Intrinsic uncertainties in future runoff changes over Europe in the next decades

For effective adaptation planning and water resources management, it is essential to assess the intrinsic uncertainties in future runoff changes over the next decades. Over Europe, runoff variations are mainly driven by precipitation, which, in turn, is influenced by large-scale atmospheric circulation over the North Atlantic. Previous studies have emphasized strong teleconnections between the European climate and the Atlantic Multidecadal Variability through air-sea interactions using reanalysis and observational datasets. However, these teleconnections have been suggested to be poorly represented in climate models. Here, we aim to quantify the influence of internal variability on future runoff changes in state-of-the-art climate models, to analyze the influence of these teleconnections on the internal variations of runoff at multi-decadal timescales, and to assess the realism of these internal variations.

We show that the intrinsic uncertainty accounts for at least 50% of the total uncertainty in near-term runoff changes over different European regions. At the source of the intrinsic uncertainty, we find a predominant role of atmospheric noise in the models, through the modulation of precipitation. The past multi-decadal variability of precipitation and large-scale atmospheric circulation is then evaluated using different observational datasets. These analyses suggest that the intrinsic uncertainty in future runoff projections is well represented in northern, western and central Europe but is underestimated over the Mediterranean region.