Global warming, weak western disturbances and strong subtropical jet stream are to be blamed, say experts
In March 2023, large parts of the country experienced hailstorms, and in the past week, these storms were also accompanied by torrents of rain. The hail and rains have led to extensive damage to standing crops in many states, such as Maharashtra, Rajasthan and Punjab.
The rainfall and the storms were caused by multiple western disturbances (WD), other WD-associated weather systems and many troughs, which are extended low-pressure areas, formed due to the interaction of the WDs and associated systems with winds blowing in from the east, mainly the Bay of Bengal. A warming Arabian Sea could also be responsible for the intense storm activity and rain.
Between March 5 and March 22, 25 states and four Union Territories suffered from hailstorms, according to an analysis of data from the India Meteorological Department (IMD) by Down To Earth. There were hailstorms on 14 of the 18 days.
The maximum wrath of the hail that is extremely detrimental to crops was incurred by Rajasthan, West Bengal and Maharashtra on seven of the 14 days. The mountain states of Uttarakhand and Himachal Pradesh were hit by hailstorms for six days.
On March 15, March 16 and March 20, there were hailstorms in 13 states. On March 18, there were hailstorms in 12 states. India received 72 per cent less rain than normal between March 1 and March 16, according to data from the IMD. This deficit was reduced to 60 per cent on March 17, to 46 per cent on March 18 and to 18 per cent on March 19. On March 20, the deficit changed to a slight excess of five per cent.
On March 21, this excess increased to 20 per cent and to 25 per cent on March 22. In a matter of six days, the entire rainfall situation of the country changed drastically.
Between March 1 and March 16, only one state and one union territory had received large excess rainfall. By March 23, 18 states had received large excess rainfall; four states had received excess rainfall.
The reasons for this excessive storm activity throughout India were multiple weather systems being active over the country simultaneously. In March, six WDs affected India, according to data from the IMD.
The rainfall and hailstorms, which were at their peak during the week from March 16 to March 23, were caused by multiple weather systems such as troughs and cyclonic circulations (swirling winds in the middle and upper troposphere — the lowest layer of the atmosphere) associated with two consecutive WDs, according to the IMD.
One of these was active between March 16 and March 20, and the second between March 19 and March 22. Another WD started affecting India from March 23. On March 19, there were eight small and large weather systems active over India, and on March 20, there were six such systems.
The IMD also cited a strong subtropical westerly jet stream, a band of winds that circles the subtropical regions of the planet in the upper layers of the troposphere, as a reason for the storm activity.
This was aided by the incursion of moisture-laden winds from the Bay of Bengal and the lowering of the freezing level in the atmosphere, which helped in the formation of hail, according to IMD.
“Since the beginning of March, the subtropical jet stream over India is strong and showing undulations, indicating troughs or elongated regions of relatively low atmospheric pressure”, Akshay Deoras, a research scientist at the National Centre for Atmospheric Science and Department of Meteorology, University of Reading, told DTE.
Unlike weak western disturbances, which mainly affect northern India, these troughs can destabilise the weather over a large part of India since they have a broad extent, he said.
“In fact, the jet stream and embedded troughs in it were able to penetrate India, reaching southern parts of the country. Furthermore, they were a bit slow moving, so this caused enhanced and widespread storm activity in India”, added Deoras.
He pointed out that the pattern was similar to what we saw during previous spring seasons, including in March 2015, for instance, but it was much weaker.
“During March 16-17, the atmosphere over several states of India was unstable, which triggered thunderstorms. Cool air brought by a trough in this period helped hails from severe thunderstorms to reach the ground without much melting”, said Deoras.
Raghu Murtugudde, a climate scientist at the University of Maryland and Indian Institute of Technology, Bombay, cited another novel reason related to the warming of the Arabian Sea for the storm activity and rains.
The warming of the Arabian Sea is a direct result of global warming occurring due to the emissions of greenhouse gases into the atmosphere from human activities.
Murtugudde told DTE:
I did see the system coming from the west but mostly over the Middle East and not from the Mediterranean region. So calling this a western disturbance may have to be revised in the coming years. More systems will come this way because of the Middle East and Arabian Sea warming.
“The mid-tropospheric winds steered the system from the Middle East and the same winds created a back flow to give rain over parts of eastern and peninsular India. I expect more such wind changes to happen during the pre-monsoon because of the Arabian Sea warming,” he added.
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