Sensitivity to climate change of the thermal structure and ice cover regime of three hydropower reservoirs

- We modify a 1D lake thermal and ice cover model for modeling hydropower reservoirs.
- The model is validated using observational data for three hydropower reservoirs.
- Climate change impacts on the thermal structure and ice cover regime are assessed.
- A combination of two climate models and two future time periods is considered.
- We discuss the uncertainties involved in the prognosis.

SummaryThis study examines the effect of climate-induced changes on the thermal state and ice cover regime of three reservoirs in Norway: Tesse, Follsjoe and Alta. The model used for the task is MyLake which is a one-dimensional deterministic model for lake ice and thermal stratification, which we modified to handle the effects of reservoir outflows. The model was first validated using observational datasets and it reproduced the vertical temperature profiles of the reservoirs, the withdrawal temperatures, and the ice cover dynamics reasonably well. The mean absolute error for vertical temperature predictions ranged from 0.7 °C to 1.13 °C. The validated model was then applied to investigate the impacts of climate change on the ice cover regime, the seasonal temperature profiles in general and the withdrawal water temperatures in particular. The climate change model forcings come from the medium level emission scenario A1B and two global circulation models (GCMs), which are dynamically downscaled using a regional climate model (RCM). Some of the predicted effects of climate change include: a reduction in ice cover duration ranging between 15 to 44 days in 2050s and 27 to 81 days in 2080s, depending on the scenarios and hydro-climatic conditions of the reservoirs. As a consequence of this, the period of stratification is lengthened by 20-31 days in 2050s, and 22-36 days in 2080s. The results also revealed that the southern near coastal reservoir (Follsjoe) is much more sensitive to the climate change signals compared to the inland (Tesse) and arctic (Alta) reservoirs.