Snow of tomorrow | The glaciers are melting - what does that mean for the water?

The IPCC Special Report on Oceans and Cryosphere in a Changing Climate (SROCC), which was published in September and contains an extra chapter on the mountain cryosphere, provides an answer. The cryosphere is everything that is frozen, i.e. glaciers, snow, ice on rivers and lakes, frozen ground, etc.

When the snow melts in spring, there is more water in the rivers - logically. And anyone who has ever passed the same glacial stream in the morning and afternoon in summer knows that the stream has more water in the afternoon. In addition to individual precipitation events, snowmelt and summer glacier runoff determine how much water arrives downstream on many rivers.

Peak water

When glaciers shrink, there is initially more water in the runoff streams and rivers because more and more ice is melting. At some point, however, a point is reached at which the discharge volumes decrease again - less ice melts in total because there is simply not much ice left. This reversal point is often referred to as "peak water". Peak water occurs earlier on small glaciers and lasts longer on large ones. In the Alps, it is assumed that peak water has already been exceeded, at least in part, or will be exceeded before the middle of the century, as well as in other mountain regions with rather small glaciers.

Things are also changing in terms of snow. Winter runoff volumes tend to increase because more snow falls than rain and is therefore not stored in the snowpack first, but ends up in the river. The timing of snowmelt is shifting forward - probably by several weeks by 2100.

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Infographic on runoff before, during and after peak water. — Infographic on runoff before, during and after peak water
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IPCC SROCC

Effects

The further you move downstream from the mountains, the smaller the impact of glacier and snow runoff on river levels. Around a quarter of the water in the Rhone usually comes from meltwater (in the extremely hot summer of 2003 it was up to 40%). The Po also carries around 20% meltwater. In the Danube, on the other hand, it is only around 3%. Accordingly, changes in the amount of meltwater have different effects on different river systems.

Hydropower

In many mountain regions, hydropower plays an important role in the energy industry. If the timing of the maximum discharge shifts, or there is generally more or less water in the relevant rivers, power plant operators have to adjust their systems. As there are many other social and economic factors that influence the profitability of hydropower plants, there are few concrete studies that quantify climate change impacts on hydropower from an economic perspective. Reservoirs can theoretically act as reservoirs that compensate for changes downstream - whether by gradually releasing water in hot, dry summers or by capturing extra water that might cause flooding further downstream.

Agriculture

Agriculture in mountainous regions uses summer glacier runoff and snowmelt water for irrigation. If this water is lacking, it is mainly those regions where there is little other water (rain) that have a problem, such as the tropical Andes, parts of Asia and some areas in the USA. Here, too, the effects are greater the closer you are to the glaciers, but for some regions, agricultural water shortages can also be expected to increase significantly downstream by the middle of the century, for example in the Rhone Valley in the Alps. In agriculture, too, there are many other important factors in addition to cryosphere-related changes in water - rising temperatures mean that some crops produce lower yields, while elsewhere, for example, apple trees and maize are now surviving at altitudes where this was previously not possible.

Drinking water

The Alpine glaciers play a relatively minor role in our drinking water. Dry mountain regions are again significantly more affected, but the effects vary greatly from place to place and it is difficult to make general statements about exactly when and where water will become scarce and to what extent. Quantitative studies are mainly available from certain parts of Nepal and the tropical Andes. In La Paz, Bolivia, meltwater contributes an average of around 15% to drinking water, with the figure rising to 27% in the dry season (figures for the period 1963-2006) and can be as high as 86% in extreme drought. Peak water does not yet seem to have been exceeded here and the available water is actually increasing. If all the glaciers that supply meltwater for La Paz have disappeared and the amount of precipitation remains the same, this results in a modeled water decrease of 12% per year or 24% in the dry season. A regional model study for Bolivia, Peru and Ecuador estimates that around 390,000 people permanently obtain more than 25% of their drinking water from glacier runoff, with the figure rising to up to 4 million in extremely dry months.

When it comes to drinking water, it should also be emphasized that other factors may be more decisive than glacier melt. In the Andes, for example, it is expected that increased water demand due to population growth and other socio-economic factors will lead to problems more quickly than disappearing glaciers.

Conclusion

Water management is a multi-layered, complex issue, even without climate change. When glaciers and seasonal snowpack change, runoff volumes and river levels also change, and a complex issue becomes even more complex.

Here is an interesting example of local water management adaptation in response to shrinking glaciers: "artificial glaciers" in Ladakh.