Teesta

Background and evolution

The Teesta's catchment lies in a seismically active zone, and its slopes are made of fractured rocks covered by thick soils. Intense monsoon rainfall regularly triggers landslides that dump debris into the river, raising its bed in the plains and increasing flood risk downstream. Warming has also caused glaciers in north Sikkim to retreat, and the meltwater has enlarged lakes such as South Lhonak, which grew steadily over several decades before it burst.

The Teesta drops steeply from more than 5,000 metres in north Sikkim to the plains in a short distance, giving it great hydropower potential and making it fast, sediment-laden and prone to landslides and flash floods. It is the lifeline of Sikkim, and in the plains of north Bengal and north-west Bangladesh it supports rice cultivation, especially in the dry season when irrigation is crucial.

In 2011 India and Bangladesh came close to an interim agreement on sharing the Teesta's dry-season flow, but the deal was not signed after objections from West Bengal, which feared reduced water for its own farmers. The issue remains one of the most sensitive in bilateral relations. This page focuses on the Teesta as an example of how a single river links Himalayan hazards, hydropower, federal politics and foreign policy, rather than on Brahmaputra basin geography covered elsewhere.