Water management in reservoirs could substantially mitigate future summer water shortages which are anticipated as a consequence of ongoing glacier retreat. A recent study by Swiss and Italian researchers has begun to explore whether dams could replicate the hydrological role of glaciers, containing and storing meltwaters at high elevations in the valleys where glaciers were once located.
Environments with snow and glaciers play a vital role in terms of water availability, and have been described as “hotspots” regarding the impacts of expected climate change. Warmer temperatures will lead to a reduction in the size and duration of snow covered areas, whilst glaciers are expected to retreat substantially. This is anticipated to significantly affect the seasonality of runoff and result in a reduction of the water yields from high mountain areas. Indeed an estimated 80% of Switzerland’s annual water supply will be lost by 2100 as glaciers in the Alps retreat under rising temperatures.
Further estimates suggest that under an average emission scenario, annual runoff contributions from presently glacierised surfaces are expected to decrease by 16% by 2070–2099 – despite nearly unchanged contributions from precipitation. This is even more pronounced during the late summer months when a decrease of about 37% is projected. The need for adequate water management strategies in the future will become paramount.
A new study jointly led by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL); the Joint Research Centre of the European Commission in Ispra, Italy; and the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) at ETH Zurich, presents for the first time an estimate for the potential of mitigation by managing water through reservoirs. The basic idea is to transfer the additional water expected to be available during spring, because of an earlier onset of the melting season, to the summer months. The team simulated the effect of climatic change on glaciers across the European Alps and estimated that two thirds of the effect on seasonal water availability could be avoided when storing water in areas becoming ice free.
The authors, Daniel Farinotti, Alberto Pistocchi and Matthias Huss, say that potential of exploiting newly deglacierised areas has not often been addressed. It has also been suggested that: “Since the exposed fore?elds are bare, non-vegetated and relatively simple in their ecosystem structure, a potential exploitation could result in comparatively limited ecological impacts. Similarly, it could be argued that an intervention in the uppermost part of a given river stretch would have only minimal consequences on river continuity.”
This led the authors to asking the “admittedly provocative” question of whether replacing glaciers by dams could be an option theoretically worth considering in order to mitigate the projected changes in summer runoff. Effectively reservoirs would replace part of the hydrological effect currently provided by glaciers and the seasonal snow pack.
In this study the authors focused on the European Alps as it is a region expected to be signi?cantly affected by future changes in snow- and glacier-fed water resources. They used the output of a global glacier model (GloGEM) in combination with latest climate projections to assess the evolution of both glacier extent and run off until the end of the century. Storage capacities required for achieving the maximum possible mitigation were then computed and compared with an estimate of retention volumes that could hypothetically be installed in newly deglacierised forefields.
As part of the research, dams were virtually placed at the locations of the current glacier terminus and the volume of each individually formed lake was calculated. Dam heights and widths were limited to a maximum of 280m and 800m respectively (the dimensions of the largest dams currently installed in the Alpine area).
According to the research team, the potential for mitigating runoff reduction in the summer months is significant, and possibly of importance for individual regions. Results showed that the potentially available volume is ten times larger than the required one, and that about a dozen of centralised dams would be sufficient for meeting the storage demand.
The authors estimated that “by 2070–2099, roughly 1km3 a−1 of water could be seasonally redistributed, and that this volume would be suf?cient to offset about two thirds of the expected changes in July–September runoff across the European Alps.”
However Farinotti et al are quick to highlight that their analysis “clearly neglects a whole series of factors”. They point out that ecological, environmental, economical, and technical considerations, amongst others, would need to be considered. While their theoretical study does not also consider competing interests “that would likely arise in case of a widespread installation of arti?cial reservoirs”.
Indeed the authors go on to mention that the typical seasonal production cycle of current hydropower infrastructure installed in the Alpine region, is exactly anti-cyclical with their proposed mitigation strategy. They state that current hydropower operators with storage typically accumulate water during summer in order to produce energy during winter.
In addition to the above limitations, the authors acknowledge that seasonally transferring a given runoff volume cannot compensate for a reduction in the total annual runoff. There would also be technical challenges in centralising the water of the many glaciers (currently about 4000) across the Alps.
Although Farinotti et al admit that their technical solution would only solve part of the problem of water shortages due to ongoing glacier retreat and snow melt, they believe their study highlights the need for alternative water management strategies.
Farinotti et al. From dwindling ice to headwater lakes: Could dams replace glaciers in the European Alps? Environ. Res. Lett. (2016) 11 054022, doi: 10.1088/1748-9326/11/5/054022