Heavy rain, especially over a short time in hilly areas, is the main cause of dangerous floods in northeastern Bangladesh. Our research looked at how huge 'rivers in the sky' – long, narrow paths carrying massive amounts of water vapor high above the Earth – contribute to this extreme rainfall and flooding.These sky rivers often form over the Indian Ocean. When they hit mountains like those in India's Meghalaya state (located upstream from Bangladesh), they can dump enormous amounts of rain. This rain then flows down rivers into Bangladesh, causing floods.

We studied weather patterns during past floods. Our key finding was that a large, persistent sky river, gathering moisture from both the Bay of Bengal and the Arabian Sea, delivered record-breaking rain to Meghalaya in June 2022. This extreme rain quickly flowed down the rivers into Bangladesh's Sylhet region, causing severe flooding within just two days.

Understanding these 'sky rivers' is crucial because they are a major driver of the worst floods in this vulnerable region. Including sky river tracking in flood forecasts could give people in northeastern Bangladesh more time to prepare before future floods happen, especially as weather patterns change.