DNA Explainer: What are cloudbursts and why are they so dangerous?

A cloudburst in the Kangra district of Himachal Pradesh on Monday (July 12) caused flash floods in Dharamshala which swept away several cars and damaged many hotels and establishments.

Rivers in the region have been overflowing after extremely heavy rainfall. Both the Prime Minister and the Union Home Minister are closely monitoring the situation. Orange alert has been sounded in the area for the next five days with the met department prediction heavy to very heavy rainfall.

Cloudbursts and accompanying flash floods have become increasingly common in the Himalayan states of Himachal Pradesh and Uttarakhand in the 21^st Century. Since 1997, the two states combined have seen at least 14 major cloudburst incidents, including the catastrophic 2013 event that caused significant damage and unprecedented casualties near the Kedarnath shrine in Uttarakhand.

In the two states, cloudbursts and resulting flooding and landslide events are estimated to have claimed more than 6,000 casualties in the last two decades. Several cloudbursts happen each year and cause significant damage. As per South Asia Network of Dams, Rivers and People, there were at least 24 reported events in Uttarakhand this year from the beginning of May to June 3, 2021.

Apart from the two hill states, India has seen some more significant cloudbursts in the recent times, majorly in the UTs of Jammu and Kashmir and Leh as well as the state of Maharashtra.

What are cloudbursts and what causes them?

Cloudburst are sudden, extreme rainfall events happering in a very short duration of time. Cloudbursts dump momentous amounts of water over a highly localized region. The term comes from the idea that clouds become akin to balloons filled with water and burst all at once. While this idea has now been proved wrong, the term has carried on.

The phenomenon that causes Cloudbursts is called orographic lift. This means when a mass of air is forced to move up to a higher terrain from a low terrain. Adiabatic cooling can raise the relative humidity to 100 per cent, which can create clouds as well as very heavy rainfall. Some sudden condensation events which result from the mixing of a warm air parcel with cooler air are also called cloudbursts.

Cloudbursts often occur with thunderstorms. When strong updrafts of air prevent precipitation, vast amounts of water can accumulate at an altitude. The phenomenon usually occurs in India in connection to monsoon clouds drifting northwards from either the Bay of Bengal or the Arabian Sea, moving up the plains to the mountains. Cloudbursts in India can be as heavy as a downpour of 75 mm per hour.

Why cloudbursts are dangerous?

Cloudbursts are dangerous due to their ability to cause heavy flash floods as well as landslide events. Ones that last for hours can cause rivers and lakes to swell to critical levels. Flash floods are extremely forceful events and cause massive destruction in their paths.

The heavy current carries everything in its way, be it people, vehicles, even houses and buildings. The 2013 catastrophic event even swept away the entire hamlet of Rambara which lies enroute to the holy shrine of Kedarnath.