Brahamaputra Basin

Brahamaputra Basin
1.7 Agro-climatic zones
Agro-climatic zone is a land unit in terms of major climate, superimposed on length of growing
period (moisture availability period) (FAO, 1983).
Agro-climatic Zones of Brahmaputra Basin: For resource development, the country has been
broadly divided into 15 agricultural regions based on agro climatic features particularly soil type,
climate including temperature and rainfall and its variation and water resources availability. Agro
climatic zone map of Brahmaputra basin are shown in Map 6.
The entire Brahmaputra basin falls in the Eastern Himalayan agro-climatic zone (Planning
commission, 1989) and climatic pattern of this region is characterized by the high rainfall, high forest
covers, heavy soil erosion and Floods (Brahmaputra Valley) etc. The Eastern Himalayan agro-climatic
zone includes Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim, Tripura,
West Bengal (Hilly region). The climate varies from tropical in the plains to Alpine in the high hills.
Nearly a third of the cultivation is of the shifting (jhum) type. Majority of population is dependent on
agriculture and allied land based activities. Shifting cultivation is traditional agricultural practice. In
West Bengal Darjiling and the further northern territory of Sikkim, the soil is brown hilly. In Karbi
Anglong and Cachar Hills in Assam and the entire territories of Arunachal Pradesh, Nagaland and
Meghalaya, the soil is classified red sandy to laterite. In the most populous part of Assam which
covers the districts of Barpeta, Dhubri, Nagaon, Darrang, Kamrup, Goalpara, Kokrajhar and Sonitpur,
the soil is alluvial, red loamy and terrai. In the Upper Brahmaputra valley comprising of the districts
of Lakhimpur, Sibsagar, Cachar, Dibrughar, Jorhat and Karimganj in Assam and Jalpaiguri & Koch
Behar in West Bengal, the soil is alluvial and red loamy. The climate of the zone is per humid to
humid. Himalayan Hills Region receives 2,700 mm of rainfall in a year. North East Hills Region
receives copious rains of about 3,528 mm in a year. Southern Hills Region receives 2,052 mm of
rains while Lower Brahmaputra receives 1,840 mm of rains. Upper Brahmaputra Region receives
rains of 2,800 mm per annum.
1.8 Agro-ecological zones
An agro-ecological zone is the land unit carved out of agro-climatic zone superimposed on landform
which acts as modifier to climate and length of growing period.
Agro–ecological Zones of Brahmaputra basin: Based on 50 years of climate data and available soil
database, the country has been divided into 20 agro-ecological zones (AEZs). Each AEZ is as uniform
as possible in terms of physiography, climate, length of growing period and soil type for macrolevel
land-use planning and effective transfer of technology. Agro-ecological zones of Brahmaputra Basin
are shown in the Map 7.
Most of the upper Brahmaputra sub basin area falls in the ‘Warm perhumid ecoregion with brown
and red hill soils’. The Brahmaputra Valley area is dominating by ‘Hot subhumid (moist) to humid
(inclusion of perhumid) eco-regions with alluvial-derived soils’. The lowermost part of the basin is
falling in the ‘Warm perhumid eco-region with red and lateritic soils ‘. Salient features of these Agroecological
Zones are:
i) Warm perhumid ecoregion with brown and red hill soils (Agro-ecoregion - 17): Physiologically
these are parts of the Eastern Himalayan range. States and Districts under this ecoregion area)
Arunachal Pradesh - Tirap district
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