Balance between calibration objectives in a conceptual hydrological model

Three different measures to determine the optimum balance between calibration objectives are compared: the combined rank method, parameter identifiability and model validation. Four objectives (water balance, hydrograph shape, high flows, low flows) are included in each measure. The contributions of these objectives to the specific measure are varied to find the optimum balance between the objectives for each measure. The methods are applied to nine middle-sized catchments, using a typical conceptual hydrological model. The results indicate that differences in the optimum balance between the combined rank method and parameter identifiability on the one hand, and model validation on the other, are considerable. The theoretical optimum balance would be a situation without trade-off between single objectives. For some catchments and measures, this situation is closely approximated. On average, the performance of combined rank method is somewhat better than that of parameter identifiability (respectively 3.6% and 5.0% below the theoretical optimum), where the performance of model validation is considerably lower (22.4% below the theoretical optimum). These results are supported by additional validation tests which gave robust results for the combined rank measure and the parameter identifiability measure, and less robust results for the model validation measure.