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Deltares | R&D Highlights 2015
In 2014, the Netherlands Meteorological Institute KNMI presented four new climate scenarios for the Netherlands and for the river basins of the Rhine and Meuse for the time horizons 2050 and 2085. Deltares estimated the impact of these climate scenarios on the extreme discharges (both high and low) of the Rhine and Meuse
In 2014, the Netherlands Meteorological Institute KNMI presented four new climate scenarios for the Netherlands and for the river basins of the Rhine and Meuse for the time horizons 2050 and 2085. Deltares estimated the impact of these climate scenarios on the extreme discharges (both high and low) of the Rhine and Meuse.
The GRADE Generator of Rainfall and Discharge Extremes was used to calculate the distribution of high discharges in the Rhine at Lobith and the Meuse at Borgharen. GRADE was developed by Deltares and KNMI as an improvement to the current extrapolation method on observed discharge series. GRADE consists of three components: very long, synthetic, rainfall series are produced by a stochastic weather generator, hydrological models of the Rhine and Meuse basins calculate the flow contribution into the main rivers, and hydrodynamic models simulate the flood propagation in the main rivers. In the case of the Rhine, the method also includes the effect of flooding upstream from Lobith.
Changes in both high and low flow statistics were calculated. The resulting discharge projections were compared with existing ones, in other words those based on KNMI’06 scenarios and the results from the international AMICE (Meuse) and RheinBlick2050 (Rhine) projects. The comparison focused on the annual cycle of the mean monthly discharge, the mean annual minimum 7-day
flow, the mean annual maximum flow and extreme flows with long return periods. The effects of the KNMI’14 scenarios on both rivers show a general tendency towards rising discharges in winter and spring, and falling discharges in - usually late - summer. In most scenarios, the mean annual discharge clearly falls as well. The range of the change in extremely high discharges for all KNMI’14 scenarios is relatively small for 2050 but becomes larger in 2085. These ranges are consistent with the ranges for extreme multi-day precipitation in the KNMI’14 scenarios. The effect of upstream flooding is taken into account for the Rhine. This includes the effect of the potential flood areas between Wesel and Lobith, which are taken into account by correcting the discharges calculated by the SOBEK 1-D model above 16,000 m3/s (start of flooding around Emmerich) for the
potential flooding volumes and considering the maximum flow over the dikes between Wesel and Lobith. The result is that, with very long return periods (above ~1250 years), the differences between the scenarios become small, largely due to the limited discharge capacity of the Rhine between Wesel and Lobith. These state-of-the-art results confirm once more that the maximum discharge at Lobith will be between 17,500 and 18,000 m3/s.
Further reading:
Sperna Weiland et al (2015). Implications of the KNMI’14 climate scenarios for the discharge of the Rhine and Meuse, Deltares report 1220042
(http://kennisonline.deltares.nl) mark.hegnauer@deltares.nl
T +31(0)88 335 8476
frederiek.spernaweiland@deltares.nl
T +31(0)88 335 8230
GRADE method for
discharge scenarios
Flood Risk
Upper panel: current method, lower panel: GRADE method Photo: Beeldbank Rijkswaterstaat
