Combined effects of pumped-storage operation and climate change on thermal structure and water quality

Abstract

The assessment of ecological impacts of pumped-storage (PS) hydropower plants on the two connected water bodies is usually based on present climatic conditions. However, significant changes in climate must be expected during their long concession periods. We, therefore, investigate the combined effects of climate change and PS operations on water temperature and quality, as well as extent and duration of stratification and ice cover, using a site in Switzerland. For this purpose, a coupled two-dimensional hydrodynamic and water quality model for the two connected water bodies is run with 150 years long synthetic stochastic meteorological forcing for both current and future climate conditions under two PS and two reference scenarios. The results show relevant synergistic and antagonistic effects of PS operations and climate change. For example, hypolimnion temperatures in September are projected to increase by < 0.6°C in a near-natural reference scenario and by~2.5°C in an extended PS scenario. Ice cover, which occurs every year under near-natural conditions in the current climate, would almost completely vanish with extended PS operation in the future climate. Conversely, the expected negative impacts of climate change on hypolimnetic dissolved oxygen concentrations are partially counteracted by extended PS operations. We, therefore, recommend considering future climate conditions for the environmental impact assessment in the planning of new or the recommissioning of existing PS hydropower plants.

Ensemble modelling of ice cover for a reservoir affected by pumped‐storage operation and climate change

“…Ice grows if the net heat flux at the ice‐water interface is negative and can melt both from the top or the bottom when the corresponding net heat fluxes are positive. Within this study, we extend the work of Kobler et al (, ) who analysed the effects of PS operation and climate change for only one model segment in the deeper part of the reservoir to the investigation of five segments at different distances from the dam, where PS flows are withdrawn and released. This allows assessing how the effects of PS operation spread throughout the reservoir.…”

“…Hourly meteorological forcing, generated with the Vector‐Autoregressive Weather Generator [VG] (Schlabing, Frassl, Eder, Rinke, & Bárdossy, ) for all four models, is based on previous studies of Kobler et al (, ). MyLake runs only with daily meteorological forcing, which was calculated by averaging the hourly data.…”

“…The temperature of the PS pumping flow was taken from previous projections of the epilimnion temperature of Upper Lake Zurich for either considering observed meteorological conditions (Kobler et al, ) or time series of current and future climate conditions developed with a weather generator (Kobler et al, ).…”

“…Similar to Kobler et al (), we generated ten synthetic time series for current (1997–2012) and future (2077–2092) climate conditions. These time series were developed using the weather generator VG (Schlabing et al, ), which allows emulating the observed variables or generating future conditions by changing mean or variability.…”

“…Here, we investigate the combined effects of PS operations and climate change on ice cover in Sihlsee, the upper reservoir of a PS scheme in Switzerland. These effects were previously assessed using the laterally averaged two‐dimensional model CE‐QUAL‐W2 both for different PS scenarios (Kobler et al, ) and interactions with projected future climate (Kobler, Wüest, & Schmid, ). However, the modifications of the ice module of CE‐QUAL‐W2 by Kobler et al () were not tested comprehensively, and therefore, uncertainties about its applicability remained.…”