an important scientific basis for adjusting land use allocation and regulating river water-sediment relationship in the Yellow River basin.This paper mainly takes the middle and lower reaches of the Yellow River basin as the research object,selects the long-term measured water and sediment and meteorological data from 1960 to 2020 at six main control stations at Longmen,Tongguan,Huayuankou,Gaocun,Aishan and Lijin to analyze the spatial-temporal variation characteristics of water and sediment in the middle and lower reaches of the Yellow River basin in recent decades,and conducts quantitative attribution analysis.The contribution degree of each influencing factor to the change of river water and sediment regime was evaluated.On this basis,the land use change and landscape pattern of the Yellow River basin in recent decades were analyzed,and the response relationship between them and the change of river water and sediment was explored.The main contents and results of this study are as follows:(Ⅰ)Study on water and sediment regime evolution in the middle and lower reaches of the Yellow River.The concentration analysis,empirical mode decomposition(EMD)method,TFFPW-MK trend test method and Morlet wavelet period analysis method are used to systematically analyze the evolution law of water and sediment regime.The results show that: on the inter-annual scale,the variation amplitude of runoff in the middle and lower reaches of the Yellow River is small,while the variation amplitude of sediment transport is large,showing an obvious decreasing trend.The abrupt change of runoff was mainly concentrated in the1970 s,1980s and around 2000,while the abrupt change of sediment transport was mainly concentrated in the 1990 s and around 2000.The results of periodic analysis show that the main period of runoff change in the middle and lower reaches of the Yellow River is 4a,and the main period of sediment transport change is 17 a.The relationship between river water and sediment has changed significantly since the construction and operation of large-scale water conservancy projects such as Longyangxia in 1986 and the development of cascaded reservoirs such as Wanjiazhai and Xiaolangdi in the late 1990 s.(Ⅱ)Quantitative attribution of water and sediment change in the middle and lower reaches of the Yellow River.The quantitative attribution analysis of river water and sediment change was carried out by means of cumulative slope change rate method,sediment attribution decomposition method and PSO-BP neural network model.The results show that the change of water and sediment in the middle and lower reaches of the Yellow River basin is mainly influenced by human activities,and the influence is continuously strengthened.The relative contribution rate of Xiaolangdi Reservoir to the runoff of each control station is about 66%,while the relative contribution rate of natural factors to the runoff change is about 33%.The sediment transport slope of each hydrographic station in the middle and lower reaches of the Yellow River has obvious changes,and the correlation between sediment transport and precipitation change is not strong.In the second stage of change,the sediment transport quantity of each hydrographic station in the middle and lower reaches of the Yellow River is greatly affected by human activities,and the impact degree is gradually deepened,and the contribution rate is above 90%.(Ⅲ)Response of water and sediment change to land use in the Yellow River Basin.Pearson correlation analysis method and redundancy analysis method were used to analyze the correlation between the percentage of land use types and landscape index and runoff and sediment respectively.The results showed that the main land use types in the Yellow River basin during 1980-2018 were grassland,cultivated land and forest land.Spatially,cultivated land to forest land and other types of land were mainly distributed in the middle and lower reaches of the Yellow River basin.The number and density of patches in the middle and lower reaches of the Yellow River basin increased,the boundary shape became more complicated,the spread degree and connectivity decreased significantly,and the overall fragmentation of landscape pattern increased.Landscape index DIVISION,CONT and LPI have strong correlation with runoff and sediment,and it is believed that land use change leads to landscape pattern change,which indirectly affects the change of water and sediment.