Runoff Response To Landscape Pattern Change In The Shehe Watershed Based On SWAT Model

Landscape pattern change is an important driving factor of hydrological change.By changing factors such as canopy interception,evapotranspiration and soil infiltration,the runoff process in the watershed is affected.To explore the spatial and temporal variation of landscape pattern,study the response mechanism of landscape pattern and hydrological process,and analyze the runoff characteristics under different landscape patterns,so as to provide scientific basis for rational adjustment of land use spatial structure,allocation of water resources,reduction of flood and drought disasters and ecological environment management in the basin.In this study,Shehe River in the upper reaches of Dahuofang Reservoir in eastern Liaoning Province was selected as the study area.Firstly,by using remote sensing technology and geographic information system technology,through land use classification,the dynamic analysis of landscape type and landscape pattern index,The characteristics of landscape pattern change in Shehe Watershed in 1987,2002 and 2015 were studied.Then,the interpreted land use maps,DEM data,soil data,runoff and meteorological data are used as data sources.The SWAT hydrological model of Shehe Watershed is constructed,and the hydrological process under different land use scenarios is simulated by using the model.Finally,based on landscape pattern change and the simulation results of SWAT model,the dynamic changes of landscape pattern and the ecological response of runoff in the watershed were discussed through correlation analysis.The main contents are as follows:(1)Land use classification and landscape pattern index of three remote sensing data from1987 to 2015 in the study area were calculated.The results show that the area of woodland and grassland first decreases and then increases,the area of farmland and construction land first increases and then decreases,and the area of mineral body continues to increase,among which the transition from forest land to farmland is the most active;the change of landscape index at type level and landscape level indicates that the landscape shape tends to be complex,fragmented,the connectivity decreases slightly,and the distribution tends to be unbalanced.(2)Collect and process the basic data needed for the operation of the model,establish the database needed for the operation of the mode,and simulate the runoff of the She River Basin.The SUFI-2 algorithm of SWAT-CUP is used to calibrate the model parameters,calibrate and validate the simulation results,determine the optimum values of 10 sensitive parameters for runoff simulation through multiple iterations,improve the localization of model parameters,simulate the annual,monthly and daily runoff process of the basin,and the fitting degree of the simulated and measured values in calibration and validation periods is good,and thesimulation of runoff at different time scales is comparable.The relationship coefficient R2 and the deterministic coefficient Ens both meet the evaluation criteria.(3)Under the land use scenarios of 1987,2002 and 2015,the runoff process under meteorological conditions in 2010-2011 was simulated.The results showed that the decrease of forest area resulted in the increase of runoff in high water year and the decrease of runoff in normal water year,and the impact of land use change on Runoff in normal water year was more significant.Three extreme land use scenarios of woodland,farmland and grassland were established,and water yield was compared with that of land use scenarios in 2015.The results showed that the runoff forest land scenario < grassland scenario < farmland scenario in flood season and the runoff farmland scenario < grassland scenario < woodland scenario in normal water period.(4)The influence of six factors including forest land,farmland,construction land,mining land and grassland on runoff coefficient was analyzed by grey correlation analysis method.The results showed that rainfall had the greatest correlation with runoff coefficient,forest land had the greatest correlation with runoff simulation in landscape type,and farmland and construction land had the closest impact on runoff coefficient.(5)Pearson correlation analysis was carried out between the change rate of landscape pattern index and the monthly average water yield of each subbasin.The results showed that there was a significant correlation between the change rate of forest land and farmland patch area and the change rate of water yield at the type level;at the landscape level,the number of patches(NP)and the average patch area were significantly correlated with the change of runoff,and the shape index(LSI)and surface were significantly correlated with the change rate of runoff.The product weighted average fractal dimension(FRAC_AM)is negatively correlated with the change rate of water yield under horizontal water condition,and the change rate of(CONTAG)and aggregation index(AI)is positively correlated with the change rate of water yield under horizontal water year meteorological condition.Compared with the change of annual runoff in flood season,the change of landscape pattern index has more significant correlation with the change of annual runoff in normal season.