Our Oversized Groundwater Footprint

A dry well in India. Credit: Bhaskaranaidu/Creative Commons

We don’t see it, smell it or hear it, but the tragedy unfolding underground is nonetheless real – and it spells big trouble.

I’m talking about the depletion of groundwater, the stores of H2O contained in geologic formations called aquifers, which billions of people depend upon to supply their drinking water and grow their food.

For a long time, we had only a vague sense of the scale of this depletion, mostly through anecdotal evidence and selected country studies. While researching my 1999 book Pillar of Sand, I gathered the best data I could find at the time, and with all the necessary caveats, estimated that about 8-10 percent of the world’s food supply depended upon the draining of underground aquifers.

About a decade later, modeling work by Marc Bierkens of Utrecht University in the Netherlands and his colleagues arrived at a global depletion estimate that produced a similar figure:  their estimated 283 billion cubic meters of groundwater depleted in 2000 is sufficient to produce 188.6 million tons of grain, equal to 10 percent of that year’s global grain production. While not all groundwater pumped from the earth is used to produce grain, the vast majority of it is.

In recent years a number of other studies, along with NASA’s GRACE (Gravity Recovery and Climate Experiment) mission, have corroborated the dangerous trend.  From the Arabian deserts to the North China Plain, and from the breadbasket of India to the fruit and vegetable bowl of the United States, we are increasingly dependent on the unsustainable use of groundwater.

In effect, we’re robbing the Peters of the future to feed the Pauls of today.

Now a new study, led by Tom Gleeson of McGill University in Montreal and published last week in the journal Nature, provides perhaps the most compelling and informative assessment to date of what’s happening with groundwater globally.

Gleeson and his team build upon the concept of our “ecological footprint,” which expresses humanity’s consumption as the area of biomass needed to support that consumption sustainably.  Today, according to the Global Footprint Network, humanity uses the equivalent of 1.5 planet Earths.  In other words, we’ve overshot sustainable levels by half an Earth.

In a creative adaptation, Gleeson’s team applied a similar approach to assessing humanity’s groundwater footprint.  They estimate that the size of the global groundwater footprint – defined as the area required to sustain groundwater use and groundwater-dependent ecosystem services — is about 3.5 times the actual area of aquifers tapped for water supplies.

Not only does a significant share of the world’s food depend on this groundwater, but an estimated 1.7 billion people – nearly one quarter of humanity – live in areas where groundwater or its dependent ecosystems are under threat.

Of the 783 aquifers analyzed, pumping from those in the Upper Ganges basin of India and Pakistan produce the largest footprint by far, with the footprint spanning 54 times the area of the aquifer itself.  Next come the aquifers of Saudi Arabia, Iran, western Mexico, and the U.S. High Plains, which includes the Ogallala, the source of water for 27 percent of U.S. irrigated land. The researchers estimated that pumping from the High Plains aquifer results in a footprint 9 times greater than the aquifer’s area. (Any ratio greater than 1 signals depletion of the aquifer; the higher the ratio, the more severe the depletion.)

Groundwater footprints of aquifers important for food production. At the bottom of the figure, the groundwater footprints (in gray) of six aquifers (in red, orange or yellow) are shown. The bigger the relative footprint size, the more severe the depletion. Courtesy of Tom Gleeson and the journal Nature.

The good news is that groundwater depletion is not ubiquitous: at current rates of use, 80 percent of aquifers around the world are not being depleted and therefore could sustain additional pumping to grow food or support expanding cities.

That said, the handful of countries that dominate the global groundwater footprint – those that are depleting the most groundwater – are among the world’s top food producers, including the United States, China, and India. Saudi Arabia has substantially depleted its own aquifers, and Saudi companies are now buying up land in Ethiopia and elsewhere to help ensure Saudi food security.

The ramifications of groundwater depletion for this and future generations are serious and mounting.   The Gleeson team’s visual depiction of the depletion drives home the urgency of taking action now to reverse the trend.

Capping groundwater pumping to match rates of aquifer replenishment would halt the depletion.  At a minimum, pumping limits could be set to slow the draining of aquifers, as has been done in parts of the Texas High Plains and elsewhere. Such measures would drive up irrigation efficiency and water productivity, and preserve more water for the next generation.

Unless we take action soon, we’ll bequeath to our children and grandchildren a whopping groundwater debt that makes food crises – and the social and political turmoil that springs from them – all but inevitable.

Sandra Postel is director of the Global Water Policy Project and lead water expert for National Geographic’s Freshwater Initiative.  She is the author of several acclaimed books, including the award-winning Last Oasis, a Pew Scholar in Conservation and the Environment, and one of the “Scientific American 50.”

Sandra Postel is director of the Global Water Policy Project and author of Replenish: The Virtuous Cycle of Water and Prosperity. From 2009-2015, she served as Freshwater Fellow of the National Geographic Society. Sandra is also co-creator of Change the Course, the national water stewardship initiative awarded the 2017 US Water Prize for restoring billions of gallons of water to depleted rivers and wetlands. The recipient of several honorary degrees, she works to bridge science, policy, and practice to promote innovative ways of securing water to meet both human and ecosystem needs.
  • Lew Warden

    In California, where I have lived all my life, it is obvious that the depletion of our acquifers has been accelerated by the spread of cities in our previously most productive farm lands and by the tax advantages given to gentlemen farmers for vineyards gracing our previously brown hillsides which attract hordes of workers from south of the border who add more stress to our infrastructure and water resources.
    We can live without wine but not without nourishing food or water. Somethings gotta go, and I’m voting for cutting out the tax advantages given to our wealthy citizens and their grand estates.

  • Kris

    companies have been stealing our water for years now and selling it to china and other places if you do some research. they move in by the natural aquifers and pump it out because they are not directly allowed to go in and pump it out. they steal it and sell it to other contries and even back to use.

  • Eric Santaw

    I have lived in Florida for 16 years and this is also quite apparent here. As sprawl is relatively unregulated, demand is outgrowing supply and no one seems to see this as a major issue. I hear conversations periodically on the radio, articles from time to time but no real movement to curb usage. Once this is truly an issue it will be too late. When will we wake up and realize that nonrenewable resources (oil included) are finite and once gone cannot be restored (or at least not in a reasonable time)?

  • Tye

    I’m thinking the water issue will actually always be in check, if we broaden our use of desalination of ocean water, which will obviously be necessary soon enough. I realize that can be over-exploited and destructive too, but I would hope that by the time we’re dependent upon saltwater, we know to be responsible. True though, we’ve reached a point where we’re bleeding Earth dry in many ways. The sad thing is, no one is going to care until it’s too late. We can either have more respect for our one and only planet and how we use and harvest the resources given, or we can start killing off half the population. Since somehow I don’t think the latter will fly, how about we wake up, world?

  • Ron Johnson

    Those who agree get their comments published here. Those who disagree, never see them appear.


  • […] Our Oversized Groundwater Footprint August 29th, 2012 | Tags: Earth, Ecological footprint, Environment, Global Footprint Network, Global hectare, Sustainability, Sustainable development, sustainable living | Category: Sustainability, Sustainability Tip of the Week […]

  • […] running dry, and vast aquifers like the Ogallala of the U.S. and the Arabian in Saudi Arabia are being drained rapidly. (See eight mighty rivers run […]

  • Barbara

    Why no mention of hydraulic fracking for natural gas? This process uses2million gallons of potable (drinking water) to start a single fracking pad. Each fracking site has approximately 2-6 pads per site. I tried to find the exact number of fracking sites for just the US, but strangely, could not get this info. I do know that in Colorado, they are proposing an additional 21,000 sites in just a single county- Meeker. In Weld county, where the majority of sites are currently located, the water rights were put up for bid between the farmers and the oil companies, guess who won? Maybe this country will wake up when we no longer have water to grow our food!!!!!!

  • […] story at National Geographic | Tagged Environment & Climate, Natural Resources, Water Conservation & Management […]

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  • […] researchers, from McGill University in Montreal and Utrecht University in the Netherlands, found the Upper Ganges is being pumped more than 50 times its ability to recharge. Read […]

  • Michael Willemsen
  • Daniel Collins

    “Capping groundwater pumping to match rates of aquifer replenishment” would mean that lowland spring-fed streams would go dry, and the water table would drop.

    The water budget should encompass the whole catchment-aquifer system from mountains to sea, and impacts of water use considered. There is no free lunch.

  • […] has increased remarkably in recent years. The bad news coming in from satellite observations and computer models is that the levels of many of the world’s most important aquifers are dropping precipitously. […]

  • John Davenport

    Is there any easily aggregated info on how what percentage of irrigated grain crops we might lose to aquifer depletion, or what percentage of aquifers currently used for intensive grain crop irrigation may go dry (or too deep to be economically feasible). Thanks!

  • John Davenport

    what percentage of aquifers serving intensive grain crop irrigation are we likely to lose by 2100?

    • Good question. The answer will depend on how much active groundwater replenishment is done, whether serious groundwater management laws are put in place and enforced, and how aggressively farmers move toward more efficient irrigation practices (which of course depends on economic or regulatory incentives). But some land, inevitably, will come out of production or be converted to dryland (non-irrigated) production.

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