Conclusion
Alpine hydropower production (HP) is benefitting from glacier water resources that have been accumulated decades and centuries ago, and that cannot be replenished in the near future. This first quantification of the HP share originating from annual glacier mass loss at the scale of an Alpine region reveals that 3.1% to 4% of the total annual Swiss HP presently originates from this transient water resource. The share will rapidly decline for all Swiss regions, resulting in a reduction of the present-day production levels of about 1.0 TWh yr-1 by mid-century. This figure is comparable to the 1.4 TWh yr-1 production loss that can be expected from the implementation of the new Swiss water protection act [47, 54]. An exception is given for the Rhone river catchment, in which the relatively large amount of glaciers will continue to provide increased amounts of melt water at least until the late 2040s. Despite of observational uncertainties, we have shown that the presented estimates are robust. We anticipate our results to have direct implications for national HP infrastructure projects, such as storage increase at high elevation sites or multipurpose projects combining HP and the regulation of interannual hydrological variability. Beyond the scale of the analyzed case study, the relevance of our results can be summarized as follows: First of all, the results for Switzerland show that the impact of glacier retreat on HP can be reliably estimated from regional electricity coefficient trends, which here was shown to be of around 1.0 kWh m-3 per 1000 m elevation increase. Second, the results for Switzerland underline that significant annual HP reduction might result from glacier retreat already in the near future; the highlighted large regional differences call for more detailed studies in Europe and elsewhere.
