[LUM#16] Dangerous thaw
Temperatures are rising and ice is melting, pouring hundreds of liters of water into rivers and streams today. But what about tomorrow? To better anticipate the consequences of glacier melt on water availability, hydrologists are seeking to gain a more detailed understanding of the dynamics of these immense ice masses.
Ice as far as the eye can see, covering more than 100,000 square kilometers. Peaks rising to over 8,000 meters above sea level. Welcome to the "third pole, " a vast glacial expanse stretching 3,600 kilometers between Afghanistan and Myanmar. "It is the third largest continental ice mass in the world after Antarctica and Greenland, " explains Pierre Chevallier*. The hydrologist knows this region well, having surveyed it many times. These field missions are essential for gaining a better understanding of the glaciers that feed ten major rivers in Asia, on which more than a billion people depend, both in the mountains and in the river basins downstream.
A third pole is now threatened by global warming. According to a study published in 2019 bythe International Centre for Integrated Mountain Development (ICIMOD), two-thirds of the glaciers in the Himalayas and Hindu Kush could melt by the end of the century if the planet continues on its current trajectory of greenhouse gas emissions. "When temperatures rise, not only is there less ice forming at the top of the glacier, but melting at the bottom of the glacier also intensifies. Already, in the Himalayas and Karakoram mountains, some glaciers are retreating," says the specialist.
Uncertainties
To better understand this phenomenon, researchers at the Hydrosciences Montpellier laboratory and their colleagues compiled the findings of more than 250 scientific articles. Their goal was to gain a better understanding of the links between global warming, changes in precipitation, and glacier retreat. "The situation is difficult to grasp and many uncertainties remain, particularly with regard to field observations and remote sensing data, but also modeling tools and their assumptions and scenarios, " explains Pierre Chevallier.
The future of these ice giants is, however, a key factor in the region, particularly for the Indus basin, where 50% of water resources come directly from snow and glaciers, while the neighboring Ganges and Brahmaputra basins are more dependent on monsoon rains. "As the glaciers melt, river flows increase , so initially there is more water available. But as the glacier shrinks and recedes, it will release less water and the resource will then dwindle," explains the hydrologist.
Optimizing water management
This is a major concern when we consider that in some countries, such as Pakistan, nearly 80% of available water resources are used for agriculture. "Much of the meltwater from glaciers is drawn from downstream rivers to irrigate agricultural production in the great plains, which are veritable breadbaskets. " And beyond concerns about the quantities of water required, this use poses a significant timing problem: "Snow and ice normally melt in the spring, when farmers need it most for grain germination. If water were to become scarce at this time of year, it would be particularly critical, " warns the hydrologist. Faced with this risk, experts are calling for this shortage to be anticipated in order to optimize water resource management and sharing. "In a context where the availability of resources fluctuates throughout the year, it is necessary to be able to ensure a satisfactory supply, in particular through the management of dams, which, for example, must not be full in order to be able to store water from melting ice, " emphasizes Pierre Chevallier.
Reducing uncertainty
But to better anticipate these changes, researchers still lack data, as highlighted in their study published in Science. "To fill these gaps, we recommend setting up an extensive observation network that places fully automatic weather stations on selected glaciers," explains the hydrologist. But also to develop comparison projects to examine the surface area and volume of glaciers, their dynamics, permafrost thawing, and snow and ice sublimation.
This data is essential for reducing uncertainty in scenarios for future change. "This consensus on the region's glacio-hydrology will help policymakers optimally plan the management of water demand and supply for agriculture, as well as hydroelectricity, household use, and sanitation," notes Pierre Chevallier. This anticipation is all the more important given that the countries concerned are experiencing rapid economic and demographic growth, which is accompanied by an increase in water demand.
© IRD – CNRS – Thibaut Vergoz, PRESHINE 2017
* HSM (UM – CNRS – IRD)
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