This paper emphasizes the different requirements for calibration and validation of lumped and distributed models. On the basis of a theoretically founded modelling protocol, the different steps in distributed hydrological modelling are illustrated through a case study based on the MIKE SHE code and the 440 km2 Karup catchment in Denmark. The importance of a rigorous and purposeful parameterisation is emphasized in order to get as few 'free' parameters as possible for which assessments through calibration are required. Calibration and validation using a split-sample procedure were carried out for catchment discharge and piezometric heads at seven selected observation wells. The validated model was then used for two further validation tests. Firstly, model simulations were compared with observations from three additional discharge sites and four additional wells located within the catchment. This internal validation showed significantly poorer results compared to the calibration/validation sites. Secondly, the validated model based on a 500 m model grid was used to generate three additional models with 1000 m, 2000 m and 4000 m grids through interpolation of model parameters. The results from the multi-scale validation suggested that a maximum grid size of 1000 m should be used for simulations of discharge and ground-water heads, while the results deteriorated with coarser model grids.
- Programområde 2: Vandressourcer