Context

This year’s floods in Assam have been merciless. In many parts of the state, both rural and urban, shoals of water drove people from their homes and forced many of them to seek shelter for their livestock.

Understanding the reasons for massive flood in Assam this year

• The Bay has a major influence on the monsoon in Northeast India.
• Two coupled ocean-atmosphere phenomena, one from the distant Pacific, La Niña and another in the tropical Indian Ocean, a negative dipole condition, combined to create high rainfall in the Bay of Bengal.
• To add to that, a warmer atmosphere because of climate change can hold more moisture leading to intense bouts of rain.
• Apart from embankment failures, a number of unofficial and media reports suggest that the devastation in the floodplains is also a consequence of the way the dams and reservoirs are operated.
• This indicates that environmental factors unique to each locality are responsible for the floods.
• The flooding pattern is usually repeated year-to-year. However, at times, this pattern is disturbed — this year for example.
• The incidence of such megafloods depends on several variables like unusually high rainfall and the failure of critical embankments.

Role of floods in the making of the floodplain environment and ecology

• Rejuvenation of ecosystem: 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.
• Landscape: This 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.
• Every year, the Brahmaputra and its tributaries — which are at the centre of Assam’s environment — transport billions of tonnes of sediment, mainly from the Eastern Himalaya, making the landscape volatile.
• Flooding helps release waters to surrounding land and distribute sediments and nutrients across the floodplains and wetlands.

How human presence has influenced floodplains

• 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: It has undermined their ability to store and absorb water and reduced their capacity to transport sediment.
• Urban floods: This year’s floods took an especially worrying proportion in several urban areas.
• Guwahati has historically been a lowland and the city has been uniquely shaped by three hills that accumulate water during the monsoon.
• Its northern side faces one of the most turbulent rivers in the world.
• However, extensive swamps, channels and their tributaries worked in tandem to make the place habitable.
• A transformation, however, took place in the 20th century, especially in the later decades, when these natural features were forced to disappear.
• From an estimated 11,000 people in 1901, the city now is home to close to 1.1 million people.
• Such a population increase is bound to have several footfalls and not all of them could have been prevented.
• What has hit the city hardest is the disappearance of some of its critical environmental features.

Way forward

• Human interventions such as dams to “tame” rivers and “stabilise” hydrologically dynamic landscapes and riverscapes should be based on guidelines that account for the environmental conditions in Northeast India, especially the fragile geology, changing rainfall patterns, high seismicity and the risk of landslides.
• Resilience of people: The rapid transformation in rainfall characteristics and flooding patterns demand building people’s resilience.
• Reconsider projects: Construction projects that impede the movement of water and sediment across the floodplain must be reconsidered.
• Use of technology: At the same time, climate-imposed exigencies demand new paradigms of early-warning and response systems and securing livelihoods and economies.

Conclusion

Floods have played a key role in Assam’s ecology. But increasing human footprint has affected the ability of flood plains to absorb water and transport sediment.

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