The ASG-Rhine project quantified the daily fractions of rain, snowmelt, and glacier ice melt components vof streamflow over the long period from 1901-2006 for the entire Rhine basin. As with every model simulation, the results contain a number of uncertainties due to uncertainties in the underlying data, the simplified process representation by the models, and model parameterization. The project carried out a number of analyses to improve the understanding of these uncertainties. Overall, the conclusion is that they do not affect the principal findings, which is owed in particular to the detailed consideration of observation-based data of glacier change as well as of the dynamics of snow and runoff generation processes in the models. The elaborate model chain adapted for this project, which allows the tracking and analysis of the three streamflow components through the system, also offers a new tool for the analysis of climate and regulation scenarios.