Conceptual hydrologic models are useful tools as they provide aninterpretable representation of the hydrologic behaviour of a catchment.Their representation of catchment's hydrological processes and physicalcharacteristics, however, implies a simplification of the complexity andheterogeneity of reality. As a result, these models may show a lack offlexibility in reproducing the vast spectrum of catchment responses. Hence,the accuracy in reproducing certain aspects of the system behaviour may bepaid in terms of a lack of accuracy in the representation of other aspects.By acknowledging the structural limitations of these models, we propose amodular approach to hydrological simulation. Instead of using a single modelto reproduce the full range of catchment responses, multiple models areused, each of them assigned to a specific task. While a modular approach hasbeen previously used in the development of data driven models, in this studywe show an application to conceptual models.The approach is here demonstrated in the case where the different models areassociated with different parameter realizations within a fixed modelstructure. We show that using a "composite" model, obtained by acombination of individual "local" models, the accuracy of the simulationis improved. We argue that this approach can be useful because it partiallyovercomes the structural limitations that a conceptual model may exhibit.The approach is shown in application to the discharge simulation of theexperimental Alzette River basin in Luxembourg, with a conceptual model thatfollows the structure of the HBV model.
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