Western disturbance linked to Nepal flood

What happened: rainfall build-up and a possible river blockage followed by sudden release

Nepal’s flash flood explanation in the account combines meteorological factors with a terrain-based mechanism. A senior India Meteorological Department official said a western disturbance moving eastward toward the Himalayas may have contributed to pre-flood weather conditions, but the available information is not sufficient to establish whether a cloudburst occurred or whether the western disturbance was a confirmed direct trigger.

Nepal is investigating whether an earthquake triggered an avalanche or landslide that blocked a river and then released water suddenly downstream. A preliminary assessment described in the account suggests an ice avalanche may have blocked the river, allowing water to accumulate before a sudden downstream release. The immediate mechanism behind the sudden water release remains under investigation.

Background: about 10 days of persistent rainfall and upstream precipitation effects

A World Meteorological Centre (Beijing) cited in the account describes persistent rainfall affecting Nepal’s southern Himalayan foothills. Nepal experienced persistent rainfall for about 10 days. Accumulated rainfall between August 16 and 25 reached heavy to intense levels at some locations.

The same World Meteorological Centre information cited in the account also points to moderate-to-heavy rain and localised intense downpours in southern Tibet upstream. The combination of local and upstream rainfall is treated as a contributor to flash flooding and debris flows in northern Nepal.