Response Of SWAT Model Parameters To Land Use Change And Its Effects On The Simulation Of Runoff

The distributed hydrological model provides an effective means for runoff simulation and hydrological response to land use change.The SWAT model is widely used to evaluate the hydrological response of land use change.The successful application of the distributed hydrological model in watersheds depends largely on the accuracy of sensitive parameter identification and calibration.However,in previous studies,first-stage land utilization was usually used to calibrate the model parameters,which were considered to reflect the runoff characteristics of the underlying surface of the basin.Therefore,the calibrated parameters were directly substituted into other land use conditions to simulate and analyze the impact of land use change on runoff.With the acceleration of economic development and the intensification of land use change,the response of the model's parameters to land use change and its effects on the simulation of runoff has not been well investigated.Therefore,it is meaningful to discuss the response of SWAT model parameters to land use change and its effects on the simulation of runoff with different time scales,which can improve the accuracy of model simulation and promote the application level of the model.So in the studies,First,the classification of land use types was interpreted through multiple periods of remote sensing images,and the characteristics of land use changes in the Shanmei Reservoir watershed in 1995,2005,and 2015 were studied.Second,Shanmei Reservoir watershed located in the southeastern China was taken as a research area and SWAT models for the simulation of the annual,monthly,daily runoff were constructed under the land use conditions of 1995,2005,and 2015 respectively.The optimal values set for the sensitive parameters under three land use conditions were determined with the method of SWAT-CUP respectively.The three optimal values sets of parameters then were applied to analyze the effects of land use change on the simulation of different time scale runoff.Finally,based on the modeling of land use in 2015 and meteorological conditions from 2011 to 2018,the land use in 1995 was replaced,and the runoff was simulated using Parm95 and Parm15 respectively.The difference of runoff response of land use change simulated by time-varying parameters(the corresponding model parameters of two phases of land use)and time-invariant parameters(land use1995+Parm15 in)was compared.The results showed that:(1)The land use pattern in the study area changed greatly from 1995 to 2015.The garden and urban land were increased while the forest was reduced significantly.(2)The SWAT models well simulated the different time scales runoff process for the three land use conditions of 1995,2005,and 2015 with the Nash-Suttcliffe(NS)was above 0.62,the coefficient of determination(R~2)above 0.78,and the absolute value of percent bias(Re)less than 25%.(3)The sensitive parameters were basically the same under different land use conditions in the Shanmei Reservoir watershed.The sensitive parameters included CN2,SOL?AWC,SOL?K,CANMX,ESCO,GW?DELAY,OV?N.(4)The values of the sensitive parameters were varied with the change of land use and the variation was coincident with the physical meaning of sensitive parameters.The values of CN2,SOL?K,CANMX,ESCO,and OV?N in the study area were gradually increased from 1995 to 2015,while the values of SOL?AWC and GW?DELAY gradually decreased.The reason for the changing trend of sensitive parameters was that the land use in the study area was changed partly from forest to garden,pasture,orchard,and urban land from 1995 to 2015,resulting in the decrease of the forest area.(5)The change of the value of sensitive parameters,caused by land use change,had little influence on the simulation of the annual and monthly runoff but significantly on the daily runoff.The influences on the daily runoff increased with the increase of the amplitude of land use change.The main reason was that SWAT model parameters were more sensitive to flood runoff.(6)The two methods of time-invariant parameters and time-varying parameters were consistent in the study of the impact of land use changes on runoff.However,the simulation method of time-invariant parameters underestimates the runoff effect of land use change.Among them,the daily-scale flood runoff was the most underestimated,and the annual and monthly runoff was relatively small.