Editing Thar Desert (section)

== History of desertification ==

===Ice-age desertification ===
{{anchor | Ice | Tibet }}
During the [[Last Glacial Maximum]] 20,000 before present, an approximately {{convert|2400000|km2|sqmi}} ice sheet covered the [[Tibetan Plateau#==Glaciology|Tibetan Plateau]],<ref>{{cite journal|first=Matthias|last=Kuhle|year=1998|title=Reconstruction of the 2.4 Million km<sup>2</sup> Late Pleistocene Ice Sheet on the Tibetan Plateau and its Impact on the Global Climate|journal=Quaternary International|volume=45/46|pages=71–108|doi=10.1016/S1040-6182(97)00008-6|bibcode=1998QuInt..45...71K}}</ref><ref>{{cite book|last=Kuhle|first=M|year=2004|chapter=The High Glacial (Last Ice Age and LGM) ice cover in High and Central Asia|title=Development in Quaternary Science 2c (Quaternary Glaciation – Extent and Chronology, Part III: South America, Asia, Africa, Australia, Antarctica)|editor1-last=Ehlers|editor1-first=J.|editor2-last=Gibbard|editor2-first=P.L.|pages=175–99}}</ref><ref name=K1999>{{cite journal|last=Kuhle|first=M.|year=1999|journal=GeoJournal|volume=47|issue=1–2|title=Tibet and High Asia V. Results of Investigations into High Mountain Geomorphology, Paleo-Glaciology and Climatology of the Pleistocene|pages=3–276|doi=10.1023/A:1007039510460| s2cid=128089823 }}
See chapter entitled: "Reconstruction of an approximately complete Quaternary Tibetan Inland Glaciation between the Mt. Everest and Cho Oyu Massifs and the Aksai Chin. – A new glaciogeomorphological southeast-northwest diagonal profile through Tibet and its consequences for the glacial isostasy and Ice Age cycle".</ref> causing excessive [[radiative forcing]] i.e. the ice in Tibet reflected at least four times more radiation energy per unit area into space than ice at higher [[latitude]]s, which  further cooled overlying atmosphere at that time.<ref>{{cite journal|last=Kuhle|first=M.|year=1988|title=The Pleistocene Glaciation of Tibet and the Onset of Ice Ages – An Autocycle Hypothesis|journal=GeoJournal|volume=17|issue=4|id=Tibet and High-Asia I. Results of the Sino-German Joint Expeditions (I)|pages=581–96|doi=10.1007/BF00209444| s2cid=129234912 }}</ref> This impacted the regional climate. Without the [[thermal low]] pressure caused by the heating, there was no [[monsoon]] over the [[Indian subcontinent]]. This lack of monsoon caused [[pluvial|extensive rainfall]] over the [[Sahara]], expansion of the Thar Desert, more dust deposited into the [[Arabian Sea]], a lowering of the [[life zone|biotic life zones]] on the Indian subcontinent, and animals responded to this shift in climate with the [[Javan rusa]] deer migrating into India.<ref name=K2001>{{cite journal|first=Matthias|last=Kuhle|year=2001|title=The Tibetan Ice Sheet; its Impact on the Palaeomonsoon and Relation to the Earth's Orbital Variations|journal=Polarforschung|volume=71|pages=1–13|issue=1/2}}</ref>

===Desertification due to drying up of Sarasvati river===
{{anchor | Sarasvati | Saraswati | IVC }} 
[[File:Sarasvati river.jpg|thumb|left|Vedic and present-day Gagghar-Hakra river-course, with [[Aryavarta]]/[[Kuru Kingdom]], and (pre-)Harappan Hakkra/Sutlej-Yamuna paleochannels as proposed by {{harvtxt|Clift et al.|2012}} and {{harvtxt|Khonde et al.|2017}}.{{refn|group=lower-alpha|See [https://www.researchgate.net/figure/Satellite-image-of-the-Indus-River-system-showing-the-study-sites-Stars-indicate_fig1_229062223 Clift et al. (2012) map] and [https://www.nature.com/articles/s41598-017-05745-8/figures/1 Honde te al. (2017) map].}} See also [https://www.google.co.uk/maps/place/Sir+Creek/@27.9238648,69.0488446,1290954m/data=!3m1!1e3!4m5!3m4!1s0x39527a0557ec4543:0x9e7e9966b79d473b!8m2!3d23.8379562!4d68.2376719 this] satellite image.<br />
1 = ancient river<br/>
2 = today's river<br/>
3 = today's Thar desert<br/>
4 = ancient shore<br/>
5 = today's shore<br/>
6 = today's town<br/>
7 = dried-up Harappan Hakkra course, and pre-Harappan Sutlej paleochannels ({{harvtxt|Clift et al.|2012}}).]]
10,000-8,000 years ago a paleo channel of [[Ghaggar-Hakra River]] - identified with the paleo [[Sarasvati River]], after confluence with [[Sutlej]] flowed into the [[Nara Canal|Nara river]] - a [[Distributary|delta channel]] of the [[Indus River]], changed its course, leaving the Ghaggar-Hakra as a system of monsoon-fed rivers which did not reach the sea and now ends in the Thar desert.{{sfn|Giosan et al.|2012}}{{sfn|Maemoku|Shitaoka|Nagatomo|Yagi|2013}}{{sfn|Clift et al.|2012}}{{sfn|Singh et al.|2017}}

Around 5,000 years ago when the monsoons that fed the rivers diminished further, the [[Indus Valley Civilisation]] (IVC) prospered in this area,{{sfn|Giosan et al.|2012}}{{sfn|Clift et al.|2012}}{{sfn|Singh et al.|2017}}{{refn|group=lower-alpha|In contrast to the mainstream view, {{harvtxt|Chatterjee|Ray|Shukla|Pande|2019}} suggest that the river remained perennial till 4,500 years ago.}} with the rise of numerous IVC urban sites at [[Kalibangan]] ([[Rajasthan]]), [[Banawali]] and [[Rakhigarhi]] ([[Haryana]]), [[Dholavira]] and [[Lothal]] ([[Gujarat]]) along this course.{{sfn|Sankaran|1999}}<ref group=web name=PIB>[http://pib.nic.in/newsite/erelcontent.aspx?relid=94098 Mythical Saraswati River], Press Information Bureau, Government of India, 20 March 2013.{{webarchive|url=https://web.archive.org/web/20161009182551/http://pib.nic.in/newsite/erelcontent.aspx?relid=94098 |date=9 October 2016}}</ref>

4,000 years ago when monsoons diminished even further, the dried-up Harkra become an intermittent river, and the urban Harappan civilisation declined, becoming localized in smaller agricultural communities.{{sfn|Giosan et al.|2012}}{{refn|group=lower-alpha|name="Giosan"|{{harvtxt|Giosan et al.|2012}}:
* "Contrary to earlier assumptions that a large glacier-fed Himalayan river, identified by some with the mythical Sarasvati, watered the Harappan heartland on the interfluve between the Indus and Ganges basins, we show that only monsoonal-fed rivers were active there during the Holocene."
* "Numerous speculations have advanced the idea that the Ghaggar-Hakra fluvial system, at times identified with the lost mythical river of Sarasvati (e.g., 4, 5, 7, 19), was a large glacier fed Himalayan river. Potential sources for this river include the Yamuna River, the Sutlej River, or both rivers. However, the lack of large-scale incision on the interfluve demonstrates that large, glacier-fed rivers did not flow across the Ghaggar-Hakra region during the Holocene
* "The present Ghaggar-Hakra valley and its tributary rivers are currently dry or have seasonal flows. Yet rivers were undoubtedly active in this region during the Urban Harappan Phase. We recovered sandy fluvial deposits approximately 5;400 y old at Fort Abbas in Pakistan (SI Text), and recent work (33) on the upper Ghaggar-Hakra interfluve in India also documented Holocene channel sands that are approximately 4;300 y old. On the upper interfluve, fine-grained floodplain deposition continued until the end of the Late Harappan Phase, as recent as 2,900 y ago (33) (Fig. 2B). This widespread fluvial redistribution of sediment suggests that reliable monsoon rains were able to sustain perennial rivers earlier during the Holocene and explains why Harappan settlements flourished along the entire Ghaggar-Hakra system without access to a glacier-fed river."
{{harvtxt|Valdiya|2013}} dispute this, arguing that it was a large perennial river draining the high mountains as late as 3700–2500 years ago. {{harvtxt|Giosan|Clift|Macklin|Fuller|2013}} have responded to, and rejected, Valdiya's arguments.}}{{sfn|Clift et al.|2012}}{{sfn|Maemoku|Shitaoka|Nagatomo|Yagi|2013}}{{sfn|Singh et al.|2017}}