Internal variability drives large runoff variations across Europe. Disentangling its effects from that of anthropogenic forcing in future regional projections is crucial for effective adaptation planning. Here, we show that internal variability is the main source of uncertainty in near-term changes in Europe compared to model and scenario uncertainty, or as important as model uncertainty for the Mediterranean. The contribution of internal variability is even larger for runoff than for precipitation or evapotranspiration over northern, western and central Europe. The inter-member differences in runoff changes are mainly explained by precipitation changes and indirectly by changes in sea level pressure. In potential disagreement with observational studies, no apparent teleconnection between runoff multi-decadal variability and the Atlantic multi-decadal variability is generally found in climate models. This misrepresentation of teleconnections might affect the multi-decadal variability of annual precipitation and therefore runoff over the Mediterranean. Indeed, the multi-decadal variability in precipitation and sea level pressure over this area is shown to be generally underestimated.

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