Editing Ogallala Aquifer (section)

==Aquifer water balance==
An aquifer is a groundwater storage reservoir in the [[water cycle]]. While groundwater is a renewable source, reserves replenish relatively slowly. The [[US Geological Survey|USGS]] has performed several studies of the aquifer, to determine what is coming in ([[groundwater recharge]] from the surface), what is leaving (water pumped out and [[baseflow]] to streams), and what the net changes in storage are (rise, fall or no change).

The [[USGS]] estimated that total water storage was about {{convert|2925000000|acre.ft|km3}} in 2005. Withdrawals from the Ogallala Aquifer for irrigation amounted to {{convert|26|km3|acre.ft|abbr=on}} in 2000. Since major groundwater pumping began in the late 1940s, overdraft from the High Plains Aquifer has amounted to {{convert|332,000,000|acre.ft|km3}}, 85% of the volume of Lake Erie.<ref>{{cite journal |last1=Perkin |first1=Joshuah |last2=Gido |first2=Keith |last3=Falke |first3=Jeffrey |last4=Crockett |first4=Harry |last5=Johnson |first5=Eric |last6=Sanderson |first6=John |title=Groundwater declines are linked to changes in Great Plains stream fish assemblages |journal=Proceedings of the National Academy of Sciences |date=July 11, 2017 |volume=114 |issue=28 |pages=7373–7378 |doi=10.1073/pnas.1618936114 |pmid=28652354 |pmc=5514705 |bibcode=2017PNAS..114.7373P |doi-access=free }}</ref> Many farmers in the Texas [[High Plains (United States)|High Plains]], which rely particularly on groundwater, are now turning away from [[irrigated agriculture]] as pumping costs have risen and as they have become aware of the hazards of overpumping.<ref>{{cite news |title= Ogallala aquifer - Water hot spots | work=BBC News |year=2003 |url= http://news.bbc.co.uk/1/shared/spl/hi/world/03/world_forum/water/html/ogallala_aquifer.stm}}</ref>

===Groundwater recharge===
The rate at which groundwater is recharged is limited by several factors. Much of the plains region is [[steppe|semiarid]], with steady winds that hasten evaporation of surface water and precipitation. In many locations, the aquifer is overlain, in the [[vadose zone]], with a shallow layer of [[caliche]] that is practically [[hydraulic conductivity|impermeable]]; this limits the amount of water able to recharge the aquifer from the land surface. However, the soil of the [[playa lakes]] is different and not lined with caliche, making these some of the few areas where the aquifer can recharge. The destruction of playas by farmers and development decreases the available recharge area. The prevalence of the caliche is partly due to the ready evaporation of soil moisture and the semiarid climate; the aridity increases the amount of evaporation, which in turn increases the amount of caliche in the soil. Both mechanisms reduce the amount of recharge water that reaches the water table.

Recharge in the aquifer ranges from {{convert|0.024|in|mm}} per year in parts of Texas and New Mexico to {{convert|6|in|mm}} per year in south-central Kansas.<ref>[https://pubs.er.usgs.gov/usgspubs/pp/pp1400B ''Geohydrology of the High Plains Aquifer in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming'']. Gutentag, E. D.; Heimes, F. J.; Krothe, N. C.; Luckey, R. R.; Weeks, J. B. 1984.</ref>

===Groundwater discharge===
[[File:Crops Kansas AST 20010624.jpg|thumb|NASA [[Advanced Spaceborne Thermal Emission and Reflection Radiometer|ASTER]] image of a roughly 557&nbsp;mi<sup>2</sup> area of fields (1443&nbsp;km<sup>2</sup>) in [[Kansas]] watered from the Ogallala Aquifer with center pivot irrigation systems]]
The regions overlying the Ogallala Aquifer are some of the most productive regions in the United States for ranching [[livestock]], and growing [[maize|corn]], [[wheat]], and [[soybeans]]. The success of large-scale farming in areas that do not have adequate [[precipitation (meteorology)|precipitation]] and do not always have perennial [[surface water]] for diversion has depended heavily on pumping groundwater for irrigation.

Early settlers of the semiarid High Plains were plagued by crop failures due to cycles of [[drought]], culminating in the disastrous [[Dust Bowl]] of the 1930s. Only after [[World War II]], when [[center-pivot irrigation]] became available, was the land mass of the High Plains aquifer system transformed into one of the most agriculturally productive regions in the world.

===Change in groundwater storage===
Ground water levels decline when the rate of extraction by irrigation exceeds the rate of recharge. At places, the water table was measured to drop more than 5&nbsp;ft (1.5&nbsp;m) per year at the time of maximum extraction. In extreme cases, the deepening of [[water well|wells]] was required to reach the steadily falling water table. In the 21st century, recognition of the significance of the aquifer has led to increased coverage from regional and international journalists.<ref>[http://www.nwanews.com/adg/Business/167660/ "Shrinking aquifer looms as big problem for farms"] {{webarchive|url=https://web.archive.org/web/20090204014036/http://www.nwanews.com/adg/Business/167660/ |date=2009-02-04 }}. Nancy Cole, ''Arkansas Democrat-Gazette''. September 24, 2006. Last accessed October 24, 2006.</ref><ref>[http://www.amarillo.com/stories/100406/opi_5471882.shtml Column - Mansel Phillips: "Too many thirsty industries, not nearly enough water"] {{Webarchive|url=https://web.archive.org/web/20130615174945/http://amarillo.com/stories/100406/opi_5471882.shtml |date=June 15, 2013 }}. Mansel Phillips, ''Amarillo Globe News''. October 4, 2006. Last accessed October 24, 2006.</ref><ref>[http://journalstar.com/news/opinion/another-sign-of-long-term-water-worries/article_56f379fb-2e2c-56e2-ad47-79b026e877ac.html "Another sign of long-term water worries"], ''Lincoln Star Journal'', October 8, 2006. Last accessed November 20, 2012</ref><ref>[[Daily Telegraph|Daily Telegraph (UK)]] Saturday Magazine Issue no 48,446 (dated 5 March 2011) pp 26-32 "High and Dry" Report by ''Charles Lawrence''</ref>

[[Water conservation]] practices ([[terrace (agriculture)|terracing]] and [[crop rotation]]), more efficient irrigation methods (center pivot and [[drip irrigation|drip]]), and reduced area under irrigation have helped to slow depletion of the aquifer, but levels are generally still dropping in areas including southwestern Kansas and the [[Texas Panhandle]]. In other areas, such as parts of eastern and central Nebraska and of the region south of [[Lubbock, Texas]], water levels have risen since 1980.

The [[center-pivot irrigator]] was described as the "villain"<ref name=NYT20May2013>{{cite news|newspaper=New York Times|title=Wells Dry, Fertile Plains Turn to Dust|date=19 May 2013|first=Michael|last=Wines|url=https://www.nytimes.com/2013/05/20/us/high-plains-aquifer-dwindles-hurting-farmers.html?smid=pl-share}}</ref> in a 2013 ''[[New York Times]]'' article, "Wells Dry, Fertile Plains Turn to Dust" recounting the relentless decline of parts of the Ogallala Aquifer. Sixty years of [[intensive farming]] using huge center-pivot irrigators has emptied parts of the High Plains Aquifer.<ref name=NYT20May2013 /> Hundreds to thousands of years of rainfall would be needed to replace the groundwater in the depleted aquifer. In Kansas in 1950, irrigated cropland covered {{cvt|250,000|acre|ha}}; with the use of center-pivot irrigation, nearly three million acres of land were irrigated.<ref name=NYT20May2013 /> In some places in the Texas Panhandle, the water table has been drained (dewatered). "Vast stretches of Texas farmland lying over the aquifer no longer support irrigation. In west-central Kansas, up to a fifth of the irrigated farmland along a {{convert|100|mi |km|adj=mid | swath}} of the aquifer has already gone dry."<ref name=NYT20May2013 />

The center-pivot irrigation system is considered to be a highly efficient system which helps conserve water. However, by 2013, as the [[water consumption]] efficiency of the center-pivot irrigator improved over the years, farmers chose to plant more intensively, irrigate more land, and grow thirstier crops rather than reduce water consumption--an example of the [[Jevons Paradox]] in practice.<ref name=NYT20May2013 /> One approach to reducing the amount of groundwater used is to employ treated recycled water for irrigation; another approach is to change to crops that require less water, such as [[sunflower]]s.<ref>[http://www.denverpost.com/news/ci_4433612 Jeremy P. Meyer, "Farmers' tower of power"], ''Denver Post'', 2 October 2006. Last accessed October 24, 2006</ref>

Several rivers, such as the [[Platte River|Platte]], run below the water level of the aquifer. Because of this, the rivers receive groundwater flow (baseflow), carrying it out of the region rather than recharging the aquifer.

The $46.1-million [[Optima Lake]] dam in western [[Oklahoma]] was rendered useless when the dropping level of the aquifer drastically reduced flow of the [[Beaver River (Oklahoma)|Beaver River]], the lake's intended source of water.<ref>Logan Layden, "If you Want to Build a New Lake in Oklahoma, Forget History",  March 28, 2013, StateImpact Oklahoma{{cite web |url= https://stateimpact.npr.org/oklahoma/2013/03/28/the-lessons-of-history-no-longer-apply-when-it-comes-to-building-lakes/  |title= The Lessons of History No Longer Apply when it comes to Building Lakes |work= StateImpact Oklahoma website |access-date= 2015-06-01}}</ref>

===Accelerated decline in aquifer storage===
The depletion between 2001 and 2008, inclusive, is about 32% of the cumulative depletion during the entire 20th century.<ref name=KonikowUSGCjan2013>{{cite report |url=http://pubs.usgs.gov/sir/2013/5079/SIR2013-5079.pdf |title= Groundwater Depletion in the United States (1900–2008)|series=Scientific Investigations Report |number=2013–5079 |pages=63 |publisher=U.S. Department of the Interior, U.S. Geological Survey|location=Reston, Virginia|first=Leonard F.|last=Konikow}}</ref> In the United States, the biggest users of water from aquifers include agricultural irrigation and oil and coal extraction.<ref name=depletion>{{cite news|title=Drop in U.S. underground water levels has accelerated: USGS|url=https://www.reuters.com/article/us-usa-water-idUSBRE94J0Y920130520
|location=Washington, DC|first=Deborah |last=Zabarenko|date=20 May 2013|work=Reuters}}</ref> "Cumulative total [[overdrafting|groundwater depletion]] in the United States accelerated in the late 1940s and continued at an almost steady linear rate through the end of the century. In addition to widely recognized environmental consequences, groundwater depletion also adversely impacts the long-term sustainability of groundwater supplies to help meet the nation’s water needs."<ref name=KonikowUSGCjan2013 /> According to Matthew Sanderson, a professor of sociology at [[Kansas State University]], these trends are exacerbated by an [[agricultural subsidy]] system and a [[United States tax code]] that encourage overinvestment in water-using technology due to a [[treadmill of production]].<ref>{{cite journal
 | last1 = Sanderson
 | first1 = Matthew R.
 | last2 = Hughes
 | first2 = Vivian
 | title = Race to the Bottom (of the Well): Groundwater in an Agricultural Production Treadmill 
 | journal = Social Problems
 | volume = 66
 | issue = 3
 | pages = 392–410
 | year = 2019
 | publisher = Oxford University Press
 | doi = 10.1093/socpro/spy011
 | url = https://academic.oup.com/socpro/article/66/3/392/5032915
 | access-date = 2024-12-09
}}
</ref> The treadmill of production is complemented by a treadmill of protection, a water conservation system whose policies delay effective long term water conservation measures to protect the water interests of its key industries in the short term.<ref>{{cite journal
 | last1 = Sanderson
 | first1 = M. R.
 | last2 = Griggs
 | first2 = B. W.
 | last3 = Schäfer
 | first3 = G. N.
 | title = Ad Astra per aquam (to the stars, through water): The Kansas Aqueduct Project as a sociotechnical imaginary in the Anthropocene
 | journal = The Anthropocene Review
 | year = 2024
 | volume = 
 | issue = 
 | pages = 
 | id = 20530196241300525
 | doi = 10.1177/20530196241300525
 | url = https://doi.org/10.1177/20530196241300525
 | access-date = 2024-12-09
}}
</ref> Robertson suggests federal policy reforms to increase incentives to conserve groundwater, such as amendments to the [[Conservation Reserve Program]], along with increased restrictions on water use at the state level.<ref>{{cite web |last1=Griggs |first1=Burke |last2=Miller-Klugesherz |first2=Jacob A. |last3=Sanderson |first3=Matthew R. |title=Farmers are depleting the Ogallala Aquifer because the government pays them to do it |url=https://theconversation.com/farmers-are-depleting-the-ogallala-aquifer-because-the-government-pays-them-to-do-it-145501 |website=The Conversation |language=en |date=9 November 2020}}</ref>

Since the 1940s, pumping from the Ogallala has drawn the aquifer down by more than {{convert|300|ft|m|sigfig=1}} in some areas. Producers have taken steps to reduce their reliance on irrigated water. Streamlined operations allow them to produce significantly greater yield using roughly the same amount of water needed four decades ago. Still, losses to the aquifer between 2001 and 2011 equated to a third of its cumulative depletion during the entire 20th century. The Ogallala is recharged primarily by rainwater, but only about one inch of precipitation actually reaches the aquifer annually. Rainfall in most of the Texas High Plains is minimal, evaporation is high, and infiltration rates are slow.<ref name="window.state.tx.us">[http://www.window.state.tx.us/specialrpt/water/96-1746.pdf Texas Water Report: Going Deeper for the Solution] {{Webarchive|url=https://web.archive.org/web/20140222144253/http://www.window.state.tx.us/specialrpt/water/96-1746.pdf |date=February 22, 2014 }} Texas Comptroller of Public Accounts. Retrieved 2/10/14.</ref>

During the 1990s, the aquifer held some three billion acre-feet of groundwater used for crop irrigation as well as drinking water in urban areas. The demand for the water outstrips its replenishment. The water level is particularly on the decline in Texas and New Mexico. Continued long-term use of the aquifer is "troublesome and in need of major reevaluation," according to the [[historian]] [[Paul H. Carlson]], [[Emeritus|professor-emeritus]] from [[Texas Tech University]] in [[Lubbock, Texas|Lubbock]].<ref>{{cite news|url=https://www.lubbockonline.com/news/20190622/caprock-chronicles-ogallala-aquifers-long-history-uncertain-future|title=Caprock Chronicles: The Ogallala Aquifer's long history, uncertain future|author=Paul H. Carlson|newspaper=[[Lubbock Avalanche-Journal]]|date=June 22, 2019|access-date=June 25, 2019|author-link=Paul H. Carlson}}</ref>