Does Water Management Reduce uncertainty of Projected Climate Change Impacts on River Discharge?

Climate change impact studies are associated with error propagation and amplification of uncertainties through model chains. Water management, especially reservoir management, reduces discharge variability. In this study we investigated how water management influences uncertainty propagation of climate change scenarios. We applied a model ensemble of (i) the regional climate model STAR (STAR 0K: no further climate change, STAR 2K and 3K: increase of mean annual temperature by 2 K and 3 K resp.; each scenario is represented by 100 realizations), (ii) the hydrological models SWIM and EGMO, and (iii) the water management model WBalMo. The study was performed in the two neighbouring catchments of the Schwarze Elster River (Germany) and the Spree River (Germany and Czech Republic). These catchments have similar climate, topography and land use, but differ in their water management. The Spree River has a higher reservoir capacity, more withdrawals and discharges from water users and more water transfers. The projected natural runoff in both catchments is similar. Compared to STAR 0K, the natural runoff decreases remarkably in the other climate scenarios. The uncertainties related to the climate projection are propagated through the hydrological model. In the Schwarze Elster River catchment, these uncertainties are slightly increased by the water management model, whereas in the Spree River catchment, due to a higher reservoir capacity and more water transfers, interannual variability and uncertainty of managed discharge are strongly moderated by water management. The results of this study imply that generally, effective water management can reduce uncertainty related to climate change impacts on river discharge. Catchments with a high storage ratio are less vulnerable to changing climate conditions. This underlines the role of water management in coping with climate change impacts. Yet, due to decreasing reservoir volumes in drought periods, reservoir management alone cannot compensate strong changes in climate conditions.