Soft combination of local models in a multi-objective framework

Conceptual hydrologic models are useful tools as they provide an interpretable representation of the hydrologic behaviour of a catchment. Their representation of catchment’s hydrological processes and physical characteristics, however, implies simplification of the complexity and heterogeneity of reality. As a result, those models often 5 show a lack of flexibility in reproducing the vast spectrum of catchment responses. Hence, the accuracy in reproducing certain aspects of the system behaviour is often paid in terms of a lack of accuracy in the representation of other aspects. By acknowledging the structural limitations of those models, a modular approach to hydrological simulation is proposed. Instead of using a single model to reproduce the 10 full range of catchment responses, multiple models are used, each of them assigned to a specific task. The approach is here demonstrated in the case where the different models are associated with different parameter realizations within a fixed model structure. We show that using a composite “global” model, obtained by a combination of individual “local” 15 models, the accuracy of the simulation is improved. We argue that this approach can be useful because it partially overcomes the structural limitations that a conceptual model might exhibit. The approach is shown in application to the discharge simulation of the experimental Alzette River basin in Luxembourg, with a conceptual model that follows the structure of the HBV model. 20