PhysiographyBrahmaputra valley  |  Barak Valley  |  Climate  |  Temperature  | 

Soil  |  Biodiversity  |  Fauna  |  Flora  |  Rivers


Geography of Assam









Assam is an important geographic location of North-East India. Situated between 8905/-960 1/ East Longitude and 2403/-27058/ North Latitude, Assam is bordered in the North and East by the Kingdom of Bhutan and Arunachal Pradesh. Along the South lie Nagaland, Manipur and Mizoram. Meghalaya lies to her South-West, Bengal and Bangladesh to her West. Although Assam is surrounded by hills and mountains in its three sides, there has been always a relation with Tibet of China and South East Asia.

Assam and the entire North East India is a transitional zone between South Asia and South East Asia. The area of Assam is 78,433sq km with population 26,655,528 in 2001.

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The structure of Assam can be divided into three units, they are

  • Karbi Plateau , which is the inner most part of the Meghalaya plateau

  • The Tertiary depositional zone which includes hills of North Cachar Hill Districts and Barali range, and

  • Plain of Brahmaputra Valley and Barak Valley.

Assam is the frontier province of on the North-East. The boundaries of Assam lies between latitudes 280 18/ and 240 North and latitudes 890 46/ and 970 4/ East. Assam comprises an area of 78,523 square kilometers (30,318 square miles). Modern Assam has 22 districts which are akin to counties in the US or the UK. Except for the districts of Karbi Anglong and North Cachar Hills, Assam is generally composed of plains and river valleys. It can be divided into three principal geographical regions: the Brahmaputra Valley in the north; the Barak Plain in the south; and the Mikir (Karbi Anglong) and Cachar Hills that divide the two regions.


The mighty Himalaya covers three sides of the province. The state shares international boundaries with Bangladesh and Bhutan. Assam serves as a gateway to the South East Asia with its capital city of Guwahati.Whereas at one time Assam had extensive international borders with China/Tibet and Burma, modern Assam's international borders are limited to those with the small country of Bhutan in the northwest and with Bangladesh to the southwest. Assam is bordered on the north by the Indian state of Arunachal Pradesh that used to be an administrative part of Assam till the 1970s. To the east of Assam are the Indian states of Arunachal Pradesh, Nagaland, and Manipur; to the south are the Indian states of Mizoram and Meghalaya; and to the west are Bangladesh and the Indian state of Tripura. Except for a narrow corridor running through the foothills of the Himalayas that connects the state with West Bengal, Assam is almost entirely isolated from India. The capital of Assam used to be Shillong in the modern state of Meghalaya for more than a hundred years till it was moved to Dispur, a suburb of Guwahati in 1972, after Meghalaya became a separate state of India.


The northern part of Assam is wholly occupied by the elongated valley of the mighty river Brahmaputra. Most of Assam's population lives in this valley. The Brahmaputra valley is bounded by the foothills of the Himalayas to the north and another lower range of hills and mountains to the south. In the center part of Assam, to the south of the hills is the Barak Valley which is contiguous with the densely populated country of Bangladesh.


The Karbi Plateau is of the pre-Cambrian origin (5 billion to 570 millions years ago). It contains very old metamorphic rocks, which are highly compressed, hard and crystalline. Other parts of Assam made up of early Tertiary sedimentary deposits (65 million to 2 million years ago) and Quaternary (about 2 million years ago to the present) alluvial deposits.


Geomorphic studies also conclude that the Brahmaputra, the life-line of Assam is older than the Himalayas. The river with steep gorges and rapids in Arunachal Pradesh entering Assam becomes a braided river (at times 10 mi/16 km wide) and with tributaries, creates a flood plain known as the Brahmaputra Valley (50-60 mi/80-100 km wide, 600 mi/1000 km long). In the south, the Barak, flows through the Cachar district with a 25-30 miles (40-50 km) wide valley and enters Bangladesh with the name Surma.


Barak Valley is situated in the south Assam. In the north there is North Cachar Hills, in the east there is Manipur Hills and in the south there is Mizoram hills. The area is 6962 sq. km.


Assam is full of streams, rivulets, and rivers which receives water from Himalaya and hills and plateaus. The water falls into to basins; they are the Brahmaputra Basin and the Barak-Surma basin.


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The Brahmaputra valley:

 The northern part of Assam is wholly occupied by the elongated valley of the mighty river Brahmaputra. Most of Assam's population lives in this valley. The Brahmaputra valley is bounded by the foothills of the Himalayas to the north and another lower range of hills and mountains to the south. The Brahmaputra Valley is the dominant physical feature of Assam. The Brahmaputra enters Assam near Sadiya at the extreme northeast corner and runs westward for nearly 450 miles before turning south to enter the plains of Bangladesh.

The river valley, rarely more than 50 miles wide, is studded with numerous low, isolated hills and ridges that abruptly rise from the plain. The valley surrounded on all sides, except the west, by mountains and is intersected by many streams and rivulets that flow from the neighboring hills to empty into the Brahmaputra.


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Barak Valley:









The Barak Valley is separated by the Karbi Anglong and North Cachar Hills from the Brahmaputra Valley in Assam. The Barak originates from the Barail Range in the border areas of Assam, Nagaland and Manipur and flowing through the district of Cachar, it confluences with the Brahmaputra in Bangladesh. Barak Valley in Assam is a small valley with an average width and length of approximately 40 to 50 km.

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With the 'Tropical Monsoon Rainforest Climate', Assam is a temperate region and experiences heavy rainfall and humidity. The location, situation and topography of Assam make its climate different from rest of India. The weather is dry in winter and hot and wet in summer. The Himalayan range protect Assam from cold wind from Central Asia in winter and but causes heavy rain as it obstruct the south-west wind from over running. In winter, the western/Mediterranean disturbances influence the climate of Assam to some extent by causing rainfall, fog and cloudy weather for days together. Mountains, valley winds, sandstorms, fogs, and cyclones are some local factors which influences the climate of Assam.

From February to April the dust is very frequent near the area of Brahmaputra. This is followed by cyclones and hailstorms in the month of April and May. They are known as Bordoisila or Kalbaisakhi. Winter lasts from October to late February. Nights and early mornings are foggy, and rain is scanty. June, July and August are the hottest months.


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The average temperature is moderate, about 84 degrees F (290C) in the hottest month of August. The average valley temperature in January is 61 degrees F (160C). In this season, the climate of the valley is marked by heavy fogs and a little rain. Assam does not have the normal Indian hot, dry season. Some rain occurs from March onwards, but the real force of the monsoon winds is faced from June onward. Rainfall in Assam ranks among the highest in the world; its annual rainfall varies from 70 inches in the west to 120 inches per year in the east. Large concentrated during the months from June to September; it often results in widespread destructive floods.


Based on the amount of rainfall, nature of temperature and humidity, terrain condition and characteristic of soil Assam can be divided into five major agro-climatic regions. They are eastern Brahmaputra Valley, The central Brahmaputra Valley, the lower Brahmaputra Valley, the Hill region, and the Barak Valley.

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The soil of Brahmaputra Valley and Barak Valley are alluvial and very fertile. But the soil in the Karbi plateau and North Cachar Hills are less fertile and consists of red soil. Soil erosion is one of the major problems of Assam.


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Assam is a global biodiversity hot spot, because Assam lies at the transitional zone of Oriental and Asiatic or Palaearctic zoogeographical realm. Some of the Typical Assamese eco-systems are:


· Tropical Rainforests


· Deciduous Forests


· Riverine Grasslands


· Bamboo Orchards and


· Numerous Wetlands


Many of such Eco-systems are now protected as national parks and reserved forests by the Assam Government. The total wildlife protected area in Assam is around 3923 sq. km.; of this 1978 sq. km. is in 5 national parks and the other 1932 sq. km. in 118 wild life sanctuaries. The Kaziranga National Park, home of the rare one horned rhinoceros, and Manas Wildlife Sanctuary are two UNESCO World Heritage Sites in Assam.


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The rich vegetation of Assam provides the place for many verities of animals. There are 230 forms of mammals and 175 species. There are 958 species and sub-species of birds in Assam out of which 208 are migratory. There are 187 species of reptile in Assam. Assam is also rich in fish-fauna.

Assam is the proud keeper of the rare one-horned Rhinoceros. About 180 species of mammals are found in Assam which includes globally threatened species. Thus the state of Assam is also the last refuge for numerous endangered species such as Golden Langur, White-winged Wood Duck, Bengal Florican, Black-breasted Parrotbill; Pygmy Hog, Greater Adjutant, Hispi Hare, Clouded Leopard, Hoolock Gibbon, Jerdon's Babbler, Gangetic Dolphin.

Some other endangered species with significant population in Assam are Tiger, Asian Elephant, Indian Bison, Buffalo, Swamp deer, Sambar, Hog, deer, Sloth Bear, Leopard cat, Jungle cat, Hog Badger, Capped Langur, Jackal, Goose, Hornbills, Ibis, Cormorants, Egret, Heron Fishing Eagle; etc.

During winter a large number of migratory birds are also seen here. Hundreds of winged species migrate to the friendly climate of Manas Wildlife Sanctuary in the winter season. Among such species are White Capped Redstars, Forktails, Cormorants and various types of ducks including the Ruddy Shelduck. The woodland birds are no less charming and include the Indian Hornbill and the Great Pied Hornbill.

With such varied and abundant wildlife Assam is day by day becoming an increasingly popular destination for wildlife tourism.


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Assam's forests cover about 20 percent of the total area. The most important forest products are timber and bamboo, firewood and lac (the source of shellac). There are about 74 species of timber, of which two-thirds are commercially exploited. Assam was also known for its Sal tree forests and Sal products, but most of such forests have depleted now. Assam is a land where one can find flowers that are exquisitely beautiful. Orchids of Assam are very beautiful and rare, so have a huge demand in the world market.

Plants like Nahar (Mesua Ferrea), Hollock (Terminatia Hollock), Sai (Shorea Robusta), Mekai (Shorea Assamica), Cham (Artocarpus Chaplasha), Chama (Michalia Champaka), Bansom (Phoebe), Bakul (Minosop elengi), Teak (tactona grandis), Silikha (terminalia chebula), Bhemora (terminalia bellerica), Arjuna (terminalia arjuna), Pada (Cedrela toona), Bagipoma (chikaasia species), Hollong (Dipterocarpas macrocarpus), Dhoona (dipterocarpus resinous), Garjun (dipterocarpas garjan), Simalia (Salmolia Malabarica), Mango (mangifera india), Sonaru (cassia alata), Jamoon (Eugenia Jamsbolana), Chere (Albizzia), Agar (Aquillaria Agallocha), Kadom (Kadamba), Gamari (Gmellina Arborea), Dimaru (fig), Aswastha (fiscus religiosa), Bat (Ficus indica), Neem (Azadarista indica), Oda (S.villosa), .Bamboo (Bamboosa), On (Dillenia), etc are abundant in the forests of Assam.









In Assam all these plants are mixed in different forests giving a mixed monsoc character. The evergreen plants like Bamboo, Nahar, Bakul, Cham, Mango, and semi evergreen Terminalia Species are found everywhere, giving all forests an evergreen canopy. The main wild plants found in the forests of Assam are bamboos, wild plantain, cane, Raidang, Ikora, Khagori, Nal, etc Grasses are found everywhere. Pure tall grass lands of Savanna type are found in the low lying riverine belt of the river Brahmaputra.



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Assam has extensive river system consisting of the Brahmaputra, the Kusiyara and the Barak and their tributaries. All the rivers in Assam are liable to floods, mainly because they receive heavy rainfall within a short time. These rivers are in their early stage of maturity and are very active agents of erosion. The river waters collect a tremendous amount of silt and other debris and raise the level of the river beds. Therefore, it becomes impossible for the main channel to cope with the vast volume of water received during the rains. The Brahmaputra River has a total drainage area of about 935,500 sq. km. So far, a total of 4, 77,163 hectares of land have been irrigated in Assam.

In Assam rivers are of great importance as they provide drinking water, water for irrigation purposes, food (fish) and livelihood (fishing) etc. Rivers also accessed as waterways thus helping in communication and transport of goods and livestock. Some of the important rivers are as follows:

Barak , Jia Bhoroli & Mora Bhoroli, Brahmaputra, Dhansiri, Dihing, Gabhoru, Manas, Bhorolu; etc.

Assam is reach in coal, petroleum, natural gas and limestone also.


References: Assam Land and People edited by Basanta Deka.