Groundwater Depletion in Colorado River Basin Poses Big Risk to Water Security

An artist’s rendering of the twin satellites of NASA’s Gravity Recovery and Climate Experiment (GRACE). Using data from this mission, scientists have determined that a vast volume of groundwater has been depleted from the Colorado River Basin over the last decade. Credit: NASA/JPL

Let’s step back for a minute and consider the implications of the study released last week on the depletion of groundwater in the Colorado River Basin.

For anyone concerned about the future of the American West, the findings of this study – which was published online in the journal Geophysical Research Letters and conducted by a team of scientists from NASA, the University of California-Irvine, and the National Center for Atmospheric Research in Boulder, Colorado—can make the heart pound.

Let’s start with a little context above ground, before going below.

Lake Mead is the largest reservoir in the United States and the granddaddy of reservoirs on the Colorado River.  This giant man-made lake, formed by the construction of Hoover Dam in the 1930s, can hold nearly two years of the Colorado River’s historic flow.

Some 40 million people – including those in Las Vegas, Los Angeles, Phoenix, Tucson and San Diego — and 4 million acres of farmland rely on water from the Colorado River Basin, much of it stored in Lake Mead.

In 2000, Lake Mead was just about full.  Then a drought hit that has more or less continued to this day.   This has been the driest 14-year period in the Colorado Basin in the last 100 years. Demand for the Colorado River’s water by the seven US states and Mexico, which share the river, now exceeds the ten-year average supply.

As a result, the level of Lake Mead has steadily dropped.  At full capacity, the lake’s level is 1,221.4 feet above mean sea level.  Today its level is at 1,080.9 feet, the lowest it has been since 1937, just after the completion of Hoover Dam.

The now-famous white bathtub ring around Lake Mead’s perimeter tells this story.

Because the lake is shaped like a coffee filter –wider at the top and narrower at greater depths – a seemingly small decline in water level represents a disproportionately large drop in the volume of water it’s storing. Today, instead of holding two year’s worth of Colorado River water, the lake holds about 9 months worth.

Water managers and officials have known for at least four decades that when surface supplies became scarce in the basin, farms and cities would turn to groundwater to meet their water needs, especially during times of drought.

But with groundwater management left to the states, there has been no overarching assessment of what’s happening to water underground – nothing equivalent to Lake Mead’s bathtub ring to signal a problem for the basin as a whole.

Until now.

The white “bathtub ring” of mineral deposits marks the decline of Lake Mead, which is able to store two years of the Colorado River’s historic annual flow.  It currently holds only 9 months worth of that flow.  Photo courtesy of US Bureau of Reclamation.
The white “bathtub ring” of mineral deposits marks the decline of Lake Mead, which is able to store two years of the Colorado River’s historic annual flow. It currently holds only 9 months worth of that flow. Photo courtesy of US Bureau of Reclamation.

Thanks to a NASA satellite mission called the Gravity Recovery and Climate Experiment, or GRACE, which began in 2002, we are getting a look at changes in water storage both above and below ground in watersheds around the world.

Using twin satellites, the GRACE mission measures the mass of the earth over time and space.  Because changes in water storage result in changes in mass, GRACE provides fairly accurate estimates of water depletion over time.

When Stephanie Castle of the University of California-Irvine and her colleagues analyzed GRACE data for the whole Colorado River Basin over the period December 2004 – November 2013, what they found stunned them: the Colorado Basin had lost nearly 53 million acre-feet of water (65 billion cubic meters) – equivalent to two full Lake Meads.

Even more striking, 77 percent of that loss – some 41 million acre-feet – was water stored underground.  That’s enough to meet the home water use of the entire US population for eight years.

(An acre-foot is the volume of water that would cover an acre of land one foot deep. It equals 325,850 gallons, roughly the amount eight people in the U.S. would use at home in a year.)

“We don’t know exactly how much groundwater we have left, so we don’t know when we’re going to run out,” Castle said in a press release announcing the study.

“This is a lot of water to lose. We thought that the picture could be pretty bad, but this was shocking.”

Now, it’s common for farms and cities to pump more groundwater during droughts in order to make up the gap between supply and demand.  The assumption is, that during times of surplus, the groundwater basins will fill back up. 

“This is a lot of water to lose. We thought that the picture could be pretty bad, but this was shocking.” — Stephanie Castle, lead author of the study.

But what if they don’t re-fill?

Some groundwater basins do not receive much recharge even in wet times. I wrote last week about how drought is leading farmers to pump more heavily from the Ogallala Aquifer beneath northwest Texas, a largely irreversible loss of groundwater.  Areas of similar “non-rechargeable” aquifers also exist in the Colorado River Basin.

In addition, virtually all the climate models indicate that the Southwest is in for hotter and drier times, meaning more losses to evaporation, less replenishment of aquifers, and higher water demand from farms and cities.

Jay Famiglietti, senior water scientist at the NASA Jet Propulsion Laboratory, Earth systems science professor at UC-Irvine, and a co-author of this study, pointed out in his post in Water Currents last week that during the severe drought of the past decade, Colorado Basin water demands have outpaced supplies by as much as 30 percent, with groundwater filling the gap.

By focusing only on the drop in Lake Mead and paying too-little attention to the drop in water levels underground, we have placed the West’s water security in serious jeopardy.

Imagine having a bank account for which  you don’t know (1) how much money is in the account, (2) how much gets withdrawn, or (3) how much will get deposited, or when.

Such a money-management circumstance would offer little hope of keeping a family fed, clothed and sheltered over the long term, much less of sending a child to college.

So, we have two choices: continue flying water-blind into the future and leave the consequences to the next generation, or get our heads out of the sand and take action to monitor, manage and balance our water books.

If we choose the second option, what’s needed is fairly clear.

First, conservation and efficiency improvements in homes, businesses and, especially, on farms – which account for some 80 percent of water consumed in the basin – remain the most cost-effective, environmentally sound ways of meeting our water demands.  While we’ve made some solid gains, we have a long way to go and many solutions yet to tap.

Second, we need to manage and regulate — yes, regulate — groundwater.  It’s a finite supply, and as long as there’s no limit on the number of straws in the cup and how much they can slurp, the water level will keep going down. Pumping limits would promote more efficient water use.

Third, we should stop letting antiquated water laws trump sound economics.  If farmers were readily able to sell or lease water to cities and conservationists, they would have incentive to invest in more efficient irrigation practices, switch to less thirsty crops, or fallow a portion of their fields so they could sell the conserved water to others.  A healthier water market could help cities meet long-term needs and even help rivers weather a drought.

This, in part, is the spirit behind the Colorado River System Conservation Program, which would pay for voluntary reductions in water use – whether by fallowing farm fields, installing more efficient irrigation systems, recycling industrial water, or other means – that benefit the basin as a whole.

Lastly, management of Colorado River Basin water is overseen by a long list of federal and state authorities.  While collaboration has improved greatly in recent years, it’s imperative to cooperate around groundwater monitoring and reporting in order to get a basin-wide view of what’s happening underground.

The findings of this study are a wake-up call, and it would be foolish beyond measure to push the snooze button.

[Disclaimer: The editors of Geophysical Research Letters asked me to serve as a reviewer of the Castle et al. manuscript, which I did.]

Sandra Postel is director of the Global Water Policy Project, Freshwater Fellow of the National Geographic Society, and author of several books and numerous articles on global water issues.  She is co-creator of Change the Course, the national freshwater conservation and restoration campaign being piloted in the Colorado River Basin.

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.
  • LaNell

    Not one word about the enormous amounts of water used by the animal agriculture business or fracking. These two industries alone are more devastating to our water supply than any other. If we want to solve this problem, we have to be honest with ourselves.

  • Horrified

    Similar depletion is occurring in Oklahoma, yet use of limited water has been approved by the state for fracking. All of this will come crashing down, with the poorest paying the greatest penalty.

  • Lorien Elsey

    I am HORRIFIED to see no mention of FRACKING as a CAUSE of the current water situation of the Colorado River. 🙁 hello?? Anybody in there??

  • nuala

    If it were not for farmers who grow all our fruits and vegetables and raise beef and sheep, the USA people would be hungry and it would be a third world country with its inhabitants starving.
    Is this what we want .Why do city developers keep giving out building permits which keep increasing the populations in cities such as Phoenix and Las Vegas. Can you imagine one large apt. complex would use in a week or a year.Why not go build in Oregon or Washington where there is a surplices of water,
    My way of thinking

  • Kwang Yi

    It’s an informative article, and I feel younger people should be made aware of this water shortage problems and the practice of conservation should be rigorously and systematically taught in school. The people in the US tend to take everything as granted. I’m living in a place where I’m being sued by HOA for implementing rain water collection system, because some people in this neighborhood believes 2 50-gallon water tank is too much of an eye-sore.

  • Bob Daniels

    Is fracking an issue in AZ, NV, UT, CA? Too many people, not enough water.

    • Of the seven Colorado Basin states, fracking is biggest in Colorado and California, though CA’s fracking would not involve much if any Colorado River water.

  • GE

    I want to know where is all this water going once it’s been used? The water isn’t disappearing. Also, where is the tech that could turn salt water into fresh water? It’s 2014!!!

  • Tom Sweetnam

    The world’s population will be 10 billion by 2040. What will fresh water demand look like then? In his seminal portent, “The Coming Anarchy”, Atlantic Monthly editor Robert Kaplan illustrates that many of the “brush wars” raging on planet Earth today, especially in Africa, are all about water and grazing land for cattle…driven by overpopulation.

    Overpopulation was the root cause of land degradation in Northern Mexico (by the 1930’s), and to this day is one of the major causes of massive illegal immigration on our southern border, again driven by overpopulation.

    I think the best primer on water history, water usage, and water politics in the Southwestern US, is Marc Reisner’s ‘Cadillac Desert’. First published in 1993, it’s still as relevant today as it was 21 years ago. PBS did an excellent documentary based on Reisner’s book.

  • Gene Holmes

    Your list of cities relying on Colorado River Basin water
    should include Denver, which gets it through a tunnel under the Continental Divide. One proposed solution is a 600 mile pipeline to Denver from the Missouri River.

  • Jeanne

    If California lawmakers would use their brains, they would allow us to use our gray water. Just think about how much water is wasted in our kitchen sinks, dishwashers, and bathtubs. Yet it is illegal to use it without going through so much red tape. All that water could be used to grow crops, water lawns and help keep the farmers in business. And therefore help keep our price of groceries from skyrocketing. and keep California green.

  • Scott haralson

    Living in Okla. I watch the Gas & Oil Pigs, use our water to make obscene profits,then replace it by pumping back poison water into the ground, all the time creating many,many 3.5 earth quakes that we never experienced prior to franking.

  • David Morales

    Aqui en el otro lado de la frontera, las personas desperdician agua como si nunca se fuese acabar, y eso debe estar en conciencia, ya que Baja California depende mucho de las aguas del Rio Colorado..

  • Dan

    Do the aquifers have any other function besides supplying humans? Are there any species or ecosystems that rely on them? Or do they mostly just exist as pockets of water?

    • Many aquifers have hydrological connections to rivers and provide critical base flows, especially during the drier summer months. When those aquifers are overpumped and water tables are drawn down, the base flows can diminish, drying up a river and greatly harming fish and aquatic life.

  • Paul Suliin

    I noticed that over 10 years (2004-2013) the groundwater in the Colorado River basin was depleted by an amount sufficient to meet the needs of the entire US for 8 years. My question is, how is that possible? Did those 7 states really use in 10 years as much water as the entire US uses in 8 years? If not then where did the water go?

    • Most of that groundwater depletion in the Colorado Basin is attributable to water used for crop production, not home use. In order to provide a sense of how much water it is (since millions of acre-feet is not something most can grasp), I made the comparison to the number of years of home water use for the US population that volume could supply, and arrived at 8 years.

  • Paul Suliin

    I noticed a couple of people mentioning gray water. Unfortunately that’s not as simple a solution as people think it is. Yes, gray water can be re-routed easily to water the same household’s lawn or garden, but remember that large-scale agriculture uses 80% of the water in the basin. That means a whole separate piping system to route gray water from households to the farms where the vast majority of the water is used. Household water conservation can have only a small effect on the current situation.

  • C.Kafura

    Way too much turf grass in suburban and urban areas. Uses a lot of high quality water. Needs to be cut with a mower using fossil fuels. Treated with pesticides and fertilizers that poison the environment. Poor ecological habitat value. Labor intensive. Also, boring in my opinion.

    Water is being transported from the west slope through tunnels under the continental divide to the front range in CO to water lawns. Water is being transported hundreds of miles in canals to water lawns in metropolitan Phoenix.

    Alternative: Gray water and rain water harvesting to grow native food, shade, and habitat producing plants.

  • Ken Hageman

    I believe that we are depleting our water resources all over the world. I also believe that conservation measures will help. But no one will EVER discuss the elephant in the room. There are just way to many humans on the planet. We are now around seven billion and population is increasing at a fast rate. In my opinion and from what I have studied a population of about 3 billion people is sustainable and even lower would be better for our planet. If mankind will not address this problem and fix it, Mother Nature surely will. We are seeing signs of it right now and it will only get more severe. I’m 68 years old and probably will miss the worst of it, but my kids and grand kids are in for a very difficult time.

  • Val

    I am amazed to see that farming and irrigation are being blamed for this. Why is there no mention of the bottled water companies pumping tremendous amounts of water for “convenience” from the aquifers? The water levels only started going down and the “drought” began when the bottled water companies started pumping. Every time you buy and drink bottled water you are contributing to the problem.

    • Val, thanks for your comment. I am no fan of bottled water, but agriculture accounts for about 85% of water consumption in the West. With the prolonged drought, more farmers have seen their surface water allocations reduced and have turned to more groundwater pumping. Better regulation and management of groundwater, in all sectors, but especially agriculture, is crucial to reducing the growing groundwater debt.

  • Brian Parks

    This is an excellent and timely article addressing the chronic water shortages in the Colorado River Basin. As the author points out, crop production accounts for about 80 percent of the basin’s water consumption. The other 20% being household and industrial use. So much can be done through water conservation to mitigate the problem taking pressure off the river and finite groundwater reserves. The internet is rife with resources and information to help water consumers make better choices to conserve water. Some examples are organic no-till farming and mulching which rebuilds soil and replenishes soil biology while conserving water. Healthy soil covered in mulch uses far less water and slows evaporation. Also growing and producing food closer to where it is being consumed rather than out in the desert. Another strategy is rainwater harvesting. 12 inches of rain a year falls on Tuscon. If all that rain was harvested locally there would be no need to divert water from the Colorado River for the city’s municipal needs. The same can be said for every city in the basin. Also xeriscaping and planting native and drought-tolerant vegetation can reduce water needs tremendously. These examples barely scratch the surface of the available strategies. There is not enough room here to list all the resources available to help steer the water consumers in the basin in a better direction. But the solutions to this growing problem are within reach. The water can and should be left in the river and in the ground. I conclude my comment with 1 useful link which can help the average water consumer tremendously: http://www.harvestingrainwater.com/

    • Thank you for your comment– I agree with your optimism about what we can accomplish if we put our minds full to it.

  • Jim

    Water is not disappearing from planet earth it is moving it’s location. Desalination plants are our best course of action and can reverse the flow of the California aqueduct.

    • It’s correct that water is not disappearing from planet earth, but the depletion of groundwater certainly makes less water accessible for future use. In most instances, desalination is not an elegant solution. De-salting sea water requires a lot of energy (less than it required 20 years ago, but still a lot). Does it make sense to adapt to water shortages and droughts by investing in solutions that will consume more energy, emit more greenhouse gases, add to global warming…and therefore increase water shortages and droughts? The big desal plant being built north of San Diego will provide less than 10% of San Diego’s drinking water. It would be far cheaper and more environmentally advantageous to achieve a 10% reduction through efficiency improvements and conservation.

  • Tom Ash

    Another great educational study and article from Sandra. With Climate Change, much of what we knew or thought about our local water conditions will change. Getting much more efficient, setting priorities for water use and utilizing the technology we have and will continue to invent is key to using our most vital resource. Sandra, please keep educating us all.

  • Billy bob

    People need to stop wasting water because the work would end up dry.

About the Blog

Researchers, conservationists, and others share stories, insights and ideas about Our Changing Planet, Wildlife & Wild Spaces, and The Human Journey. More than 50,000 comments have been added to 10,000 posts. Explore the list alongside to dive deeper into some of the most popular categories of the National Geographic Society’s conversation platform Voices.

Opinions are those of the blogger and/or the blogger’s organization, and not necessarily those of the National Geographic Society. Posters of blogs and comments are required to observe National Geographic’s community rules and other terms of service.

Voices director: David Braun (dbraun@ngs.org)

Social Media