Simulation Study Of Runoff In Southern Hilly Rice Irrigation Areas Based On SWAT Model

Rice is one of the major agricultural crops in the southern hilly irrigation areas of China,and the demand for water resources is very high,leading to a conflict between supply and demand in the area.The SWAT(Soil and Water Assessment Tool)model has been widely used as a basin hydrological model in watershed studies around the world,and has The SWAT(Soil and Water Assessment Tool)model has been widely used as a watershed hydrological model in watershed studies around the world,and has yielded good results.In this paper,a typical small watershed in the southern hilly rice irrigation area,the Yangshudang(YSD)watershed,was selected as the study target,and runoff simulation and runoff response under changing environment were carried out based on the SWAT model.The SWAT model was set up and run based on DEM data,land use and soil data,and meteorological data;the reliability of the model in the YSD watershed was evaluated using SWAT-CUP;different rainfall station input scenarios,different land use accuracy scenarios,and different land use patterns and pond and weir catchment area ratios were set up to analyse different inputs at the rainfall and subsurface levels.The main conclusions are as follows:(1)15 parameters with high sensitivity in the model of the YSD watershed were identified,and the efficiency of parameter rate setting was improved for rate setting validation.The results show that the R2 and NSE values for both the rate and validation periods are greater than 0.6,and the RSR values are less than 0.7,indicating that the SWAT model can better simulate the runoff change process in the YSD watershed.(2)By setting up seven different rainfall station network distribution methods,the SWAT model’s nearest neighbor method and Tyson polygon interpolation method were used to process rainfall data and analyze the spatial differences in rainfall in the study area,and to investigate the effects of the number,layout and rainfall level of rainfall stations on the runoff simulation effect.The results show that the number and distribution of rainfall stations have significant effects on runoff,the more the number of rainfall stations and the more uniform the spatial distribution,the better the runoff simulation effect;as for the rainfall level:the smaller the rainfall level,the better the simulation effect of the model.(3)Based on different precision land use data,six scenarios were set up to analyse the influence of land use data precision and different land use division thresholds on the runoff simulation effect.The results show that the results of 5 m precision land use simulation are indeed better than 10 m,but within a certain division threshold,the difference between the two simulation effects is small.The runoff response was studied for different land use patterns and different pond and weir catchment area ratios.The results show that land use changes have an impact on the catchment yield,daily runoff at the outlet of the catchment and peak flows,and that the catchment yield and runoff volumes tend to increase to varying degrees as the proportion of paddy land shifted to arable land increases.Secondly,increasing the catchment area ratio of ponds and weirs can increase the interception of surface runoff and farm drainage by ponds and weirs,resulting in a reduction in flow...