Managing climate change in drinking water reservoirs: potentials and limitations of dynamic withdrawal strategies

Abstract

Background: Climate change induced a rise in surface water temperature and a prolongation of summer stratification in drinking water reservoirs. Stratification and temperature are important factors for drinking water production because they influence bio-geo-chemical processes and thus affect water quality. Most drinking water reservoirs have outlet structures that allow water to be withdrawn from different depths at variable rates. The thermal structure of these reservoirs can thus be managed actively by means of dynamic withdrawal schemes. Results: We employed the hydro-physical General Lake Model to simulate the effects of different withdrawal strategies on temperatures and stratification in three German reservoirs. In particular, we assessed the potential of depth- and time-variable withdrawal to mitigate the impacts of climate change. We found that deep water temperatures (25 m below surface) and the end of summer stagnation are strongly controlled by the withdrawal regime. Specifically, the simulated impact of the withdrawal scheme was of the same order of magnitude as the observed impact of climate change over the last 30 years. However, the end of ice cover, the onset of summer stagnation, and near-surface temperatures (3 m depth) were rather insensitive to altered withdrawal strategies. Conclusions: Our results suggest that an adaption of withdrawal depth and timing will partly compensate for the effects of climate change. Dynamic withdrawal should thus be considered as an integral part of future reservoir management strategies.