What are cloudburst incidents and are they rising across India?

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Last Updated23/08/2022

Recently, 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 day.

India Meteorological Department: Cloudburst features very heavy rainfall over a localized area at a very high rate of the order of 10 cm per hour featuring strong winds and lightning over a geographical region of approximately 20 to 30 Sq Kms.
By this definition, 5 cm of rainfall in a half-hour period over the same area would also be categorized as a cloudburst.

India, as a whole, receives about 116 cm of rainfall over the entire year.
This means if the entire rainfall everywhere in India during a year was spread evenly over its area, the total accumulated water would be 116 cm high.
However, there is huge geographical variations in rainfall within the country, and some areas receive over 10 times more than that amount in a year.
For e.g. Cherrapunji and Mawsynram in the Khasi Hills (Meghalaya) receive rainfall over 1080 cm in a year while Jaisalmer (Rajasthan) rarely gets more than 9 cm of rainfall during the same period

Cloudbursts are not uncommon events, particularly during the monsoon months.
Most of these happen in the Himalayan states where the local topology, wind systems, and temperature gradients between the lower and upper atmosphere facilitate the occurrence of such events.
However, not every event that is described as a cloudburst is actually, by definition, a cloudburst. That is because these events are highly localized.
They take place in very small areas which are often devoid of rainfall measuring instruments. The consequences of these events, however, are not confined to the small areas.
Because of the nature of terrain, the heavy rainfall events often trigger landslides and flash floods, causing extensive destruction downstream.
This is the reason why every sudden downpour that leads to destruction of life and property in the hilly areas gets described as a “cloudburst”, irrespective of whether the amount of rainfall meets the defining criteria

IMD forecasts rainfall events well in advance, but it does not predict the quantum of rainfall — in fact, no meteorological agency does.
The forecasts can be about light, heavy, or very heavy rainfall, but weather scientists do not have the capability to predict exactly how much rain is likely to fall at any given place.
Therefore, specific cloudburst events cannot be forecast. No forecast ever mentions a possibility of a cloudburst. But there are warnings for heavy to very heavy rainfall events, and these are routinely forecast four to five days in advance.

As per the IMD, there is no long-term trend that suggests that cloudbursts are rising.
However, the incidents of extreme rainfall, as also other extreme weather events, are increasing, not just in India but across the world.
While the overall amount of rainfall in India has not changed substantially, there is an increasing proportion of rainfall in a short span of time.
That means that the wet spells are very wet, and are interspersed with prolonged dry spells even in the rainy season.