Bangladesh is a densely populated, low-lying, mainly riverine country located in South Asia with a coastline of on the northern littoral of the Bay of Bengal. The delta plain of the Ganges (Padma), Brahmaputra (Jamuna), and Meghna Rivers 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 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 surges 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.
Physical geography
The physical geography of Bangladesh is varied and has an area characterised by two distinctive features: a broad deltaic plain subject to frequent flooding, and a small hilly region crossed by swiftly flowing rivers. The country has an area of (according to BBS 2020) or (according to CIA World Factbook 2021) and extends north to south and east to west. Bangladesh is bordered on the west, north, and east by a land frontier with India and, in the southeast, by a short land and water frontier of with Myanmar. On the south is a highly irregular deltaic coastline of about , fissured by many rivers and streams flowing into the Bay of Bengal. The territorial waters of Bangladesh extend , and the exclusive economic zone of the country is .
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 above sea level occur in the northern part of the plain, most elevations are less than 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 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, highlands in the north, northwest at the Mymensingh-Tangail region and the Barendra area of Rangpur ang Rajshahi division. 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 , with altitudes from above sea level. Saka Haphong Mountain is the highest peak in Bangladesh with an elevation of , located in the south-eastern 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 , that attain a maximum elevation.
In Bangladesh forest cover is around 14% of the total land area, equivalent to 1,883,400 hectares (ha) of forest in 2020, down from 1,920,330 hectares (ha) in 1990. In 2020, naturally regenerating forest covered 1,725,330 hectares (ha) and planted forest covered 158,070 hectares (ha). Of the naturally regenerating forest 0% was reported to be primary forest (consisting of native tree species with no clearly visible indications of human activity) and around 33% of the forest area was found within protected areas. For the year 2015, 100% of the forest area was reported to be under public ownership.
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 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. 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 south-eastern border with Myanmar and India, are the least densely populated.
Climate
Bangladesh is divided between a monsoon-influenced humid subtropical climate in the northern half (north of Dhaka), and a tropical monsoon climate in the southern half which is 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 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. In general, maximum summer temperatures range between . 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 during the day and around at night.
Winds are mostly from the north and northwest in the winter, blowing gently at in northern and central areas and near the coast. From March to May, violent thunderstorms, called northwesters by local English speakers, produce winds of up to . During the intense storms of the early summer and late monsoon season, southerly winds of more than cause waves to crest as high as in the Bay of Bengal, which brings disastrous flooding to coastal areas. 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 , most parts of the country receive at least 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 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 subcontinent, 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.
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 winds and waves 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 of critically needed embankments.
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 of crops were reported destroyed, and relief work was rendered even more challenging than usual because the flood made transportation exceedingly difficult. 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 or less, people without warm clothing and living in inadequate homes may die from the cold.
Climate change
River systems
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.