Model performance before and after the introduction of some alternative routines for calculation of evaporation, snow accumulation and melt with the PULSE/HBV runoff model were compared. The results showed that improvements were, in the best cases, small. Sometimes model fits deteriorated as a result of increased model complexity. On the basis of these, and from other experiences of attempts of model improvements, the success potentials for various efforts of model sophistication are discussed. It is hypothesised that model improvement cannot be achieved by increasing the complexity of some sub-routines, without considering the problems that are linked to spatial resolution of driving variables and the spatial distribution of physiographic parameters. It is suggested that physically based and conceptual schools of modelling can meet in a landscape mosaic context, with development of distributed models, based on information generally available from maps, remote-sensing images and meteorological stations.

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