Water And Sediment Response To Land Use And Climate Change Based On SWAT Model

The characteristics and governance of soil and water loss in the Loess Plateau are always the focus.In recent years,with the development of the soil and water conservation,the environmental deterioration of the Loess Plateau had been effectively alleviated and suppressed.But there appeared new problems,runoff-sediment yield had decreased rapidly.It was mainly due to local climate change and frequent human activities.Therefore,the objectives of this study were to model the effects of the changes of land use and climate on reducing runoff-sediment yield in the Luoyugou watershed based on SWAT model.The main conclusions were as follows:(1)The SWAT model was applicable to simulate the runoff-sediment yield in Luoyugou watershed.The coefficient of determination(R2)and the Nash-Sutcliffe coefficient(Ens)were used to evaluate the applicability of the model.During calibration period(1986-1995),the R2 and Ens for runoff were 0.79?0.75,for sediment were 0.79?0.67.During validation period(1996-2000),the R2 and Ens for runoff were 0.80?0.65,for sediment were 0.70?0.63.Therefore,the SWAT model met the application standards(R2>0.6,Ens?0.5).(2)The uncertainty of the SWAT model is acceptable.The results showed that there was obvious phenomenon that "equifinality for different parameters" in the process of parameter iteration.The change of the objective function value(Ens)with CN2 is obvious,which tends to be stable after rising P-factor and R-factor were used to evaluate the model uncertainty.The P-factor and R-factor for runoff were 0.67?1.08,for sediment were 0.63?1.03,which were in accordance with the requirement of model uncertainty(the requirements of model uncertainty were P>0.6 and R<1.5).(3)The simulated results of scenarios of different land use patterns on runoff-sediment yield showed that the runoff-sediment yield was influenced by the concentration of forest land.Compared with the low concentration of forest,runoff amount and sediment under high concentrated forest decreased at most of 4%and 27%respectively.However,there was a threshold of concentration,and if the concentration degree was greater than the threshold value,the watershed runoff-sediment yield was almost invariable.The runoff and sediment yield under various land use types with the same area proportion were related to their distributive location.when forest land locates in upper of the watershed,the maximum reduced proportion of runoff-sediment yield at upper and middle were 23.8%%50.89%and 12.3%?33.03%respectively,Compared with land locates in middle or lower of the watershed.Therefore,the optimization of land use pattern in the source of runoff-sediment yield should be valued.(4)The simulated results of scenarios of future climate change on runoff-sediment yield showed that,when the temperature was constant,the rainfall increased by 5%,10%,15%and 20%(Scenario 1),the runoff-sediment yield in Luoyugou watershed increased,and the range of increasing was enlarged,the amplitude of runoff increased was higher than sediment increased.When the rainfall was constant,the maximum temperature and the minimum temperature rose 0.3?(Scenario 2-0),runoff-sediment yield decreased 2.5%and 1.5%respectively.When the rainfall increased,the maximum temperature and the minimum temperature rose 0.3?(Scenario 2),the runoff-sediment yield increased,but the increasing amplitude was lower than that in Scenario 1,the differences between them enlarged along with the increased of rainfall,the runoff-sediment yield of Scenario 2 reduced by 4%?3%compared with Scenario 1.It indicated that there was an interactive effect between rainfall and temperature on runoff-sediment yield.The effect of temperature was amplified with the increase of rainfall.The runoff-sediment yield was also influenced by the uniformity of rainfall distribution in the watershed.