Editing Himalayas (section)

==Hydrology==
{{multiple image
| align             = right
| direction         = vertical
| image1            = Confluence of Indus and Zanskar rivers.jpg
| caption1          = Confluence of the [[Indus River]] and [[Zanskar River]] in the Himalayas
| image2            = Himalayas, Pheriche, Nepal.jpg
| caption2          = [[Imja Khola]] river valley in [[Solukhumbu]], Nepal
}}

Despite their scale, the Himalayas do not form a major [[continental divide]], and a number of rivers cut through the range, particularly in the eastern part of the range. As a result, the main ridge of the Himalayas is not clearly defined, and mountain passes are not as significant for traversing the range as with other mountain ranges. Himalayas' rivers drain into two large systems:<ref>{{Cite web |title=Himalayas - Rivers, Glaciers, Peaks {{!}} Britannica |url=https://www.britannica.com/place/Himalayas/Drainage |access-date=2024-03-28 |website=www.britannica.com |language=en}}</ref>
* The western rivers combine into the ''Indus Basin''. The [[Indus River|Indus]] itself forms the northern and western boundaries of the Himalayas. It begins in Tibet, at the confluence of Sengge and Gar rivers, and flows north-west through India into Pakistan before turning south-west to the [[Arabian Sea]]. It is fed by several major tributaries draining the southern slopes of the Himalayas, including the [[Jhelum River|Jhelum]], [[Chenab River|Chenab]], [[Ravi River|Ravi]], [[Beas River|Beas]], and [[Sutlej]] rivers, the five rivers of the [[Punjab, India|Punjab]].
* The other Himalayan rivers drain the ''Ganges-Brahmaputra Basin''. Its main rivers are the [[Ganges]], the [[Brahmaputra]], and the [[Yamuna]], as well as other tributaries. The Brahmaputra originates as the [[Yarlung Tsangpo River (Tibet)|Yarlung Tsangpo River]] in western Tibet, and flows east through Tibet and west through the plains of [[Assam]]. The Ganges and the Brahmaputra meet in [[Bangladesh]] and drain into the [[Bay of Bengal]] through the world's largest river delta, the [[Sunderbans]].<ref name=gits4u/>

The northern slopes of [[Gyala Peri]] and the peaks beyond the [[Yarlung Tsangpo River|Tsangpo]], sometimes included in the Himalayas, drain into the [[Irrawaddy River]], which originates in eastern Tibet and flows south through Myanmar to drain into the [[Andaman Sea]]. The [[Salween]], [[Mekong]], [[Yangtze River|Yangtze]], and [[Yellow River]] all originate from parts of the Tibetan Plateau that are geologically distinct from the Himalaya mountains and are therefore not considered true Himalayan rivers. Some geologists refer to all the rivers collectively as the ''circum-Himalayan rivers''.<ref name=circum/>

===Glaciers===
[[File:Annapurna I, south face.jpg|thumb|South Annapurna Glacier]]
The great ranges of central Asia, including the Himalayas, contain the third-largest deposit of ice and snow in the world, after [[Antarctica]] and the [[Arctic]].<ref name=pbs_nature/> Some even refer to this region as the "Third Pole".<ref name=":0">{{Cite journal |last1=Kulkarni |first1=Anil V. |last2=Karyakarte |first2=Yogesh |date=2014 |title=Observed changes in Himalayan Glaciers |url=https://www.jstor.org/stable/24099804 |journal=Current Science |volume=106 |issue=2 |pages=237–244 |jstor=24099804}}</ref> The Himalayan range encompasses about 15,000 glaciers, which store about {{convert|12000|km3|abbr=on}}, or 3600–4400 [[Gigatonne|Gt]] (10{{Superscript|12}} kg)<ref name=":0" /> of fresh water.<ref name=IPPC2007/> Its glaciers include the [[Gangotri Glacier|Gangotri]] and [[Yamunotri]] ([[Uttarakhand]]) and [[Khumbu Glacier|Khumbu]] glaciers ([[Mount Everest]] region), [[Langtang]] glacier ([[Langtang]] region), and [[Zemu Glacier|Zemu]] ([[Sikkim]]).

Owing to the mountains' latitude near the [[Tropic of Cancer]], the permanent [[snow line]] is among the highest in the world, at typically around {{convert|5500|m|abbr=on|-2}}.<ref>{{cite journal|last1=Shi |first1=Yafeng |last2=Xie |first2=Zizhu |last3=Zheng |first3=Benxing |last4=Li |first4=Qichun |url=http://itia.ntua.gr/hsj/redbooks/126/iahs_126_0111.pdf |archive-url=https://web.archive.org/web/20130424125203/http://itia.ntua.gr/hsj/redbooks/126/iahs_126_0111.pdf |archive-date=24 April 2013 |title=Distribution, Feature and Variations of Glaciers in China |journal=World Glacier Inventory |year=1978 |url-status=dead }}</ref> In contrast, equatorial mountains in [[New Guinea]], the [[Rwenzoris]], and [[Colombia]] have a snow line some {{convert|900|m|abbr=on|-1}} lower.<ref>{{cite book|last1=Henderson-Sellers|first1=Ann|last2=McGuffie|first2=Kendal|title=The Future of the World's Climate: A Modelling Perspective|pages=199–201|isbn=978-0-12-386917-3|year=2012|publisher=Elsevier }}</ref> The higher regions of the Himalayas are snowbound throughout the year, in spite of their proximity to the tropics, and they form the sources of several large [[perennial stream|perennial rivers]].
[[File:KhumbuIcefall.jpg|thumb|left|[[Icefall]] on [[Khumbu Glacier]]]]
In recent years, scientists have monitored a notable increase in the rate of [[Retreat of glaciers since 1850|glacier retreat]] across the region as a result of climate change.<ref>{{Cite journal|last1=Lee|first1=Ethan|last2=Carrivick|first2=Jonathan L.|last3=Quincey|first3=Duncan J.|last4=Cook|first4=Simon J.|last5=James|first5=William H. M.|last6=Brown|first6=Lee E.|date=2021-12-20|title=Accelerated mass loss of Himalayan glaciers since the Little Ice Age|journal=Scientific Reports|language=en|volume=11|issue=1|pages=24284|doi=10.1038/s41598-021-03805-8|issn=2045-2322|pmc=8688493|pmid=34931039| bibcode=2021NatSR..1124284L }}</ref><ref>{{cite news|url=https://www.reuters.com/article/environment-nepal-climate-glaciers-dc/vanishing-himalayan-glaciers-threaten-a-billion-idUSDEL18761020070604|title=Vanishing Himalayan Glaciers Threaten a Billion|date=4 June 2007|newspaper=Reuters |access-date=13 March 2018}}</ref> For example, glacial lakes have been forming rapidly on the surface of debris-covered glaciers in the Bhutan Himalaya during the last few decades. Studies have measured an approximately 13% overall decrease in glacial coverage in the Himalayas over the last 40–50 years.<ref name=":0" /> Local conditions play a large role in glacial retreat, however, and glacial loss can vary locally from a few m/yr to 61 m/yr.<ref name=":0" /> A marked acceleration in glacial mass loss has also been observed since 1975, from about 5–13 Gt/yr to 16–24 Gt/yr.<ref name=":0" /> Although the effect of this will not be known for many years, it potentially could mean disaster for the hundreds of millions of people who rely on the glaciers to feed the rivers during the dry seasons.<ref name=":0" /><ref>{{Cite journal|last1=Kaushik|first1=Saurabh|last2=Rafiq|first2=Mohammd|last3=Joshi|first3=P.K.|last4=Singh|first4=Tejpal|date=April 2020|title=Examining the glacial lake dynamics in a warming climate and GLOF modelling in parts of Chandra basin, Himachal Pradesh, India|journal=Science of the Total Environment|language=en|volume=714|pages=136455|doi=10.1016/j.scitotenv.2019.136455|pmid=31986382|bibcode=2020ScTEn.71436455K|s2cid=210933887}}</ref><ref>{{Cite journal|last1=Rafiq|first1=Mohammd|last2=Romshoo|first2=Shakil Ahmad|last3=Mishra|first3=Anoop Kumar|last4=Jalal|first4=Faizan|date=January 2019|title=Modelling Chorabari Lake outburst flood, Kedarnath, India|url=http://link.springer.com/10.1007/s11629-018-4972-8|journal=Journal of Mountain Science|language=en|volume=16|issue=1|pages=64–76|doi=10.1007/s11629-018-4972-8|bibcode=2019JMouS..16...64R |s2cid=134015944|issn=1672-6316}}</ref><ref>{{cite web|url=http://en.people.cn/90001/90781/90879/6222327.html|title=Glaciers melting at alarming speed|date=24 July 2007|publisher=People's Daily Online|access-date=17 April 2009|archive-date=11 October 2017|archive-url=https://web.archive.org/web/20171011182931/http://en.people.cn/90001/90781/90879/6222327.html|url-status=dead}}</ref> The global climate change will affect the water resources and livelihoods of the Greater Himalayan region.<ref>{{Cite book |url=http://www.nap.edu/catalog/13449 |title=Himalayan Glaciers: Climate Change, Water Resources, and Water Security |date=2012|publisher=National Academies Press |isbn=978-0-309-26098-5 |location=Washington, D.C.|doi=10.17226/13449 }}</ref>

===Lakes===
{{See also|List of Alpine lakes in India}}
[[File:Gurudongmar Lake Sikkim, India (edit).jpg|thumb|[[Gurudongmar Lake]] in Sikkim]]

The Himalayan region is dotted with hundreds of lakes.<ref name="O'Neill_2019">{{cite journal |last1=O'Neill |first1=A. R.| date=2019 |title=Evaluating high-altitude Ramsar wetlands in the Sikkim Eastern Himalayas |journal=Global Ecology and Conservation |volume=20 |issue=e00715 |pages=19 |doi=10.1016/j.gecco.2019.e00715 |doi-access=free }}</ref> [[Pangong Tso]], which is spread across the border between India and China, at the far western end of Tibet, is among the largest with a surface area of {{cvt|700|km2|||}}.

South of the main range, the lakes are smaller. [[Tilicho Lake]] in Nepal, in the Annapurna massif, is one of the highest lakes in the world. Other lakes include [[Rara Lake]] in western Nepal, [[Phoksundo Lake|She-Phoksundo Lake]] in the [[Shey Phoksundo National Park]] of Nepal, [[Gurudongmar Lake]], in [[North Sikkim]], [[Gokyo Lakes]] in [[Solukhumbu]] district of [[Nepal]], and [[Lake Tsongmo]], near the Indo-China border in Sikkim.<ref name="O'Neill_2019"/>

Some of the lakes present the danger of a [[glacial lake outburst flood]]. The [[Tsho Rolpa]] glacier lake in the [[Rolwaling Himal|Rowaling Valley]], in the [[Dolakha District]] of Nepal, is rated as the most dangerous. The lake, which is located at an altitude of {{convert|4580|m|abbr=on}}, has grown considerably over the last 50 years due to glacial melting.<ref>{{cite web| url = http://rolwaling.tripod.com/glof/| title = Photograph of Tsho Rolpa}}</ref><ref>[[Glacial lake outburst flood#Monitoring|Tsho Rolpa]]</ref> The mountain lakes are known to geographers as ''[[tarn (lake)|tarns]]'' if they are caused by glacial activity. Tarns are found mostly in the upper reaches of the Himalaya, above {{cvt|5500|m|||}}.<ref>{{cite web|url=http://www.highestlake.com/highest-lake-world.html|title=Highest Lake in the World|first=Carl|last=Drews|access-date=14 November 2010|archive-date=18 August 2012|archive-url=https://web.archive.org/web/20120818141925/http://www.highestlake.com/highest-lake-world.html|url-status=dead}}</ref>

Temperate Himalayan wetlands provide important habitat and layover sites for migratory birds. Many mid and low altitude lakes remain poorly studied in terms of their hydrology and biodiversity, like Khecheopalri in the Sikkim Eastern Himalayas.<ref name="oneill_khecheopalri">{{cite journal |last1=O'Neill |first1=Alexander |display-authors=etal |date=25 February 2020 |title= Establishing Ecological Baselines Around a Temperate Himalayan Peatland |journal= Wetlands Ecology & Management |volume=28 |issue=2 |pages=375–388 | doi=10.1007/s11273-020-09710-7 |bibcode=2020WetEM..28..375O |s2cid=211081106 }}</ref>