QSWAT Model Calibration and Uncertainty Analysis for Stream Flow Simulation in the Patapur Micro- Watershed Using Sequential Uncertainty Fitting Method (SUFI-2)

Abstract

The Patapur micro-watershed situated in semi-arid region needs effective management of resources for sustainable agriculture. The Soil and Water Assessment Tool (SWAT), a semi distributed physically based model, was chosen and set up in the Patapur micro-watershed for hydrologic modeling. SWAT-CUP (SWAT-Calibration and Uncertainty Programs) was used for model calibration, sensitivity and uncertainty analysis, following the Sequential Uncertainty Fitting (SUFI2) technique. The model calibration was performed for the period (2009–2014), with initial 3 years of warm up (2009–2012), then, the model was validated for the subsequent 2 years of data (2014– 2006). To assess the competence of model calibration and uncertainty, two indices, the p-factor (observations bracketed by the prediction uncertainty) and the r-factor (achievement of small uncertainty band), were taken into account. The results had shown that p-factor for daily, monthly and annual time step were 0.07 (7%), 0.11(11%), 1.0 (100%), respectively while r-factor for daily, monthly and annual were 0.07 (7%), 0.33 (33%) and 0.0 (0%), respectively, while during the validation p factor and r-factor for daily, monthly and annual were 0.85, 0.17 and 1, respectively. Whereas r-factor for daily, monthly and annual time step were 0.05 (5%), 0.24(24%) and 0, respectively. After a rigorous calibration and validation, the goodness of fit was further assessed through the use of the coefficient of determination (R2 ) and the Nash–Sutcliffe efficiency (NS) between the observed and the final simulated values. The results indicated that R2 and NS were 0.88 and 0.87, respectively, during the daily calibration. The validation also indicated a satisfactory performance with R2 of 0.63 and NS of 0.64. The results would be useful to the hydrological community, water resources managers involved in agricultural water management and soil conservation, as well as to those involved in mitigating natural hazards such as droughts and floods.