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By Rachel Leven
Groundwater is being depleted at a rapidly accelerating pace, posing potential problems for irrigation and surface water flow, according to a U.S. Geological Survey study released May 20.
U.S. groundwater supplies were depleted by more than two times the volume of Lake Erie between 1900 and 2008, the study said. However, 25 percent of that amount--or 800 cubic kilometers of the 1000 cubic kilometers depleted--occurred between 2000 and 2008, indicating a rapid increase in the depletion rate, USGS said.
The rate, which has been increasing since the 1950s, is unlikely to continue accelerating, but is still unsustainable, Leonard Konikow, the study's author, told BNA.
The study, Groundwater Depletion in the United States (1900-2008), said the rate of depletion could affect farmers' ability to irrigate their crops, the amount of money different regions of the country spend on importing water, and local governments' water management policies.
Since 1950, the use of groundwater resources for agricultural, industrial, and municipal purposes has greatly expanded in the United States, according to the study.
More than 50 percent of U.S. residents use groundwater for drinking or household purposes, according to USGS. However, groundwater is mostly used for irrigation while industrial activities also account for significant amount. Groundwater depletion occurs when water is removed from an aquifer at a faster rate than it can be recharged, the USGS said.
The High Plains (Ogallala) Aquifer and Gulf Coastal Plans came in with the highest level of groundwater depletion, at 340.9 cubic kilometers and 266 cubic kilometers depleted from 1900 to 2008, respectively, according to the study. To find these long-term depletion estimates, Konikow analyzed 40 aquifer systems and subareas, as well as a single “broader diffuse land use category [or] agricultural and land drainage where the water table has been permanently lowered,” the report indicated.
While different towns and regions may have different water use and demand patterns, the greatest predictor of groundwater depletion is climate, according to Konikow.
Greater amounts of precipitation allow certain areas to replenish their water supplies better than those with less precipitation. Humid weather also allows the groundwater to charge naturally, limiting depletion.
There could be several causes for groundwater depletion levels, analysts who follow groundwater issues, told BNA. Increasing drought conditions around the United States, drilling wells and pumps, increased population, and ethanol production, which requires more water for irrigating corn, are the most likely causes.
Many local areas are already feeling the stress of groundwater depletion.
In Phoenix, farmers sold their land because it was too costly to irrigate their crops, Konikow said. It is getting more expensive to pump groundwater for irrigating crops in the southern high plains, and in California there has been a renewed problem with land subsidence, Bill Alley, director of science and technology for the National Ground Water Association, told BNA.
Other towns and regions, which have not felt the stress yet, could be affected as depletion continues. Certain residents could see increased saltwater intrusion, resulting in costs for moving wells further inland, or effects on surface water flow, Alley stated.
In Texas, some irrigated cropland is not being used due to lack of water, or the cost of pumping water that is too deep, Texas Water Resources Institute Associate Director Kevin Wagner said.
“The most serious effects will be locally in the areas with the most serious depletion problems,” Konikow said. “They will have to cut back on use of groundwater or import from other areas, [which] is challenging both financially and politically.”
While groundwater depletion's greatest effects will be seen on a local or regional basis, Konikow said depletion could have a “small, but not trivial” impact on sea-level globally. Groundwater decreases account for approximately 2 percent of global sea-level rise, according to the study.
While the report showed significant increases since 1950 in water depletion, Konikow said changes in policy and water management can help put the U.S. on the path of reversal in a matter of years or even months.
Water management and importing water solutions lie on a local or regional level because groundwater availability is generally controlled by the states, Alley said. Getting the local community's input and participation is key to success and reversal.
In Texas, some farmers have switched to more efficient irrigation technology and more heat and drought-resistant crops are being developed, Wagner said. The institute has also held educational programs for agriculture producers.
“Everybody's pretty cognizant that their water is dwindling there, so they've been very receptive,” Wagner said. “To maintain their way of life, they're going to have to change their irrigation practices.”
Groundwater Depletion in the United States (1900-2008) is available at http://pubs.usgs.gov/sir/2013/5079/SIR2013-5079.pdf.
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