News: Over 20 people have been killed in destruction caused by cloudbursts and flash floods in different parts of Himachal Pradesh and Uttarakhand over the last three days.
GS Paper 1: Important Geophysical Phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc., geographical features and their location-changes in critical geographical features (including water-bodies and ice-caps) and in flora and fauna and the effects of such changes.
GS Paper 3: Disaster and Disaster Management.
What are cloudbursts?
- Phenomenon of short spells of very heavy rainfall over a small geographical area is known as cloudbursts. Cloudbursts are common in hilly regions.
- A cloudburst is a localized but intense rainfall activity. A place receives about 10% of annual rainfall within an hour in case of cloudbursts.
- Cloudbursts can cause widespread destruction
- However, not all instances of very heavy rainfall, are cloudbursts.
Which event can be described as a cloudburst?
- Definition of Cloudburst: Rainfall of 10 cm or more in an hour over a roughly 10 km x 10-km area is classified as a cloudburst event. By this definition, 5 cm of rainfall in a half- hour period over the same area would also be categorized as a cloudburst.
Cloudbursts are common during the monsoon months:
- Cloudbursts happen casually in Himalayan states due to the local topology, wind systems, and temperature gradients between the lower and upper atmosphere.
- Description of an event as cloudbursts is difficult as these events are highly localized and took place place in very small areas devoid of rainfall measuring instruments .
Consequences of cloudbursts are not confined to small areas:
- Cloudbursts cause extensive downstream destruction due to nature of terrain as heavy rainfall events trigger landslides and flash floods.
- This led to cloudburst as misnomer in the hilly areas irrespective of whether the amount of rainfall meets the defining criteria as every sudden downpour that leads to destruction of life and property is considered as cloudbursts.
- In most of the cases actual cloudburst events in remote locations aren’t recorded.
Can cloudbursts be forecast?
- Possibility of specific cloudburst events cannot be forecasted. But heavy to very heavy rainfall events are routinely forecasted four to five days in advance. Even, possibility of extremely heavy rainfall, that may result in cloudburst kind of situations, are forecast six to 12 hours in advance.
- No meteorological agency or weather scientists including India Meteorological Department(IMD) predict the quantum of rainfall i.e. how much rain is likely to fall at any given place but they can forecasts rainfall events in advance.
- Most of the forecasts are for a relatively large geographical area (region, a state, a meteorological sub-division, or district), and it is uncertain to forecast for smaller area.
- Current technologies are unfeasible to forecast rainfall over a very small area as it requires a very dense network of weather instruments, and computing capabilities.
Are cloudburst incidents increasing?
- There is no direct long-term trend suggesting that cloudbursts are rising.
- However, there is well established facts that incidents of extreme rainfall or weather events are increasing across the world.
- Incase of India, there is no substantial change in overall amount of rainfall but an increasing proportion of rainfall is happening in a short span of time meaning that the wet spells are very wet, and are interspersed with prolonged dry spells even in the rainy season, due to climate change suggesting that cloudburst events might also be on the rise.