Western Disturbance
Prelims:
Geography
Mains:
GS Paper I –
Important Geophysical Phenomena, GS Paper III – Disaster and Disaster
Management
Current relevance:
A
devastating flash flood in Nepal may have resulted from persistent
Himalayan rainfall influenced by a western disturbance.
Highlights:
About Nepal flood:
1.
Nepal
experienced persistent rainfall for around 10 days along the southern
Himalayan foothills.
2.
The
combination of local rainfall and upstream rainfall contributed to the
flash flood and associated debris flows in northern Nepal.
Causes of the Flash Flood:
1.
Preliminary
information suggests that an earthquake occurred shortly before the flash
flood in the affected region.
2.
The
earthquake is being investigated as a possible trigger for an avalanche or
landslide.
3.
It indicates
that an ice avalanche may have temporarily blocked the river, leading to
the accumulation of water upstream.
4.
The
sudden breach of this temporary blockage may have released the
accumulated water rapidly, producing a flash flood and debris flows
downstream.
Western Disturbance:
1.
The
western disturbance initially produced rainfall over parts of northern
India and subsequently moved eastwards towards the Himalayas.
2.
Its
eastward movement was associated with increased rainfall activity towards
the Northeast and Himalayan region.
3.
The
interaction of the weather systems with hilly terrain may have
contributed to the conditions preceding the flood.
4.
The
western disturbance persisted as a cyclonic circulation over north Haryana.
5.
However,
the western disturbance should be treated only as a possible contributor to
the broader rainfall environment, rather than an established direct cause
of the flash flood.
Key Geographical &
Disaster-Management:
1.
Multiple
hazards can interact:
Himalayan floods may result from the combined effects of rainfall,
earthquakes, landslides, avalanches and temporary river blockages rather
than a single trigger.
2.
Upstream-downstream
linkage: Rainfall in southern
Tibet can influence downstream flood conditions in Nepal, highlighting the
transboundary nature of Himalayan River hazards.
3.
Cloudburst
not established:
Available information was insufficient to conclude that a cloudburst had
occurred; rainfall measurements from Nepal would be required to establish
exceptionally intense precipitation.
4.
Transboundary
cooperation: India
and Nepal have mechanisms for sharing hydrological and weather-forecast
information, which are relevant for managing cross-border Himalayan
hazards.
Source: THE HINDU - https://www.thehindu.com/sci-tech/energy-and-environment/western-disturbance-linked-to-nepal-floods/article71393352.ece