Thursday, June 02, 2016

Dam Backup Plan for Glacier Ice Loss

Illustration of the potential mitigation through water management. Volume surplus (light blue) is the runoff volume that, according to the projection, will be in excess to the runoff in the reference period during late spring and early summer. This volume could potentially be transferred into late summer and early autumn (arrow) in order to partially compensate (light green) the runoff reduction caused by glacier depletion. Volume deficit (light red) is the net reduction in annual runoff. The example refers to Glacier de la Girose, France. (Credit: Click to Enlarge.
Building dams at the bottom of disappearing glaciers to capture the runoff from melting mountain snow will be needed later this century to prevent widespread water shortages in the summer months.

A study of the Alpine glaciers that feed the major European rivers – the Danube, Po, Rhine and Rhone – show that the summer flow will be severely affected by the loss of many of the 3,800 glaciers in the mountains.

The effect will be the equivalent of a cubic kilometer of water being lost to the summer water supply − about 80% of Switzerland’s current total consumption.

Currently, the summer flow is high, because the glaciers are losing ice mass rapidly.  Increased temperatures have seen the glaciers retreating up the mountains for more than 50 years.  About 75% of the melting occurs between July and September.  Some smaller glaciers are already disappearing, and as more do so the summer supply will slump.

Water supply
The study, published in Environment Research Letters, was conducted in the Alps, which are the world’s best-documented glaciers.  They are especially vulnerable to climate change because many are small.

But the problems faced by the people who live downstream and rely on them for water supply and crop irrigation are shared by millions across the world.  Large populations, particularly in South America and Central Asia, face a severe problem each summer as their glaciers disappear.

The figures for the Alps show that, between 2010 and 2039, the extra summer glacier melt flow will be around 20%.  Between 2040 and 2069, the flow would gradually reduce, and from 2070 to the end of the century it is expected to have dropped on average by 37%, leading to severe shortages.  In areas where glaciers disappear much earlier, the effects will be far more dramatic.
The project, led by the European Commission's Joint Research Center and the Swiss Federal Institute for Forest, Snow and Landscape Research, looked at the possibility of building dams on the bare slopes left by the retreating glaciers to capture runoff from winter rain and spring snowmelt and release it gradually in the summer to compensate for the lack of glacier melt.

Preserve ecology
The study says the plan would also have the benefit of not destroying local vegetation and habitat that had yet to colonize the bare rocks, and it would also preserve the ecology of existing streams that might otherwise dry up in the summer.

But the researchers, realizing that it is impractical and far too expensive to build a dam for every disappearing glacier, calculated that it would be possible to build a dozen large dams at strategic collecting points in order to regulate the flow of rivers downstream.

This would help regulate water flow in the larger rivers, serving hydro-electric schemes and making up for about two-thirds of the losses expected.  But the researchers accept that these larger dams would not help isolated smaller communities upstream that had lost their local glaciers.

Read more at Dam Backup Plan for Glacier Ice Loss

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