Effects Of Land Use Change On Runoff And Sediment In The Xujiang River Basin Based On SWAT Model

The study of spatial-temporal variation trends of land use types and its influence on runoff and sediment can not only provide a reference for land use planning in the basin,but also find the causes of soil erosion disasters in the basin,and provide scientific basis for rational planning of production,ecology and living space in the basin.The Xujiang River Basin is located in the upper reaches of the Fuhe River.In recent years,the development of large-scale orchards has aggravated the current situation of soil erosion in the basin.In this study,spatial analysis,land use transfer matrix and dynamic land use attitude were used to investigate the spatio-temporal change and topographic differentiation of land use in Xujiang River basin from 2000 to 2020.SWAT model was simulated based on land use data,DEM data,soil data and meteorological data,and the applicability of SWAT model in Xujiang River Basin was evaluated.Three land use scenarios were established to simulate the runoff and sediment changes in the Xujiang River Basin,and the responses of runoff and sediment to land use changes were analyzed from three levels of the Xujiang River Basin,sub-basins and hydrological response units.The main research conclusions are as follows:(1)The main land use types in the Xujiang River Basin are forest land and orchards.The transfer of land use types in the basin is concentrated between forest land and orchards,cultivated land and orchards,and the conversion area of forest land and cultivated land to orchards is the largest.In addition,the dynamic degree of comprehensive land use in the watershed is relatively large during the whole period,and the land use in the watershed has been undergoing drastic changes.65.13%of the watershed area is located in the 82-300 m elevation range,in which the land use types are the most and the area is the most concentrated.Cultivated land,construction land and water areas are mainly distributed in the range of 0°-5°,which are greatly affected by slope;forest land and orchards are less affected by the slope,and are distributed in all slope ranges.(2)Through the SWAT model of Xujiang River Basin,the calibration and verification results show that the SWAT model has good suitability in the Xujiang River Basin.In this paper,the Xujiang River Basin is divided into 31 sub-basins and 1796 HRUs.Through parameter sensitivity analysis,model calibration and verification by SWAT-CUP software,7 sensitive parameters of runoff simulation and 4 sensitive parameters of sediment discharge simulation are selected.The NSE and R~2 of the simulated runoff values in the regular period and the verification period are:0.85,0.85 and 0.88,0.80,and the simulated value of the sediment load in the period and the verification period NSE and R~2 are:0.81,0.73 and 0.87,0.74,indicating that the SWAT model has high simulation accuracy in the Xujiang River Basin.(3)Three combination scenarios of meteorological data and land use data were set to analyze the variation characteristics of runoff and sediment discharge in Xujiang River Basin,sub-basin and HRU under the three scenarios.The results showed that the runoff coefficient and sediment yield increased with the increase of cultivated land and orchard area or the decrease of forest land.The runoff capacity of each land use type from large to small for construction land,cultivated land,orchard,forest land,sediment capacity from large to small for cultivated land,orchard,forest land;the runoff and sediment yield capacity of cultivated land increased year by year with the increase of tillage years,and the runoff yield capacity of construction land and orchard decreased gradually with the increase of time,and the runoff yield capacity of forest land was less affected by time.The change of forest land and cultivated land has the greatest influence on runoff.The increase of cultivated land and orchard area increases runoff,and the increase of forest land area reduces runoff.The change of cultivated land and orchard area has a great influence on sediment discharge.The change of runoff and sediment transport is not only related to the area of land use type,but also related to the mutual transformation between land use types.Returning farmland to forest reduces runoff and sediment transport,and reclamation of forest land increases runoff and sediment transport.