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Sunday, August 01, 2021

Warming Arabian Sea turning hotbed for intense cyclones: Study

Climatologically, the North Indian Ocean region -- covering Arabian Sea and Bay of Bengal -- record five cyclones a year, four of which originate in Bay of Bengal. May and November are the active months in a year.

Written by Anjali Marar | Pune |
Updated: July 19, 2021 9:08:07 am
Mumbai Bandra-Worli Sea link closed due to Cyclone Tauktae

Researchers have noted a 52 per cent rise in storms in Arabian Sea since 2001, with it turning into a perfect ocean basin for the development of cyclones. Moreover, cyclones in Arabian Sea have been found to make slower progress, attracting as much energy available while at sea and finally turning into severe intensity cyclones when they hit the coast.

In May, Cyclone Tauktae formed close to Lakshadweep, travelled northwards and hit the Gujarat coast. The storm was so severe that it retained its intensity for 24 hours after landfall and brought rain over parts of Rajasthan, Delhi and Uttar Pradesh. Normally, cyclones fizzle out upon reaching land.

Storms intensify and sustain depending on the energy availability through heat load in oceans and moisture. The study has also highlighted that accumulated cyclone energy — total wind energy during the lifespan of a storm — in Arabian Sea has nearly tripled, indicating the extent of warming that it might have undergone in recent years.

Climatologically, the North Indian Ocean region — covering Arabian Sea and Bay of Bengal — record five cyclones a year, four of which originate in Bay of Bengal. May and November are the active months in a year.

Climate scientists, however, are now observing a departure to this, especially in terms of intensity and severity of storms formed over Arabian Sea during recent decades.

“Earlier, the Southwest Indian Ocean region would be cooler. But there is a larger change observed in the sea surface temperatures recorded over Arabian Sea than over Bay of Bengal. In addition, the availability of moisture is much higher in Arabian Sea whereas Bay of Bengal appears to be turning moisture-deficit,” said Roxy Mathew Koll, senior scientist at Indian Institute of Tropical Meteorology (IITM), Pune, who was part of the recent study published in Climate Dynamics by Springer.

A look at cyclones that have formed over Arabian Sea in the last four years and their intensities indicate that all were severe cyclones (wind speed 89 to 117 kmph) or more. These include ‘extremely severe’ Mekanu in 2018, ‘very severe’ Vayu in 2019, ‘severe’ cyclonic storm Nisarga in 2020, and ‘very severe’ Tauktae in 2021. Three of these hit either Gujarat or Maharashtra, indicating growing vulnerabilities of India’s West coast.

In 2019 alone, four cyclones — Vayu, Hikka, Kyarr and Maha — originated in Arabian Sea and remained one of the most active years for storms in the recent past.

In most storms recorded during 2001 to 2019 in Arabian Sea, there has been an 80 per cent rise in the cyclone’s duration, said researchers from Savitribai Phule Pune University, National Institute of Technology-Rourkela and KBC North Maharashtra University, who were also part of this joint study.

Overall, November was found to be the most conducive month for cyclogenesis and intensification in both Arabian Sea as well as Bay of Bengal, the study noted.

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