| Land use/land cover change (LUCC) and its hydrological environment effect has received more and more attention and emphasis by international academia and governments. Soil erosion as one of the major environmental effect which is triggered by land use change, is the important reason causes land degradation, reservoir sedimentation, the deterioration of the ecological environment. Quantify the law of sediment yield and runoff transport under LUCC has great significance on help people definite the man-earth relationship and guide human activities.The upper Yangtze River region has important ecological and geographical location in our country, water loss and soil erosion has become the important problem influencing the local ecological environment. In this paper, the Lancang River and Lizixi River Basin were selected as the study area, built the distributed model based on SWAT model to study the law of sediment yield and runoff transport under LUCC. The main research contents and conclusions are as follows:(1) Study the method of build the distributed model based on SWAT model, state the river extraction and sub-basin divide based on DEM, the establishment and supplemented of meteorological station, soil database established, the simulation method choice, model parameter sensitivity analysis, the results of the model output and calibrate the model. Focus on analyze the methods which were applied to the study area by using SWAT model.(2) The Lancang River Basin distributed model was built based on SWAT model, the model was validated and calibrated by using the monthly-runoff and monthly-sediment yield. Finally, the Ens of runoff>0.79,the R2of runoff>0.82, the Ens of sediment yield>0.51, the R2of sediment yield>0.72, the model can well simulate the runoff and sediment yield process. Simulated the soil erosion under the land use map of1975and1985, the results showed that the middle and lower reaches of the Lancang River area was vulnerable to erosion. Selected the top-five sub watersheds which have the most variation in soil erosion, analyzed the variation of land use change and soil erosion in each sub watershed. The results showed that soil erosion decreased with the increase of forest and grassland in each sub watershed. Defined a parameter named soil erosion increment to evaluate the influence of slope on soil erosion, the results showed that soil erosion increases with the increase of slope, manage the farmland with slope>25°has obvious effect on prevent soil and water loss.(3) The Lizixi River Basin distributed model was built based on SWAT model, the model was validated and calibrated by using the daily-runoff and daily-sediment yield. Finally, the Ens of runoff>0.52,the R2of runoff>0.78, the Ens of sediment yield>0.51, the R2of sediment yield>0.72, so the SWAT model has good applicability in the medium scale region. The extreme hypothetical method was applied to simulated the soil erosion under the land use map of1986when the farmland land plant different crops, the simulation results show that wheat contribute to the minimum soil erosion, followed by sweet potato, corn and rape. The effects of slope on soil erosion was studied, the conclusion was similar to the study of Lancang River; simulation results show that in terms of erosion, manage1km2farmland with slope>25°was equal to manage4.1km2farmland with slope5～15°or manage1.8km2farmland with slope15～25°(4) Applied the scenario simulation method to study the influence of rainfall and soil type on sediment yield variation, the results show that the rainfall has positive correlation with the soil erosion which caused by land use change, the greater the rainfall, the bigger the soil erosion variation. Simulation of different soil types showed that when the underlying surface was loess the variation which caused by land use change was the largest, followed by black soil, red soil and purple soils. |
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