Bangladesh Geography Bangladesh covers an area of 147,570 sq km, a little more than the size of Greece. It extends from 20'34N to 26'38N latitude and from 88'01E to 92'41E longitude. Maximum extension is about 440 km in the E-W direction and 760 km in the NNW-SSE direction. The Indian States of west bengal, assam, Meghalaya and tripura border Bangladesh in the west, north and east respectively. Myanmar forms the southern part of the eastern frontier. The total length of the land border is about 4,246 km, of which 93.9% is shared with India and about 6.1% with Myanmar. The country is bounded in the south by the bay of bengal. Although Bangladesh is a small country, the length of the coastline is more than 580 km. The territorial waters of Bangladesh extend 12 nautical miles (22.22 km) and the area of the high seas extending to 200 nautical miles (370.40 km) measured from the base lines constitutes the economic zone of the country. The Bay of Bengal is well-known for its cyclones, which whip up its water, sending them crashing onto the coastal plains of the offshore islands, occasionally causing floods. Bangladesh is fringed on the southwest by the huge expanse of mangrove forest known as sundarbans, the abode of the famous Royal bengal tiger.
Bangladesh has seven principal administrative units known as divisions. These are barisal, chittagong, dhaka, khulna, rajshahi, sylhet and rangpur. There are 64 districts (zilas) under these divisions and again the districts have been divided into 462 upazilas and 34 thanas. The country has about 95 to 119 enclaves inside India. The areas of these enclaves range from 0.4 ha to 20.72 sq km.
Population ranks first in the world in terms of population density and is considered the 8th most populous country in the world. The figure of 131.27 million (2001) inhabitants corresponds to 890 persons per sq km. The sex ratio of the population is about 104 males per 100 females. The intercensal growth rate of population is 1.48 per annum (up to 2001 census) and the literacy rate is 32.40% (2001) for the population of age seven years and above. There are four ethnic groups in Bangladesh: Dravidian, proto-Australian, Mongolian and Bangali. The Dravidian element of population is represented mainly by the Oraons, a tribe of central Indian origin. This group is - with only a few thousand persons - the smallest ethnic element in the country. The khasia and santals, mainly labourers in the tea gardens at Sylhet, belong to the proto-Australian group.
The Mongolian group of Bangladesh's population is confined to the hills along the southern spur of the shillong plateau, in chittagong hill tracts and Madhupur forest. The Mongolian group consists of about 500,000 to 600,000. chakma, Tipra, garo, Murang and Moghs are the major Mongoloid tribes in Bangladesh. The Chittagong Hill Tracts host 13 tribes, who are divided into nearly a hundred sub-tribes. The Bangalis are by far the largest group of all, constituting about 98% of the total population of the country. This group is non-tribal and heterogeneous in origin. In respect to religion, about 88% of people in Bangladesh are Muslims, 11% Hindus, the rest being Buddhists, Christians and animists.
Bangladesh is one of the least urbanised areas of South Asia. According to the Census of January 2001, the percentage of urban population is 23.39 while that of rural population 76.61. There are only four cities (city corporations), although there are more than 100 towns of varying sizes. Dhaka, the capital and the largest metropolis of the country, has a population of 9.91 million. Chittagong, the port city, is the second most important metropolis, having population of 3.20 million. A number of industrial areas have been developed in the city. Khulna, in the southwest, has become a commercial and industrial centre; the mongla port and the growth of Daulatpur industrial area have contributed to increasing its population to 1.23 million. Rajshahi, well-known as a centre of education, is the fourth largest city, having a population of 0.65 million.
Relief and physiography With about half of its surface below the 10m-contour line, Bangladesh is located at the lowermost reaches of the three mighty rivers, the ganges, the brahmaputra and the meghna. Coinciding with the division of the country based on altitude and relief, the land can be divided into three major physical units: Tertiary hills (66 million years to 2 million years before the present), pleistocene terraces (2 million years to 0.1 million years before the present) and Recent plains (began forming about 0.1 million years ago and still being formed). The heavy monsoon rainfall coupled with the low altitude of major parts of the country makes floods an annual phenomenon in Bangladesh.
Quaternary (began about 2 million years ago and extends to the present) sediments, deposited mainly by the Ganges (padma), Brahmaputra (jamuna) and Meghna rivers and their numerous distributaries, cover about three-quarters of Bangladesh. The physiography and drainage pattern of the vast alluvial plains in the central, northern and western regions experienced considerable alterations in recent times. The deposition of Quaternary sediments was influenced and controlled by structural activities. The eastward shift of the Ganges and tista as well as the significant westward shift of the Brahmaputra during the last 200 years gives evidence of epeirogenic movements even in recent days. Hillocks and hills are confined to a narrow strip along the southern spur of the Shillong Plateau, to the eastern and southern portions of Sylhet district and to the Chittagong Hill Tracts in the southeast of the country bordering upon the Indian states of Tripura and Mizoram and Myanmar.
In the context of physiography, Bangladesh may be classified into three distinct regions: (A) floodplains, (B) terraces, and (C) hills each having distinguishing characteristics of its own. For detailed physiography, the country has been divided into 24 sub-regions and 54 units. Major regions and sub-regions are detailed below:
(i) Old Himalayan Piedmont plain; (ii) Tista floodplain; (iii) Old Brahmaputra floodplain; (iv) Jamuna (Young Brahmaputra) floodplain; (v) Haor basin; (vi) Surma-Kushiyara floodplain; (vii) Meghna floodplain - (a) Middle Meghna floodplain, (b) Lower Meghna floodplain, (c) Old Meghna Estuarine floodplain, (d) Young Meghna Estuarine floodplain; (viii) Ganges River floodplain; (ix) Ganges Tidal floodplain; (x) Sundarbans; (xi) Lower Atrai basin; (xii) Arial beel; (xiii) Gopalganj-Khulna peat basin; (xiv) Chittagong Coastal plain; (xv) Northern and Eastern Piedmont plain; (xvi) Pleistocene uplands (a) barind tract, b) madhupur tract and (c) tippera surface; (xvii) Northern and Eastern hills (a) Low Hill Ranges (Dupi Tila and Dihing formations), (b) High hill or Mountain ranges (Surma and Tipam formations).
piedmont plains comprise gently sloping land at the foot of hills, where colluvial and alluvial sediments derived from the hills have been deposited by rivers or streams. A portion of the himalayan piedmont plain stretches into Bangladesh at the northwestern corner of the country - which occupies most of Dinajpur region. The piedmont deposits may possibly be as old as Late Pleistocene or Early Holocene, but they are younger than the madhupur clay. The Old Brahmaputra floodplain stretching from the southwestern corner of the Garo Hills along the eastern rim of the Madhupur Tract down to the Meghna river exhibits a gentle morphology composed of broad ridges and depressions. The latter are usually flooded to a depth of more than one metre, whereas the ridges are subject to shallow flooding only in the monsoon.
The Brahmaputra-Jamuna floodplain, a dual name, is used for the mighty Brahmaputra, because the Jamuna channel is comparatively new and this course must be clearly distinguished from that of the older Brahmaputra. Before 1787, Brahmaputra's course swung east to follow the course of the present old brahmaputra. In that year, apparently, a severe flood had the effect of turning the course southwards along the Jenai and Konai rivers to form the broad braided Jamuna channel. The change in course seems to have been completed by 1830. Due to the upliftment of the two large Pleistocene blocks of Barind and Madhupur, the zone of subsidence between those turned to a rift valley and became the new course of the Brahmaputra as the great Jamuna. The broad high Ganges Floodplain stretches from Premtali in godagari upazila- the western border of the country, south of the Barind Tract, as far as shujanagar upazila (pabna) in the east, where it slopes into the Jamuna floodplain. The old Brahmaputra river in its course built up the Meghna Floodplain, which includes the low and fertile Meghna-Shitalakkhya doab, enriched by the Titas distributary, as well as the diaras and chars of the Meghna, especially between Bhairab Bazar and daudkandi. The vast floodplain of the Meghna is an earlier build-up of the lower course of the Old Brahmaputra. Haor basin, a large, gentle depressional feature, is bounded by the Old Brahmaputra floodplain in the west, the Meghalaya Plateau's foothills in the north and by the Sylhet High Plain in the east. Its greatest length, both E-W and N-S direction is just over 113 km. Numerous lakes (beels) and large swamps (haors) cover this saucer-shaped area of about 7,250 sq km. The sinking of this large area into its present saucer-shape seems to be intimately connected with the upliftment of Madhupur Tract.
The ganges-brahmaputra delta is one of the largest delta in the world. It is noteworthy that the Bangladesh portion of the delta alone occupies about 46,620 sq km, that is approximately a little less than one- third of the country's land area (about 32%) including the rivers. The area drawn along the Ganges and Padma as far south as the lower course of the feni river in the southeast belongs physiographically to the delta of the Ganges, Brahmaputra (Jamuna) and Meghna rivers. This vast deltaic land can be subdivided into five units, viz Moribund delta, Central Delta Basins, Immature Delta, Mature Delta and Active Delta. The Ganges is, by far, the greatest builder of the delta and has deposited the sediments of nearly four-fifths of the total.
Pleistocene upland extends from the lalmai hills of comilla district and adjacent low hills in the east through Dhaka and Rajshahi divisions to West Bengal in India. The river systems of the Meghna and the Jamuna trisect the Pleistocene upland, giving rise to three blocks of high lands that exhibit smooth rolling topography. The Barind Tract, the Madhupur Tract (Madhupur Garh), and the Tippera Surface form the three blocks. The Ganges limits the western, and the buriganga and dhaleshwari, the two distributaries of the Jamuna, limit the southern extremities of the Pleistocene uplands. In the northern most strip of Rajshahi Division, Pleistocene upland merges with the piedmont of Himalayas and in the district of mymensingh it slopes down to the alluvial plains. Pleistocene upland covers an area of about 10% of Bangladesh, with an average elevation of more than 15m above MSL (mean sea level).
The Eastern and Northern Frontier Hilly Region represents the hill areas of Bangladesh and comprises two main sub-regions - Chittagong Hill Tracts and Foot Hills of the shillong massif. The Chittagong Hill Tracts, the only extensive hill area of the country, consists of hills, hillocks, valleys and forests, is quite different in aspect from other parts of Bangladesh. The region lies in the southeastern part of the country bordering Myanmar in the southeast and the Indian states of Tripura in the north and Mizoram in the east. Generally, the hill ranges and river valleys are longitudinally aligned. The coastal plain is partly sandy and partly composed of saline clay; it extends from the Feni river to cox's bazar and varies in width from 1 to 16 km. The region has a number of offshore islands and one coral island, st martin's island, off the coast of Myanmar. The central portion of the Chittagong Hill Tracts hosts an artificial lake, the kaptai lake. It covers an area of about 767 sq km in the dry season and about 1,036 sq km in the monsoon.
The Foot Hills of the Shillong Massif are subdivided into three major tectonic units from west to east - the Garo Hills, Khasi Hills and Jaintia Hills laying almost entirely on Indian territory. Merely the southern fringes of this highly elevated block form a narrow strip of hills and hillocks in Bangladesh territory.
Hydrography the Ganges-Padma, the Brahmaputra-Jamuna, and the Surma-Meghna and their numerous tributaries and distributaries are the arteries of the drainage system of Bangladesh. The karnafuli, the sangu, the matamuhuri, the Feni, and the naf along with their feeding channels drain the water of the high hill ranges of the districts of Chittagong and Chittagong Hill Tracts directly to the Bay of Bengal. Many small streams that originate from the westernmost hill ranges also independently fall into the bay.
The pride of Bangladesh is its river network, of which the Ganges-Padma, the Jamuna, the Brahmaputra, the Meghna, the surma, the Karnafuli, and the Tista are most important, and their tributaries and distributaries numbering around 700, with a total length of about 24,140 km, flow down to the Bay of Bengal. The country possesses the world's longest unbroken beach, 120 km in length from Cox's Bazar to Teknaf.
The combined drainage basin of the three great rivers - Ganges-Padma, Brahmaputra-Jamuna and Meghna has a size of about 1.72 million sq km. These rivers carry an immense freight of sediments into the Bay of Bengal. The Brahmaputra-Jamuna, for instance, transports about 1.2 million tons of sediment per day. The silt freight carried each year by the Ganges, Brahmaputra and Meghna river systems into the Bay of Bengal amounts to almost 2.4 billion tons.
Climate characterised by tropical monsoon climate. Bangladesh has three distinct seasons: the pre-monsoon hot season (Summer) from March through May, rainy monsoon season which lasts from June through October, and a cool dry winter season from November through February. However, March may also be considered as the spring season, and the period from mid-October through mid-November may be called the autumn.
The pre-monsoon hot season is characterised by high temperature and occurrence of thunderstorms. April is the hottest month in the country when mean temperature ranges from 27'C in the east and south to 31'C in the west-central part of the country. After April, increasing cloud-cover dampens temperature. Wind direction is variable in this season, especially during its early part. Rainfall accounts for 10 to 25 percent of the annual total, which is caused by thunderstorms.
Southerly or south-westerly winds, very high humidity, and heavy rainfall and long consecutive days of rainfall characterise the rainy season, which coincides with summer monsoon. Rainfall of this season accounts for 70 to 85 percent of the annual total. This is caused by the tropical depressions that enter the country from the bay of bengal.
Low temperature, cool air blowing from the west or northwest, clear sky, and meagre rainfall characterise the cool dry season. Average temperature in January varies from 17°C in the northwest and northeastern parts of the country to 20°C-21°C in the coastal areas. Minimum temperature in the extreme northwest in late December and early January reaches 3°C to 4°C.
Mean annual temperature everywhere is about 25°C, whereas mean monthly temperatures range between 18°C in January and 30°C in April-May. Extreme temperature ranges between 40'C and 43°C, except near the coast where the range is narrower. Ground frost is occasionally experienced on exposed hill sites, but not on the plains. Significant differences in seasonal temperatures occur across the country. In general, the highest pre-monsoon temperatures occur in the west. The length of the winter with minimum temperatures below 15°C ranges between 35 and 40 days near the coast to over 100 days in the extreme northwest.
During the monsoon, the average rainfall varies from about 890 mm in the western districts of Rajshahi, bogra, kushtia and jessore to more than 2,030 mm in the southeastern and northeastern parts of the country, with a maximum exceeding 5,000 mm in the extreme northeast at the Foot Hills of the Shillong Massif. The high rate of precipitation results in regularly occurring floods. Besides the summer rains known as the monsoon, the winter depressions originating from the Mediterranean and the so-called nor'westers (Kalbaisakhi - calamities of Baisakh, mid-April to mid-May) in April and May contribute to the annual precipitation. The Nor'wester-period shows a comparable trend with about 250 mm precipitation in the west and about 635 mm in the east. During the dry season from November to March, precipitation amounts to 50 mm, with the maximum in December. Rainfall declines from November to March and is excessive from June to October. The annual precipitation decreases from east to west. The lowest atmospheric pressure occurs all over Bangladesh in June and July- the storm-season. Winds are mostly from the north and northeast in winter, blowing gently at a rate of 1.61 to 3.22 km per hour in northern and central areas and 3.22 to 6.44 km per hour near the coast. During the period of the Nor'westers (March to May), wind speeds may rise to 50 to 65 km per hour.
In the early summer (April and May) and late in the monsoon (September to November), storms of very high intensity often occur. These may create winds with speeds of more than 160 km per hour, piling up the waters of the Bay of Bengal to crests as high as six metres that crash with tremendous force onto the coastal areas and the offshore islands, inundating them and causing heavy losses of life and property. Coinciding with the hottest time, ie the pre-monsoon months, violent thunderstorms - Nor'westers occur predominantly in the districts of Dhaka, faridpur and Pabna. These thunderstorms are characterised by sudden shifting wind directions, a sharp fall in temperatures and wind velocities of up to 150 km/hr. Rainfall ranges from a few millimetres to as much as 526 mm as recorded at noakhali on 30th April 1983. Hail showers are common, but they often have devastating effects.
Day-length and sunshine at Dhaka varies from 10.7 hours in December to 13.6 hours in June and sunshine ranges from 5.4-5.8 hours per day in the monsoon to 8.5-9.1 hours per day in the winter and pre-monsoon seasons. These figures are broadly representative for the whole country, except that eastern border areas have about one hour less sunshine per day in the monsoon than other areas, and the coastal fringe has about one hour per day more sunshine in the dry season. [Masud Hasan Chowdhury]
Bibliography Haroun Er Rashid, Geography of Bangladesh, University Press Limited, Dhaka, 1991; FH Khan, Geology of Bangladesh, University Press Limited, Dhaka, 1991; Klaus-Ulrich Reimann, Geology of Bangladesh, GebrFCder Borntraeger, Berlin-Stuttgart, 1993; Hugh Brammer, The Geography of the Soils of Bangladesh, University Press Limited, Dhaka, 1996; Rafique Ahmed, Abhaoa O Jalabayu Vijnan (Meteorology and Climatology, in Bangla), Department of Geography and Environmental Studies, University of Rajshahi, Bangladesh, 1997; Bangladesh Bureau of Statistics (BBS), 1997 Statistical Year Book of Bangladesh, BBS, Dhaka, 1998.