When the clouds collapse

Altostratus cloud: It is formed by lifting of a large, stable air mass that causes water vapour to condense into cloud. Photo: N. Shiva Kumar  

The devastation that ravished Uttarakhand recently will soon be forgotten without any remedies rendered, even as experts continue discussing what needs to be done or not to avoid any such future calamities.

Meanwhile, the monsoons continue to sweep the length and breadth of the Indian subcontinent as the wafting and whirling winds push cotton clouds in different directions. Sometimes even individuals who specialise in Nephology, the study of clouds, wonder at nature’s art of cloud composing — ranging from mild to wild with collateral connotations. The same life-giving rain clouds, which are a vital ingredient for Indian agriculture, also turn lethal at will creating chaos.

The ‘culprit’ cloud that created havoc in the hills of Uttarakhand is supposedly a cloudburst which is a creation of billions of droplets bound together and pregnant with gallons of water. These massive coagulated clouds with heavy water content hover over a very small location unlike storms that spread anywhere from five to 50 km range and convert into a downpour. The dead weight of the cloud is so massive and unbearable that it simply collapses under its own weight with such ferocity that mountains become molehills, accompanied by thunder and lightning.

Meteorologists explain cloudburst as an extreme amount of precipitation, sometimes with hail and thunder, which is capable of creating flash-flood conditions. Colloquially, the term cloudburst may be used to describe any sudden heavy, brief rainfall in massive volumes. Unlike cyclones, forecasting a cloudburst is mission impossible due to the very dynamics of rapid developing cloud cover.

Dr. O.P. Singh, head of the Delhi region of the Indian Meteorological Department (IMD), says: “A cloudburst can occur anytime and at any place which is affected by convective weather systems. Surrounded by oceans on three sides, peninsular India is a favoured location for the genesis of convective weather systems. In a short span of time, if the right combinations of atmospheric conditions like instability, moisture content and triggering mechanisms are available, cloudbursts are possible. It is not necessary that cloudbursts happen only in the mountains or high altitudes as the weather systems have compatibility and criticality in space and time. This implies that the smaller scale weather structures like tempest, tornado, cloudburst, etc. have shorter life span whereas large scale systems like tropical cyclones have a longer life span.”

He further explains that the large scale features, which are conducive for occurrence of severe thunderstorms associated with cloudburst, are predictable two to three days in advance. However, the specific location and time of cloud burst can be predicted in NOWCAST mode only, i.e. a few hours in advance, when the genesis of thunderstorm has already commenced. To detect these sudden developments, a Doppler Weather Radar (DWR), a powerful tool for time and location specific prediction of cloudburst, can be deployed a few hours in advance. Coupled with satellite imagery this can prove to be useful inputs for extrapolation of cloudbursts anywhere in India.

According to Dr. Singh, the Chhotanagpur plateau spread across north Odisha, West Bengal and Jharkhand is the world’s most vulnerable spot for formation of severest thunderstorms. The mountainous regions are another favoured location for cloudburst due to undulating geographical features. Cloudburst can occur not only in the monsoon seasons but also during March to May which is known for severe convective weather activities. There is a convention in meteorological parlance that when the rainfall is more than 10cm (100mm) per hour over a limited area, then it is called a cloudburst.

On June 16-17, the lashing sheets of rain in Uttarakhand made mountains into free flowing mud and slush as the explosive package joined the existing river current. Rivers suddenly turned semi-solid and flowed with frightening force as liquid mud made its own path breaking down anything that came across its way.

Even though the frequency of cloudbursts has been increasing over the years because of constantly changing climatic conditions and global warming, India does not have a secure system to predict cloudburst. Strangely, the IMD does not even use the terminology of cloudburst to describe the phenomenon but merely calls it meso-scale thunderstorm.

To tackle the cloudburst occurrences, the IMD will be “introducing” the word cloudburst shortly for their climatological jargon. Until then, high-resolution numerical models and meso-scale observations, high-performance computers and Doppler Weather Radar (DWR) will be installed in the higher reaches of the Himalayas by the Department of Science and Technology. Can these actions and precautions prevent natural disasters? According to scientists, the answer is “no”, but the impact can be minimised by preparedness and proactive disaster management.

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Printable version | Jun 20, 2021 4:05:12 PM | https://www.thehindu.com/sci-tech/energy-and-environment/when-the-clouds-collapse/article5007280.ece

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