GUWAHATI, Aug. 25 -- Debiram Panika was at work in a nearby town when the Dikhow River tore through his village in Assam's Sivasagar district last month. When he returned, his wife Dipika and their four-year-old daughter Radhika were gone. His surviving daughter made it through only by clinging to a bamboo bush as the surge swept everything else away.

Panika's account, documented in a ground report, is one of more than 700,000 displacement stories produced by floods that have left at least 100 dead, some 1.2 million people directly affected, and 2,700 villages across Upper Assam in ruins. The disaster began when heavy rainfall struck the Naga Hills of Nagaland on July 18 and 19, sending water crashing through a river system that, researc...