Why do cloudbursts occur more in places?

Source: By The Indian Express

Sudden, “highly-localised rains” in Amarnath, Jammu and Kashmir, on 8 July 2022 caused flooding and led to the deaths of at least 16 people and injuries to more than 20 others. Those who died were at a camp near the cave, a site of pilgrimage.

Many politicians tweeted out messages of condolence and mentioned cloudburst-induced floods, as was earlier stated by officials. However, the Indian Meteorological Department (IMD) later said on 9 July 2022 that a cloudburst may not have actually occurred.

We explain what cloudbursts are, the basis on which heavy rains can constitute a cloudburst, and how they can lead to deadly flash floods.

What is a cloudburst?

A cloudburst refers to an extreme amount of rain that happens in a short period, sometimes accompanied by hail and thunder, and this has a precise definition. The India Meteorological Department (IMD) defines it as unexpected precipitation exceeding 100mm (or 10 cm) per hour over a geographical region of approximately 20 to 30 square km. Significant amounts of rainfall such as this can result in floods.

Basically, all instances of cloudbursts involve heavy rain in a short period, but all instances of heavy rain in a short period are not cloudbursts if they do not fit this criterion.

According to weather scientists, the shrine reported 31 mm of rainfall between 4:30 pm and 6:30 pm on 8 July 2022, which does not fit the definition. “The flash floods could have been triggered due to rainfall in the higher reaches of the mountains near the Amarnath cave shrine,” IMD Director General Mrutyunjay Mohapatra told PTI.

Why do cloudbursts occur in hilly areas like Amarnath?

Experts have said it is difficult to predict when exactly a cloudburst will occur, and there is little definitive data on the exact number of cloudbursts that occur in India. Due to their definition dealing with a very small area, it is difficult to accurately predict and identify cloudbursts immediately. However, they are more likely to occur in mountainous zones mainly because of terrain and elevation.

This is because, in hilly areas, sometimes saturated clouds ready to condense into rain cannot produce rain, due to the upward movement of the very warm current of air. Instead of falling downwards, raindrops are carried upwards by the air current. New drops are formed and existing raindrops increase in size. After a point, the raindrops become too heavy for the cloud to hold on to, and they drop down together in a quick flash.

A study published in 2020 examined the meteorological factors behind the cloudburst over the Kedarnath region, where a cloudburst aided the devastating 2013 floods. It found that during a cloudburst, the relative humidity and cloud cover was at the maximum level with low temperature and slow winds. “It is expected that because of this situation a high amount of clouds may get condensed at a very rapid rate and result in a cloudburst,” wrote the team.

Last year, a cloudburst occurred in the Amarnath region around the same time. However, as the Amarnath yatra had been previously closed due to the Covid-19 pandemic, it did not lead to loss of life there.