Parameter identification and uncertainty analysis for simulating streamflow in a river basin of Eastern India

Uncertainty is inherent in modelling studies. However, the quantification of uncertainties associated with a model is a challenging task, and hence, such studies are somewhat limited. As distributed or semi-distributed hydrological models are being increasingly used these days to simulate hydrological processes, it is vital that these models should be equipped with robust calibration and uncertainty analysis techniques. The goal of the present study was to calibrate and validate the Soil and Water Assessment Tool (SWAT) model for simulating streamflow in a river basin of Eastern India, and to evaluate the performance of salient optimization techniques in quantifying uncertainties. The SWAT model for the study basin was developed and calibrated using Parameter Solution (ParaSol), Sequential Uncertainty Fitting Algorithm (SUFI-2) and Generalized Likelihood Uncertainty Estimation (GLUE) optimization techniques. The daily observed streamflow data from 1998 to 2003 were used for model calibration, and those for 2004-2005 were used for model validation. Modelling results indicated that all the three techniques invariably yield better results for the monthly time step than for the daily time step during both calibration and validation. The model performances for the daily streamflow simulation using ParaSol and SUFI-2 during calibration are reasonably good with a Nash-Sutcliffe efficiency and mean absolute error (MAE) of 0.88 and 9.70m(3)/s for ParaSol, and 0.86 and 10.07m(3)/s for SUFI-2, respectively. The simulation results of GLUE revealed that the model simulates daily streamflow during calibration with the highest accuracy in the case of GLUE (R-2=0.88, MAE=9.56m(3)/s and root mean square error=19.70m(3)/s). The results of uncertainty analyses by SUFI-2 and GLUE were compared in terms of parameter uncertainty. It was found that SUFI-2 is capable of estimating uncertainties in complex hydrological models like SWAT, but it warrants sound knowledge of the parameters and their effects on the model output. On the other hand, GLUE predicts more reliable uncertainty ranges (R-factor=0.52 for daily calibration and 0.48 for validation) compared to SUFI-2 (R-factor=0.59 for daily calibration and 0.55 for validation), though it is computationally demanding. Although both SUFI-2 and GLUE appear to be promising techniques for the uncertainty analysis of modelling results, more and more studies in this direction are required under varying agro-climatic conditions for assessing their generic capability. Copyright (c) 2015 John Wiley & Sons, Ltd.