Explained | What is a cloudburst?

Cloudburst may be accompanied with hail and thunder

An intense downpour hit Baltal base camp of Shri Amarnath Yatra in central Kashmir's Ganderbal district on July 8, claiming 16 lives and leaving several injured. Similar incidents happened at Bhadrachalam in Telangana as rains continued to batter India. Yesterday, Telangana Chief Minister K Chandrasekhar Rao claimed that cloudbursts in some parts of India are the result of a conspiracy by some countries.

While the IMD later clarified that the highly localised rains in Jammu and Kashmir were not a result of a cloudburst, let us understand what exactly is this natural phenomenon.

Also Read | Amarnath Cloudburst: IAF deploys eight helicopters

What is cloudburst?

A cloudburst is an extreme downpour in a short period of time. It may be accompanied with hail and thunder. According to the Indian Meteorological Department (IMD), an unexpected precipitation exceeding 100mm (or 10 cm) per hour over a geographical region of approximately 20 to 30 square km is a cloudburst.

Is a cloudburst different from rainfall?

Rain is condensed water falling from a cloud which may or may not be intense, however a cloudburst in a sudden heavy downpour. Rain over 100mm per hour is categorised as a cloudburst. Heavy rainfall can be classified as a cloudburst only if it fits this criteria set by the IMD. It is very difficult to predict the cloudbursts due to its very small scale in space and time. To monitor or nowcast (forecasting few hours lead time) the cloudburst, one needs dense radar network over the cloudburst-prone areas or a very high resolution weather forecasting models to resolve the scale of cloudburst.

How and where does a cloudburst occur?

Cloudbursts do occur at plains, however, mountainous regions are more prone to cloudbursts due to orography (the geographical features of a mountain). A cloudburst occurs when warm air current from the ground or below the clouds rushes up and carries the falling raindrops up with it. As a result, new raindrops that are formed are heavier and denser. After a point, the raindrops become too heavy for the cloud and it falls down together in a short period over a small area, causing a cloudburst.

What are some of the worst cloudbursts in India?

Great Musi flood, 1908: On 26 September, 1908, Hyderabad’s surrounding areas witnessed a cloudburst. It was caused due to a cyclone in the Bay of Bengal. The city had recorded 153.2 mm rainfall on 27 September, 1908.

Mumbai cloudburst, 2005: On 26 July, 2005, Mumbai received an astonishing 944 mm of rain in just 24 hours. It lead to a big chaos in the city.

Uttarakhand cloudburst, 2013: In 2013, Uttarakhand’s Kedarnath received unprecedented heavy rainfall between 14 and 17 June. The estimated toll was around 10,000, with over 3,000 persons missing, as per the state government.