Evaluation of streamflow simulation by SWAT model for two small watersheds under snowmelt and rainfall
The degradation of the river water quality in Canadian rural catchments\nis of concern. In these catchments, the Soil Water Assessment Tool\n(SWAT) model can help better understand the problems related to diffuse\npollution. The numerous documented applications of SWAT have been\ndominated by areas uniquely driven by rainfall. Given that Canadian\nhydroclimatic conditions differ due to the presence of a seasonal\nsnowpack of long duration, evaluation of the hydrological performance\nneeds to be performed prior to attempting any water quality simulations.\nThe objective of the present work is to evaluate the hydrological\nbehaviour of the SWAT model under snowmelt and rainfall for two small\nwatersheds located in southeastern Canada. Different calibration\nschemes are evaluated including seasonal effects. One-year calibration\ngave satisfactory daily performances measured with Nash-Sutcliffe\nefficiency (NS) ranging between 61 and 83% and deviations of volume\n(D<sub>v</sub>) between -10 and 1%, while in validation, NS was 40-73%\nand D<sub>v</sub> between -20 and -3%. The SWAT model has difficulties\nin reconciling both seasons. When winter and summer data are used\nseparately to calibrate the model, the model performance is still\nmuch better for the winter season than for the summer one. However,\nthe latter is considerably improved when only summer observations\nare provided for calibration. Conversely, calibration based strictly\non the winter observations provides no real advantage over that based\non all available data. A two-step composite calibration, which optimizes\nthe SWAT snow accumulation and melt-related parameters on the winter\ndata, after all other model parameters have been optimized on the\nsummer data, provides a compromise. Copyright © 2008 IAHS Press.