Groundwater depletion rate accelerating worldwide

Sep 23, 2010
Global map of groundwater depletion, measured in cubic meters of water per year.

In recent decades, the rate at which humans worldwide are pumping dry the vast underground stores of water that billions depend on has more than doubled, say scientists who have conducted an unusual, global assessment of groundwater use.

These fast-shrinking subterranean reservoirs are essential to daily life and agriculture in many regions, while also sustaining streams, wetlands, and and resisting land subsidence and salt water intrusion into fresh . Today, people are drawing so much water from below that they are adding enough of it to the oceans (mainly by evaporation, then precipitation) to account for about 25 percent of the annual across the planet, the researchers find.

Soaring global depletion bodes a potential disaster for an increasingly globalized agricultural system, says Marc Bierkens of Utrecht University in Utrecht, the Netherlands, and leader of the new study.

"If you let the population grow by extending the irrigated areas using groundwater that is not being recharged, then you will run into a wall at a certain point in time, and you will have hunger and social unrest to go with it," Bierkens warns. "That is something that you can see coming for miles."

He and his colleagues will publish their new findings in an upcoming issue of , a journal of the American Geophysical Union.

In the new study, which compares estimates of groundwater added by rain and other sources to the amounts being removed for agriculture and other uses, the team taps a database of global groundwater information including maps of groundwater regions and water demand. The researchers also use models to estimate the rates at which groundwater is both added to aquifers and withdrawn. For instance, to determine groundwater recharging rates, they simulate a groundwater layer beneath two soil layers, exposed at the top to rainfall, evaporation, and other effects, and use 44 years worth of precipitation, temperature, and evaporation data (1958-2001) to drive the model.

Applying these techniques worldwide to regions ranging from arid areas to those with the wetness of grasslands, the team finds that the rate at which global groundwater stocks are shrinking has more than doubled between 1960 and 2000, increasing the amount lost from 126 to 283 cubic kilometers (30 to 68 cubic miles) of water per year. Because the total amount of groundwater in the world is unknown, it's hard to say how fast the global supply would vanish at this rate. But, if water was siphoned as rapidly from the Great Lakes, they would go bone-dry in around 80 years.

Groundwater represents about 30 percent of the available fresh water on the planet, with surface water accounting for only one percent. The rest of the potable, agriculture friendly supply is locked up in glaciers or the polar ice caps. This means that any reduction in the availability of groundwater supplies could have profound effects for a growing human population.

The new assessment shows the highest rates of depletion in some of the world's major agricultural centers, including northwest India, northeastern China, northeast Pakistan, California's central valley, and the midwestern United States.

"The rate of depletion increased almost linearly from the 1960s to the early 1990s," says Bierkens. "But then you see a sharp increase which is related to the increase of upcoming economies and population numbers; mainly in India and China."

As groundwater is increasingly withdrawn, the remaining water "will eventually be at a level so low that a regular farmer with his technology cannot reach it anymore," says Bierkens. He adds that some nations will be able to use expensive technologies to get fresh water for food production through alternative means like desalinization plants or artificial groundwater recharge, but many won't.

Most water extracted from underground stocks ends up in the ocean, the researchers note. The team estimates the contribution of groundwater depletion to sea level rise to be 0.8 millimeters per year, which is about a quarter of the current total rate of sea level rise of 3.1 millimeters per year. That's about as much sea-level rise as caused by the melting of glaciers and icecaps outside of Greenland and Antarctica, and it exceeds or falls into the high end of previous estimates of groundwater depletion's contribution to sea level rise, the researchers add.

Explore further: Increase in reported flooding a result of higher exposure

More information: The paper by Bierkens et al. is still "in press".

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User comments : 9

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trekgeek1
4 / 5 (1) Sep 23, 2010
Well, we better get fusion power down quickly so we have enough power to run desalinization facilities 24/7. It would be amazing, using sea water to create power to filter sea water. Is there anything water can't do?
sstritt
1 / 5 (1) Sep 23, 2010
Well, we better get fusion power down quickly so we have enough power to run desalinization facilities 24/7. It would be amazing, using sea water to create power to filter sea water. Is there anything water can't do?

Wouldn't want to hold my breath for fusion power. It is, as they say, 30 years away, and always will be. That's a bit pessimistic, but there may be easier ways such as the new nano-pore membranes to filter the salt
LuckyBrandon
1 / 5 (5) Sep 23, 2010
before too long we would deplete the sea water...thats infinitely more stupid than using the freshwater...at least we can make fresh water out of salt water....once thats gone, we're screwed....
fusion power doesnt help the dwindling fresh water supply though...so that statement is somewhat baseless isnt it? unles i misunderstood...

i think we need to focus more on how to concentrate and make our own H2O without the need to tap the natural resevoirs...
harryhill
1 / 5 (2) Sep 23, 2010
Drawing water from the ocean means that other things (animals) are also drawn into the system.The oceans are in bad enough shape without adding more injury.
For most people, water is just something to use. From what I can see in the the arid region of Utah, not much is done to conserve water. When water is short, the only idea is to look for more...not conserve.
JCurtis
3.8 / 5 (4) Sep 24, 2010
The root of this problem is of course the rapidly increasing population of the planet. More people need more water for themselves, their crops, and their animals. There is a limit to growth and it will be imposed by the lack of water.
Tank
4.3 / 5 (6) Sep 24, 2010
before too long we would deplete the sea water.thats infinitely more stupid than using the freshwater.at least we can make fresh water out of salt water.once thats gone, we're screwed.
fusion power doesnt help the dwindling fresh water supply though.so that statement is somewhat baseless isnt it? unles i misunderstood.
i think we need to focus more on how to concentrate and make our own H2O without the need to tap the natural resevoirs...


I'm not sure where to start...wow.

Deplete sea water. Ok I feel bad that I actually looked for this number but, world water usage is 0.0003% of the ocean volume. And, freshwater pretty much always ends up back in the ocean.

Fusion is a bit odd of a choice but the key here is a more abundant power supply would make desalinization cheaper and easier.

Make H20, ok.....There is really no where to go with that, with only 150 characters left, or even with 150,000 char.

I absolutely hope that my meter is dead and this was just sarcasm.
LuckyBrandon
2 / 5 (3) Sep 25, 2010
@Tank-
i cant believe you looked that up either...but that number would rise substantially if we started desalinization at a high rate, which we are bound to begin doing as soon as we find a better method...and it will likely immediately cause desal plants to be built globally...vastly raising that number from that alone...

Yes the creation of H2O from scratch was more in jest...but a nice thought...and I bet feasible at some point (not saying that point isnt 10,000 years from now)...honestly its more likely we'd harvest from space....
ThanderMAX
5 / 5 (2) Sep 27, 2010
before too long we would deplete the sea water...thats infinitely more stupid than using the freshwater...at least we can make fresh water out of salt water....once thats gone, we're screwed....


You can't deplete ocean water, because it's a closed
system(everything is inside/around earth). Any water usage will eventually reach either ground aquifers or onto ocean (via river/rain).

Unless some aliens tries to suck ocean water as seen in sci-fi movie, water will always be with us.
GSwift7
1 / 5 (1) Sep 27, 2010
The problem of fresh water isn't really a global problem as much as a regional problem. You could have an endless supply of water from a 'magic fountain' in the middle of Tibet and it wouldn't do any good for the people in California. We already have the technology to desalinate water at an astounding rate. There are numerous desalination plants around the world. I believe one of the big ones is used for the Miami FL area. The problem is cost per volume, not really supply. As areas start to have trouble with ground water supply, they will naturally convert to other sources, whether that means piping in water from other places, or desalination is just a matter of economics really. Poor places already suffer from severe water shortage because they can't afford the available methods to supply it, such as Somalia and Ethiopia. This isn't a new crisis. I did a science class report on this way back in the 80's.