Modelling water availability and water allocation strategies in the Scheldt basin. Sub report 4-4. Analyses of hydrological models for climate change modelling – VHM

The water balance model of the Scheldt and Meuse basins will be used in order to perform low flow forecasts and calculate climate change scenarios. Within the current subtask is investigated which is the most appropriate hydrological model for the sub catchments of the water balance model of the Scheldt basin in order to meet this prerequisite. This sub report describes the calibration and evaluation of the VHM model, a lumped conceptual model for continuous rainfall-runoff simulation (Willems P., 2014) developed by the Hydraulics Division in KU Leuven in Belgium. The optimization during calibration is performed based on an automatic procedure, followed by a visual control. During the optimization routine the parameter sets are selected based on 2 criteria: (1) absolute error on cumulated total flow at each time step, and (2) logarithmic Nash-Sutcliff efficiency. The first criterion aims to model the global flow pattern, the latter focuses mainly on the low flows. Overall, the performance of the calibrated VHM models is similar compared to the other lumped rainfall-runoff models already calibrated: PDM, NAM and WETSPA. The summarized results for each of the gauged sub catchments within the study area, allow the user to get insight in the performance of the VHM model for each of the involved sub catchments. Based on this information and the evaluation of the NAM, PDM and WETSPA models, the user can make a well-grounded decision on which model to use for the considered objective.