Explained: Why cloudbursts are not so rare in India anymore

More than 50 people were declared dead till Sunday in destruction caused by cloudbursts and flash floods in different parts of Himachal Pradesh, Uttarakhand and Odisha over the last three days.

Heavy rainfall over isolated areas in the two hill states have triggered landslides and flash floods, leading to disruption in rail and road traffic and destruction of life and property.

What are cloudbursts?

A localised intense rainfall activity can be categorised as a cloudburst. It generally occurs over a small geographical area for a short spell, but the intensity of rainfall can cause widespread destruction. This weather phenomenon is most common in hilly regions.

However, not all instances of heavy rainfall are cloudbursts. According to The Indian Express, rainfall of 10 cm or more in an hour over a roughly 10 km x 10 km area is classified as a cloudburst event. By this definition, 5 cm of rainfall in a half- hour period over the same area would also be categorized as a cloudburst.

In a normal year, India receives about 116 cm of rainfall over the entire year. To put it into perspective, during a cloudburst, a place receives about 10 per cent of this annual rainfall within an hour.

The situation is worse than what Mumbai experienced on 26 July, 2005. At the time, Mumbai had received 94 cm of rain over a 24-hour period, which resulted in over 400 deaths.

Are cloudburst incidents increasing?

Even though there is no long-term trend suggesting an increase in incidents of cloudburst, it has been well established that incidents of extreme rainfall and other extreme weather events are increasing.

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Even though the overall amount of rainfall in India has not changed much, an increasing proportion of rainfall is happening in a short span of time. In simple words, the wet spells are very wet, and are interspersed with prolonged dry spells even in the rainy season.

This kind of pattern, attributed to climate change, does suggest that cloudburst events might also be on the rise.

According to a report by Down To Earth, which cites Kireet Kumar, scientist at GB Pant National Institute of Himalayan Environment and Sustainable Development, the main reason for this increase is rising temperatures due to climate change.

“Rainfall depends on temperature which impacts wind patterns and cloud formation. With increasing temperatures, such events are on the rise,” he said.

Another scientist from the institute, Sandeep Mukherjee, said that high temperatures result in increased moisture levels.

He added, “This moisture content then manifests itself in the form of either pre-monsoon thunderstorms in the Indo-Gangetic Plains or cloud bursts or hailstorms in mountainous regions like Uttarakhand.”

As per the Down To Earth report, Mukherjee also talked about the possibility of there being a link between forest fires and extreme rainfall events. However, no study has been done so far to establish this correlation.

“Theoretically, it can be said that forest fires and rainfalls are linked because fires give out a lot of smoke and other particulate matter which can aid rainfall if there is moisture in the air. This is the basic idea behind artificial rainfall. However, no studies have been done in India to test this,” he said.

Some of the recent cloudburst incidents

2013 Uttarakhand

In 2013, Uttarakhand’s Kedarnath received unprecedented heavy rainfall between 14 and 17 June.

The banks of the Chorabari lake collapsed due to a cloudburst, resulting in a major flash flood that caused widespread damage in the ecologically fragile Himalayan region.

As per Free Press journal, the rainfall led to the melting of the Chorabari glacier and the eruption of the Mandakini river. The floods affected large parts of Uttarakhand, Himachal Pradesh and Western Nepal.

The heavy rainfall caused massive flash floods and landslides resulting in the death of residents and tourists as well as extensive damage to property. Reportedly the worst hit was the Kedarnath.

Worse, bad weather delayed the launch of relief and rescue operations after the Kedarnath deluge. The magnitude of the tragedy at that time could also not be immediately realised.

Several roads, buildings and other structures were washed away and the estimated toll was around 10,000, with over 3,000 persons missing, as per the state government.

Free Press Journal quoted ecologist Chandra Prakash Kala as saying “the approximate cost of damaged bridges and roads was $285 million, dam projects worth $ 30 million and loss to state tourism worth $195 million.”

Mumbai cloudburst 2005

On 26 July, 2005, Mumbai received an astonishing 944 mm of rain in just 24 hours, the highest rainfall in a century.

What happened next was pure chaos – flights were cancelled, trains halted, water and power supply stopped, schools and offices were shut, cell phone networks were down.

Locals were left stranded in offices, schools, colleges and even in their cars. Many had to seek help from strangers. Thousands more were stranded at the train stations, bus depots and the airport.

It took a few days for things to return to normal and waters to recede.

Thousands were left dead.

Every time it rains heavily in Mumbai, people remember 26 July.

Jammu and Kashmir 2010

In 2010, flash floods, caused by a cloudburst transformed the picturesque landscape of Leh into a virtual disaster zone with buildings, houses and schools completely destroyed.

The cloudburst triggered torrential rains, mudslides and flash floods.

It claimed about 180 lives and injured about 400 people besides causing widespread damage to public and private property.

A number of government offices, and the Indo-Tibetan Border Police camp were damaged and communication lines snapped.

Telephone towers and highways leading to the region were also affected and the Leh-Srinagar highway blocked.

It took the army and air force several hours to clear the Leh airport, where parts of the runway were covered in six inch slush.
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With inputs from agencies_

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