Comparison of CMIP5 climate model projections and preliminary KNMI’14 scenarios with earlier climate assessments for the Rhine and Meuse

Summary
In this study we assessed potential changes in discharge for the Meuse and Rhine using (1) a selection of 191 simulations from the recently developed Coupled Model Intercomparison Project (CMIP5) datasets and (2) a preliminary version of the KNMI’14 scenarios for the Rhine and Meuse basins. A final version of the latter is still under development. To generate discharge projections, the HBV models for the Meuse and Rhine were run with the climate datasets which were down-scaled to the HBV sub-catchments by KNMI. The results of the discharge change analysis were compared with existing discharge change projections i.e. those based on KNMI’06 and the results from the AMICE and RheinBlick2050 projects. The analysis focussed on monthly mean discharge cycle, minimum and maximum flow. It should be noted that the comparison may be influenced by the use of different hydrological model versions, climate bias-correction / down-scaling methods and potential evaporation in the different scenario analysis.
Results indicate that for both rivers there is a general tendency towards increasing spring discharge and decreasing late summer discharge. For the Meuse mean and maximum discharge are projected to increase whereas minimum discharge is projected to decrease. For the Rhine maximum discharge is also consistently projected to increase and minimum flow is projected to decrease. Mean annual discharge will clearly increase according to most (preliminary) KNMI’14 scenarios and the CMIP5 projections.
Comparison of the new projections with the existing scenarios resulted in the following conclusions:
- The new climate change scenarios (KNMI’14 and CMIP5) for the Meuse basin are overall in agreement with the existing scenarios datasets (KNMI’06 and RheinBlick2050). Except that according to this analysis the majority of CMIP5 scenarios project a decrease instead of increase in annual mean flow and more specifically a large decrease for late summer.
- For the Rhine, projected discharge changes are overall smallest in the KNMI’14 scenarios and the scenario band-with is often relatively narrow compared to the other scenario sets.
- According to the new scenario sets annual mean discharge for the Rhine will increase for all locations, with a smallest increases at Trier. Large late summer discharge decreases are projected by part of the CMIP5 models, whereas the KNMI’14 scenarios project relatively moderate decreases compared to all other scenario datasets.