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Current Affairs

Tree rings contain proof of Brahmaputra floods

Date: 03 December 2020 Tags: Climate Change

Issue

A new study looking at water flow in mighty Brahmaputra River suggests that scientists are underestimating the river's potential for catastrophic flooding as climate warms. 

 

Background

The revelation comes from examinations of tree rings, which showed rainfall patterns going back centuries before instrumental and historical records.

 

Details

  • The new study, based on the rings of ancient trees in and around the river's watershed, shows that the post-1950s period was actually one of the driest since the 1300s.

  • The rings show that there have been much wetter periods in the past, driven by natural oscillations that took place over decades or centuries.

  • The river routinely floods surrounding areas during the July-September monsoon season, when moisture-laden winds bring rain along its length, from its Himalayan headwaters on down to the coastal plain.

  • As with the Nile, the flooding has a good side, because the waters drop nutrient-rich sediment to replenish farmland, and some degree of flooding is essential for rice cultivation.

  • Higher temperatures drive more evaporation of ocean waters, and the water ends up as rainfall on land during the monsoon.

  • As a result, warming climate will intensify the monsoon rains in coming decades, and in turn increase seasonal flooding.

  • The tree rings do show some other relatively dry times, in the 1400s, 1600s, and 1800s. But they also show very wet periods of extreme flooding in the relatively brief modern instrumental period. The worst lasted from about 1560-1600, 1750-1800, and 1830-1860.

  • Human vulnerability to floods along the Brahmaputra has increased in recent years due not only to sheer water volume, but because population and infrastructure are growing fast.

 

Brahmaputra River

  • The Brahmaputra is one of the world's mightiest rivers, flowing under a variety of names and braided routes some 2,900 miles through Tibet, northeast India, and Bangladesh.

  • Near its mouth, it combines with Ganga River to create the world's third largest ocean outflow, behind only the Amazon and the Congo. (It is tied with Venezuela's Orinoco.)

  • At points, it is nearly 12 miles wide. Its delta alone is home to 130 million Bangladeshis and many millions more live upstream.