Study On SWAT Model Optimization And Runoff Effects Of Land Use Change

Simulating the hydrological process in a changing environment is a hotspot of scholars'current research.The main direction is to analyze the effect of the changing environment on the status of water resources,ecological environment,and social economy.In this paper,taking the Panjiang River Basin in North and South China as an example,the SWAT model is established and optimized based on the karst characteristics of the area to simulate the runoff of the watershed.At the same time,the mathematical analysis was used to statistically analyze the land use status of the study area on the GIS platform,and the runoff response to land use change under time advancement and under extreme scenarios was obtained.The study mainly obtained the following results:(1)Collect the DEM,soil,land use,and meteorology data of the North and South Panjiang River Basin,and use the SWAT model to build a distributed hydrological model of the basin.The total area of the study area is 79604.90km~2,the area of karst area is 55781.59km~2 and the area of clastic rock area is 23823.31km~2.The study area is divided into 140 sub-watersheds and 861 hydrological response units.The model performs monthly runoff simulation.The simulation period is from January 2012~December 2015.The model was identified and verified,and the monthly runoff simulation analysis of 6 hydrological stations in the basin showed that the model can meet the research accuracy of hydrological cycle in the area.(2)Aiming at the characteristics of karst water system,introduce a pond module to describe the rapid recharge of groundwater in depressions by assigning higher hydraulic conductivity coefficients to the bottom of the pond,and modify the original hydrological cycle process and related algorithms of the SWAT model to construct a distributed hydrological model suitable for karst areas.Comparing the changes of base flow before and after,the improved SWAT model reflects the characteristics of depressions and sinkholes,improves the flow distribution between surface runoff and base flow,and more accurately characterizes the runoff process of karst watershed.(3)Based on the three-phase land use data of 2000,2005,and 2010,analyze the impact of land use change on runoff over time.The average annual simulated runoff in 2000,2010 and 2015 were 515.165,515.208 and 515.475m3/s respectively.August and September had the largest runoff,March had the smallest runoff.The change rate of runoff caused by land use change in different years shows that the change rate of runoff as a whole is small.The overall maximum change rate in June is 0.11%,and the minimum change rate is unchanged.It shows that the runoff has little response to the existing three-stage land use change.(4)Based on the 2015 land use data,analyze the hydrological effects caused by land use changes under three scenarios.The annual average runoff is 564.26,429.08,and 499.48 m3/s under scenarios S1,S2,and S3,respectively,indicating that cultivated land will increase runoff,forest land and grassland will reduce runoff,and the effect of forest land is more significant.Simulate the response of each hydrometeorological element under the three setting scenarios.The simulated water production results S1,S2,and S3 are 408.40,322.43,and 392.49mm;the surface runoff simulation results S1,S2,and S3 are 61.78,50.31,and 60.04,mm respectively,indicating that the cultivated land program has the advantages of water production and surface runoff;The evapotranspiration simulation results S1,S2,and S3 are 408.40,322.43,and 392.49mm,respectively,the forest evapotranspiration is the largest;The underground runoffs S1,S2,and S3 are 61.78,50.31,and 60.04mm,and the soil runoffs S1,S2,and S3 are 43.73,47.97,and46.84mm,which are the largest in forest land.The runoff simulated by S1,S2,and S3 in the flood season is 694.78,545.03,and 626.10 m3/s respectively;in the non-flood season,it is 313.13,433.75,and 372.86 m3/s,It shows that the land use type of agricultural land in the flood season has the advantage of runoff compared to grassland,and the land use type of grassland has the advantage of runoff compared to the forest land.