Arupjyoti Saikia and Jagdish Krishnaswamy write

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This year floods in Assam were ruthless. In many parts of the state, both rural and urban, shoals have driven people from their homes and forced many to seek shelter for their livestock. In many places people have failed to save standing crops. Granaries were damaged and mud houses were filled with sand brought in by flooding rivers. The receding waters – before the start of another flood cycle – could leave more wreckage behind. Ironically, however, they also offer hope for depleted soil.

The story of this year’s floods begins 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 the other from the tropical Indian Ocean, a negative dipole condition, have combined to create heavy rainfall in the Bay of Bengal. Weeks before the usual monsoon season, the rains had already flooded the basin. To add to this, a warmer atmosphere due to climate change can retain more moisture, leading to intense rain events. Parts of the northeast saw a month and a half of rain in 10 to 12 days.

This is just one cycle of annual floods – more are likely to occur this month and in August, possibly later as well. There are lessons to be learned from the current cycle of floods, which have occurred in places that have not been prone to flooding in recent years. This indicates that local environmental factors are responsible for flooding.

Assam is hit by several rounds of floods every year. The lowlands and river areas bear the brunt of the flood. The flood pattern usually repeats itself from year to year. However, sometimes this pattern is disturbed – this year for example. Such massive floods are also not unusual in Assam. But there is no standard model for the recurrence of unpredictable mega floods. In the last century they occurred in 1934, 1950, 1954, 1955, 1966, 1988 and 2004 – this list is by no means exhaustive.

The incidence of these mega-floods depends on several variables such as exceptionally high rainfall and the failure of critical embankments. In addition to the toll they take, such floods can negatively reconfigure the landscape.

How, then, do we make sense of these floods? We should start by appreciating the key role of floods in shaping the environment and ecology of the floodplains of Assam. Floods cause disruption and damage, but they also generate an abundance of fish and rejuvenate floodplain ecosystems throughout the Brahmaputra, including Kaziranga. This landscape has been shaped over millions of years with the help of an active monsoon environment and mighty rivers that carry weathered sediments from the ever-rising Himalayas. Every year, the Brahmaputra and its tributaries – which are central to Assam’s environment – transport billions of tons of sediments, mainly from the Eastern Himalayas, making the landscape unstable.

Rivers and their surrounding hydrological landscapes interact in many ways and produce many effects. Shoreline erosion is one of them. Floods are among the mediators of these interactions. Floods help release water to surrounding lands and distribute sediments and nutrients to floodplains and wetlands. For millions of years, this deposition of sediments in the floodplains produced at least two results: raising the lowlands and regularly adjusting the beds of the rivers. These helped to keep the impacts of the floods at a moderate level. Such processes have been going on for centuries but certain historical circumstances, notably their low intensity on floodplains, have allowed humans to adapt to the vagaries of nature. The prosperity and general well-being of a large majority of Assam’s population, especially in rural areas, critically depends on their ability to survive the vagaries of flooding. The annual floods were a natural means of enriching the soils, which tend to become impoverished.

Things started to change quite drastically in the 20th century. As the human footprint intensified on the floodplains, the landscape was increasingly “developed and landscaped”. The developed and planned landscape has affected floodplains in two ways: it has undermined their ability to store and absorb water and reduced their ability to transport sediment.

This year’s flooding has taken on particularly worrying proportions in several urban areas. Silchar in southern Assam and Guwahati have been badly affected. Guwahati has always been a plain and the city has been uniquely shaped by three hills which accumulate water during the monsoon. Its north side faces one of the most turbulent rivers in the world. However, extensive swamps, canals and their tributaries worked in tandem to make the place livable. A transformation, however, took place in the 20th century, particularly in later decades, when these natural features were forced to disappear. From approximately 11,000 inhabitants in 1901, the city now has nearly 1.1 million inhabitants. Such an increase in population will necessarily have several impacts and not all of them could have been avoided. What has hit the city hardest is the disappearance of some of its key environmental features. Today, like Guwahati, Assam’s floodplains and the people who live there are even more vulnerable to severe flooding due to climate change.

In addition to levee failures, a number of unofficial and media reports suggest that floodplain devastation is also a consequence of the way dams and reservoirs are operated. Such human interventions to “tame” rivers and “stabilize” hydrologically dynamic landscapes and river landscapes should be based on guidelines that take into account the environmental conditions in northeast India, especially the fragile geology. , the evolution of rainfall patterns, strong seismicity and the risk of landslides. This, however, did not happen.

Rapidly changing rainfall patterns and flooding patterns require building people’s resilience. A business as usual vision of infrastructure development will not help achieve this goal. Construction projects that impede the movement of water and sediment through the floodplain should be reconsidered. The region’s historical experiences offer several valuable lessons on flood adaptation. At the same time, climate-imposed demands require new paradigms of early warning and response systems and securing livelihoods and economies.

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

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