Groundwater: The Resource We Can't See, but Increasingly Rely Upon
We’re pumping from aquifers at unsustainable rates—can new technologies save this vital resource?
It has taken some 70 years of steady, unsustainable pumping for portions of the Ogallala Aquifer under the Great Plains to become nearly desiccated.
People have used groundwater for thousands of years, especially in arid regions such as the Middle East and North Africa, where hand-dug wells and subsurface tunnel systems collected and diverted it for early societies. These ancient methods amounted to skimming the shallow groundwater off the top of massive aquifer systems—the vast stores of invisible groundwater beneath the continents that account for more than 95 percent of all circulating fresh water on Earth.
That early skimming was limited by the primitive know-how of the time. But beginning in the 19th century, technological developments were opening our access to groundwater as advancements in drilling for extracting petroleum were spun off and developed for the water well industry. Still, even into the 1940s, most pumping reached only shallow depths of less than 30 feet, removing water at modest rates. That changed radically after World War II, when more sophisticated pumping technology, as well as the cheap, petroleum-based energy to power it, came to the fore. Soon we were pumping so much water from aquifers that we were beginning to “overdraft” them—taking out more than could be replenished at sustainable rates. Today, a little more than a half-century later, the world gets about 35 percent of its fresh water this way, making it a sizable—and quite new—development in world history.
This new availability of water, especially in arid regions, together with the advent of relatively cheap chemical fertilizers, has helped fuel the Green Revolution, increasing agricultural production around the globe, especially in the developing world. But it has come with a cost that cannot be sustained without new ways of managing our water resources.
Think about it this way: All your money is in two bank accounts—accounts A and B. You know what your balance, deposits, and withdrawals are in Account A. But you don’t know much about Account B—except that when A gets depleted, large amounts of cash are withdrawn from B. Even if B has lots of money and you don’t immediately feel the impact, it’s hardly the path to financial security. But that’s how civilization has been managing water—Account A representing surface water and B, groundwater. And because of the vast volume of groundwater beneath the continents, we didn’t always notice the impact and correct our mismanagement. Now we have entered an era of scarcity as a growing world population is increasing demand and creating a drain on groundwater in aquifers across many regions, including the United States, China, India, the Middle East, and Australia.
There were clues we were making mistakes, but too often water users and managers didn’t know enough about the consequences of their overexploitation to connect cause and effect. Just as accelerated pumping is a relatively new development in human history, the science of groundwater and how to manage it—known as hydrogeology or groundwater hydrology—is even more recent, beginning to mature in the past 20 to 30 years. For example, in California’s Central Valley, which contains one of North America’s largest aquifers, intensive pumping in the mid-20th century dried up massive wetlands that once covered 20 percent of the area. But most water managers didn’t yet understand the connection between groundwater and surface water and didn’t attribute the disappearance of wetlands to the pumping.
Despite the vast volume of fresh groundwater on Earth, we can pump only a relatively small fraction of it before overdraft occurs and the subsequent problems arise, even if they may not seem immediately alarming or connected to the pumping. Groundwater overdraft almost always causes groundwater level declines and surface water depletion, and sometimes leads to degradation of groundwater quality and land subsidence.
It may take decades for these changes to become obvious and even longer for an aquifer’s “tank” to become empty. It has taken some 70 years of steady, unsustainable pumping for portions of the Ogallala Aquifer under the Great Plains to become nearly desiccated.
But we are learning the errors of our ways and are slowly starting to change our practices.
In California, which has seen the harsh consequences of overpumping exacerbated by climate change in recent years, proactive groundwater regulation is being enacted. These initiatives—together with earlier regulatory efforts by other states and countries, including Australia—mark a change in how we think about groundwater, treating it less like an extractive resource, which we pump limitlessly and hope for the best, to one that is managed and replenishable. This approach employs science-based methods, many of them relatively new, to determine how to bring groundwater basins into balance by reducing the pumping, increasing recharge, or both.
What has become known is that managed aquifer recharge involves diverting alternative sources of water—usually surface water, including storm flows, or treated urban wastewater—onto land where the water can be infiltrated in ponds or injected into wells. Studies by the University of California and the California Department of Water Resources indicate that recharge can be increased enough to eliminate overdraft in some aquifers. But research from the Public Policy Institute of California cautions that in other places it will require large reductions in pumping and with it significant changes in land and water use.
Still another potential recharge idea involves crop irrigation. An unintended consequence of irrigating crops above many aquifer systems has been the substantial increase in recharge. This is because just 50 to 90 percent of irrigation water is typically consumed by the crop; most of the rest soaks downward to recharge the groundwater supply. Studies by the University of California, Davis have shown that diverting high river flows onto farmland in winter, when fields are fallow, may substantially increase recharge.
But these efforts are not enough by themselves. Throughout the world, the consequences of decades of high pumping rates necessitate new approaches to manage groundwater, which unlike surface water is difficult to observe and measure. Fortunately, development of new hydrologic technologies is showing the way.
By gathering data from water wells, along with geological and geophysical measurements, we can apply our knowledge of physics and the chemistry of water as it moves underground to determine flow rates and directions. This allows hydrogeologists to create mathematical models to determine what we cannot see: changes in the amount of water underground and the impact our management of pumping and recharges is having so we can avoid overdrafts.
Just as importantly, our ability to do this has improved dramatically in the last 20 to 30 years thanks to technological advancements. While we have been able to monitor individual wells for decades, new and relatively easy-to-deploy wireless sensor networks now allow us to monitor groundwater levels across a groundwater basin in real time nearly as easily as we can a surface reservoir. As articulated recently by NASA and the National Research Council, this, along with improved satellite monitoring and analyses of groundwater storage, can provide us with more knowledge of these underground reservoirs than we’ve ever had before.
Now that scientific developments make it much more feasible to manage groundwater nearly as intuitively and transparently as we do surface water, we can embark on a new phase of groundwater development in which we devote as much effort to recharging aquifers as we do to pumping from them.
This is true not only for more developed countries but also for the rest of the world. The worldwide problem with overdrafted aquifers exists because those with the best technology for pumping exported it while doing little to expand new, innovative management methods for groundwater. The biggest challenge will be to export and help deploy those methods globally.
These improved methods of monitoring groundwater, as well as advancements in surface water monitoring, will help us develop more accurate and reliable models of the entire water system—giving us the big picture that will help avoid overdrafting aquifers. But key to that is ensuring an integrated approach to managing groundwater and surface water—those two “bank accounts” that are essential to maintain as we enter this looming time of water scarcity. We must be creative. For example, we can turn the negative of overdrafted aquifers into a positive by using them for underground water storage. In California, where every major river has been dammed, the available space for underground storage of water in the Central Valley is about three times greater than the total surface reservoir capacity in the entire state. More capacity is literally just below our feet.
This integrated approach will require some new thinking and planning on our part. Until now, for example, surface water reservoirs have primarily been operated with the objectives of maximizing water storage, generating hydropower, and providing flood control. To jointly manage surface water and groundwater means we must think of the total watershed storage and the infrastructure requirements, such as conveyance canals to move water where it is needed not just for immediate use but for aquifer replenishment.
It may be a challenge to determine where the water will be found to accomplish the recharge our aquifers require, but some promising potential sources include the alternative management of river flood flows where it can be accomplished wisely, the redistribution of some surface reservoir stores to the groundwater systems, and of course conservation and water reuse. While the recent decades of water resources management have been influenced by groundwater overexploitation, we are facing a dynamic transition in which important changes are in store. If we keep working on modern groundwater regulatory initiatives, apply the right technologies, develop water conveyance infrastructure, and work to replenish aquifer systems, the future for water could be very different from the past.