Evaluating hydrologic change for a set of European catchments by performance-based weighting of an ensemble of hydrologic and climate models

Hydrologic variability is expected to change throughout Europe due to climate change. However, ensemble projections of future changes in discharge show large variation because of the uncertainty in climate projections. The robustness of the change signal can potentially be improved by performance-based weighting. Here we analyze future change projections from an ensemble of three hydrological models (CWatM, LISFLOOD and wflow_sbm) forced with climate datasets from the Coordinated Downscaling Experiment - European Domain (EURO-CORDEX). The experiment focusses on nine river basins spread over Europe. The basins have different climate and catchment characteristics that strongly influence the hydrological response. We evaluate the ensemble consistency, the geographical variation therein and apply two weighting approaches; (1) the Climate model Weighting by Independence and Performance (ClimWIP) that focuses on meteorological variables and (2) the Reliability Ensemble Averaging (REA) that is here applied to catchment specific discharge statistics.

In Southern and Northern-Europe the ensemble consistency is high. There is a strong climate change signal. In Central Europe the differences between models are more pronounced. Analysis of the weighting method reveal that both weighting methods favor projections from similar GCMs and assign high weights to a single or few best performing GCMs.