Assam floods worsen as Himalayan warming, monsoon shifts combine

Floods in Assam are hitting harder and arriving with less warning as a tangle of climate-driven factors – Himalayan snowmelt, back-to-back Bay of Bengal weather systems, and sprawling human settlements – combine in ways that older flood models never captured, according to a new analysis.

Climate Trends, a Delhi-based climate research organisation, released the analysis Friday. It identifies the state's unique geography as the baseline: about 40 percent of Assam's land is flood-prone, with the Brahmaputra's ever-shifting course constantly eroding banks and redrawing floodplains. But the analysis said recent changes have made the situation worse.

One trigger this year has been a persistent series of monsoon systems over the Bay of Bengal during July. Mahesh Palawat, vice president for meteorology and climate change at Skymet Weather, said in a statement that back-to-back systems kept feeding moisture into the northeastern states, maintaining conditions favourable for rainfall and sometimes triggering cloudbursts.

Warmer air holds more water vapour – about 7 percent more for every 1°C rise in average temperature, studies show. That raises the intensity, duration and frequency of precipitation. When a high-intensity rainfall event hits, it creates bigger flood peaks and keeps water standing longer, the analysis said.

Warming has also accelerated snow and glacier melt in the eastern Himalayas, swelling the Brahmaputra and its tributaries. Human interventions – deforestation, urbanisation, unplanned land-use changes – reduce natural water retention and increase runoff, the analysis added.