Does glacier melt threaten the power supply in Switzerland?

As glaciers retreat, the water supply from glacier melt will gradually decrease. If the ice melts completely, the annual amount of water will be determined only by precipitation; i.e. rain and snow. The speed of this development depends primarily on the degree of glaciation of the catchment areas, their direction of exposure and altitude.

In the case of reservoirs in catchment areas with little or no glacial influence, such as Salanfe in the Valais Alps or Hongrin in the Vaud Prealps, the availability of water and the resulting energy production depends very little or not at all on glacial inflows, but essentially on annual precipitation.

Global warming will cause the flow rate to increase earlier in the year, particularly in spring, as precipitation is more likely to be in the form of rain than snow and snowmelt occurs earlier. By the end of summer, however, the reservoirs will receive less water due to the dwindling water volumes from glacier melt.  

Climate models also forecast less precipitation in summer and a slight increase in winter. This changing precipitation pattern will have an effect on the flow rate regardless of the glacier melt.

In the heavily frozen catchment areas, the flow rates are at record highs that have never been reached since the hydropower plants were commissioned. This phenomenon is caused by the particularly hot summers and the resulting accelerated glacier melt. For example, the Gebidem dam in Valais has been experiencing overflows that last up to several days a year for some years. In this case, the full potential of the inflow cannot be harnessed due to the low capacity of the existing installations. After all, when the Gebidem dam was put into operation in 1969 the installations were designed for much smaller flow rates.

Another consequence of global warming is the increase in sediment of glacial origin transported by the water. This is due mainly to erosion under the glacier, recently exposed glacier forefields or walls, and moraines destabilised by the melting permafrost.

This transported sediment remains in reservoirs, regulating reservoirs or specially designed retention basins. If the sediment remains in these basins for a long time, the usable volume for hydropower production is reduced and may hamper use of the works. Therefore, the sediment is regularly removed by flushing or excavated by dredger and taken away. Global warming may mean that such measures occur more often in the future.

The glaciology department at ETH Zurich has conducted several studies in order to assess the potential effects of glacier retreat on hydropower production. These studies look at the glacial catchment areas of the power plants operated by Alpiq and consider the latest climate scenarios for Switzerland.

Climate change is forcing us to think about how to operate our hydroelectric plants in the hydrology of the future. In ice-covered watersheds, where flow rates are increasing, we are thinking about how to adapt existing facilities to this new situation. This may involve raising dams, increasing production capacity or building additional facilities.

The increasing sediment and consequent silting up of certain basins and/or water intakes means alternatives to flushing processes are being sought in order to reduce the impact on aquatic ecology and water losses during hydropower production.

Numerous simulations have been performed to estimate when the Gorner glacier will disappear. It seems that even in the worst-case scenario of climate development – in terms of the development of greenhouse gas concentrations – it will still exist in 2100. But in this extreme case, slightly less than 20% of the current volume of the Gorner glacier will remain.