MELTDOWN: The melting of mountain glaciers around the world may not contribute as much to water supplies as thought, new research argues.
Image: Abhishekjoshi/Flickr
From the Andes to the Himalayas, scientists are starting to question exactly how much glaciers contribute to river water used downstream for drinking and irrigation. The answers could turn the conventional wisdom about glacier melt on its head.
A growing number of studies based on satellite data and stream chemistry analyses have found that far less surface water comes from glacier melt than previously assumed. In Peru's Rio Santa, which drains the Cordilleras Blanca mountain range, glacier contribution appears to be between 10 and 20 percent. In the eastern Himalayas, it is less than 5 percent.
"If anything, that's probably fairly large," said Richard Armstrong, a senior research scientist at the Boulder, Colo.-based Cooperative Institute for Research in Environmental Sciences (CIRES), who studies melt impact in the Himalayas.
"Most of the people downstream, they get the water from the monsoon," Armstrong said. "It doesn't take away from the importance [of glacier melt], but we need to get the science right for future planning and water resource assessments."
The Himalayan glaciers feed into Asia's biggest rivers: the Indus, the Ganges and the Brahmaputra in India, Pakistan and Bangladesh, and the Yellow and Yangtze rivers in China. Early studies pegged the amount of meltwater in these river basins as high as 60 or 70 percent. But reliable data on how much water the glaciers release or where that water goes have been difficult to develop. Satellite images can't provide such regular hydrometeorological observations, and expeditions take significant time, money and physical exertion.
New methods, though, are refining the ability to study this and other remote glacial mountain ranges. Increasingly, scientists are finding that the numbers vary depending on the river, and even in different parts of the same river.
Creeping hyperbole
"There has been a lot of misinformation and confusion about it," said Peter Gleick, co-director of the California-based Pacific Institute for Studies in Development, Environment and Security. "About 1.3 billion people live in the watersheds that get some glacier runoff, but not all of those people depend only on the water from those watersheds, and not all the water in those watersheds comes from glaciers. Most of it comes from rainwater," he said.
A key step forward came last year when scientists at Utrecht University in the Netherlands, using remote sensing equipment, found that snow and glacier melt is extremely important to the Indus and Brahmaputra basins, but less critical to others. In the Indus, they found, the meltwater contribution is 151 percent compared to the total runoff generated at low elevations. It makes up about 27 percent of the Brahmaputra -- but only between 8 and 10 percent for the Ganges, Yangtze and Yellow rivers. Rainfall makes up the rest.
That in itself is significant, and could reduce food security for 4.5 percent of the population in an already-struggling region. Yet, scientists complain, data are often inaccurately incorporated in dire predictions of Himalayan glacial melt impacts.
"Hyperbole has a way of creeping in here," said Bryan Mark, an assistant professor of geography at Ohio State University and a researcher at the Byrd Polar Research Center.
Mark, who focuses on the Andes region, developed a method of determining how much of a community's water supply is glacier-fed by analyzing the hydrogen and oxygen isotopes in water samples. He recently took that experience to Nepal, where he collected water samples from the Himalayan glacier-fed Kosi River as part of an expedition led by the Mountain Institute.
Based on his experience in the Rio Santa -- where it was once assumed that 80 percent of water in the basin came from glacier melt -- Mark said he expects to find that the impact of monsoon water is greatly underestimated in the Himalayas.
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9 Comments
Add CommentThe information on sources of water is important and reassuring. One wants to know, however, what the "big picture" is for water, locally, here and there in the world. Glacier melt probably has little to do with the extinction of aquifers, for instance, especially extinctions which have already happened (Texas) or are happening (various). A water-supply map of the world, showing sources as percents (aquifer, rainfall, snowfall, glacier-melt, man-made-transfers) would be helpful to policymakers.
Reply | Report Abuse | Link to this"The answers could turn the conventional wisdom about glacier melt on its head." meaning that river water contributes to glaciers instead of glaciers contributing to river water? Huh, learn something new every day.
Reply | Report Abuse | Link to thisThis is all well and good for a particular snapshot of the system. But what happens during droughts and how does the contribution vary seasonally? My hypothesis would be that the role of glaciers is not so much in their day to day contribution but rather stabilizing the flow. So during periods of drought the glaciers would contribute a much higher percentage which may mitigate more extreme drought conditions in the watershed.
Reply | Report Abuse | Link to thisA couple of billion more people, increased food production through irrigation, increasing contamination of groundwater and increased potential for drought conditions may make any future decrease in glacial contributions to potable water supplies relatively insignificant.
Reply | Report Abuse | Link to thisRobert Schmidt may wish to reflect on the coupling of river surface evaporation and distance traveled- the farther the glacial water component moves, the less of it remains.
Reply | Report Abuse | Link to thisYo Poker Player,
Reply | Report Abuse | Link to thisAllow me to introduce you this thing called science. One of the great definitions of science is an error correction method. I like that. What you perceive as a weakness is a strength.
Now if only we could get Anthony Watts to admit to his errors...
pokerplyer: please help me get up to speed: on which side of the decimal point are these errors occuring?
Reply | Report Abuse | Link to thisPoker Player Says: I could point out a number of errors by the IPCC that SA has not chosen to discuss scientifically.
Reply | Report Abuse | Link to thisOh, please do. Just be sure you are careful not repeat lies and out of context quotes. You know like the Sunday Times having to retract the utterly bogus story about the Amazon rainforest. I would normally just point you to the retraction on the paper itself but apparently it has disappeared. But you know the Internet does not forget. Here is a scan of the apology.
http://www.realclimate.org/docs/ST_Correction_img007%5B1%5D.jpg
How about the Sunday Times being forced to issue a retraction for blatantly lying about the head of the IPCC?
Here is the Sunday Times retraction, it is still there:
Dr. Pachuri Retraction
http://www.telegraph.co.uk/news/7957631/Dr-Pachauri-Apology.html
But I am sure you are not just going to repeat easily debunked information that only a credulous ideologue swallows without a hint of skepticism. Am I right?
Pokerplayer: How about an article on the ability of GCMs to accurately predict actual conditions. Or maybe one on the design criteria for the current GCMs.
Trent Says: Happy to oblige:
Comparing Global Temperature Predictions
http://www.skepticalscience.com/comparing-global-temperature-predictions.html
I do hope you are not going to object to the article you requested simply because it is on Skeptical Science. That would be, uh, let me think here... Oh yes, an ad Hominem.
But do go on. I am sure you want to talk about Himalayan Glaciers and the typo in a subsection of a 3,000 page document and how such mistakes discredit the other 2,999 pages.
For much of the western US it is snow melt and not glaciers which is more critical. Of course if one has a somewhat empty dam or two, as on the Colorado, water can be stored at anytime.
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