An Improved Framework for Watershed Discretization and Model Calibration: Application to the Great Lakes Basin

This paper reports on recent progress towards improved predictions of the land surface-hydrological modelling system MESH (Modelisation Environmentale–Surface et Hydrologie) via its calibration over the Laurentian Great Lakes Basin. Accordingly, a “global” calibration strategy is utilized in which parameters for all land class types are calibrated simultaneously to a number of sub-basins and then validated in time and in space. Model performance was evaluated based on four performance metrics, including the Nash-Sutcliffe (NS) coefficient and simulated versus observed hydrographs. Results from two calibration approaches indicate that in the model validation mode, the global strategy generates preferred results over an alternative calibration strategy, referred to as the “individual” strategy, in which parameters are calibrated to a single sub-basin with a dominant land type individually and then validated in another sub-basin with the same dominant land type. The global calibration strategy was relatively successful despite the high problem dimensionality (51 model parameters calibrated) and relatively small number of model evaluations (1000 parameter sets evaluated per trial) used in the automatic calibration procedure. NS values for spatial validation range from 0.10 to 0.72 with a median of 0.41 for the 15 subbasins considered. Results also confirm that a careful model calibration and validation is unavoidable before any application of the model.