Tuesday, August 22, 2023

How and Why of Cloudbursts:

A  lot is being mentioned recently about "Cloudbursts " in our Hill States...which are causing landslides and loss of lives and property.

But why is every heavy fall classified as a "Cloudburst" ?

The term "cloudburst" arose from the notion that clouds were akin to water balloons and could burst, resulting in heavy precipitation.

Cloudbursts are driven by the convergence of warm monsoon winds and cold air, often catalysed by topography.  Rather than falling down, raindrops get larger in dimension and are forced up because of the air current. Finally, they will be heavier to carry and fall down, directing to more rainfall than normal.

cloudburst is an extreme amount of precipitation, dumping large amounts of water, in a short period of time, sometimes accompanied by hail and thunder, capable of creating flooding and landslides. Cloudbursts can quickly pour 25 mm of the precipitation, corresponds to 25,000 metric tons per square kilometre.

Rainfall rate equal to or greater than 100 millimetres (3.9 in) per hour is a cloudburst.

Cloudburst is a geo-hydrological hazard. The aggressiveness in nature and the scale of destruction of rainfall is scary at times. 

.At times, a large amount of runoff from higher elevations is mistakenly conflated with a cloudburst. 

Rapid precipitation from cumulonimbus clouds is possible in which large droplets can grow rapidly by coagulating with smaller droplets which fall down slowly. It is not essential that cloudbursts occur only when a cloud clashes with a solid body like a mountain, they can also occur when hot water vapor mingles into the cold resulting in sudden condensation.

The magnitude of cloudbursts stands out, as India typically receives around 116 cm of annual rainfall. During these events, a small region can amass about 10% of this annual rainfall in just an hour.

{ Note: Vagarians  previously mentioned several times that it is not "Climate Change" which is causing casualties in HP, Uttarakhand 

But it is the large tourists influx to Himalayas defying warnings, illegal unauthorized constructions which  leads to catastrophic loss of life and property. With better connections and fast communication, the news spreads fast.
There is no proof to show that the rainfall in HP, Uttarakhand has broken any records.}

Record cloudbursts...These events are going on since more than 100 years.
1 minute1.5 inches (38.10 mm)Basse-Terre, Guadeloupe26 November 1972
5.5 minutes2.43 inches (61.72 mm)Port Bell, Panama29 November 1911
15 minutes7.8 inches (198.12 mm)Plumb Point, Jamaica12 May 1916
20 minutes8.1 inches (205.74 mm)Curtea de Argeș, Romania7 July 1947
40 minutes9.25 inches (234.95 mm)Guinea, Virginia, United States24 August 1906
1 hour9.84 inches (250 mm)Leh, Ladakh, IndiaAugust 5, 2010 
1 hour5.67 inches (144 mm)Pune, Maharashtra, IndiaSeptember 29, 2010 
1.5 hours7.15 inches (182 mm)Pune, Maharashtra, IndiaOctober 4, 2010 
2 hours3.94 inches (100 mm)Pithoragarh, Uttarakhand, IndiaJuly 1, 2016
26 July 2005 ..

1 hour highest rainfall at Mumbai Scz : 190.3 mms (3.30 to 4.30 pm)

3 hour highest rainfall at Mumbai Scz : 381 mms (2.30 pm to 5.30 pm)

6 hour highest rainfall at Mumbai Scz : 648.4 mms (2.30 pm to 8.30 pm)

On July 18, 2009, 245 millimetres (9.6 in) of rainfall occurred in just 4 hours in Karachi, which caused massive flooding in the metropolis city.

1.On October 20, 2021, a cloudburst occurred above Pethanaickenpalayam town of Salem districtTamil Nadu. This resulted in 213 mm rain in a single day. 

2.On December 2, 2015 the city of Chennai recorded 494 mm rains eventually causing 2015 South India floods.
3.A rainfall of 2.47 inches (63 mm) in 3 minutes was registered by an automatic rain gauge at Porto Bello, Panama, on November 29, 1911, and one of 1.50 inches (38 mm) in 1 minute was registered at the Barot rain gauge near Les Abymes, Guadeloupe, on November 26, 1970. 

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