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Coupling of SUFI 2 and SWAT for Improving the Simulation of Streamflow in an Agricultural Watershed of South Dakota

Abstract

Sushant Mehan, Ram P Neupane and Sandeep Kumar

Calibration and validation of process based hydrological models are two major processes while simulating the water balance components of watershed systems. However, these processes need a better understanding of the parameters which influence hydrologic processes within the system. In this study, we used SWAT model to simulate the stream flow for Skunk Creek (SK) watershed in South Dakota for the period from 1980-2000. Model calibration and validation were performed for both daily and monthly time periods using SUFI-2 within SWAT-CUP using 24 parameters selected from past available literature. Our calibration outputs for the period from 1987-1994 showed a good correlation between observed and model simulated values with NSE=0.56 and R2=0.70 for daily simulation. However, the model showed a better performance for monthly simulation with NSE and R2 values of 0.84 and 0.84 respectively. During validation period (1995-2000), the NSE and r2 values were 0.55 and 0.44, respectively for daily simulation and these statistical values were 0.76 and 0.77, respectively for monthly time step. Following calibration, the overall effect of each parameter used was ranked using global sensitivity function within SWAT-CUP. From the analysis, SOL_AWC was found to be the most sensitive parameter with absolute t-value of 17.50 and p-value of 0.00 to simulate the stream flow of the SK watershed. The CH_K2 was observed as the least sensitive parameter with t-statistic and p-value of 0.02 and 0.97, respectively. It was concluded from the study that coupling of the SWAT and SWAT-CUP made the calibration process quicker and reliable to simulate local hydrology within the watershed.