In the past, cyclones in the Arabian Sea were considered rare occurrences. However, in recent years, both the number and intensity of cyclones in the region have significantly increased. The latest cyclone, Cyclone Biparjoy, currently forming over the Arabian Sea, is projected to have the longest lifespan ever recorded in the area.

This begs the question: what has caused this once-rare phenomenon of cyclone formation to become so common in the Arabian Sea?

Scientists point to global warming as the primary factor behind this shift. Climate change has been attributed to a wide range of problems worldwide, including heatwaves and health issues. The rise in both the quantity and severity of cyclones in the Arabian Sea can be seen as another consequence of this global phenomenon.

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The Indian Meteorological Department (IMD) stated that between 1965 and 2022, a total of 13 cyclones formed in the Arabian Sea during the month of June. Out of these, two made landfall on the Gujarat coast, one on the Maharashtra coast, one on the Pakistan coast, three on the Oman-Yemen coasts, and six dissipated over the sea.

Arabian Sea less prone to cyclonic events?

The India Meteorological Department (IMD) said cyclones "do not form" in the Arabian Sea during the months of January, February and March and are rare in April, July, August and September. "They generally form in the southeast Arabian Sea and adjoining central Arabian Sea in the months of May, October, November and December and in east central Arabian Sea in the month of June," the IMD informed.

This is because the waters in the Bay of Bengal "form a natural hotspot for cyclones" since it is warmer than that in the Arabian Sea. "High-intensity cyclones were relatively less frequent in the Arabian Sea than in the Bay of Bengal because of lower sea surface temperature (SST) and unfavourable wind shear,” Preeti Tewari, an associate professor of geography at the University of Delhi, was quoted by a report in science journal Nature as saying in 2021.

Therefore, the Arabian Sea is said to be comparatively less prone to cyclonic storms than the Bay of Bengal as "almost 50 percent of the storms do not sustain over its waters since the west-central and north Arabian Sea have a colder sea temperature than other adjacent regions", said a report published by the Gujarat government.

The report, analysing the cyclone pattern from "the last few years", suggested that the Arabian Sea started receiving tropical cyclones of high intensity in a small time interval. "For instance, in 15 years (1998 to 2013), five extremely severe cyclones originated in the Sea," it added.

Meanwhile, another report by the UN Intergovernmental Panel in 2019 concluded that "the intensity of the tropical cyclones in the region is reaching its extreme".

Year-wise Frequency of cyclonic activity in Arabian Sea

(Credit: gidm.gujarat.gov.in)

The phenomena behind the increased number of cyclones

Scientists have found "a strong link between the accelerated warming of the Arabian Sea and the frequency and intensity of cyclones in the sea". Madhavan Nair Rajeevan, secretary in the Ministry of Earth Sciences, said the Arabian Sea has been heating faster, "partly due to global warming".

"Warming is seen not only in the top layers but also in the deeper ocean layers, which we call ocean heat content...Due to increases in the sea surface temperature (SST) and ocean heat content, Arabian sea cyclones are intensifying," he was quoted as saying.

The science report published in the Nature listed a few major reasons for the rise in the number and intensity of cyclones in the Arabian Sea:

1. Warming of sea surface

2. Warming of deeper waters

3. Indian Ocean is warming up the fastest of all the oceans, that too in its north which is the Arabian Sea

4. Unusual process of the upwelling and winter convection failing to offer build-up of carbon dioxide

5. An increase in the anthropogenic aerosols was reported to cause an increase in storm intensity over the Arabian Sea

Sanchez-Franks was quoted by Nature as saying: "Oceans are absorbing more of the excess anthropogenic heat – about 90 percent –than any other component of the climate system. This heat is absorbed, stored and then redistributed by the oceans."

The government report also cites other scientists as saying that the "La Niña-like conditions in Pacific...resulted in an anomalous cyclonic circulation throughout the middle troposphere, along with increased relative humidity over the Arabian Sea, thereby providing favourable conditions for cyclogenesis".

An analysis by a group of scientists founds that while the Bay of Bengal experiences two to four cyclones per year, annual cyclones in the Arabian Sea of Category 2 and 3 have increased only after 1995. "Category 4 cyclones started occurring in the Arabian Sea only after 1995," they said.

Supporting the argument, PK Dinesh Kumar of, the National Institute of Oceanography of the Arabian Sea, reportedly witnessed "a warming of 10 milli-degree per year from 1960 to 1995 which increased to 14 milli-degree post year 1995".

Life span

Warm temperatures not only increase their intensity but their lifespan. According to the IMD, the life span of a severe cyclonic storm in the Indian seas averages about four days from the time it forms until the time it enters the land.

The life period of Cyclone Biparjoy, which developed over the southeast Arabian Sea at 5.30 am on June 6, is about seven days and 12 hours so far.

The extremely severe Cyclone Kyarr of 2019 over the Arabian Sea had a life of 9 days and 15 hours. It developed over the east-central Arabian Sea, had multiple recurvatures and weakened over the southwest Arabian Sea.

The very severe cyclonic storm Gaja of 2018 over the southeast Bay of Bengal had a life span of 9 days and 15 hours, news agency PTI reported.

Before 2023, only two cyclones crossed the Gujarat coast in June. One was a severe cyclone in 1996 and the other was an extremely severe cyclonic storm in 1998, it said.

(With inputs from PTI)

First Published:Jun 13, 2023 1:24 PM IST