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August 9th, 2012
Two articles examining a recent study that shows the impact that agriculture is having upon the world’s water resources. The first, via NPR, comments:
This map is disturbing, once you understand it. It’s a new attempt to visualize an old problem — the shrinking of underground water reserves, in most cases because farmers are pumping out water to irrigate their crops.
The map itself isn’t hard to grasp. The colored areas show the world’s largest aquifers — areas which hold deposits of groundwater. The blue ones are doing fine; more rainfall is flowing into them than is being pumped out of them for homes or irrigating fields. As a result, these aquifers can continue to play a vital role in the environment. (Water in most aquifers doesn’t just sit there. It flows slowly, underground, and ends up sustaining rivers and lakes and all the creatures who live there.)
The aquifers that are painted red, orange, or yellow, meanwhile, are being drained rapidly. How rapidly? That brings us to the complicated part of this graphic.
 See those large grey shapes, below the map? Each one is a magnified reflection of an over-exploited aquifer. The amount of magnification represents the amount of water that people are currently pumping out of that aquifer, compared to the rate of natural replenishment. Tom Gleeson, at Montreal’s McGill University, and Ludovicus P. H. van Beek, at Utrecht University, in the Netherlands, created this graphic for an article they published in this week’s issue of the journal Nature.
They call those magnified shapes the “groundwater footprint” of each aquifer’s exploitation. The footprint of the Upper Ganges aquifer, for instance, is 54 times bigger than the aquifer itself. Think about that footprint this way: It’s the size, on a map, of the area that would be required to catch enough rainfall to replenish that aquifer and make up for all the water currently being pumped out of it.
Some of these aquifers are being exploited at a stunning rate, but what’s truly alarming is how many people depend on that over-exploitation for their food. These aquifers include the Upper Ganges, covering densely populated areas of northern India and Pakistan, and the North China plain, which is the heart of corn-growing in that country. The aquifer of Western Mexico has become a large source of fruit and vegetable production for the U.S.
The High Plains aquifer in the United States, meanwhile, is having a particularly bad year. Farmers are pumping even more than usual, because of the drought afflicting this part of the country, and it is getting less replenishment from rainfall. So water levels in the aquifer are falling even faster, leaving less water for the region’s rivers, birds, and fish.
This can’t go on forever. Already, many farmers are being forced to dig deeper wells to get at that water. But bigger changes are on the way: New irrigation technologies that use water much efficiently; a shift to different crops that demand less water; and in some areas, they’ll just have to stop using those underground stores of water altogether.
The second, via Reuters, looks at the report as well:
The world is depleting underground water reserves faster than they can be replenished due to over-exploitation, according to scientists in Canada and the Netherlands.
The researchers, from McGill University in Montreal and Utrecht University in the Netherlands, combined groundwater usage data from around the globe with computer models of underground water resources to come up with a measure of water usage relative to supply.
That measure shows the groundwater footprint – the area above ground that relies on water from underground sources – is about 3.5 times bigger than the aquifers themselves.
The research suggests about 1.7 billion people, mostly in Asia, are living in areas where underground water reserves and the ecosystems that rely on them are under threat, they said.
Tom Gleeson from McGill, who led the study, said the results are “sobering”, showing that people are over-using groundwater in a number of regions in Asia and North America.
Over 99 percent of the world’s fresh and unfrozen water sits underground, and he suggests this huge reservoir that could be crucial for the world’s growing population, if managed properly.
The study, published in the journal Nature, found that 80 percent of the world’s aquifers are being used sustainably but this is offset by heavy over-exploitation in a few key areas.
Those areas included western Mexico, the High Plains and California’s Central Valley in the United States, Saudi Arabia, Iran, northern India and parts of northern China.
“CRITICAL TO AGRICULTURE”
“The relatively few aquifers that are being heavily exploited are unfortunately critical to agriculture in a number of different countries,” Gleeson told Reuters. “So even though the number is relatively small, these are critical resources that need better management.”
Previous research has shown that it takes about 140 liters of water to grow the beans that go into one cup of coffee, whether they are cultivated in arid Ethiopia or the Colombian rain forest.
“The effect of this water use on the supply of available water will be very different,” the researchers wrote. “Until now, there has been no way of quantifying the impact of such agricultural groundwater use in any consistent, global way.”
Gleeson said limits on water extraction, more efficient irrigation and the promotion of different diets, with less or no meat, could make these water resources more sustainable.
Water sitting in underground aquifers was the subject of research by British researchers published in April that mapped huge reserves sitting under large parts of Africa that could provide a buffer against the effects of climate change, if used sustainably.
A team from the British Geological Survey and University College London estimated that reserves of groundwater across Africa are about 100 times the amount found on the continent’s surface.
Some of the largest reserves are under the driest North African countries like Libya, Algeria, Egypt and Sudan, but some schemes to exploit them are not sustainable.
The biggest is Libya’s $25 billion Great Manmade River project, built by the regime of slain dictator Muammar Gaddafi to supply cities including Tripoli, Benghazi and Sirte with an estimated 6.5 million cubic meters of water a day.
The network of pipes and boreholes is sucking water out of the ground that was deposited in the rocks under the Sahara an estimated 40,000 years ago, but is not being replenished.
It is unclear how long this water source will last, with estimates ranging between 60 and 100 years.