Editing Lake Chad (section)

==Hydrology==
[[File:Megachad en disappearance of lake chad.jpg|thumb|346x346px|Shrinking of Lake Chad over the last 7000 years, with the outline of the [[British Isles]] for size comparison]]
[[File:Lake Chad.jpg|thumb|right|275px|Lake Chad 1972–2007]]
The Chad Basin covers an area of about {{convert|1|e6km2|sqmi|abbr=on}}, and is injected by the [[Chari River|Chari]], [[Logone River|Logone]], and [[Yobe River]]s.<ref name=r4>{{cite encyclopedia |author=Wen Yunzhao |title=Lake Chad |encyclopedia=Encyclopedia of China |edition=03 |location=Beijing |publisher=Encyclopedia of China Publishing House |url=https://www.zgbk.com/ecph/words?SiteID=1&ID=563293 |accessdate=2023-06-11 |language=zh-cn |archive-date=13 June 2023 |archive-url=https://web.archive.org/web/20230613163405/https://www.zgbk.com/ecph/words?SiteID=1&ID=563293 |url-status=live }}</ref><ref name=w2/> The water supply of the lake is seasonal. Most of the precipitation comes from the [[Adamawa Plateau]] in the south of the basin, which is transported to the lake basin through the Chari River and the Logone River. The two contribute 95% of the total inflow of Lake Chad, while the Yobe River only contributes less than 2.5%.<ref name=hd3/> The lake seeps through the underground to the lowest point of the Chad Basin, the [[Bodélé Depression]], approximately {{convert|480|km|mi|abbr=on}} northeast of Lake Chad, with the deepest point reaching an elevation of only {{convert|155|m|ft|abbr=on}} above sea level. This takes away most of the salinity and maintains the low salinity of Lake Chad. The southwestern waters of Lake Chad being freshwater, and the water in the northeast is only slightly salty.<ref name=4d>{{cite journal |author1=袁宣民 |title=乍得湖的环境、安全及其脆弱性 |trans-title=The environment, security and vulnerability of Lake Chad |journal=世界科学 |date=2016 |issue=7 |pages=21–23 |url=https://worldscience.cn/c/2016-07-14/587434.shtml |language=zh-cn |access-date=2023-06-13 |archive-date=2023-03-21 |archive-url=https://web.archive.org/web/20230321201808/https://worldscience.cn/c/2016-07-14/587434.shtml }}</ref><ref name=hd3/>

The water volume of most large lakes in Africa depends on rainfall and evaporation, which means that temperature and precipitation are crucial for regulating the water balance of these bodies of water, and any fluctuations can cause significant changes in their water level and area.<ref>{{cite journal |author1=Richard Ogutu-Ohwayo |author2=Vianny Natugonza |author3=Laban Musinguzi |author4=Mark Olokotum |author5=Shamim Naigaga |title=Implications of climate variability and change for African lake ecosystems, fisheries productivity, and livelihoods |journal=Journal of Great Lakes Research |volume=42 |issue=3 |pages=498–510 |doi=10.1016/j.jglr.2016.03.004 |year=2016}}</ref> Lake Chad is a shallow inland lake, and the rainfall in the Chad basin is very sensitive to small changes in atmospheric circulation, so the surface area of Lake Chad is greatly affected by climate change.<ref name=f1/><ref>{{cite journal |last1=Leblanc |first1=M. |last2=Favreau |first2=G.|last3=Tweed |first3=S. |title=Remote sensing for groundwater modelling in large semiarid areas:Lake Chad Basin, Africa |journal=Hydrogeology Journal |year=2007 |volume=15 |pages=97–100 |doi=10.1007/s10040-006-0126-0 |url=https://www.researchgate.net/publication/29650900 |language=en }}</ref> Dry climate due to vegetation loss from overgrazing and deforestation and large-scale irrigation projects that diverted water from the rivers that feed the lake are the main reasons for the shrinkage of Lake Chad.<ref name=tr5/> The [[Atlantic multidecadal oscillation]] and the [[El Niño–Southern Oscillation]] have affected precipitation in the [[Sahel]] region. From the early 1960s to the mid-1980s, the lake water level decreased by {{convert|3|m|ft|abbr=on}} compared to the average level from 1900 to 2010.<ref>{{cite journal |title=Combined effect of El Niño southern oscillation and Atlantic multidecadal oscillation on Lake Chad level variability |author1=Churchill Okonkwo |author2=Belay Demoz |author3=Ricardo Sakai |author4=Charles Ichoku |author5=Chigozie Anarado |author6=Jimmy Adegoke |author7=Angelina Amadou |author8=Sanusi Imran Abdullahi |author9=Nir Krakauer |journal=Cogent Geoscience |date=2015-12-15 |volume=1 |issue=1 |doi=10.1080/23312041.2015.1117829 |doi-access=free }}</ref>

In 1870, the area of Lake Chad was about {{convert|28000|km2|sqmi|abbr=on}}. The lake was able to flow out of the [[Bahr el-Ghazal (wadi in Chad)|Bahr el-Ghazal]] during the rainy season. At the turn of the 20th century the area of Lake Chad shrank briefly, and reached a new high in the middle of the 20th century and overflowed from the Bahr el-Ghazal again.<ref name=w2/> A major drought started in the Sahel region in the late 1960s and caused severe damage in 1972 and 1984. It was thought to be related to vegetation loss, global warming, and sea surface temperature anomalies.<ref name=f1>{{cite book|last=Evans|first=T.|chapter=The effects of changes in the world hydrological cycle on availability of water resources|editor-last1=Bazzaz|editor-first1=F.|editor-last2=Sombroek|editor-first2=W.|title=Global climate change and agricultural production|year=1996|publisher=FAO / John Wiley & Sons|isbn=92-5-103987-9|chapter-url=https://www.fao.org/3/W5183E/w5183e04.htm |archive-date=2023-06-18 |archive-url=https://web.archive.org/web/20230618010145/https://www.fao.org/3/W5183E/w5183e04.htm |language=en }}</ref> During this period, Lake Chad shrunk considerably and fluctuated in the range of {{convert|2000|to|5000|km2|sqmi|abbr=on}} thereafter.<ref name=7g/>

From June 1966 to January 1973, the area of Lake Chad shrank from {{convert|22772|to|15400|km2|sqmi|abbr=on}},<ref name=tr5>{{cite web|url=http://www.unep.org/dewa/vitalwater/article116.html|title=Lake Chad: almost gone|publisher=[[United Nations Environment Programme]] (UNEP)|access-date=2015-12-05|archiveurl=https://web.archive.org/web/20081216142751/http://www.unep.org/dewa/vitalwater/article116.html|archivedate=2008-12-16}}</ref> further shrunk to {{convert|4398|km2|sqmi|abbr=on}} in 1975,<ref name=7g/> and only {{convert|1756|km2|sqmi|abbr=on}} in February 1994.<ref name=tr5/> Since then, the area of Lake Chad has entered a relatively stable stage with a slight increase.<ref>{{cite journal |author1=Wengbin Zhu |author2=Jiabao Yan|author3=Shaofeng Jia |title=Monitoring Recent Fluctuations of the Southern Pool of Lake Chad Using Multiple Remote Sensing Data: Implications for Water Balance Analysis |journal=Remote Sensing |date=2017 |page=1032 |issue=10|volume=9|doi=10.3390/rs9101032 |doi-access=free }}</ref> From 1995 to 1998, it fluctuated within the range of {{convert|1200|to|4500|km2|sqmi|abbr=on}}. The area once reached {{convert|5075|km2|sqmi}} in 2000,<ref name=7g>{{cite journal |author1=刘甜甜 |author2=刘荣高 |author3=葛全胜 |title=基于多源遥感数据的非洲乍得湖水面变化监测 |trans-title=Monitoring of water surface change in Lake Chad in Africa based on multi-source remote sensing data|journal=地理科学进展 |year=2013 |volume=32 |issue=6 |pages=906–912 |doi=10.11820/dlkxjz.2013.06.007 |doi-access=free |language=zh-cn}}</ref> and the average area of surface water from 2013 to 2016 was about {{convert|1876|km2|sqmi|abbr=on}}, with the largest area being {{convert|2231|km2|sqmi|abbr=on}} in July 2015.<ref name=Buma>{{cite journal |author1=Willibroad Gabila Buma |author2=Sang-Il Lee |author3=Jae Young Seo |title=Recent surface water extent of Lake Chad from multispectral sensors and GRACE |journal=Sensors |date=2018 |doi=10.3390/s18072082|issue=7|volume=18|page=2082 |pmid=29958481 |pmc=6069056 |doi-access=free }}</ref>