New Delhi: The thunderstorms and squalls billowing through Delhi may not be record breaking but their frequency is unprecedented. With wind speed hitting 107 km/hour, Sunday’s squall was the third most intense since 2000, and it’s already the fourth one this summer.
The month of May is known to be the stormiest, said Dr. Mrutyunjay Mohapatra, a senior scientist with the Indian Meteorological Department (IMD). However, India’s rising temperatures and a higher rate of western disturbances carrying moisture across Central Asia into northwest India have triggered four squalls over this part of the country since the beginning of the month.
On May 2, wind speed reached 69 km/hour, on May 7th, it was 64 km/hour and on May 8th, it was 50 km/hour.
Sunday’s wind speed has been outdone only by a storm on May 10, 2006 when the wind speed hit 141 km/hour and on May 30, 2014 when it hit 122 km/hour.
A storm is referred to as a squall when the wind speed hits 45 km/hour for at least a minute.
Mohapatra pointed out that the timing of these thunderstorms and squalls was in keeping with climatology, as May has the most frequent and most intense storms.
However, the number of these storms is rising with changing climate conditions. Mohapatra said that while 'western disturbances' could be attributed as the 'trigger' for the storms, the primary factor causing such high-intensity storms is the rising heat.
Climate change means India, like the rest of the world, is facing rising temperatures and heatwave-like conditions. IMD, in February, predicted the summer of 2018 to be longer and hotter than normal. Mercury before Sunday’s storm had reached 43 degrees Celsius.
As the temperature rises, and the surface heat builds up, the air rises, explained Mohapatra. As it reaches cooler heights, the air too cools, causing instability in the atmosphere. Delhi and surrounding areas have been moisture-laden because of the western disturbance.
This moisture condensed into rain clouds that lead to the thunderstorm on Sunday. When there is no moisture, the hot landmass gets a dust storm instead of a thunderstorm, as the loose dust particles rise with the warm air. This, Mohapatra said, is what has been happening in Rajasthan.
Different parts of India have different 'triggers' that cause storms. In Delhi and Haryana, storms are usually triggered by western disturbances that lead to the formation of cyclonic conditions over the area. Storms in the eastern parts of the country are often triggered by a 'trough', an area of atmospheric low pressure. In southern states, storms are often triggered by wind discontinuity over parts of south India.
With rise in global temperatures, not only India, but the world is looking at more intense heat waves, higher instability in the atmosphere and therefore an increased frequency of storms.
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