India, Aug. 14 -- Under a pewter sky, Mintu Devi is hurrying back home. Charcoal-edged clouds are starting to give way to clots of darkness. In her village of Khak Maksudpur in Bihar's Gopalganj district, this is a warning. Near the horizon, the greys still soften into a faint wash of silver-blue and the river is mellow. But once the ochre hue dissolves, the Gandak river will rage.

This village - one of hundreds located in sandy riverine islands that flood with alarming regularity - once boasted of more than 1,000 residents. "But now, only 350 are left. Those of us who cannot go anywhere," said Mintu, an anganwadi worker. Villages get marooned during the monsoon, often during high tide at night, forcing the able-bodied to scurry to the e...