Spatial And Temporal Distribution Of Water And Sediment Changes In The Yanhe River Basin And Its Response To Land Use Changes

With the intensification of climate change and human activities,the runoff and sediment in yanhe river basin have undergone profound changes.Taking the yanhe river basin as the research object,this paper analyzes the rainfall,runoff,sediment change rules,land use change and driving factors of the yanhe river basin based on the hydrological and sediment data from 1952 to 2015 and the six remote sensing images of 1985,1995,2000,2005,2010and 2015.On this basis,the Regional Soil and Water Loss Model was used to simulate the process of soil and water loss in typical years(1985,1995,2000,2005,2010,2015),and analyze the spatial and temporal distribution characteristics of runoff and sediment and the response to land use change in yanhe river basin from 1985 to 2015.The research results can provide some theoretical support for the analysis of the causes of the decrease of water and sand in yanhe river basin,and also provide theoretical basis for the planning of land use,the treatment of soil erosion and the rational allocation of water and soil resources in the basin.The main research results are as follows:(1)The analysis of the variation characteristics of water and sediment in yanhe river basin shows that the rainfall,runoff and sediment transport in yanhe river basin from 1952 to2015 all show a decreasing trend,and the decreasing trend of sediment transport is more significant than that of runoff.The abrupt changes of runoff and sediment transport occurred in 1971 and 1996.The decrease of runoff and sediment transport was mainly caused by rainfall and human activities.During 1952-1971 and 1971-2015,the impact of rainfall on runoff was 55.28%and 14.45%respectively,and the impact of rainfall on sediment was14.35%and 3.91%respectively.The influence of human activities on runoff was 44.72%and85.65%,and the influence of human activities on sediment was 44.72%and 96.09%,respectively.Therefore,human activities have become the most important factor affecting the reduction of water and sediment in yanhe river basin,and the effect on the reduction of sediment is greater than the effect on the reduction of water in the basin.(2)In the yanhe river basin from 1985 to 2015,the proportion of cultivated land in the basin area decreased by 50.77%,the forest area increased by 217.14%,and the grassland area decreased by 13.26%.The conversion rate of cultivated land,woodland and grassland was ranked as follows:farmland>grassland>woodland,the area of farmland transferred to grassland was larger than that transferred to woodland,and the increase of woodland area mainly came from grassland.The direct driving force of land use change in river basin is the implementation of ecological restoration and governance policies,and the development of industrial mineralization,urbanization and adjustment of industrial structure are the most important driving forces of land use change.(3)Using the simulation results show that the regional soil erosion model in spatial scales,yan spatial distribution characteristics of watershed runoff and sediment discharge,have rivers and valleys,the characteristics of small slope,valley slope is the main source of river aquatic sand production area,where the valleys and steep slope runoff and sediment is bigger.From 1985 to 2015,the spatial variation of runoff and sediment transport in yanhe river basin was significantly different.On the time scale,the runoff and sediment transport volume in yanhe river basin from 1985 to 2015 showed a downward trend,with the total runoff volume and sediment transport volume decreasing by 52.20%and 75.00%respectively,indicating that the change of sediment transport volume was greater than the change of runoff.From 1985 to 2015,the soil erosion degree in the basin changed from severe erosion to micro erosion.(4)The response analysis of runoff and sediment change to land use change in yanhe river basin shows that during 1985-1995,the cultivated land area decreased by 2.97%,the forestland and grassland area increased by 2.58%and 1.42%respectively,and the runoff and sediment transport volume in the basin decreased by a small amount.From 1995 to 2000,the cultivated area decreased by 20.61%,the forestland area increased by 126.22%,the runoff decreased by 15.04%,and the sediment transport decreased by 12.50%.From 2000 to 2005,the forestland area increased by 356km~2,while the grassland area decreased by 364km~2,the cultivated land area decreased by 49km~2,the runoff increased by 10.34%,and the sediment transport increased by 21.43%.From 2005 to 2010,cultivated land decreased by 29.43%,forest area increased by 71.23%,runoff decreased by 35.34%,and sediment transport decreased by 43.01%.From 2010 to 2015,a large amount of cultivated land was transferred to grassland,with an obvious increase in residential land,an increase in runoff and a decrease in sediment transport.Therefore,the measures of returning farmland to forest(grass)and the soil and water conservation and control project in yanhe river basin are effective.