What is Cloudburst ?

Cloudburst is a sudden rainfall which can be quite unexpected, very abrupt, characterized by flash floods. In other words, cloudburst is an extreme amount of precipitation, sometimes with hail and thunder which normally lasts no longer than a few minutes but is capable of creating havoc condition of a flood, landslides, avalanches, mudflow, earth-flow, rock-fall, subsidence, slumps, soil-creep and mass wasting. In some cloudbursts, up to 13 cm (5 inches) of rain can fall in one hour, often in the form of extremely large droplets.

The main characteristic of a cloudburst is caused by a phenomenon known as Langmuir Precipitation, in which drops of rain fuse together to create large drops as they fall, falling quickly as they grow. The Langmuir Precipitation process is applicable only to those clouds which do not extend beyond the freezing point. The temperature in the uppermost part of the cloudburst seldom falls below 5°C. The occurrence of precipitation from such cumulus-nimbus clouds involves the coalescence of cloud droplets of different sizes. Since the rate of fall of these unequal rain-drops is different, they collide with each other within the cloud, and the larger drops grow at the expense of smaller ones. The size of the raindrops become sufficiently large which fall faster and results into a cloudburst. Sometimes, the rain in cloudburst falls so fast and is large that it is actually scary, fearful and frightening.

According to the meteorologists, the rainfall rate equals to greater than 10 cm (about 4 inches) per hour in a cloudburst. There are cases when more than 20 mm (2 cm) of rainfall fall in a few minutes in a cloudburst. The extremes of rainfall in cloudbursts have been given in the table.

DurationRainfallLocationDate
1 minute38.10 mm (1.5 inche)Basse-Terre, Guadeloupe (West Indies)26 November, 1970
15 minute19.12 mm (7.9 inche)Plumb-Point, Jamaica12 May, 1916
1 hour250 mm (9.84 inche)Leh (Ladakh) India6 August, 2010
10 hours940 mm (37 inche)Mumbai, India26 July, 2005
20 hours2329 mm (91.69 inche)Ganges Delta, IndiaJanuary, 1966

In the Indian subcontinent, a cloudburst usually occurs when moisture-laden monsoon clouds drift northward from the Bay of Bengal or the Arabian Sea across the Northern Plains, then on to the Himalaya and burst, bringing as high as 10 cm rainfall per hour. Some of the devastating cloudburst of India in recent years have been given in the table.

Date of cloudburstPlace of cloudburstDeaths
July, 1970Alaknanda Basin, Uttarakhand500
August, 1998Golpara400
15 August, 1997Chirgaon, Shimla District (H.P)115
17 August, 1998Milpa village, Kumaun Division (Uttarakhand)250
26 July, 2004Mumbai cloudburst>5000
6 August, 2010Leh-Ladakh>1000
16 June, 2013Kedarnath cloudburst, Uttarakhand>10,000*