Hydropower and glacier retreat: what is at stake?

Especially during hot summers like the one in 2018, the Swiss glaciers are a precious source of water, in particular for hydropower production. But as we all know, glaciers are continuously retreating, meaning that they release water that was accumulated years to centuries ago, and that cannot be replenished by precipitation in the near future. Therefore, an interdisciplinary SCCER-SoE research team including glaciologists, hydrologists, and hydraulic engineers decided to quantify the following aspects: How strongly relies Swiss hydropower production on waters released by glaciers? How big are the local variations? How might hydropower production evolve in the future? To answer these questions, we needed to compile the most recent data sets on Swiss water resources and hydropower infrastructure, and on the glacier mass evolution in the past and in the future.

Less hydropower production because of glacier retreat by the end of this century

According to our estimates, since 1980 3.0 % to 4.0 % of Swiss hydropower production was directly provided by losses in glacier volume. This corresponds to between 1.0 and 1.4 TWh per year, or the annual electricity consumption of roughly 230,000 Swiss households. Glacier mass loss will continue to feed the Swiss hydropower plants in the future, but the production directly related to this contribution will drop to around 0.4 TWh per year by 2070-2090. In other words, the calculations anticipate a reduction in hydropower production of up to 1 TWh per year resulting from the fact that the glaciers will not continue to release such large amounts of waters as they do at the moment.

However, there are strong regional differences (Figure 1). In the Rhone river catchment, with its large valley glaciers, between 6.5 % and 8.5 % of the annual hydropower production stemmed from glacier mass loss in the recent past. This share is likely to only marginally decrease between 2040 and 2060, but will drop by half from 2070 to 2090.

Hydropower production from annual glacier mass loss in the major hydropower production catchments.

Glacier meltwater: more important for Swiss hydropower production than one might think

Knowing that glaciers cover only around 2.5 % of the Swiss territory, the significance of glacier mass depletion for Swiss-wide hydropower production might be surprising at first glance. There are two reasons for its importance: First, the high electricity coefficients (that is the amount of electricity that can be produced with a given amount of water) of hydropower schemes exploiting glacier water. Second, the fact that glacier water is turbined multiple times along its path between the glaciers and the Country borders. In the Rhone catchment, for example, some waters are used up to nine times before leaving Switzerland, whilst some hydropower schemes in the Valais and the Berner Oberland can produce more than 3 kWh per m3 of water.

These Swiss-wide analysis highlights that glacier mass depletion should receive more attention in the context of the Energy Strategy 2050. The projected production reduction of 1 TWh per year from 2070 to 2090, for example, is comparable to the expected production decrease of 1.4 TWh per year due to the implementation of the Swiss water protection act. It is also of the same order of magnitude as the expected increase of hydropower production from additional small hydropower projects.

Future hydropower production depends on the producers

But what are the implications for hydropower production during future hot summers? It is important to point out that our analysis focused on annual hydropower production and its relation to glacier mass loss. The actual future hydropower production during hot summers will depend on how the hydropower producers adapt their production to the evolving water offer in the coming decades.