Guwahati: The devastating floods that affected Assam and neighbouring states in 2026 were worsened by rapid urbanisation, deforestation, land degradation and other local vulnerabilities, while the rainfall itself remained within historical norms, according to a new attribution study by World Weather Attribution (WWA).
The study found no clear evidence that human-caused climate change had altered the intensity or likelihood of the heavy monsoonal rainfall linked to the floods. However, the researchers cautioned that limited weather data and difficulties in modelling rainfall in hilly areas created some uncertainty around the findings.
At least 99 people were killed, hundreds of thousands were displaced and around 45,000 hectares of cropland were inundated during the floods, according to the study. Between late June and early August, Upper Assam districts including Sivasagar, Charaideo and Jorhat, along with hill catchments in Nagaland and Arunachal Pradesh, experienced heavy monsoonal rainfall.
The resulting floods and landslides damaged infrastructure, agricultural land and livelihoods and forced large numbers of people into relief camps.
Scientists from India, Sweden, the Netherlands, the United Kingdom and the United States analysed historical weather records and climate models as part of the study. They found that the heaviest three-day and 30-day rainfall totals associated with the floods were events expected roughly once every one to two years.
The researchers said environmental degradation had increased the impact of the rainfall. Rapid urbanisation, deforestation, wetland destruction and riverbank erosion have reduced natural drainage capacity, increasing flood levels and downstream impacts.
The study also raised concerns over the reliance on concrete infrastructure and hard embankments. According to the researchers, embankments can trap silt, raise riverbeds and block natural drainage, increasing the risk of flooding and catastrophic breaches.
The researchers said flood management should combine physical infrastructure with social and nature-based measures. They recommended restoring floodplains, conserving wetlands and expanding anticipatory disaster risk management through localised early warning systems.
The study also linked some existing vulnerabilities to historical land-use patterns. It said past land reallocation had contributed to some indigenous communities living on marginal and flood-prone riverbanks and sandbars, known locally as chars. These patterns have left many low-income agricultural families vulnerable to repeated displacement.
Mariam Zachariah, a research associate in extreme weather and climate change at the Centre for Environmental Policy, Imperial College London, said the analysis found no discernible role of climate change in the rainfall linked to the floods, while cautioning that the region remains vulnerable to future warming.
Emmanuel Raju, director of the Copenhagen Centre for Disaster Research at the University of Copenhagen, said low-income agricultural families and displaced communities had been among those most affected.
He called for a shift towards flood management approaches that work with natural river systems, including wetland restoration and early action.
Friederike Otto, professor of climate science at the Centre for Environmental Policy, Imperial College London, said the findings showed that not every disaster should be attributed to climate change.
She said sustainable land management, ecosystem protection and better management of exposure to disaster risks were also important for building resilience.
The study said climate change could continue to alter monsoon patterns across South Asia as global temperatures rise, making proactive management of land and rivers increasingly important.