Evaluation of COUP Model for simulation of soil frost depth at Bijar synoptic station

The aim of this research was the evaluation of COUP Model for simulation of soil frost depth at Bijar synoptic station. The simulations were first carried out based on the default parameter values. Afterwards, 30 parameters that had a close relationship with soil frost depth were selected and calibration of the model was performed with adopting Generalized Likelihood Uncertainty Estimation (GLUE) method and simulations of the model for before and after calibration cases were compared. The periods of 1992-2006 and 2007-2009 were selected for model calibration and validation, respectively. On the basis of comparisons between model simulations and observations for soil temperatures at 20 and 50 cm depths and soil frost depth for before and after calibration, the results showed dramatically better performance after calibration compared with before that. The results of model validation showed a good correspondence between simulations and observations at more cases and the model simulations were able to follow observation fluctuations. However, some differences were available between simulations and observations. Some parts of differences are attributed to non-contribution of soil moisture data at calibration procedure and the other parts were attributed to uncertainties in model structure and its governing equations.