Cyclone Vayu, the severe cyclonic storm that just skirted past Gujarat’s Saurashtra coast on Thursday, once again brought the focus on the increasing frequency of such weather occurrences in the Arabian Sea.
The past few years have seen a number of such cyclonic storms in the region starting with Cyclone Nilofar in 2014 that impacted the coasts of Oman, Pakistan and India with wind speeds as high as 205 km/hr.
Until then, such severe cyclonic storms were only aberrations. Among such unusual weather occurrences along the Western Coast have been the devastating floods in Kerala last year resulting from abnormally high amounts of rainfall.
Unlike the Bay of Bengal, storms in the Arabian Sea would not reach such high intensities because of dry air blowing in from the Arabian Peninsula.
“The ratio of the number of cyclonic storms in the Arabian Sea to the ones recorded in the Bay of Bengal is just 1:4,” said Sunitha Devi, a scientist at the Indian Meteorological Department (IMD).
But, what prevailing conditions even lead to the formation of these storms in the first place?
Kerala Agriculture University researcher Dr CS Gopakumar explains that among the factors aiding the formation of spiraling winds are sea surface temperatures.
“Bay of Bengal is the most congenital for the development of cyclones as its has sea surface temperatures of 26 to 27.5 degrees. Then, there is the convergence of the waters at the ground level and a divergence at the upper levels,” said Kumar, who works with the institute of Academy of Climate Education and Research.
Both Sunitha Devi and Dr Gopakumar agree that the number of cyclonic storms in the Arabian Sea is on the rise. “Even though studies don’t indicate a significant change, the frequency of storms in the Arabian sea has increased,” Devi decisively said.
Recalling a study by scientists Hiroyuki Murakami, GA Vecchi and S Underwood, Gopakumar explained that the increase in the number of storms essentially results from global warming. “So, what is happening is that the Arabian Sea is getting as warm as the temperatures in the Bay of Bengal,” Gopakumar said.
Many researchers have even looked into the impact of carbon emissions on these weather patterns.
While the 2017 study that Gopakumar quoted (Increasing Frequency of Extremely Severe Cyclonic Storms Over the Arabian Sea) was inconclusive about the direct impact of emissions, another study showed the correlation.
The study by AT Evan, C Chung, V Ramanathan and JP Kossin tracked cyclone and emissions data of the past 30 years and noted that increased emissions not only impacted level of solar absorption on the surface but also the wind shear (change in wind velocity), another factor affecting the formation of cyclones.
What has happened as a result is the increased intensity of the extremely severe cyclonic storms (ESCs) in both the pre and post-monsoon seasons. In fact, until 2014, ESCSs were not even observed in the post-monsoon seasons.
As Gopakumar ominously emphasises, “It is unlikely that this trend will stop unless any concerted efforts are made.”
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