Guwahati: It is one of the biggest paradoxes of this year’s monsoon in Assam. While devastating floods claimed lives, displaced thousands and inundated vast stretches of the state, official rainfall data tells a seemingly contradictory story: Assam has actually received significantly less rainfall than normal this season.
According to the India Meteorological Department’s (IMD) district rainfall data for the period from June 1 to July 29, Assam received 594.4 mm of rainfall against a normal of 839.6 mm—a 29% deficit that places the state in the ‘Deficient’ rainfall category.
So how did a state with below-normal rainfall experience one of its most destructive flood spells?
The answer lies not only in the rain that fell over Assam but also in what happened hundreds of kilometres upstream across the vast Brahmaputra river basin.
Unlike many parts of India, Assam’s rivers are fed by catchments spread across Arunachal Pradesh, Nagaland, Bhutan and the Tibetan plateau.
Heavy rainfall over these upstream regions rapidly swells the Brahmaputra and its tributaries before the water flows downstream into the Assam plains. As a result, flood risk in Assam is often determined by rainfall across the entire basin rather than within the state alone.
This year’s monsoon provided a textbook example of that phenomenon. Repeated spells of intense rainfall and cloudbursts over Arunachal Pradesh and Nagaland caused rivers to rise sharply, sending large volumes of water into Upper Assam and inundating districts even as many parts of the state continued to register below-average seasonal rainfall.
The scale of the disaster was evident during the visit of the Inter-Ministerial Central Team (IMCT), which toured the worst-affected districts before meeting senior Assam government officials.
During the briefing, the state government described the floods as “totally unprecedented”, noting that Sivasagar and Charaideo have historically never been flood-prone districts.
Officials told the team that the disaster was triggered by exceptionally heavy rainfall in Nagaland on July 19, when the state recorded 181% above-normal rainfall. The rainfall was particularly intense in Mokokchung (493% above normal), followed by Wokha (108%) and Mon (45%).
Combined with localised extremely heavy rainfall in Charaideo and Sivasagar, the runoff led to widespread inundation across the affected districts.
Meteorologists point out that seasonal rainfall totals and flood risk are not always directly linked. The IMD’s rainfall figures represent cumulative rainfall over nearly two months and do not show how rainfall was distributed over time. A few days of exceptionally heavy rain concentrated over river catchments can trigger severe flooding even if the overall seasonal rainfall remains below normal.
But researchers say rainfall alone does not explain the scale of the destruction.
Dr Mirza Zulfiqur Rahman, a researcher on the Brahmaputra river basin, argues that decades of unplanned infrastructure development on Assam’s floodplains have made extreme rainfall events far more damaging.
“The infrastructural layering on the floodplain has increased over the years. We saw it many years ago in Kaziranga, and now here. The planning has not been there to map out the drainage of the floodplain. Infrastructure has disrupted the area’s settled drainage, and populations are totally unprepared for such a high incidence of rainfall. The infrastructure accentuates and amplifies the disaster manifold.”
Rahman said the recurring pattern reflects a failure to invest in scientific understanding of the Brahmaputra floodplain.
“We simply wait for the next disaster to happen because the government seems to have enough resources for disaster compensation, but seems inept at allocating necessary resources for proper scientific study of the floodplains we live in, to assess how our infrastructure interventions have seriously jeopardised the natural drainage of the Assam floodplains.”
His observations reinforce concerns that embankment breaches, sedimentation of river channels and blocked natural drainage have reduced the rivers’ capacity to carry excess water during periods of intense rainfall.
The district-wise rainfall pattern further illustrates the contrast. Only Charaideo recorded excess rainfall during the period, while Cachar, Dhemaji, Dibrugarh, Kokrajhar, Lakhimpur, Majuli, Sribhumi, Tamulpur, Tinsukia and West Karbi Anglong received normal rainfall.
Most of Assam’s remaining districts fell into the Deficient or Large Deficient categories, highlighting that the floods were not the result of widespread above-normal rainfall across the state.
Scientists have also increasingly observed that a warming climate is associated with more frequent episodes of short-duration, high-intensity rainfall across the Himalayan and Northeast region. While no single flood event can be attributed to climate change alone, such intense rainfall episodes are making flood forecasting and disaster management more challenging.
Rahman believes the solution also lies in rethinking development across the entire Brahmaputra basin rather than treating floods as isolated state-level events.
“In the name of economic connectivity, we are damaging our ecological connectivity, and the result is huge economic loss and suffering to people and non-humans alike.”
He advocates what he describes as a “bioregional governance” approach for the Brahmaputra, arguing that river management must transcend administrative boundaries because the basin functions as a single ecological system.
The paradox assumes renewed significance as the IMD has forecast another spell of heavy to very heavy rainfall over parts of Arunachal Pradesh and Nagaland, with authorities warning that runoff from these upstream catchments could once again affect districts in Upper Assam.
The 2026 monsoon offers an important lesson for disaster managers and policymakers: seasonal rainfall totals alone do not determine flood risk. In a river system as vast and interconnected as the Brahmaputra, the timing, intensity and location of rainfall often matter far more than the cumulative seasonal average.
The unprecedented flooding in Sivasagar and Charaideo—districts long regarded as outside Assam’s traditional flood belt—shows that flood preparedness can no longer rely solely on historical flood patterns.
As Rahman argues, effective flood management will require both basin-wide weather monitoring and a deeper scientific understanding of how infrastructure, floodplains and upstream landscapes interact across the Brahmaputra basin.
Also Read: Question from Manipur: How does the government view ‘Village Volunteers?’
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