View source for Geography of Bangladesh

{{Short description|Geography of Bangladesh}}
{{EngvarB|date=February 2017}}
{{Use dmy dates|date=January 2022}}
[[Image:Map of Bangladesh-en.svg|thumb|right|Map of Bangladesh]]

[[Bangladesh]] is a densely populated, low-lying, mainly [[riverine]] country located in South Asia with a coastline of {{convert|720|km|mi|0|abbr=on}} on the northern [[littoral]] of the [[Bay of Bengal]]. The delta plain of the [[Ganges River|Ganges (Padma)]], [[Brahmaputra River|Brahmaputra (Jamuna)]], and [[Meghna River]]s and their tributaries occupy 79 percent of the country. Four uplifted blocks (including the Madhupur and Barind Tracts in the centre and northwest) occupy 9 percent and steep hill ranges up to approximately {{convert|1000|m}} high occupy 12 percent in the southeast (the [[Chittagong Hill Tracts]]) and in the northeast. Straddling the [[Tropic of Cancer]], Bangladesh has a tropical [[monsoon]] climate characterised by heavy seasonal rainfall, high temperatures, and high humidity. Natural disasters such as floods and [[cyclones]] accompanied by [[storm surge]]s periodically affect the country.  Most of the country is intensively farmed, with rice the main crop, grown in three seasons. Rapid urbanisation is taking place with associated industrial and commercial development.  Exports of garments and shrimp plus remittances from Bangladeshis working abroad provide the country's three main sources of foreign exchange income.

{{coord|24|00|N|90|00|E|display=title}}

==Physical geography==
[[File:Land cover bangladesh.jpg|thumb|Land cover map of Bangladesh<ref>{{Cite journal|last1=Uddin|first1=Kabir|last2=Matin|first2=Mir A.|last3=Meyer|first3=Franz J.|date=January 2019|title=Operational Flood Mapping Using Multi-Temporal Sentinel-1 SAR Images: A Case Study from Bangladesh|journal=Remote Sensing|language=en|volume=11|issue=13|pages=1581|doi=10.3390/rs11131581|bibcode=2019RemS...11.1581U|doi-access=free}}</ref>]]
[[File:him.ogg|thumb|''Satellite photographs (from Terra-MODIS) and computer-generated models help visualise Bangladesh's place in the world. Located in South Asia, it is virtually surrounded by India and the Bay of Bengal to the south. But in many ways, the country's fate is dominated by the world's highest mountain range looming to the north-the Himalayas.<ref name="NASA">{{cite web
| last = [[NASA]]/Goddard Space Flight Center
| first = Scientific Visualization Studio
| date = 18 April 2002
| url = http://svs.gsfc.nasa.gov/vis/a000000/a002400/a002431/index.html
| title = Himalayas Exaggerated (version 2.2)
| format = MPEG
| access-date = 30 April 2007
}}</ref>]]

The [[physical geography]] of Bangladesh is varied and has an area characterised by two distinctive features: a broad [[river delta|deltaic]] [[plain]] subject to frequent flooding, and a small hilly region crossed by swiftly flowing rivers. The country has an area of {{convert|147570|sqkm}} (according to BBS 2020)<ref name="bbs">{{cite book|title= বাংলাদেশ পরিসংখ্যান বর্ষগ্রন্থ ২০২০ – Bangladesh Statistics annual book 2020 |url= http://bbs.portal.gov.bd/sites/default/files/files/bbs.portal.gov.bd/page/b2db8758_8497_412c_a9ec_6bb299f8b3ab/2021-08-11-04-54-154c14988ce53f65700592b03e05a0f8.pdf|url-status=live |publisher= Bangladesh Statistics Bureau |page=21|ISBN= 978-984-475-047-0}}</ref> or {{convert|148460|sqkm}} (according to CIA World factbook 2021)<ref name="bdarea">{{cite web|url=https://www.cia.gov/the-world-factbook/countries/bangladesh|title=South Asia :: Bangladesh — The World Factbook|publisher=Central Intelligence Agency|accessdate=13 November 2020|archive-date=12 November 2021|archive-url=https://web.archive.org/web/20211112184540/https://www.cia.gov/the-world-factbook/countries/bangladesh/|url-status=live}}</ref> and extends {{convert|820|km}} north to south and {{convert|600|km}} east to west. Bangladesh is bordered on the west, north, and east by a {{convert|4095|km}} land frontier with India and, in the southeast, by a short land and water frontier ({{convert|193|km}}) with [[Myanmar]]. On the south is a highly irregular deltaic coastline of about {{convert|580|km}}, fissured by many rivers and streams flowing into the [[Bay of Bengal]]. The [[territorial waters]] of Bangladesh extend {{convert|12|nmi|km}}, and the exclusive economic zone of the country is {{convert|200|nmi|km}}.

Roughly 80% of the landmass is made up of fertile alluvial lowland called the Bangladesh Plain. The plain is part of the larger Plain of Bengal, which is sometimes called the Lower Gangetic Plain. Although altitudes up to {{convert|105|m}} above sea level occur in the northern part of the plain, most elevations are less than {{convert|10|m}} above sea level; elevations decrease in the coastal south, where the terrain is generally at sea level. With such low elevations and numerous rivers, water—and concomitant flooding—is a predominant physical feature. About {{convert|10000|sqkm}} of the total area of Bangladesh is covered with water, and larger areas are routinely flooded during the monsoon season.

The only exceptions to Bangladesh's low elevations are the [[Chittagong Hills]] in the southeast, the Low Hills of Sylhet in the northeast, and highlands in the north and northwest. The Chittagong Hills constitute the only significant hill system in the country and, in effect, are the western fringe of the north–south mountain ranges of Myanmar and eastern India. The Chittagong Hills rise steeply to narrow ridgelines, generally no wider than {{convert|36|m}}, with altitudes from {{convert|600|to|900|m}} above sea level. At {{convert|1052|m}} altitude, the highest elevation in Bangladesh is found at [[Saka Haphong]], in the southeastern part of the hills. Fertile valleys lie between the hill lines, which generally run north–south. West of the Chittagong Hills is a broad plain, cut by rivers draining into the Bay of Bengal, that rises to a final chain of low coastal hills, mostly below {{convert|200|m}}, that attain a maximum elevation of {{convert|350|m}}. West of these hills is a narrow, wet coastal plain located between the cities of [[Chittagong]] in the north and [[Cox's Bazar]] in the south.

About 67% of Bangladesh's nonurban land is arable. Permanent crops cover only 2%, meadows and pastures cover 4%, and forests and woodland cover about 16%. The country produces large quantities of quality timber, bamboo, and sugarcane. Bamboo grows in almost all areas, but high-quality timber grows mostly in the highland valleys. Rubber planting in the hilly regions of the country was undertaken in the 1980s, and rubber extraction had started by the end of the decade. A variety of wild animals are found in the forest areas, such as in [[Sundarbans|the Sundarbans]] on the southwest coast, which is the home of the [[royal Bengal tiger]]. The alluvial soils in the Bangladesh Plain are generally fertile and are enriched with heavy silt deposits carried downstream during the rainy season.

==Human geography==

Urbanisation is proceeding rapidly, and it is estimated that only 30% of the population entering the labour force in the future will be absorbed into agriculture, although many will likely find other kinds of work in rural areas. The areas around [[Dhaka]] and [[Comilla]] are the most densely settled. [[Sundarbans|The Sundarbans]], an area of coastal tropical jungle in the southwest and last wild home of the [[Bengal tiger]], and the [[Chittagong Hill Tracts]] on the southeastern border with Myanmar and India, are the least densely populated.

==Climate==
{{See also|List of Bangladesh tropical cyclones}}
Bangladesh has a [[tropical monsoon climate]] characterized by wide seasonal variations in rainfall, high temperatures, and high humidity. Regional climatic differences in this flat country are minor, though some variations can be seen between the weather pattern of the Northern and southern region, as the piedmontal plains of the northern region has a Monsoon influenced [[Humid subtropical climate]]. According to [[Bangladesh Meteorological Department]], there are four seasons in [[Bangladesh]] depending on the temperature, rainfall and direction of wind- mild and cool Winter from December to February, hot and sunny Summer or pre Monsoon season from March to May, somewhat cooler and very wet [[Monsoon]] season from June to September and plesent, shorter and cooler Autumn or post monsoon season in October–November.<ref>{{Citation|title=MET-report-08-2016|date=2016|url=https://www.met.no/publikasjoner/met-report/met-report-2016/_/attachment/download/b50e3f06-4485-4f34-b642-0a1e86f12c7d:a483b63367b0f087f3bd9410e135a5e0837d1927/MET-report-08-2016.pdf|publisher=[[Bangladesh Meteorological Department]], [[Norwegian Meteorological Institute]]}}</ref> In general, maximum summer temperatures range between {{convert|38|and|41|C|F|1}}. April is the hottest month in most parts of the country. January is the coolest month, when the average temperature for most of the country is {{convert|16|-|20|C|F}} during the day and around {{convert|10|°C}} at night.

Winds are mostly from the north and northwest in the winter, blowing gently at {{convert|1|to|3|km/h|mph|1}} in northern and central areas and {{convert|3|to|6|km/h|mph|1}} near the coast. From March to May, violent thunderstorms, called northwesters by local English speakers, produce winds of up to {{convert|60|km/h|mph|1}}. During the intense storms of the early summer and late monsoon season, southerly winds of more than {{convert|160|km/h|mph|1}} cause waves to crest as high as {{convert|6|m|ft|1}} in the Bay of Bengal, which brings disastrous flooding to coastal areas.[[File:Koppen-Geiger Map BGD present.svg|thumb|217x217px|Bangladesh map of Köppen climate classification zones]]
Heavy rainfall is characteristic of Bangladesh causing it to flood every year. Except for the relatively dry western region of Rajshahi, where the annual rainfall is about {{convert|1600|mm|in|1|abbr=on}}, most parts of the country receive at least {{convert|2300|mm|in|1|abbr=on}} of rainfall per year. Because of its location just south of the foothills of the Himalayas, where monsoon winds turn west and northwest, the region of Sylhet in northeastern Bangladesh receives the greatest average precipitation. From 1977 to 1986, annual rainfall in that region ranged between {{convert|3280|and|4780|mm|in|1|abbr=on}} per year. Average daily humidity ranged from March lows of between 55 and 81% to July highs of between 94 and 100%, based on readings taken at selected stations nationwide in 1986.

About 80% of Bangladesh's rain falls during the monsoon season. The monsoons result from the contrasts between low and high air pressure areas that result from differential heating of land and water. During the hot months of April and May hot air rises over the Indian subcontinent, creating low-pressure areas into which rush cooler, moisture-bearing winds from the Indian Ocean. This is the southwest monsoon, commencing in June and usually lasting through September. Dividing against the Indian landmass, the monsoon flows in two branches, one of which strikes western India. The other travels up the Bay of Bengal and over eastern India and Bangladesh, crossing the plain to the north and northeast before being turned to the west and northwest by the foothills of the Himalayas.

[[File:Agriculture of Bangladesh 11.jpg|thumb|Bangladesh has a tropical climate]]Natural calamities, such as floods, tropical cyclones, tornadoes, and tidal bores—destructive waves or floods caused by flood tides rushing up [[estuaries]]—ravage the country, particularly the coastal belt, almost every year. Between 1947 and 1988, 13 severe cyclones hit Bangladesh, causing enormous loss of life and property. In May 1985, for example, a severe cyclonic storm packing {{convert|154|km/h|mph|1|adj=on}} winds and waves {{convert|4|m|ft|1}} high swept into southeastern and southern Bangladesh, killing more than 11,000 persons, damaging more than 94,000 houses, killing some 135,000 head of livestock, and damaging nearly {{convert|400|km|mi|1}} of critically needed embankments.

[[File:Flooding after 1991 cyclone.jpg|thumb|Flooding after the [[1991 Bangladesh cyclone]]]]
Annual monsoon flooding results in the loss of human life, damage to property and communication systems, and a shortage of drinking water, which leads to the spread of disease. For example, in 1988 two-thirds of Bangladesh's 64 districts experienced extensive flood damage in the wake of unusually heavy rains that flooded the river systems. Millions were left homeless and without potable water. Half of Dhaka, including the runway at the Shahjalal International Airport—an important transit point for disaster relief supplies—was flooded. About {{convert|2000000|t|ST LT|0}}<!-- ??? --> of crops were reported destroyed, and relief work was rendered even more challenging than usual because the flood made transportation exceedingly difficult. [[Daulatpur–Saturia tornado|A tornado in April 1989]] killed more than 600 people, possibly many more.

There are no precautions against cyclones and tidal bores except giving advance warning and providing safe public buildings where people may take shelter. Adequate infrastructure and air transport facilities that would ease the suffering of the affected people had not been established by the late 1980s. Efforts by the government under the Third Five-Year Plan (1985–90) were directed toward accurate and timely forecast capability through agrometeorology, marine meteorology, oceanography, hydrometeorology, and seismology. Necessary expert services, equipment, and training facilities were expected to be developed under the United Nations Development Programme.

Cold weather is unusual in Bangladesh. When temperatures decrease to {{convert|8|C|F|0}} or less, people without warm clothing and living in inadequate homes may die from the cold.<ref>{{cite news |title= Cold Wave Kills 102 People in Bangladesh |work= Los Angeles Times |date= 6 January 1995 |page= 6 |url=http://articles.latimes.com/1995-01-06/news/mn-16935_1_worst-cold-wave |quote= "Temperatures plunged to 39 degrees this week in northern Bangladesh, killing people too poor to afford jackets or sweaters. It was the lowest temperature recorded in Bangladesh since 1964 when the temperature dropped to 38 degrees."|access-date=4 February 2015 }}</ref><ref>{{cite news |title= 33 in Northern Bangladesh Are Reported Killed by Cold |work= The New York Times |agency= Associated Press |date= 29 December 1989 |page= A3 |url= https://www.nytimes.com/1989/12/29/world/33-in-northern-bangladesh-are-reported-killed-by-cold.html|quote= "A cold wave is normally tropical northern Bangladesh has killed at least 33 people in the last week, a newspaper reported today. Temperatures in the region have hovered around {{convert|42|°F|°C}} since Monday, and the newspaper said the victims were laborers and other poor people who were unable to protect themselves from the cold." |access-date=4 February 2015}}</ref><ref>{{cite news |title= Hundreds Dead in Bangladeshi Cold Spell |work= The Washington Post |date= 6 January 1998 |page= A14 |quote= "In northern Bangladesh, temperatures dipped to 46 degrees Sunday, the Independent newspaper said. Although the temperature was above freezing, it was cold enough to kill people in tropical Bangladesh, where half the population of 120 million people can't afford enough food or warm clothes."}}</ref>

{{Weather box
|width = auto
|location = Dhaka (1981–2010)
|metric first = Yes
|single line = Yes
|collapsed = Yes
|Jan record high C = 31.1
|Feb record high C = 34.4
|Mar record high C = 40.6
|Apr record high C = 42.2
|May record high C = 41.1
|Jun record high C = 36.7
|Jul record high C = 35.0
|Aug record high C = 36.1
|Sep record high C = 36.7
|Oct record high C = 37.4
|Nov record high C = 34.4
|Dec record high C = 30.6
|year record high C = 42.2
|Jan high C = 25.1
|Feb high C = 28.3
|Mar high C = 32.5
|Apr high C = 33.8
|May high C = 33.4
|Jun high C = 32.5
|Jul high C = 31.8
|Aug high C = 32.1
|Sep high C = 32.0
|Oct high C = 31.8
|Nov high C = 29.7
|Dec high C = 26.5
|year high C = 30.8
|Jan mean C = 18.6
|Feb mean C = 22.0
|Mar mean C = 26.3
|Apr mean C = 28.4
|May mean C = 28.8
|Jun mean C = 29.0
|Jul mean C = 28.7
|Aug mean C = 28.9
|Sep mean C = 28.5
|Oct mean C = 27.4
|Nov mean C = 24.0
|Dec mean C = 20.0
|year mean C = 25.9
|Jan low C = 13.1
|Feb low C = 16.2
|Mar low C = 20.8
|Apr low C = 23.8
|May low C = 24.8
|Jun low C = 26.2
|Jul low C = 26.3
|Aug low C = 26.4
|Sep low C = 25.9
|Oct low C = 23.9
|Nov low C = 19.4
|Dec low C = 14.8
|year low C = 21.8
|Jan record low C = 6.1
|Feb record low C = 6.7
|Mar record low C = 10.6
|Apr record low C = 16.7
|May record low C = 14.4
|Jun record low C = 19.4
|Jul record low C = 21.1
|Aug record low C = 21.7
|Sep record low C = 21.1
|Oct record low C = 17.2
|Nov record low C = 11.1
|Dec record low C = 7.2
|year record low C = 6.1
|rain colour = green
|Jan rain mm = 7.5
|Feb rain mm = 23.7
|Mar rain mm = 61.7
|Apr rain mm = 140.6
|May rain mm = 278.4
|Jun rain mm = 346.5
|Jul rain mm = 375.5
|Aug rain mm = 292.9
|Sep rain mm = 340.0
|Oct rain mm = 174.5
|Nov rain mm = 31.1
|Dec rain mm = 12.1
|unit rain days =
|Jan rain days = 2
|Feb rain days = 3
|Mar rain days = 5
|Apr rain days = 10
|May rain days = 15
|Jun rain days = 14
|Jul rain days = 17
|Aug rain days = 16
|Sep rain days = 13
|Oct rain days = 7
|Nov rain days = 2
|Dec rain days = 1
|Jan humidity = 71
|Feb humidity = 64
|Mar humidity = 62
|Apr humidity = 71
|May humidity = 76
|Jun humidity = 82
|Jul humidity = 83
|Aug humidity = 82
|Sep humidity = 83
|Oct humidity = 78
|Nov humidity = 73
|Dec humidity = 73
|year humidity =
|Jan sun = 220.3
|Feb sun = 225.3
|Mar sun = 256.3
|Apr sun = 237.8
|May sun = 220.9
|Jun sun = 142.2
|Jul sun = 131.5
|Aug sun = 140.6
|Sep sun = 152.7
|Oct sun = 228.6
|Nov sun = 236.3
|Dec sun = 242.6
|year sun = 2435.1
|source 1 = [[Bangladesh Meteorological Department]]<ref name=climatereportdhaka>
{{cite web
| archive-url = https://web.archive.org/web/20181224171550/http://bmd.gov.bd/file/2016/08/17/pdf/21827.pdf
| archive-date = 24 December 2018 | url = http://bmd.gov.bd/file/2016/08/17/pdf/21827.pdf
| title = Climate of Bangladesh
| publisher = Bangladesh Meteorological Department
| pages = 19–23
| access-date = 24 December 2018}}</ref><ref name = dhakaBMDrainyday>
{{cite web
| archive-url = https://web.archive.org/web/20170709184139/http://bmd.gov.bd/file/2016/08/17/pdf/54.pdf
| archive-date = 9 July 2017
| url = http://www.bmd.gov.bd/?/p/=Normal-Monthly-Rainy-Day
| title = Normal Monthly Rainy Day
| publisher = Bangladesh Meteorological Department
| access-date = 26 April 2018}}</ref><ref name = dhakaBMDhumidity>
{{cite web
| archive-url = https://web.archive.org/web/20181224172119/http://bmd.gov.bd/file/2016/08/17/pdf/52.pdf
| archive-date = 24 December 2018
| url = http://www.bmd.gov.bd/?/p/=Monthly-Humidity-Normal-Data
| title = Normal Monthly Humidity
| publisher = Bangladesh Meteorological Department
| access-date = 26 April 2018}}</ref>
|source 2 = Sistema de Clasificación Bioclimática Mundial (extremes 1934–1994),<ref name=extremesDhaka>{{cite web | url = http://www.globalbioclimatics.org/pdf/ba-dacca.pdf | title = Bangladesh – Dacca | publisher = Centro de Investigaciones Fitosociológicas | language = es | access-date = 23 February 2013 | archive-date = 20 September 2015 | archive-url = https://web.archive.org/web/20150920032430/http://www.globalbioclimatics.org/pdf/ba-dacca.pdf | url-status = live }}</ref> [[Deutscher Wetterdienst]] (sun, 1961–1990)<ref name = dhakaDWD>{{cite web
| url = ftp://ftp-cdc.dwd.de/pub/CDC/observations_global/CLIMAT/multi_annual/sunshine_duration/1961_1990.txt
| archive-url = https://web.archive.org/web/20171017195327/ftp://ftp-cdc.dwd.de/pub/CDC/observations_global/CLIMAT/multi_annual/sunshine_duration/1961_1990.txt
| url-status = dead
| archive-date = 2017-10-17
| title = Station 41923 Dhaka
| work = Global station data 1961–1990—Sunshine Duration
| publisher = Deutscher Wetterdienst
| access-date = 26 April 2018
}}</ref><ref>{{Cite web |url=ftp://ftp-cdc.dwd.de/pub/CDC/help/stations_list_CLIMAT_data.txt |archive-url=https://web.archive.org/web/20171017195318/ftp://ftp-cdc.dwd.de/pub/CDC/help/stations_list_CLIMAT_data.txt |url-status=dead |archive-date=2017-10-17 |title=Station ID for Dhaka is 41923 |access-date=26 April 2018 }}</ref><ref>{{cite web |url=https://www.ogimet.com/cgi-bin/gsynres?ind=41923&ano=2021&mes=10&day=16&hora=0&min=0&ndays=30 |title=41923: Dhaka (Bangladesh) |author=<!--Not stated--> |date= 15 October 2021|website=ogimet.com |publisher=[[OGIMET]] |access-date= 15 October 2021|quote=}}</ref>
|date=November 2012
}}

=== Climate change ===
{{Excerpt|Climate change in Bangladesh|paragraphs=1,2,3|file=no}}

==River systems==
[[Image:Ganges River Delta, Bangladesh, India.jpg|thumb|right|300px|Ganges River Delta, Bangladesh and India]]
[[File:Urban-Rural Population and Land Area Estimates, v2, 2010 Bangladesh (13873798283).jpg|thumb|300px|Population density and height above sea level in Bangladesh (2010). Bangladesh is especially vulnerable to [[sea level rise]].]]
The rivers of Bangladesh mark both the physiography of the nation and the life of the people. About 700 in number, these rivers generally flow south. The larger rivers serve as the main source of water for cultivation and as the principal arteries of commercial transportation. Rivers also provide fish, an important source of protein. Flooding of the rivers during the monsoon season causes enormous hardship and hinders development, but fresh deposits of rich silt replenish the fertile but overworked soil. The rivers also drain excess monsoon rainfall into the Bay of Bengal. Thus, the great river system is at the same time the country's principal resource and its greatest hazard.

The profusion of rivers can be divided into five major networks. The Jamuna-Brahmaputra is {{convert|292|km}} long and extends from northern Bangladesh to its confluence with the Padma. Originating as the [[Yarlung Tsangpo River (Tibet)|Yarlung Tsangpo River]] in China's Xizang Autonomous Region ([[Tibet]]) and flowing through India's state of [[Arunachal Pradesh]], where it becomes known as the Brahmaputra ("Son of Brahma"), it receives waters from five major tributaries that total some {{convert|740|km}} in length. At the point where the Brahmaputra meets the Tista River in Bangladesh, it becomes known as the [[Jamuna River (Bangladesh)|Jamuna]]. The Jamuna is notorious for its shifting subchannels and for the formation of fertile silt islands ([[List of islands of Bangladesh|chars]]). No permanent settlements can exist along its banks.

The second system is the Padma-Ganges, which is divided into two sections: a {{convert|258|km}} segment, the Ganges, which extends from the western border with India to its confluence with the Jamuna some {{convert|72|km}} west of Dhaka, and a {{convert|126|km}} segment, the Padma, which runs from the Ganges-Jamuna confluence to where it joins the [[Meghna River|Meghna]] River at Chandpur. The Padma-Ganges is the central part of a deltaic river system with hundreds of rivers and streams—some {{convert|2100|km}} in length—flowing generally east or west into the Padma.

The third network is the [[Surma-Meghna River System]], which courses from the northeastern border with India to Chandpur, where it joins the Padma. The Surma-Meghna, at {{convert|669|km}} by itself the longest river in Bangladesh, is formed by the union of six lesser rivers. Below the city of Kalipur it is known as the Meghna. When the Padma and Meghna join, they form the fourth river system—the Padma-Meghna—which flows {{convert|145|km}} to the Bay of Bengal.

This mighty network of four river systems flowing through the Bangladesh Plain drains an area of some {{convert|1.5|e6sqkm|sqmi}}. The numerous channels of the Padma-Meghna, its distributaries, and smaller parallel rivers that flow into the Bay of Bengal are referred to as the Mouths of the Ganges. Like the Jamuna, the Padma-Meghna and other estuaries on the [[Bay of Bengal]] are also known for their many chars.

[[File:Goalundo -1 (10).jpg|thumb|[[Goalundo Ghat]] in central Bangladesh]]
A fifth river system, unconnected to the other four, is the [[Karnaphuli]]. Flowing through the region of Chittagong and the Chittagong Hills, it cuts across the hills and runs rapidly downhill to the west and southwest and then to the sea. The Feni, Karnaphuli, Sangu, and Matamuhari—an aggregate of some {{convert|420|km}}—are the main rivers in the region. The port of Chittagong is situated on the banks of the Karnaphuli. The Karnaphuli Reservoir and Karnaphuli Dam are located in this area. The dam impounds the Karnaphuli River's waters in the reservoir for the generation of hydroelectric power.

The Ganga–Brahmaputra rivers contribute nearly 1000&nbsp;million tons/yr of [[sediment]]. The sediment contributed from these two rivers forms the Bengal Delta and [[Submarine fan]], a vast structure that extends from Bangladesh to the south of the Equator which is up to 16.5&nbsp;km thick, and contains at least 1130&nbsp;trillion tonnes of sediment accumulating over the last 17 million years at an average rate of 665&nbsp;million tons/yr.<ref>{{cite journal|url= http://www.iisc.ernet.in/currsci/apr252003/1041.pdf |title= A sediment budget for the Ganga–Brahmaputra catchment|first=Robert|last=Wasson|year=2003|journal=Current Science|volume=84|issue=8|pages=1041–1047}}</ref> The Bay of Bengal used to be deeper than the [[Mariana Trench]], the present deepest ocean point.

During the annual monsoon period, the rivers of Bangladesh flow at about {{convert|140000|m3/s}}, but during the dry period they diminish to {{convert|7000|m3/s}}. Because water is so vital to agriculture, more than 60% of the net arable land, some {{convert|91000|sqkm}}, is cultivated in the rainy season despite the possibility of severe flooding, and nearly 40% of the land is cultivated during the dry winter months. Water resources development has responded to this "dual water regime" by providing flood protection, drainage to prevent over flooding and waterlogging, and irrigation facilities for the expansion of winter cultivation. Major water control projects have been developed by the national government to provide irrigation, flood control, drainage facilities, aids to river navigation and road construction, and hydroelectric power. In addition, thousands of tube wells and electric pumps are used for local irrigation. Despite severe resource constraints, the government of Bangladesh has made it a policy to try to bring additional areas under irrigation without salinity intrusion.

Water resources management, including gravity flow irrigation, flood control, and drainage, were largely the responsibility of the Bangladesh Water Development Board. Other public sector institutions, such as the Bangladesh Krishi Bank, the Bangladesh Rural Development Board, the Bangladesh Bank, and the [[Bangladesh]] Agricultural Development Corporation were also responsible for the promotion and development of minor irrigation works in the private sector through government credit mechanisms.

==Coastal systems==
[[File:Erosion and siltation map of coastal Bangladesh (1989 to 2018).jpg|thumb|Morphological changes: the process of erosion and acceleration in the coastal area of Bangladesh between 1989 and 2018<ref>{{Cite journal|date=December 2020|title=Coastal morphological changes: Assessing long-term ecological transformations across the northern Bay of Bengal|journal=Environmental Challenges|language=en|volume=1|pages=100001|doi=10.1016/j.envc.2020.100001|issn=2667-0100|doi-access=free|last1=Uddin|first1=Kabir|last2=Khanal|first2=Nishanta|last3=Chaudhary|first3=Sunita|last4=Maharjan|first4=Sajana|last5=Thapa|first5=Rajesh Bahadur}}</ref>]]
Bangladesh coastal areas are covering the south part of Bangladesh. The main rivers of Bangladesh derived from the Himalayas carry a high level of sediment and deposit it across the Bay of Bengal. This has led to major changes in the coastal region between 1989 and 2018. Over 30 years of morphological changes many islands are losing land area. However, there has been an overall net gain in the land area due to the regular acceleration process in other parts of those islands. In the west, new islands were found, but no significant changes were observed. At the mouth of the Meghna estuary, noticeable variable changes have been observed with the formation of many new islands.

In 1989, the land area was only 28835&nbsp;km<sup>2</sup> (56.06%), while the water area was 22600&nbsp;km<sup>2</sup> (43.94%) with the region falling among 20° 34’ N to 26°38 N and 88° 01’ N to 92° 41’ E, and with an area of 147,570&nbsp;km<sup>2</sup>. In 2018, the land area increased to 29426&nbsp;km<sup>2</sup> (57.21%); an increase of 590&nbsp;km<sup>2</sup> (1.15%).  The land area in 1999 and 2009 was 56.49% and 56.68%, respectively, with a total increase of 0.19%. The island reformation tendency showed that the new land area increased every year by an average of 20&nbsp;km<sup>2</sup> (0.038) along the coastal region of Bangladesh. Plant growth has been observed in the newly formed islands over a period of 30 years. In the early stages, the islands are usually muddy waste areas that gradually changed into grasslands and Trees.<ref>{{cite journal |last1=Uddin |first1=Kabir |last2=Nishanta |first2=Khanal |last3=Sunita |first3=Chaudhary |last4=Sajana |first4=Maharjan |last5=Rajesh Bahadur |first5=Thapa |title=Coastal morphological changes: Assessing long-term ecological transformations across the northern Bay of Bengal |journal=Environmental Challenges |date=1 December 2020 |volume=1 |pages=100001 |doi=10.1016/j.envc.2020.100001 |language=en |issn=2667-0100|doi-access=free }}</ref>

A recent global remote sensing analysis suggested that there were 2,262&nbsp;km<sup>2</sup> of tidal flats in Bangladesh and is therefore ranked 14th in terms of how much tidal flat occurs there.<ref>{{cite journal |last1=Murray |first1=N.J. |last2=Phinn |first2=S.R. |last3=DeWitt |first3=M. |last4=Ferrari |first4=R. |last5=Johnston |first5=R. |last6=Lyons |first6=M.B. |last7=Clinton |first7=N. |last8=Thau |first8=D. |last9=Fuller |first9=R.A. |title=The global distribution and trajectory of tidal flats |journal=Nature |date=2019 |volume=565 |pages=222–225 |doi=10.1038/s41586-018-0805-8 |url=https://www.nature.com/articles/s41586-018-0805-8}}</ref> The analysis showed that the tidal flats of the Meghna River estuary have undergone considerable geomorphological change over a 33-year period, from 1984 to 2016, now only occurring in 17.1% of their initial extent despite expanding in area by 20.6%.

==Area and boundaries==

'''Area:'''
<br />''total:'' 147,610&nbsp;km<sup>2</sup>
<br />''country comparison to the world:'' 85
<br />''land:'' 130,170&nbsp;km<sup>2</sup>
<br />''water:'' 18,290&nbsp;km<sup>2</sup>

'''Land boundaries:'''
<br />''total:'' 4,427&nbsp;km
<br />''border countries:'' Myanmar 271&nbsp;km, India 4,156&nbsp;km

'''Coastline:''' 580&nbsp;km

'''Maritime claims:'''
''territorial sea:'' {{convert|12|nmi|km mi|1|abbr=on}}<ref>{{Cite web |url=https://www.cia.gov/the-world-factbook/countries/bangladesh/ |title=South Asia :: Bangladesh — The World Factbook |website=Central Intelligence Agency |access-date=1 August 2020}}</ref>
<br />''contiguous zone:'' {{convert|18|nmi|km mi|1|abbr=on|lk=in}} <!-- Not 24 nmi??? -->
<br />''exclusive economic zone:'' {{convert|200|nmi|km mi|1|abbr=on}}
<br />''continental shelf:'' up to the outer limits of the [[continental margin]]

'''Elevation extremes:'''
<br />''lowest point:'' Indian Ocean 0 m
<br />''highest point:'' [[Mowdok Taung]] in the Mowdok range at 1052 m (at N 21°47'12" E 92°36'36"), ''NOT'' [[Keokradong]] (883 m not 1,230 m) or [[Tazing Dong]] (985 m not 1,280 m as sometimes reported){{citation needed|date=August 2018}}

==Resources and land use==
'''Natural resources:''' natural gas, [[arable land]], timber, coal

'''Land use:'''
<br />''Arable land:'' 58.96%
<br />''Permanent crops:'' 6.53%
<br />''other:'' 34.51% (2012)

'''[[Irrigated]] land:''' 50,000&nbsp;km<sup>2</sup> (2008)

'''Total renewable water resources:''' 1,227&nbsp;km<sup>3</sup> (2011)

'''Freshwater withdrawal (domestic/industrial/agricultural):'''
<br />''total:'' 35.87&nbsp;km<sup>3</sup>/yr (10%/2%/88%)
<br />''per capita:'' 238.3 m<sup>3</sup>/yr (2008)

==Environmental concerns==
{{main|Environmental issues in Bangladesh}}
'''Natural hazards:'''
Much of the country is submerged by floodwater in the monsoon season (and traditional settlements and agriculture are adapted to this); damaging floods occur when rivers rise higher than normal; tropical cyclones (hurricanes) and storm surges; droughts; riverbank erosion along the country's major rivers and in the Meghna estuary; earthquakes; possibly tsunamis.

'''Environment – current issues:'''
Country very densely populated (1,125 per km<sup>2</sup>); rapid urbanisation taking place; many people landless, and many live on and cultivate land exposed to floods, riverbank erosion or cyclones; groundwater used for drinking water and irrigation is widely contaminated with naturally-occurring arsenic in some floodplain areas; water-borne diseases prevalent; surface water widely polluted by industrial, agricultural and urban effluents, affecting domestic supplies and inland fisheries; intermittent water shortages because of falling water tables in some northern and central parts of the country; increasing water and [[soil salinity]] in some coastal areas, especially in the south-west, due to abstraction of river and groundwater upstream; [[soil retrogression and degradation|soil degradation]] due to intensive cropping, depletion of organic matter and unbalanced use of fertilisers; deforestation and soil erosion in hill areas.

'''Environment – international agreements:'''
<br />''party to:''
Biodiversity, Climate Change, Climate Change-Kyoto Protocol, Desertification, Endangered Species, Environmental Modification, Hazardous Wastes, Law of the Sea, Ozone Layer Protection, Ship Pollution, Wetlands

==See also==
* [[2007 South Asian floods]]
* [[Bangladesh Climate Change Resilience Fund]]
* [[List of islands of Bangladesh]]

==References==
{{Reflist}}

; Attribution
{{Refbegin}}
* {{country study|country=Bangladesh|abbr=bd}}
* {{CIA World Factbook}}
* {{StateDept}}
{{Refend}}

==Further reading==
* Bangladesh Bureau of Statistics Yearbook of Bangladesh (published periodically online).
* {{Cite book|last=Brammer|first=H.T|title=he Physical Geography of Bangladesh|year=2012|publisher=University Press|location=Dhaka, Bangladesh|isbn=978-984-506-049-3}}
* {{cite book| last1 = Rashid | first1 = Haroun Er | title = Geography of Bangladesh | date = 1991 | publisher = University Press| location = Dhaka, Bangladesh | isbn = 978-984-05-1159-4}}

== External links ==
* [https://web.archive.org/web/20060605111526/http://eusoils.jrc.it/esdb_archive/EuDASM/Asia/lists/cbd.htm Soil Maps of Bangladesh, European Digital Archive on the Soil Maps of the world]
{{clear}}
{{Bangladesh topics}}
{{GeoSouthAsia}}
{{Geography of Asia}}
{{Asia topic|Climate of}}

[[Category:Geography of Bangladesh| ]]
[[Category:Articles containing video clips]]