Uttarakhand has already recorded multiple incidents of cloudburst this month. With 16 people reported dead so far and several others remain missing, painful memories of the 2013 disaster which killed 5,000 people and damaged property across the state are flooding back in.
A cloudburst is a short-term extreme precipitation event that takes place over a small area and not a breaking open of cloud to release huge amounts of water. If rainfall of about 10 cm or above per hour is recorded over a place that is roughly 10 km x 10 km in area, it is classified as a cloudburst event. So a 5 cm rainfall in half an hour would also get classified as cloudburst.
To put this in perspective, India, in a normal year, gets about 116 cm of rains in the entire year. A cloudburst event would therefore account for 10-12 per cent of the annual rainfall of that area in just one hour!
Since rainfall is measured by ground stations, of which Uttarakhand does not have many, the scale of last week’s cloudburst is not exactly known. And since these are localised events, it is possible they do not get recorded even by a good network of ground stations.
This is also why ‘cloudburst’ is very often used loosely for any sudden heavy downpour. Often, the Met department is not in a position to say if a particular rainfall event qualifies to be called so. So if a short-duration heavy rainfall leads to damage to life and property, it does also get described as a cloudburst.