Nepal's devastating floods, which have killed more than 1,000 people, highlight a risk that extends beyond its borders into India, as the two countries share a vast and volatile network of Himalayan rivers. Experts say the link between flooding in Nepal and disaster in India is not straightforward, since it depends not only on rainfall in Nepal but also on conditions on the Indian side, including river levels, embankments, drainage and development.

Nepal has more than 6,000 rivers and streams, most flowing south into India and the Ganges, with the Kosi, Gandaki and Karnali among the major systems. Seven to nine major rivers cross into the Indian plains, with Bihar the worst affected state, as roughly three-quarters of north Bihar is officially flood-prone; eastern Uttar Pradesh is also significantly at risk but often overlooked, hydrologists say. Specialists describe flooding as a three-part chain: rainfall, often concentrated in the lower Siwaliks and Chure hills rather than the high Himalayas, determines the peak flow reaching the border, while conditions in India determine the severity of the resulting disaster, as illustrated by the catastrophic 2008 Kosi embankment failure.