Making sense of Assam floods: Why rivers turned violent in the 20th century and how climate change is making them more unpredictable

Source: The post is based on the article “Making sense of Assam floods: Why rivers turned violent in the 20th century and how climate change is making them more unpredictable” published in “Indian Express” on 6^th July 2022.

Syllabus: GS 3 – Disaster and disaster management.

Relevance: To understand the impacts of increasing floods in the northeast.

News: This year Assam floods disrupted normal life. The current cycle of flooding occurred in places that have not been flood-prone in recent years. This indicates that environmental factors unique to each locality are responsible for the floods.

What are the advantages of floods in the northeast?

Every year, the Brahmaputra and its tributaries transport billions of tonnes of sediment, mainly from the Eastern Himalayas. This raised the lowlands and regularly adjusted river beds.

Floods cause disruption and damage but they also generate a bounty of fish and rejuvenate flood-plain ecosystems all along the Brahmaputra, including in the Kaziranga.

The entire Assam landscape has been shaped over millions of years with the help of an active monsoonal environment and mighty rivers that carry sediments weathered from the still-rising Himalaya.

What are the environmental factors responsible for increased Assam floods?

Two coupled ocean-atmosphere phenomena combined to create high rainfall in the Bay of Bengal. a) La Niña in the Pacific, and b) A negative dipole condition in the tropical Indian Ocean.

To add to that, a warmer atmosphere because of climate change can hold more moisture leading to intense bouts of rain.

All this made Parts of the Northeast to experience a month-and-a-half of rains in 10-12 days. But there is no standard pattern for the recurrence of mega, unpredictable floods. In the last century, they occurred in 1934, 1950, 1954, 1955, 1966, 1988 and 2004.

How human footprint intensified floods in the northeast?

From an estimated 11,000 people in 1901, Guwahati now is home to close to 1.1 million people. Almost all cities witnessed an increase in population. As the human footprint intensified on the floodplains, the landscape was increasingly “developed and engineered”.

The engineered and planned landscape has affected the floodplains in two ways: 1) It has undermined their ability to store and absorb water and 2) Reduced floodplain capacity to transport sediment.

Human interventions to “tame” rivers and “stabilise” hydrologically dynamic landscapes and riverscapes by building dams and reservoirs. But the operation of dams and reservoirs has also devastated the floodplains.

What should be done?

Northeast India has fragile geology, changing rainfall patterns, and high seismicity and also face the risk of landslides. Along with the rapid transformation in rainfall characteristics and flooding patterns demands building people’s resilience.

Construction projects that impede the movement of water and sediment across the floodplain must be reconsidered.

Climate-imposed exigencies demand new paradigms of early-warning and response systems and securing livelihoods and economies in the northeast.