scorecardresearch
Follow Us:
Friday, August 12, 2022

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

Arupjyoti Saikia and Jagdish Krishnaswamy write: 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

Written by Arupjyoti Saikia , Jagdish Krishnaswamy |
Updated: July 28, 2022 2:21:13 pm
The incidence of such megafloods depends on several variables like unusually high rainfall and the failure of critical embankments. (Express/Tora Agarwala)

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. In many places, people failed to save standing crops. Granaries were damaged and mud houses were filled with sand brought by the rivers in spate. The retreating waters — before the onset of another flood cycle — could leave behind more wreckage. Ironically, however, they also offer hope for the depleted soil.

The story of this year’s floods starts in the Bay of Bengal. As we know, 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. Weeks before the usual monsoon season, rains had already drenched the basin. To add to that, a warmer atmosphere because of climate change can hold more moisture leading to intense bouts of rain. Parts of the Northeast experienced a month-and-a-half of rains in 10-12 days.

This is just one cycle of the annual floods — more are likely to come this month and in August, perhaps later as well. There are lessons to learn from the current cycle of flooding, which 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.

Assam is hit by several rounds of floods every year. The lowlands and riverine areas bear the brunt of the deluge. The flooding pattern is usually repeated year-to-year. However, at times, this pattern is disturbed — this year for example. Such massive floods are also not unusual in Assam. But there is no standard pattern to the recurrence of mega, unpredictable floods. In the last century, they occurred in 1934, 1950, 1954, 1955, 1966, 1988 and 2004 – this list is by no means exhaustive.

Subscriber Only Stories
UPSC Key-August 10, 11, and August 12, 2022: Why you should read ‘Euthana...Premium
What is border post 918 which provides shade to both India and Pakistan?Premium
Ravi Shankar Prasad: ‘(Nitish) is nothing on his own… He may be honest bu...Premium
Explained: Baloch separatism and the coercive accession of the Khanate of...Premium

The incidence of such megafloods depends on several variables like unusually high rainfall and the failure of critical embankments. Besides the toll they take, such floods can adversely reconfigure the landscape.

How, then, do we make sense of these floods? We should begin by appreciating the key role of floods in the making of the floodplain environment and ecology of Assam. 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. 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.

The rivers and their surrounding hydrological landscapes interact in several ways and produce many effects. River bank erosion is one of them. Floods are among the mediators of these interactions. Flooding helps release waters to surrounding land and distribute sediments and nutrients across the floodplains and wetlands. Over millions of years, this depositing of sediment into the floodplains has produced at least two results: Raising the lowlands and regularly adjusting river beds. These ensured that impacts of flooding remained moderate. Such processes have been going on for centuries but certain historical circumstances, especially their low intensity on the floodplains, allowed humans to adapt to nature’s quirks. The prosperity and general well-being of a large majority of the population of Assam, especially in rural areas, critically depend on their ability to survive the capricious ways of floods. The annual floods were a natural way to enrich the soils, which have a propensity to get depleted.

Advertisement

Things began to change rather drastically in the 20th century. 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.

This year’s floods took an especially worrying proportion in several urban areas. Silchar in southern Assam and Guwahati were badly hit. 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. Today, like Guwahati, Assam’s floodplains and the people living there are even more vulnerable to severe flooding because of climate change.

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. Such human interventions 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. This, however, has not happened.

Advertisement

The rapid transformation in rainfall characteristics and flooding patterns demand building people’s resilience. A business-as-usual vision of infrastructure development will not help achieve this. Construction projects that impede the movement of water and sediment across the floodplain must be reconsidered. The region’s historical experiences offer several valuable lessons in adaptation to floods. At the same time, climate-imposed exigencies demand new paradigms of early-warning and response systems and securing livelihoods and economies.

Saikia is a Guwahati based environmental historian and Jagdish Krishnaswamy is a hydrologist and ecologist with the Indian Institute for Human Settlements, Bengaluru

📣 Join our Telegram channel (The Indian Express) for the latest news and updates

For all the latest Opinion News, download Indian Express App.

  • Newsguard
  • The Indian Express website has been rated GREEN for its credibility and trustworthiness by Newsguard, a global service that rates news sources for their journalistic standards.
  • Newsguard
First published on: 05-07-2022 at 06:38:31 pm
0 Comment(s) *
* The moderation of comments is automated and not cleared manually by indianexpress.com.

Featured Stories

Advertisement
Advertisement
Advertisement
Advertisement