Analysis of seasonal terrestrial water storage variations in regional climate simulations over Europe

Land-surface processes play a major role in the climate system, and their validation is crucial to improve current climate models. Here we investigate the seasonal evolution of terrestrial water storage (TWS) (includes all water stored on land) in an ensemble of 30-year-long climate simulations from the PRUDENCE archive (9 regional and 2 global models), representing current and future climatic conditions. For validation purposes we employ a recently published basin-scale water-balance (BSWB) data set of diagnosed monthly TWS variations, where the term variations refers to monthly changes in TWS. The analysis is conducted in five large-scale European domains composed of major river basins. This analysis shows that the climatology of most models lies within the interannual variability of the BSWB data set in the investigated regions, but the different models sometimes display considerable discrepancies in the seasonal evolution of TWS. In particular, we find that all models suffer from a considerable underestimation of interannual TWS variability. The deviations of the individual models from the BSWB data set can be linked to biases in the hydrological fluxes (i.e., precipitation, runoff, evapotranspiration). The simulated future changes for the Intergovernmental Panel on Climate Change (IPCC) A2 scenario suggest an enhancement of the seasonal cycle of TWS, with drier soils in summer. Mainly in the Central European domain, several models show a reduction of the year-to-year variability of summer TWS variations, indicating an exhaustion of the models' soil water reservoirs by the end of summer under future climatic conditions.