• Energy Research

Abstract Hydropower plays a significant role in the transition towards a low-carbon power system, being a renewable energy source that can complement solar and wind power, which are highly intermittent. However, hydropower is itself dependent on local weather conditions and climate variability. Moreover, extreme climate conditions, such as hot-dry compound events, can have a major impact on hydropower production (HP). Here, we examine the impacts of hot-dry conditions on HP under current and future climate scenarios in Switzerland, a country where hydropower provides the biggest share (60%) of the total electricity production. Overall, our results point out that the impacts of hot-dry conditions on HP are case-specific. We found that hot-dry compound conditions during the warmer months negatively impact HP in power plants with little or no water storage capacity (run-of-river schemes). On the contrary, schemes with large, seasonal accumulation lakes and significant glacier resources will continue to be able to produce high amounts of HP during hot-dry conditions in summer, which is an important result for Alpine hydropower.

Abstract Hydropower plays a significant role in the transition towards a low-carbon power system, being a renewable energy source that can complement solar and wind power, which are highly intermittent. However, hydropower is itself dependent on local weather conditions and climate variability. Moreover, extreme climate conditions, such as hot-dry compound events, can have a major impact on hydropower production (HP). Here, we examine the impacts of hot-dry conditions on HP under current and future climate scenarios in Switzerland, a country where hydropower provides the biggest share (60%) of the total electricity production. Overall, our results point out that the impacts of hot-dry conditions on HP are case-specific. We found that hot-dry compound conditions during the warmer months negatively impact HP in power plants with little or no water storage capacity (run-of-river schemes). On the contrary, schemes with large, seasonal accumulation lakes and significant glacier resources will continue to be able to produce high amounts of HP during hot-dry conditions in summer, which is an important result for Alpine hydropower.

Post-processing has received much attention during the last couple of years within the hydrological community, and many different methods have been developed and tested, especially in the field of flood forecasting. Apart from the different meanings of the phrase “post-processing” in meteorology and hydrology, in this paper, it is regarded as a method to correct model outputs (predictions) based on meteorological (1) observed input data, (2) deterministic forecasts (single time series) and (3) ensemble forecasts (multiple time series) and to derive predictive uncertainties. So far, the majority of the research has been related to floods, how to remove bias and improve the forecast accuracy and how to minimize dispersion errors. Given that global changes are driving climatic forces, there is an urgent need to improve the quality of low-flow predictions, as well, even in regions that are normally less prone to drought. For several catchments in Switzerland, different post-processing methods were tested with respect to low stream flow and flooding conditions. The complexity of the applied procedures ranged from simple AR processes to more complex methodologies combining wavelet transformations and Quantile Regression Neural Networks (QRNN) and included the derivation of predictive uncertainties. Furthermore, various verification methods were tested in order to quantify the possible improvements that could be gained by applying these post-processing procedures based on different stream flow conditions. Preliminary results indicate that there is no single best method, but with an increase of complexity, a significant improvement of the quality of the predictions can be achieved.

Post-processing has received much attention during the last couple of years within the hydrological community, and many different methods have been developed and tested, especially in the field of flood forecasting. Apart from the different meanings of the phrase “post-processing” in meteorology and hydrology, in this paper, it is regarded as a method to correct model outputs (predictions) based on meteorological (1) observed input data, (2) deterministic forecasts (single time series) and (3) ensemble forecasts (multiple time series) and to derive predictive uncertainties. So far, the majority of the research has been related to floods, how to remove bias and improve the forecast accuracy and how to minimize dispersion errors. Given that global changes are driving climatic forces, there is an urgent need to improve the quality of low-flow predictions, as well, even in regions that are normally less prone to drought. For several catchments in Switzerland, different post-processing methods were tested with respect to low stream flow and flooding conditions. The complexity of the applied procedures ranged from simple AR processes to more complex methodologies combining wavelet transformations and Quantile Regression Neural Networks (QRNN) and included the derivation of predictive uncertainties. Furthermore, various verification methods were tested in order to quantify the possible improvements that could be gained by applying these post-processing procedures based on different stream flow conditions. Preliminary results indicate that there is no single best method, but with an increase of complexity, a significant improvement of the quality of the predictions can be achieved.

Past studies on the impacts of climate change (CC) on Alpine hydropower production have focused on high-head accumulation power plants. We provide one of the first comprehensive, simulation-based studies on CC impacts on Alpine Run-of-River (RoR) production, also considering effects of environmental flow requirements and technical increase potential. We simulate future electricity production under three emissions scenarios for 21 Swiss RoR plants with a total production of 5.9 TWh a-1. The simulations show an increase in winter production (4% to 9%) and a decrease in summer production (-2% to -22%), which together lead to an annual decrease of about -2% to -7% by the end of the century. The production loss due to environmental flow requirements is estimated at 3.5% of the annual production; the largest low-elevation RoR power plants show little loss, while small and medium-sized power plants are most affected. The potential for increasing production by optimising the design discharge amounts to 8% of the annual production. The largest increase potential is related to small and medium-sized power plants at high elevations. The key results are: i) there is no linear relationship between CC impacts on streamflow and on RoR production; the impacts depend on the usable streamflow volume, which is influenced by the Flow Duration Curve, environmental flow requirements, and design discharge; ii), the simulated production impacts show a strong correlation (>0.68) with the mean catchment elevation. The plants at the highest elevations even show an increase in annual production of 3% to 23%, due to larger shares of precipitation falling as rain instead of snow. These general results are transferable to RoR production in similar settings in other Alpine locations and should be considered in future assessments. Future work could focus on further technical optimisation potential, considering detailed operational data.

Past studies on the impacts of climate change (CC) on Alpine hydropower production have focused on high-head accumulation power plants. We provide one of the first comprehensive, simulation-based studies on CC impacts on Alpine Run-of-River (RoR) production, also considering effects of environmental flow requirements and technical increase potential. We simulate future electricity production under three emissions scenarios for 21 Swiss RoR plants with a total production of 5.9 TWh a-1. The simulations show an increase in winter production (4% to 9%) and a decrease in summer production (-2% to -22%), which together lead to an annual decrease of about -2% to -7% by the end of the century. The production loss due to environmental flow requirements is estimated at 3.5% of the annual production; the largest low-elevation RoR power plants show little loss, while small and medium-sized power plants are most affected. The potential for increasing production by optimising the design discharge amounts to 8% of the annual production. The largest increase potential is related to small and medium-sized power plants at high elevations. The key results are: i) there is no linear relationship between CC impacts on streamflow and on RoR production; the impacts depend on the usable streamflow volume, which is influenced by the Flow Duration Curve, environmental flow requirements, and design discharge; ii), the simulated production impacts show a strong correlation (>0.68) with the mean catchment elevation. The plants at the highest elevations even show an increase in annual production of 3% to 23%, due to larger shares of precipitation falling as rain instead of snow. These general results are transferable to RoR production in similar settings in other Alpine locations and should be considered in future assessments. Future work could focus on further technical optimisation potential, considering detailed operational data.

The European Alps are well positioned to contribute significantly to the energy transition. In addition to sites with above-average potential for wind and solar power, the “water towers” of Europe provide flexible, low-carbon power generation as well as energy storage. In the future, hydropower systems are expected to become more than mere electricity generators, serving a key role as flexible complements to intermittent power generators and as providers of large-scale seasonal and daily energy storage. Energy transition on national and European scales can be facilitated by expanding the capacity of pumped storage hydropower (PSHP) plants. Yet the extension of hydropower production, in particular PSHP, remains controversial, primarily due to environmental concerns. Focusing on 2 Alpine countries, Austria and Switzerland, this paper provides a system view of hydropower production and energy storage in the Alps. It discusses advantages and drawbacks of various assessment tools and identifies gaps and needs for the integrated assessment of PSHP plants. It concludes that instruments that evaluate the impacts and sustainability of PSHP projects need to be developed, elaborated, and applied in a participatory manner, in order to promote public dialogue, increase social acceptance, and, ideally, encourage energy consumers to become advocates of a sustainable energy future. Mountain Research and Development, 36 (2) ISSN:0276-4741 ISSN:1994-7151