Ensemble of models shows coherent response of a reservoir’s stratification and ice cover to climate warming

Water temperature, ice cover, and lake stratification are important physical properties of lakes and reservoirs that control mixing as well as bio-geo-chemical processes and thus influence the water quality. We used an ensemble of vertical one-dimensional hydrodynamic lake models driven with regional climate projections to calculate water temperature, stratification, and ice cover under the A1B emission scenario for the German drinking water reservoir Lichtenberg. We used an analysis of variance method to estimate the contributions of the considered sources of uncertainty on the ensemble output. For all simulated variables, epistemic uncertainty, which is related to the model structure, is the dominant source throughout the simulation period. Nonetheless, the calculated trends are coherent among the five models and in line with historical observations. The ensemble predicts an increase in surface water temperature of 0.34 K per decade, a lengthening of the summer stratification of 3.2 days per decade, as well as decreased probabilities of the occurrence of ice cover and winter inverse stratification by 2100. These expected changes are likely to influence the water quality of the reservoir. Similar trends are to be expected in other reservoirs and lakes in comparable regions. Projekt DEAL; European Social Fund (ESF); Saxonian state parliament; National Science Foundation ABI development Grant [DBI 1759865]; European Union's Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant [722518]; WATExR project, ERA4CS, an ERA-NET by JPI Climate; MINECO (ES); FORMAS (SE); BMBF (DE); EPA (IE); RCN (NO); IFD (DK); European Union [690462]; NSF [DEB-1926050, DBI-1933016]; BMBF [FKZ 01LR 2005A] Published version Open Access funding enabled and organized by Projekt DEAL. Johannes Feldbauer is holder of a scholarship from the European Social Fund (ESF) and his work is co-financed by public tax funds as decided by the Saxonian state parliament. Robert Ladwig was funded through a National Science Foundation ABI development Grant (#DBI 1759865). Jorrit P. Mesman was funded by the European Union's Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 722518 (MANTEL ITN). Tadhg N. Moore was funded by: the WATExR project which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by MINECO (ES), FORMAS (SE), BMBF (DE), EPA (IE), RCN (NO), and IFD (DK), with co-funding by the European Union (Grant Number: 690462) and also by NSF Grants DEB-1926050 and DBI-1933016. Thomas U Berendonk, Thomas Petzoldt, and Johannes Feldbauer also received funding from the BMBF project FKZ 01LR 2005A-Forderma ss nahme "Regionale Informationen zum Klimahandeln" (RegIKlim).