How can aquifers be depleted

Hydro Resources drills a well near Sublette, Kansas. The Ogallala is being depleted in Kansas, and some areas have only a few decades of water remaining. Click image to enlarge. Moreover, 13 of the aquifers are depleted to the point that regional water availability is threatened. More than 2 billion people rely on aquifers as their primary water source. The water held underground in layers of rock and soil is an essential emergency supply during droughts, when rivers and streams shrivel, as is the case today in California.

Too much groundwater pumping can cause rivers to dry up, the land surface to sink, and wetlands to evaporate. From northern China to the Middle East , from North Africa to the Central Valley of California , a common and unsettling story is unfolding: the effort to produce massive grain and food surpluses that will feed billions and to supply drinking water to the largest knots of humanity on the planet is taxing aquifers beyond their capacity.

The two studies were published online today in the journal Water Resources Research. The lack of knowledge — due to the cost and complexity of groundwater-monitoring systems — is unacceptable, Famiglietti said. The studies bring together two aspects of groundwater that are rarely considered together: the flow of water into and out of an aquifer and the stock of water sitting underground.

A bank account is a common analogy. An account holder must know both deposits and withdrawals the flows and the account balance the stock. An irrigation system in Ningxia, China. The groundwater resources on the North China Plain are slowly being drained. GRACE will detect changes in the total amount of water that is stored underground, a measure that incorporates both human withdrawals — for irrigation, household use, or mining — and natural variations due to drought or flood.

Water withdrawal statistics, compiled by local or national agencies and a typical source of information for researchers, do not provide such a full picture. According to the study, which used data from to , the three basins with the highest depletion rates cover a variety of ecosystems and manmade pressures:.

According to the study on groundwater stocks, commonly accepted estimates of groundwater storage have little relationship to actual conditions.

Estimates developed in and , which are still cited today, assumed that each aquifer had the same characteristics, that the depth to water and the water-holding capacity of the soil were the same. They are not. By altering the assumptions of those original studies, based on findings from regional groundwater studies — which are smaller in scope but have more detailed information on local conditions — the research team found a much emptier balance sheet.

The regional estimates were between 10 and 1, times lower than the rough estimates from 40 years ago, an astonishing difference. Knowing how much water an aquifer holds is important for understanding its resilience to periods of depletion. A large storage capacity allows for more pumping before the aquifer is drained. The study draws a comparison between two aquifers in North Africa — the Nubian and the Sahara. But the Sahara has roughly 10 years until 90 percent of the water is gone, according to the lowest storage estimate.

Groundwater depletion is primarily caused by sustained groundwater pumping. Some of the negative effects of groundwater depletion:. Excessive pumping can lower the groundwater table, and cause wells to no longer be able to reach groundwater. As the water table lowers, the water must be pumped farther to reach the surface, using more energy. In extreme cases, using such a well can be cost prohibitive.

Groundwater and surface water are connected. This coincides with a nationwide trend of groundwater declines.

A study of 40 aquifers across the United States by the U. Geological Survey reports that the rate of groundwater depletion has increased dramatically since , with almost 25 cubic kilometers six cubic miles of water per year being pumped from the ground. This compares to about 9. Scarce groundwater supplies also are being used for energy. A recent study from CERES, an organization that advocates sustainable business practices, indicated that competition for water by hydraulic fracturing—a water-intensive drilling process for oil and gas known as "fracking"—already occurs in dry regions of the United States.

The February report said that more than half of all fracking wells in the U. Satellites have allowed us to more accurately understand groundwater supplies and depletion rates. GRACE has given us an improved picture of groundwater worldwide, revealing how supplies are shrinking in several regions vulnerable to drought: northern India , the North China Plain, and the Middle East among them. As drought worsens groundwater depletion, water supplies for people and farming shrink , and this scarcity can set the table for social unrest.

Saudi Arabia, which a few decades ago began pumping deep underground aquifers to grow wheat in the desert, has since abandoned the plan, in order to conserve what groundwater supplies remain, relying instead on imported wheat to feed the people of this arid land.

Managing and conserving groundwater supplies becomes an urgent challenge as drought depletes our surface supplies. Because groundwater is a common resource —available to anyone with well—drilling equipment-cooperation and collaboration will be crucial as we try to protect this shrinking line of defense against a future of water scarcity. Dennis Dimick grew up on a hilly Oregon farm named Spring Hill, where groundwater from a spring provided his family's—and the farm's—water supply.

You can follow him on Twitter, Instagram , and flickr. The National Geographic Society supports a project to restore freshwater ecosystems. You can find out more about Change the Course here , and how by pledging to reduce your own water footprint you can restore 1, gallons of water to the Colorado River. All rights reserved. To learn more about global water wars, watch Parched. Share Tweet Email. Read This Next Wild parakeets have taken a liking to London. Animals Wild Cities Wild parakeets have taken a liking to London Love them or hate them, there's no denying their growing numbers have added an explosion of color to the city's streets.

But whether we can see it or not, the areas of the world that are most reliant on groundwater are depleting it far faster than it can be replenished by natural processes. Critical aquifers, most of which irrigate the most productive agricultural regions in the world, include those in:.

Population growth is one of the major threats to aquifers. More humans mean more human activities, whether household, agricultural, or industrial.

Industrialization and rising living standards are contributing to water demand. The aquifer under Karachi, Pakistan, is enormous, but it is contaminated with industrial arsenic and, to make matter worse, it is being progressively depleted.

But contamination is not just a problem in the developing world. Large areas of the Jakarta, Indonesia, are quickly sinking into the Java Sea. One might expect to hear the problem is climate change -associated sea level rise, but aquifer depletion is the greater problem. When aquifers are emptied under the city, the land under the city begins to subside.