Climate trends in the Brahmaputra river basin
The Brahmaputra river basin
Source: Angsi Glacier
Mouth: Bay of Bengal
Length: 2,900 km
Area: 543,400 km 2 76
Countries: China (50%), India (36%), Bangladesh (7%), Bhutan (7%) 77
Main tributaries: Dibang, Lohit, Dhansiri, Kolong, Kameng, Manas, Raidak, Jaldhaka, Teesta, Subansiri
ranging from a monthly average of 8,408 million m 3 in the driest month to 115,996 million m 3 in the wettest. The estimated total water use in the Brahmaputra basin is approximately 27,457 million m 3 /year, of which 2% is used in China (Tibet), 1% in Bhutan, 43% in India and 54% in Bangladesh. Agriculture and domestic use account for 98% of water use in the basin. Current infrastructure does not allow all potential users access to the water in the Brahmaputra river. Despite this, however, demand still exceeds water availability in the driest months (January to March). As water infrastructure improves and access to water increases, the amount of water available downstream might be further reduced. During the dry months, the pressure on ecosystems and environmental flows may be critical. While the river can meet human demand for water during the monsoon season, water demand estimates do not include demand for sustaining
Starting from an elevation of 5,300 m, the Brahmaputra river flows across southern Tibet, passing through the Himalayas, descending onto the Assam plain, and finally emptying into the Bay of Bengal. The river undergoes a dramatic reduction in altitude as it passes through one of the world’s deepest gorges in the Himalayas and enters the Assam plain, depositing large amounts of sediment downstream. In the Assam and Bangladesh plains, the river flows in highly-braided channels (numerous channels that split apart and join again) separated by small islands. The river relies on both the monsoon and snow and glacial melt and, as such, is characterized by a large and variable flow. 78 The monthly average flow rate varies from 3,244 m 3 /s in March to 44,752 m 3 /s in July. The average annual flow rate is 19,160 m 3 /s, the fourth highest in the world.
ecosystems and the environmental flow of the river. The high pre-monsoon and monsoon flow is critical for the spawning of many species of fish in the river and its estuary. The Brahmaputra river basin is particularly prone to floods and erosion. The floods are caused by a combination of natural factors, such as the monsoon system and weak geological formations, and anthropogenic factors, such as deforestation and high population growth. 79 Floods cause devastation every year, affecting people and the vital agricultural economic base of the region. Climate trends Precipitation The Brahmaputra basin receives an average of just over 1,100 mm of rain annually. Of the annual total, 70% is received during the monsoon season (June– September) and 20% in the pre-monsoon season. Winter is the driest season.
The annual average water availability in the Brahmaputra basin is about 608,000 million m 3 ,
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