As part of its Programme Rhine 2040 entitled ‘The Rhine and its Catchment – Sustainably Managed and Climate-resilient’ (ICPR, 2020), the ICPR mandated its climate expert group (formerly EG KLIMA, now EG HCLIM) with an update of the ICPR climate scenarios by 2024. While the previous ICPR scenarios, published in 2011, were based on information of the 4th assessment report of the Intergovernmental Panel on Climate Change (IPCC) (IPCC, 2007), this update generally relies on the 5th IPCC assessment report (IPCC, 2014). In line with many national climate impact assessments, HCLIM selected a high emission scenario (RCP8.5) because this scenario is regarded as more relevant for ICPR management questions than more moderate or optimistic scenarios.
This report is based on observations and on five hydrological simulation data sets compiled as part of various national and regional studies which differ in models and methods applied. In order to compare these studies, decisions have been made with respect to time periods (reference 1981-2010; present 1991-2020; near future 2031-2060; distant future 2071-2100), indicators (mean, low and high flow), and gauging stations or subcatchments. Guiding principles for these decisions were a) comparability with the previous scenario report on the discharge scenarios of the Rhine (ICPR, 2011) as well as b) the best possible comparability between the data pools provided by the different participants. Despite this effort, a certain level of heterogeneity between data from the different sources remains. This results in an overall higher spread of results compared to the previous report, and somewhat limited comparability between individual gauging stations.
In summary, the evaluation of long-term changes in the past (observations) and the future (projections of RCP8.5) largely support the pre-existing picture of a change towards more rain-fed flow regimes rather than snow- and glacier-fed flow regimes in the Rhine catchment. This leads to decreasing summer flows, increasing winter flows, almost unchanged annual flows, and – in many river sections and tributaries – an intensification of low and high flow extremes. The sequence of extreme low flow years after 2010 does not fit into this picture, because it shows decreases in all indicators (high and low flow) and seasons (including winter).

The report itself can be found here.