Editing Geography of Bangladesh (section)

==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 patterns of the northern and southern regions, as the piedmontal plains of the former have a monsoon-influenced [[humid subtropical climate]]. According to [[Bangladesh Meteorological Department]], there are six 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 pleasant, 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]]|access-date=18 June 2021|archive-date=24 June 2021|archive-url=https://web.archive.org/web/20210624195927/https://www.met.no/publikasjoner/met-report/met-report-2016/_/attachment/download/b50e3f06-4485-4f34-b642-0a1e86f12c7d:a483b63367b0f087f3bd9410e135a5e0837d1927/MET-report-08-2016.pdf|url-status=live}}</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_v2_BGD_1991–2020.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 south-eastern 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 [[Hazrat Shahjalal International Airport|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.

{{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= |archive-date=16 October 2021 |archive-url=https://web.archive.org/web/20211016011703/https://www.ogimet.com/cgi-bin/gsynres?ind=41923&ano=2021&mes=10&day=16&hora=0&min=0&ndays=30 |url-status=live}}</ref>
| date = November 2012
}}

[[File:A foggy winter morning.jpg|thumb|Winter morning in Bangladesh]]
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= https://www.latimes.com/archives/la-xpm-1995-01-06-mn-16935-story.html |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 |archive-date= 4 February 2015 |archive-url= https://web.archive.org/web/20150204073116/http://articles.latimes.com/1995-01-06/news/mn-16935_1_worst-cold-wave |url-status= live }}</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 |archive-date= 4 February 2015 |archive-url= https://web.archive.org/web/20150204070056/http://www.nytimes.com/1989/12/29/world/33-in-northern-bangladesh-are-reported-killed-by-cold.html |url-status= live }}</ref><ref>{{cite news |title= Hundreds Dead in Bangladeshi Cold Spell |newspaper= 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>

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