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Why Assam floods: The obvious answer is Brahmaputra, but there's so much more to it
The floodwaters spreading across Assam this week have killed almost a dozen people, displaced over 3.63 lakh and inundated 15 districts.
The floodwaters spreading across Assam this week have killed almost a dozen people, displaced over 3.63 lakh and inundated 15 districts from Sivasagar to Tinsukia.
The Army joined the National Disaster Response Force (NDRF), State Disaster Response Force (SDRF) and fire and emergency services in relief operations in upper Assam as the Brahmaputra and its tributaries remained above danger levels.
The Assam State Disaster Management Authority (ASDMA) put the official death toll at 10. Sivasagar was the worst-affected district, with nearly 1.58 lakh people displaced.
Rail services were disrupted, with floodwaters inundating tracks and forcing trains to be diverted, cancelled or short-terminated. Tea gardens too have been submerged, crops damaged and landslides reported near Guwahati.
But this is not an uncommon crisis in Assam. Nearly 40% of the state is flood-prone, according to the Rashtriya Barh Ayog, (the National Flood Commission established by the Government in 1976).
Annual floods have struck the state for decades, with particularly severe disasters in 2018, 2020, 2021, 2022 and 2024. The question of why requires looking not just at the rain, but at the river and Assam’s topography.
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A river that floods
Assam sits in the floodplain of the Brahmaputra, one of the world’s largest rivers that carries vast amounts of sediment.
The river begins on the Tibetan plateau, flows through Arunachal Pradesh and Assam, and is joined by more than 50 tributaries before eventually reaching the Bay of Bengal. Every monsoon, enormous volumes of water arrive from rainfall, Himalayan snowmelt and those tributaries cascading down from the hills.
According to the Assam government, Brahmaputra’s average annual discharge is about 20,000 cumec. For reference, one cumec is roughly equal to 1,000 litres of water flowing per second.
Geography makes flooding easy here, but experts say rainfall is only one part of the story. The scale and frequency of flooding in Assam is also shaped by what has been done, and not done, over many decades.
A river slowed by its own sediment
Dhrubajyoti Sahariah, a geography professor and floodplain researcher at Gauhati University, told HT the fundamental problem is the speed and load of water being carried by the river.
After Pasighat, the river’s slope flattens all the way to Dhubri. As the water slows, it loses the energy to carry the sediment it has picked up in the mountains.
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“It’s one of the highest sediment-carrying rivers in the world,” Sahariah said.
The result is that enormous quantities of sand and silt are deposited across the floodplain each year. Sahariah said the volume of sediment now coming down from the hills is increasing, and this wasn’t just a natural trend.
Deforestation steering the problem
A key reason for increasing sedimentation, which increases the risks of landslides, is severe deforestation, Sahariah said.
Districts such as Lakhimpur, Biswanath and Dhemaji are particularly vulnerable, drained by rivers including the Siang, Jiadhal, Subansiri, Ranganadi and Dikrong, which flow from the hills composed of loose, sandy material that is inherently prone to erosion and landslides.
“A slight rain, high rain can trigger excessive landslide, excessive soil erosion. But it has increased due to deforestation,” he told HT.
Sahariah believes flood management has focused too heavily in downstream areas — on embankments and structural interventions. “Contrary to working on the downstream, we should work on upstream, especially in the soil conservation measure,” he said.
He also pointed to reports of illegally cut logs accumulating in dam reservoirs as evidence of the scale of deforestation in the hills.estation upstream.
Why Assam gets so much rain
Assam’s location makes it one of India’s naturally wettest regions, where the monsoon arrives with considerable force.
Assam is among India's wettest states, receiving an average annual rainfall of around 2,800-3,000 mm, with nearly 70% of it falling during the southwest monsoon (June-September). While states such as Goa, Meghalaya, Sikkim and Arunachal Pradesh typically receive higher annual rainfall, Assam consistently ranks among the country's top five to seven rainiest states, as per the India Meteorological Department (IMD).
“Monsoon rainfall in Assam is due to the combined influence of moisture incursion from the Bay of Bengal due to south-westerly winds at the lower levels of the atmosphere, favourable topography, active monsoon synoptic systems like cyclonic circulation, and presence of monsoon trough over the northeast region,” Sunit Das, senior scientist at the IMD, told HT.
Sahariah also pointed out that in the longer term, climate crisis was affecting the intensity of rain, and consequently, the intensity of flooding too.
What climate change is doing, he said, is amplifying the peaks. “The flood peaks... are higher... greater devastation and extreme events are on the rise,” he said.
70 years of embankments
Assam has responded to annual flooding primarily by building embankments. According to the Rashtriya Barh Ayog, since the 1950s, the state has constructed 423 embankments along the Brahmaputra and its tributaries. Approximately 295 have already exceeded their intended lifespan — making breaches increasingly common and the infrastructure increasingly unreliable.
Sahariah said this approach has a deeper limitation: the Brahmaputra is an avulsive river, one that keeps shifting its course. No embankment can hold a river that decides to flow somewhere else entirely.
“The Brahmaputra floodplain is a very young floodplain and it’s still not stable and very avulsive in nature. So, this type of direct structural measures may not always be feasible,” he said.
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The toll accumulated over these decades of embankment-building reflects their limits. According to ASDMA data, at least 838 people died in Assam floods between 2013 and 2022, with 2022 recording 181 deaths — the highest in a decade.
Data from the Asian Disaster Reduction Centre (ADRC), an international organisation that pushes for disaster resilience, said that the average number of people affected from flooding in Assam annually rose from around 8.6 lakh in the 1950s to over 45 lakh by the early 2000s. Economic losses in this time-frame increased over 120-fold.
What would help
Sahariah advocates a basin-wide approach — managing the Brahmaputra as an integrated river system rather than responding to isolated points of flooding. But he argued that the shift must be behavioural as much as structural.
“We need to train the dwellers to how to live with the floods,” he said, pointing to the state’s Mising community, who have traditionally built homes designed for life on the floodplain.
“Somehow we are moving away from this traditional technology. We are adopting new house buildings or probably building homes in the floodplain itself, but without adopting the traditional floodplain measures,” he said.
When the water recedes
The destruction comes to fore when floodwaters withdraw. In Dhemaji, the Dikhari River changed course entirely in the latest floods, cutting through a settlement and destroying homes, farmland and public infrastructure. A railway bridge too collapsed in the region.
In the Lohit Khabolu area, villagers constructed a bamboo bridge themselves after damaged crossings left communities cut off from schools and hospitals.
“We have lost everything," one villager told local outlet Northeast Now. “Our house, belongings and farmland have all been destroyed. We are now living in a temporary shelter built on raised bamboo platforms and surviving on the relief provided by the government.”
“The river never flowed through this part of the village earlier,” said another. “After changing its course, it swept away houses and cattle.”
For communities like theirs, the floods are not a seasonal interruption. They are a permanent rearrangement.
What the government has done
The Assam government has activated the Assam State Disaster Management Authority (ASDMA), with the National Disaster Response Force (NDRF), State Disaster Response Force (SDRF), Army and local administration carrying out rescue and evacuation operations across the worst-hit districts.
Relief camps and distribution centres have been opened, while food, drinking water, medicines and other essential supplies are being distributed to affected families, as per PTI. State ministers have also been deputed to flood-hit districts to monitor relief operations, assess damage and coordinate rehabilitation efforts.
Union home minister Amit Shah has spoke to chief minister Himanta Biswa Sarma on June 29 about flood-related assistance.
Long-term measures
The Assam government says it is shifting from a relief-based approach to long-term flood mitigation. On July 15, Himanta Biswa Sarma announced a ₹150-crore flood mitigation project for Jorabat, to be implemented as part of the proposed Guwahati Ring Road, The Assam Tribune reported. It was aimed at providing a permanent solution to recurring flash floods in the area.
Assam's Water Resources Department follows a three-tier flood management strategy comprising immediate, short-term and long-term measures. These include construction and strengthening of embankments, anti-erosion works, drainage improvement, river training and integrated flood management projects, alongside improved forecasting and disaster preparedness, government data says.
