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{{Short description|Unsustainable extraction of groundwater}}
{{about|groundwater extraction|financial uses of the term|Overdraft}}'''Overdrafting''' is the process of extracting [[groundwater]] beyond the [[dynamic equilibrium|equilibrium]] yield of an [[aquifer]]. Groundwater is one of the largest sources of [[fresh water]] and is found underground. The primary cause of groundwater depletion is the excessive pumping of groundwater up from underground aquifers.

There are two sets of yields: safe yield and [[sustainable yield]]. Safe yield is the amount of groundwater that can be withdrawn over a period of time without exceeding the long-term recharge rate or affecting the aquifer integrity.<ref>{{Cite web |title=Safe Yield |url=https://www.watereducation.org/aquapedia/safe-yield |access-date=2022-12-19 |website=Water Education Foundation |language=en}}</ref><ref>{{Cite web |title=Safe yield |url=https://solareis.anl.gov/glossacro/dsp_wordpopup.cfm?word_id=5165#:~:text=Glossary%20Term,basin%27s%20physical%20and%20chemical%20integrity. |access-date=2022-12-19 |website=solareis.anl.gov}}</ref> Sustainable yield is the amount of water extraction that can be sustained indefinitely without negative hydrological impacts, taking into account both [[groundwater recharge|recharge rate]] and [[surface water]] impacts.<ref>{{Cite web |title=Perennial/safe/sustainable yield |url=https://solareis.anl.gov/glossacro/dsp_wordpopup.cfm?word_id=5038 |access-date=2022-12-19 |website=solareis.anl.gov}}</ref>{{Better source needed|reason=The current source is insufficiently reliable ([[WP:NOTRS]]).|date=December 2022}}

There are two types of aquifers: confined and unconfined. In confined aquifers, there is an overbearing layer called [[aquitard]], which contains impermeable materials through which groundwater cannot be extracted. In unconfined aquifers, there is no aquitard, and groundwater can be freely extracted from the surface. Extracting groundwater from unconfined aquifers is like borrowing the water: it has to be recharged at a proper rate. Recharge can happen through artificial recharge and natural recharge.<ref name="University of California">{{cite book |last1=Lassiter |first1=Allison |title=Sustainable Water Challenges and Solutions from California |date=July 2015 |publisher=University of California |isbn=9780520285354}}</ref>

Insufficient recharge can lead to depletion, reducing the usefulness of the aquifer for humans. Depletion can also have impacts on the environment around the aquifer, such as soil compression and [[Groundwater-related subsidence|land subsidence]], local climatic change, soil chemistry changes, and other deterioration of the local environment.

== Mechanism ==
When groundwater is extracted from an aquifer, a [[cone of depression]] is created around the [[well]]. As the drafting of water continues, the cone increases in radius. Extracting too much water (overdrafting) can lead to negative impacts such as a drop of the [[water table]], [[land subsidence]], and loss of surface water reaching the streams. In extreme cases, the supply of water that naturally recharges the aquifer is pulled directly from streams and rivers, lowering their water levels. This affects wildlife, as well as humans who might be using the water for other purposes.<ref name="University of California"/>

The natural process of aquifer recharge takes place through the percolation of surface water. An aquifer may be artificially recharged, such as by pumping [[reclaimed water]] from [[wastewater management]] projects directly into the aquifer. An example of is the [[Orange County Water District]] in [[California]].<ref>{{cite web |title=Orange County Water District |url=https://www.ocwd.com/}}</ref> This organization takes wastewater, treats it to a proper level, and then systematically pumps it back into the aquifers for artificial recharge.

Since every groundwater basin [[groundwater recharge|recharges]] at a different rate depending on [[precipitation]], [[vegetative cover]], and [[soil conservation]] practices, the quantity of groundwater that can be safely pumped varies greatly among regions of the world and even within provinces. Some aquifers require a very long time to recharge, and thus overdrafting can effectively dry up certain sub-surface [[water supplies]]. [[Groundwater-related subsidence|Subsidence]] occurs when excessive groundwater is extracted from rocks that support more weight when saturated. This can lead to a capacity reduction in the aquifer.<ref>{{cite web |url=http://ga.water.usgs.gov/edu/earthgwlandsubside.html |title=Land subsidence |work=The USGS Water Science School |publisher=United States Geological Survey |date=2015-08-20 |access-date=2013-04-06 |archive-date=2013-11-10 |archive-url=https://web.archive.org/web/20131110184628/http://ga.water.usgs.gov/edu/earthgwlandsubside.html |url-status=dead }}</ref>

Changes in freshwater availability stem from natural and human activities (in conjunction with [[climate change]]) that interfere with groundwater recharge patterns. One of the leading anthropogenic activities causing groundwater depletion is [[irrigation]]. Roughly 40% of global irrigation is supported by groundwater, and irrigation is the primary activity causing groundwater storage loss across the U.S.<ref name=":4">{{Cite journal|last1=Condon|first1=Laura E.|last2=Maxwell|first2=Reed M.|date=June 2019|title=Simulating the sensitivity of evapotranspiration and streamflow to large-scale groundwater depletion|journal=Science Advances|language=en|volume=5|issue=6|pages=eaav4574|bibcode=2019SciA....5.4574C|doi=10.1126/sciadv.aav4574|issn=2375-2548|pmc=6584623|pmid=31223647}}</ref>

== Around the world ==
{{see also|Environmental impact of irrigation}}

{| class="wikitable sortable"
|+Ranking of countries that use groundwater for [[irrigation]].<ref>{{Cite book|title = The Atlas of Water|last = Black|first = Maggie|publisher = University of California Press|year = 2009|location = Berkeley and Los Angeles, California|pages = 62|isbn=9780520259348}}</ref>
|-
!Country!! Million [[hectare]]s ({{convert|1|e6ha|abbr=on}})<br/>irrigated with groundwater
|-
|[[Irrigation in India|India]]||26.5
|-
|[[Irrigation districts in the United States|USA]]||10.8
|-
|[[Irrigation in China|China]]||8.8
|-
|[[Irrigation in Pakistan|Pakistan]]||4.9
|-
|[[Irrigation in Iran|Iran]]||3.6
|-
|[[Irrigation in Bangladesh|Bangladesh]]||2.6
|-
|[[Irrigation in Mexico|Mexico]]||1.7
|-
|[[Irrigation in Saudi Arabia|Saudi Arabia]]||1.5
|-
|[[Irrigation in Italy|Italy]]||0.9
|-
|[[Irrigation in Turkey|Turkey]]||0.7
|-
|[[Irrigation in Syria|Syria]]||0.6
|-
|[[Irrigation in Brazil|Brazil]] ||0.5
|}
This ranking is based on the amount of groundwater each country uses for agriculture. This issue is becoming significant in the United States (most notably in California), but it has been an ongoing problem in other parts of the world, such as was documented in [[Punjab, India|Punjab]], India, in 1987.<ref>{{Cite journal|jstor = 4400350|title = Ground Water Depletion in Punjab|journal = Economic and Political Weekly|volume = 28|issue = 44|pages = 2397–2401|last1 = Dhawan|first1 = B. D.|year = 1993}}</ref>

=== United States ===
In the U.S., an estimated 800 km<sup>3</sup> of groundwater was depleted during the 20th century.<ref name=":4" /> The development of cities and other areas of highly concentrated water usage has created a strain on groundwater resources. In post-development scenarios, interactions between surface water and groundwater are reduced; there is less intermixing between the surface and subsurface ([[interflow]]), leading to depleted water tables.<ref>{{Cite journal|last=Sophocleous|first=Marios|date=February 2002|title=Interactions between groundwater and surface water: the state of the science|url=http://link.springer.com/10.1007/s10040-001-0170-8|journal=Hydrogeology Journal|language=en|volume=10|issue=1|pages=52–67|bibcode=2002HydJ...10...52S|doi=10.1007/s10040-001-0170-8|issn=1431-2174|s2cid=2891081}}</ref>

Groundwater recharge rates are also affected by rising temperatures which increase surface evaporation and transpiration, resulting in decreased water content of the soil.<ref>{{Cite journal|last1=Green|first1=Timothy R.|last2=Taniguchi|first2=Makoto|last3=Kooi|first3=Henk|last4=Gurdak|first4=Jason J.|last5=Allen|first5=Diana M.|last6=Hiscock|first6=Kevin M.|last7=Treidel|first7=Holger|last8=Aureli|first8=Alice|date=August 2011|title=Beneath the surface of global change: Impacts of climate change on groundwater|url=https://linkinghub.elsevier.com/retrieve/pii/S0022169411002988|journal=Journal of Hydrology|language=en|volume=405|issue=3–4|pages=532–560|bibcode=2011JHyd..405..532G|doi=10.1016/j.jhydrol.2011.05.002|s2cid=18098122 }}</ref> Anthropogenic changes to groundwater storage, such as over-pumping and the depletion of water tables combined with climate change, effectively reshape the hydrosphere and impact the ecosystems that depend on the groundwater.<ref>{{Cite journal|last1=Orellana|first1=Felipe|last2=Verma|first2=Parikshit|last3=Loheide|first3=Steven P.|last4=Daly|first4=Edoardo|date=September 2012|title=Monitoring and modeling water-vegetation interactions in groundwater-dependent ecosystems: GROUNDWATER-DEPENDENT ECOSYSTEMS|journal=Reviews of Geophysics|language=en|volume=50|issue=3|doi=10.1029/2011RG000383|doi-access=free}}</ref>

==Accelerated decline in subterranean reservoirs==
According to a 2013 report by research hydrologist Leonard F. Konikow<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> at the [[United States Geological Survey]] (USGS), the depletion of the [[Ogallala Aquifer]] between 2001{{ndash}}2008 is about 32% of the cumulative depletion during the entire 20th century.<ref name=KonikowUSGCjan2013 /> In the United States, the biggest users of water from aquifers include agricultural [[irrigation]], and [[oil drilling|oil]] and [[coal mining|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
|publisher=Reuters
}}</ref> According to Konikow, "Cumulative total 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 />

As reported by another USGS study of withdrawals from 66 major US aquifers, the three greatest uses of water extracted from aquifers were [[irrigation]] (68%), public [[water supply]] (19%), and "self-supplied industrial" (4%). The remaining 8% of groundwater withdrawals were for "self-supplied domestic, [[aquaculture]], [[livestock]], [[mining]], and [[Electric power|thermoelectric power]] uses."<ref>{{cite web |first1= Molly A. |last1= Maupin |first2= Nancy L. |last2= Barber |name-list-style= amp |url= http://pubs.usgs.gov/circ/2005/1279/ |title= Estimated Withdrawals from Principal Aquifers in the United States, 2000 |publisher= United States Geological Survey |id= Circular 1279 |date= July 2005}}</ref>

== Environmental impacts ==
{{More citations needed section|date=June 2021}}
The [[environmental impact|environmental impacts]] of overdrafting include:

* [[Groundwater-related subsidence]]: the collapse of land due to lack of support (from the water that is being depleted). The first recorded case of land subsidence was in the 1940s. Land subsidence can be as little as local land collapsing or as large as an entire region's land being lowered. The subsidence can lead to infrastructural and ecosystem damage.
* Lowering of the [[water table]], which makes water harder to reach streams and rivers
* Reduction of water volume in streams and lakes because their supply of water is being diminished by surface water recharging the aquifers
* Impacts on animals that depend on streams and lakes for food, water, and [[habitat]]
* Deterioration to [[air quality]] and [[water quality]]
* Increase in the [[Water prize|cost of water]] to the consumer due to a lower water table—more energy is needed to pump further down, so operating costs increase for companies, who pass on the expense to the consumer
* Decrease in [[Crop yield|crop production]] from lack of water (a large loss in the U.S. in particular, where 60% of irrigation relies on groundwater)
* Disturbances to the [[water cycle]]

===Groundwater related subsidence===
{{excerpt|Groundwater-related_subsidence}}

===Climatic changes===

Aquifer [[drawdown (hydrology)|drawdown]] or overdrafting and the pumping of [[fossil water]] may be contributing to [[sea-level rise]].<ref>{{cite web|url=http://www.uu.nl/EN/Current/Pages/Wereldwijdonttrekkenvangrondwaterleidttotzeespiegelstijging.aspx|title=Rising sea levels attributed to global groundwater extraction |publisher=University of Utrecht|access-date=February 8, 2011}}</ref> By increasing the amount of [[moisture]] available to fall as precipitation, severe weather events are more likely to occur. To some extent, moisture in the atmosphere accelerates the probability of a [[global warming]] event. The [[correlation coefficient]] is not yet scientifically determined.

== Socio-economic effects ==
Scores of countries{{How many|date=May 2022}} are overpumping aquifers as they struggle to satisfy their growing water needs, including each of the big three [[grain]] producers: [[China]], [[India]], and the [[United States]]. These three, along with several other countries where water tables are falling, are home to more than half the world's people.{{Cn|date=June 2021}}

Water is intrinsic to [[Biological growth|biological]] and [[economic growth]], and overdrafting reduces its available supply. According to [[Liebig's law of the minimum]], population growth is therefore impeded. Deeper [[Water well|wells]] must be [[Well drilling|drilled]] as the water table drops, which can become expensive. In addition, the [[Energy conversion efficiency|energy needed]] to extract a given volume of water increases with the amount the aquifer has been depleted. The deeper the water is extracted the worse the quality of the water becomes, which increases the cost of filtration. [[Saltwater intrusion]] is another consequence of overdrafting, leading to a reduction in [[water quality]].{{Cn|date=June 2021}}

== Possible solutions ==
Since recharge is the natural replenishment of water, ''artificial [[Groundwater recharge|recharge]]'' is the man-made replenishment of groundwater, though there is only a limited amount of suitable water available for replenishing.<ref name=":0">{{Cite book|title = Sustainable Water|last = Lassiter|first = Allison|publisher = University of California Press|year = 2015|location = Oakland California|pages = 186}}</ref>

In areas where recharge alone will not work, decreased [[water use]] can also be used. Notably, this requires actions such as switching to less water-intensive crops. Consumptive use refers to the water that is naturally taken from the system (for example, in [[transpiration]]){{Necessary?|date=December 2022}}.<ref name=":0" />

==See also==
*[[Cone of depression]]
*[[Groundwater recharge]]
*[[Groundwater-related subsidence]]
*[[Drinking water]]
*[[Overexploitation]]
*[[Water scarcity|Water crisis]]
*[[Human overpopulation]]

==References==
{{Reflist}}

== External links ==
*[https://web.archive.org/web/20110607214828/http://www.issues.org/19.1/glennon.htm The Perils of Groundwater Pumping], Issues in Science and Technology

{{Water}}
{{Natural resources}}
{{Human impact on the environment}}

[[Category:Aquifers]]
[[Category:Environmental impact of agriculture]]
[[Category:Environmental issues with water]]
[[Category:Water supply]]
[[Category:Water and the environment]]

Overdrafting - Revision history

Ajay Kumar: Created a new article