The streamflow of the river Rhine and its tributaries consists of rain, snowmelt, and glacier ice melt. These components have already changed in the past decades due to global warming. This project quantified the daily fractions of the rain, snowmelt, and glacier ice melt components for a future climate scenario for all tributaries and along the main river Rhine. An ensemble of projections until 2100 suggests wetter winters and drier summers in the future. Hydrological model simulations with this forcing show that the rain component will dominate the seasonal variability of streamflow in the future more than it has in the past. Snow will melt earlier in winter and spring, resulting in less seasonal water storage in the snowpack. Glacier retreat will continue, and despite different rates of retreat of individual glaciers, the joint ice melt component in the main river Rhine is projected to decrease rapidly and almost disappear by the end of the century. Special stress-test model experiments show that the declining melt components will especially affect low flows downstream. At the end of the century, this means that in hot and dry summers comparable to those in 2003 or 2018 buffering ice melt or low flow augmentation will no longer be available. Overall, according to the simulations, streamflow variability and low flow extremes will increase. Despite the uncertainties reflected in the range of downscaled and bias-corrected climate model data, the projected changes are a clear mandate to reconsider water uses and conservation goals along the river.

The CHR members met live in Wageningen in the Netherlands. This meeting was followed by the CHR jubilee symposium. The pandemic situation was by that time acceptable only for vaccinated people.