Uncertainty Associated with SWAT Model for the Estimation of Stream flow for Kosi Basin, India

Abstract

The outputs from Hydrological models generally undergo certain uncertainties from different sources of errors (error in input parameters, model structure or due to model simplifications, unknown or non-ascertainable relations within the model). Relatively, it is easy to control parameter uncertainty through various calibration procedures. In this study an important tool called Soil and Water Assessment Tool(SWAT), which is an eco-hydrological model was used to simulate the Kosi basin. SWAT-CUP was the interface used for sensitivity analysis, model calibration and uncertainty assessment using Sufi-2 algorithm. The first 4 years (1987-90) was taken as warmup period and the period of (1987-99) was calibrated then the model was validated for the next 8 years (2000-2007). In this process, p-factor refers to the percentage of observations covered by 95PPU band while r-factor describes the average of 95PPU band width divided by the standard deviation. In calibration, the p and r factors were obtained as 0.31 and 0.22 and in validation, their values are 0.31 and 0.24 respectively. The coefficient of determination (R2 ) and Nash–Sutcliffe efficiency (NSE), was used to check the goodness of fit between observed and ultimate best simulated results. The results obtained during calibration indicated R2 and NSE values were 0.63 and 0.43 respectively. The validation also yielded satisfactory values of R2 and NSE as 0.70 and 0.51 respectively. The output of statistical Analysis indicated a perfect match between the observed data and the best simulated data values which showed that the model was well calibrated for streamflow simulation.