Editing Drought (section)

== Impacts ==
[[File:Global Drought Total Economic Loss Risk Deciles (5457316295).jpg|thumb|Global drought total economic loss risk]]
[[File:DroughtinNamibia.jpg|thumb|right|Pair of dead oryx in Namibia during the [[2018–19 Southern Africa drought]].]]
[[File:Ruins_at_Farina.JPG|thumb|After years of drought and dust storms the town of [[Farina, South Australia|Farina]] in [[South Australia]] was abandoned.]]
Drought is one of the most complex and major [[natural hazards]], and it has devastating impacts on the environment, economy, water resources, agriculture, and society worldwide.<ref name=":3">{{Cite journal|last1=Gebrechorkos|first1=Solomon H.|last2=Peng|first2=Jian|last3=Dyer|first3=Ellen|last4=Miralles|first4=Diego G.|last5=Vicente-Serrano|first5=Sergio M.|last6=Funk|first6=Chris|last7=Beck|first7=Hylke E.|last8=Asfaw|first8=Dagmawi T.|last9=Singer|first9=Michael B. |last10=Dadson |first10=Simon J.|year=2023|title=Global high-resolution drought indices for 1981–2022|url=https://essd.copernicus.org/articles/15/5449/2023/|journal=Earth System Science Data|volume=15|issue=12|pages=5449–5466|doi=10.5194/essd-15-5449-2023|issn=1866-3516|doi-access=free|bibcode=2023ESSD...15.5449G|hdl=10754/693396|hdl-access=free}} [[File:CC-BY icon.svg|50px]] Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License]</ref>

One can divide the impacts of droughts and water shortages into three groups: environmental, economic and social (including health).

=== Environmental and economic impacts ===
[[File:Mixed Douglas-fir - Western Redcedar forest, with some Western Redcedar dying from drought; Arlington, Washington, 2018 (29721380337).jpg| thumb|right | Western red cedar dying from drought, US, 2018]]
Environmental effects of droughts include: lower surface and subterranean water-levels, lower flow-levels (with a decrease below the minimum leading to direct danger for amphibian life), increased [[Water pollution|pollution of surface water]], the drying out of [[wetland]]s, more and larger [[wildfire]]s, higher deflation intensity, [[Biodiversity loss|loss of biodiversity]], worse health of trees and the appearance of pests and dendroid diseases.<ref name="Zimmer">{{cite journal|last1=Zimmer|first1=Katarina|title=Dead trees around the world are shocking scientists|journal=Knowable Magazine|date=17 August 2023|doi=10.1146/knowable-081723-2|doi-access=free|url=https://knowablemagazine.org/article/food-environment/2023/dead-trees-shocking-scientists}}</ref><ref name="Hartmann">{{cite journal|last1=Hartmann|first1=Henrik|last2=Bastos|first2=Ana|last3=Das|first3=Adrian J.|last4=Esquivel-Muelbert|first4=Adriane|last5=Hammond|first5=William M.|last6=Martínez-Vilalta|first6=Jordi|last7=McDowell|first7=Nate G.|last8=Powers|first8=Jennifer S.|last9=Pugh|first9=Thomas A.M. |last10=Ruthrof |first10=Katinka X.|last11=Allen|first11=Craig D.|title=Climate Change Risks to Global Forest Health: Emergence of Unexpected Events of Elevated Tree Mortality Worldwide|journal=Annual Review of Plant Biology|date=20 May 2022|volume=73|issue=1|pages=673–702|doi=10.1146/annurev-arplant-102820-012804|doi-access=free|pmid=35231182|bibcode=2022ARPB...73..673H|issn=1543-5008}}</ref> Drought-induced mortality of trees lacks in most [[climate model]]s in their representation of forests as [[Carbon sink|land carbon sink]].<ref>{{Cite news|last=Greenfield|first=Patrick|date=2024-10-14|title=Trees and land absorbed almost no CO2 last year. Is nature's carbon sink failing?|url=https://www.theguardian.com/environment/2024/oct/14/nature-carbon-sink-collapse-global-heating-models-emissions-targets-evidence-aoe|access-date=2024-11-02|work=The Guardian|issn=0261-3077}}</ref>

Economic losses as a result of droughts include lower agricultural, forests, game and fishing output, higher food-production costs, lower energy-production levels in hydro plants, losses caused by depleted water tourism and transport revenue, problems with water supply for the [[Energy industry|energy sector]] and for technological processes in metallurgy, mining, the chemical, paper, wood, foodstuff industries etc., disruption of [[Water supply|water supplies]] for municipal economies.

Further examples of common environmental and economic consequences of drought include:
* Alteration of [[Functional diversity (ecology)|diversity of plant communities]], which can have an impact on net [[primary production]] and other [[ecosystem service]]s.<ref>{{Cite journal|last1=Griffin-Nolan|first1=Robert J.|last2=Blumenthal|first2=Dana M.|last3=Collins|first3=Scott L.|last4=Farkas|first4=Timothy E.|last5=Hoffman|first5=Ava M.|last6=Mueller|first6=Kevin E.|last7=Ocheltree|first7=Troy W.|last8=Smith|first8=Melinda D.|author-link8=Melinda D. Smith|last9=Whitney|first9=Kenneth D. |last10=Knapp |first10=Alan K.|date=September 2019|editor-last=Jones|editor-first=Holly|title=Shifts in plant functional composition following long-term drought in grasslands|journal=Journal of Ecology|volume=107|issue=5|pages=2133–2148|bibcode=2019JEcol.107.2133G|doi=10.1111/1365-2745.13252|issn=0022-0477|doi-access=free}}</ref>
* [[Wildfires]], such as [[Australian bushfires]] and [[wildfires in the United States]], become more common during times of drought and may cause human deaths.<ref name="autogenerated1">{{cite web|title=TFS Article|url=http://txforestservice.tamu.edu/shared/article.asp?DocumentID=406&mc=fire|archive-url=https://web.archive.org/web/20030711082443/http://txforestservice.tamu.edu/shared/article.asp?DocumentID=406&mc=fire|archive-date=11 July 2003|work=tamu.edu}}</ref>
* [[Dust Bowl]]s, themselves a sign of [[erosion]], which further erode the [[landscape]]
* [[Dust storms]], when drought hits an area suffering from desertification and [[erosion]]
* [[Habitat]] damage, affecting both [[Terrestrial ecoregion|terrestrial]] and [[Aquatic ecosystem|aquatic]] wildlife<ref>C.Michael Hogan. 2010. [http://www.eoearth.org/article/Abiotic_factor?topic=49461 ''Abiotic factor''. Ed. Emily Monosson. Encyclopedia of Earth. National Council for Science and the Environment, Washington DC] {{webarchive |url= https://web.archive.org/web/20130608071757/http://www.eoearth.org/article/Abiotic_factor?topic=49461 |date= June 8, 2013 }}</ref>
* [[Snake]] migration, which results in snake-bites<ref>{{cite news|date=2007-01-20|title=Asia-Pacific – Australians face snake invasion|url=http://news.bbc.co.uk/2/hi/asia-pacific/6282075.stm|publisher=BBC News}}</ref>
* Reduced [[electricity generation|electricity production]] due to reduced water-flow through [[hydroelectric energy|hydroelectric]] [[dam]]s<ref>[http://www.dailyestimate.com/article.asp?idcategory=35&idSub=175&idArticle=12286 Drought affecting US hydroelectric production | Daily Estimate] {{webarchive |url= https://web.archive.org/web/20111002124428/http://www.dailyestimate.com/article.asp?idcategory=35&idSub=175&idArticle=12286 |date= October 2, 2011 }}</ref>
* Shortages of water for [[Private industry|industrial]] users<ref>{{cite web|url=http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2005/03/06/MNGE2BL7161.DTL|title=Parched village sues to shut tap at Coke / Drought-hit Indians say plant draining groundwater|work=San Francisco Chronicle|date=2005-03-06}}</ref><ref>{{cite web|url=http://www.greenpeace.org/international/news/sweden-nuclear-closure-040806|title=Sweden closes nuclear plants over safety fears|publisher=Greenpeace International|access-date=2016-02-06|archive-url=https://web.archive.org/web/20090110184749/http://www.greenpeace.org/international/news/sweden-nuclear-closure-040806|archive-date=2009-01-10|url-status=dead}}</ref>

=== Agricultural impacts ===
{{Further|Effects of climate change on agriculture}}[[File:Soil moisture and climate change.svg|thumb|upright=1.35|[[Effects of climate change|Impacts of climate change]] on soil moisture at 2&nbsp;°C of global warming. A reduction of one [[standard deviation]] means that average soil moisture will approximate the ninth driest year between 1850 and 1900.]]Droughts can cause land degradation and loss of soil moisture, resulting in the destruction of cropland productivity.<ref>{{Cite journal|last1=Seka|first1=Ayalkibet Mekonnen|last2=Zhang|first2=Jiahua|last3=Prodhan|first3=Foyez Ahmed|last4=Ayele|first4=Gebiaw Teshome|last5=Finsa|first5=Mekuanenet Mulunhie|last6=Sharma|first6=Til Prasad Pangali|last7=Melesse|first7=Assefa Mekonnen|year=2022|title=Hydrological drought impacts on water storage variations: a focus on the role of vegetation changes in the East Africa region. A systematic review|url=https://link.springer.com/10.1007/s11356-022-23313-0|journal=Environmental Science and Pollution Research|volume=29|issue=53|pages=80237–80256|doi=10.1007/s11356-022-23313-0|issn=0944-1344|pmid=36197619|bibcode=2022ESPR...2980237S|s2cid=252713722}}</ref> This can result in diminished [[crop yield|crop growth or yield productions]] and [[carrying capacity]] for [[livestock]]. Drought in combination with high levels of grazing pressure can function as the tipping point for an ecosystem, causing [[Woody plant encroachment|woody encroachment]].<ref>{{Cite journal|last1=Koch|first1=Franziska|last2=Tietjen|first2=Britta|last3=Tielbörger|first3=Katja|last4=Allhoff|first4=Korinna T.|date=November 2022|title=Livestock management promotes bush encroachment in savanna systems by altering plant–herbivore feedback|journal=Oikos|volume=2023|issue=3|doi=10.1111/oik.09462|issn=0030-1299|s2cid=253299539|doi-access=free}}</ref>

Water stress affects plant development and quality in a variety of ways: firstly drought can cause poor germination and impaired seedling development.<ref>{{cite journal|vauthors=Farooq M, Wahid A, Kobayashi N, Fujita D, Basra SM|date=March 2009|title=Plant drought stress: effects, mechanisms and management|url=https://www.agronomy-journal.org/articles/agro/abs/2009/01/a7175/a7175.html|journal=Agronomy for Sustainable Development|volume=29|issue=1|pages=185–212|doi=10.1051/agro:2008021|bibcode=2009AgSD...29..185F|s2cid=12066792}}</ref> At the same time plant growth relies on cellular division, cell enlargement, and differentiation. Drought stress impairs [[mitosis]] and cell elongation via loss of [[turgor pressure]] which results in poor growth.<ref name=":1">{{cite journal|display-authors=6|vauthors=Fahad S, Bajwa AA, Nazir U, Anjum SA, Farooq A, Zohaib A, Sadia S, Nasim W, Adkins S, Saud S, Ihsan MZ, Alharby H, Wu C, Wang D, Huang J|date=29 June 2017|title=Crop Production under Drought and Heat Stress: Plant Responses and Management Options|journal=Frontiers in Plant Science|volume=8|pages=1147|doi=10.3389/fpls.2017.01147|pmc=5489704|pmid=28706531|doi-access=free}}</ref> Development of leaves is also dependent upon turgor pressure, concentration of nutrients, and carbon assimilates{{Clarify|date=March 2022}} all of which are reduced by drought conditions, thus drought stress lead to a decrease in leaf size and number.<ref name=":1" /> Plant height, biomass, leaf size and stem girth has been shown to decrease in maize under water limiting conditions.<ref name=":1" /> Crop yield is also negatively effected by drought stress, the reduction in crop yield results from a decrease in photosynthetic rate, changes in leaf development, and altered allocation of resources all due to drought stress.<ref name=":1" /> Crop plants exposed to drought stress suffer from reductions in leaf water potential and transpiration rate. [[Water-use efficiency]] increases in crops such as wheat while decreasing in others, such as potatoes.<ref>{{cite journal|display-authors=6|vauthors=Kahiluoto H, Kaseva J, Balek J, Olesen JE, Ruiz-Ramos M, Gobin A, Kersebaum KC, Takáč J, Ruget F, Ferrise R, Bezak P, Capellades G, Dibari C, Mäkinen H, Nendel C, Ventrella D, Rodríguez A, Bindi M, Trnka M|date=January 2019|title=Decline in climate resilience of European wheat|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=116|issue=1|pages=123–128|bibcode=2019PNAS..116..123K|doi=10.1073/pnas.1804387115|pmc=6320549|pmid=30584094|doi-access=free}}</ref><ref>{{cite journal|vauthors=Abbate PE, Dardanelli JL, Cantarero MG, Maturano M, Melchiori RJ, Suero EE|year=2004|title=Climatic and Water Availability Effects on Water-Use Efficiency in Wheat|journal=Crop Science|volume=44|issue=2|pages=474–483|doi=10.2135/cropsci2004.4740}}</ref><ref name=":1" />

Plants need water for the uptake of nutrients from the soil, and for the transport of nutrients throughout the plant: drought conditions limit these functions leading to stunted growth. Drought stress also causes a decrease in photosynthetic activity in plants due to the reduction of photosynthetic tissues, stomatal closure, and reduced performance of photosynthetic machinery. This reduction in photosynthetic activity contributes to the reduction in plant growth and yields.<ref name=":1" /> Another factor influencing reduced plant growth and yields include the allocation of resources; following drought stress plants will allocate more resources to roots to aid in water uptake increasing root growth and reducing the growth of other plant parts while decreasing yields.<ref name=":1" />

=== Social and health impacts ===
The most negative impacts of drought for humans include [[crop failure]], [[food crisis]], famine, malnutrition, and [[poverty]], which lead to loss of life and [[mass migration]] of people.<ref name=":3" />

There are negative effects on the health of people who are directly exposed to this phenomenon (excessive [[heat wave]]s). Droughts can also cause limitations of water supplies, increased water pollution levels, high food-costs, stress caused by failed harvests, [[water scarcity]], etc. Reduced water quality can occur because lower water-flows reduce dilution of pollutants and increase [[contamination]] of remaining water sources.<ref>Mosley LM (2014). Drought impacts on the water quality of freshwater systems; review and integration. Earth-Science Reviewss. {{doi|10.1016/j.earscirev.2014.11.010}}.</ref><ref>10. Mosley LM, Zammit B, Leyden E, Heneker TM, Hipsey MR, Skinner D, and Aldridge KT (2012). The Impact of Extreme Low Flows on the Water Quality of the Lower Murray River and Lakes (South Australia). Water Resources Management 26: 3923–3946.</ref>

This explains why droughts and water scarcity operate as a factor which increases the gap between [[Developed country|developed]] and [[Developing country|developing countries]].<ref>{{Cite journal|last=Prokurat|first=Sergiusz|year=2015|title=Drought and water shortages in Asia as a threat and economic problem|url=http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.desklight-95d2a7ec-8c5f-474d-84ed-8b8baed8f8c0/c/235_PDFsam_Joms_3_26_2015.pdf|url-status=live|journal=Journal of Modern Science|volume=26|issue=3|archive-url=https://ghostarchive.org/archive/20221009/http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.desklight-95d2a7ec-8c5f-474d-84ed-8b8baed8f8c0/c/235_PDFsam_Joms_3_26_2015.pdf|archive-date=2022-10-09|access-date=4 August 2016}}</ref>

Effects vary according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food-sources. Areas with populations that depend on water sources as a major food-source are more vulnerable to famine.
[[File:Queuing for registration in the heat of the sun (5977577531).jpg|thumb|People displaced by a drought in [[Somalia]] arriving at a camp in [[Dolo Odo|Dolo Ado]], Ethiopia, 2011]]
Further examples of social and health consequences include:
* [[Water scarcity]], [[Harvest|crop failure]], [[famine]]<ref>{{cite book|last1=García|first1=R. V.|title=The constant catastrophe : malnutrition, famines, and drought|last2=Escudero|first2=J. C.|date=1981|publisher=Pergamon Press|isbn=9781483189666|edition=1st|location=Oxford; New York|page=3}}</ref> and [[hunger]] – drought provides too little water to support food crops; [[malnutrition]], [[dehydration]] and related diseases
* [[Mass migration]], resulting in [[internally displaced person|internal displacement]] and international [[refugee]]s
* Social [[unrest]]
* [[War]] over natural resources, including water and food
* [[Cyanotoxin]] accumulation within food chains and water supply (some of which are among the most potent toxins known to science) can cause cancer with low exposure over the long term.<ref>
{{cite web|title=Toxins from freshwater algae found in San Francisco Bay shellfish|url=http://news.ucsc.edu/2016/10/microcystin-toxin.html|access-date=5 November 2017}}
</ref> High levels of [[microcystin]] appeared in [[San Francisco Bay Area]] salt-water shellfish and fresh-water supplies throughout the state of California in 2016.

=== Loss of fertile soils ===
{{See also|Aeolian processes}}
[[Aeolian processes|Wind erosion]] is much more severe in arid areas and during times of drought. For example, in the [[Great Plains]], it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years.<ref>{{Cite book|author=Wiggs, Giles F.S.|title=Arid Zone Geomorphology: Process, Form and Change in Drylands|publisher=John Wiley & Sons|year=2011|isbn=978-0-470-71076-0|editor=Thomas, David S.G.|page=588|chapter=Geomorphological hazards in drylands|chapter-url=https://books.google.com/books?id=swz4rh4KaLYC&pg=PA588}}
</ref>

[[Loess]] is a homogeneous, typically nonstratified, porous, [[friable]], slightly coherent, often calcareous, fine-grained, [[silt]]y, pale yellow or buff, windblown ([[Aeolian processes|Aeolian]]) [[sediment]].<ref>{{cite journal|author=F. von Richthofen|year=1882|title=On the mode of origin of the loess|url=https://zenodo.org/record/1880729|journal=Geological Magazine (Decade II)|volume=9|issue=7|pages=293–305|bibcode=1882GeoM....9..293R|doi=10.1017/S001675680017164X|s2cid=131245730}}</ref> It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess often stands in either steep or vertical faces.<ref>{{cite book|author1=K.E.K. Neuendorf|title=Glossary of Geology|author2=J.P. Mehl, Jr.|author3=J.A. Jackson|publisher=[[Springer-Verlag]], New York|year=2005|isbn=978-3-540-27951-8|page=779}}</ref> Loess tends to develop into highly rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world.<ref>{{cite book|author=Arthur Getis|url=https://archive.org/details/introductiontoge00geti/page/99|title=Introduction to Geography, Seventh Edition|author2=Judith Getis and Jerome D. Fellmann|publisher=[[McGraw-Hill]]|year=2000|isbn=978-0-697-38506-2|page=[https://archive.org/details/introductiontoge00geti/page/99 99]}}</ref> Loess deposits are geologically unstable by nature, and will erode very readily. Therefore, windbreaks (such as big trees and bushes) are often planted by farmers to reduce the wind erosion of loess.<ref name="Erosion" />