Generally, India gets 5 cyclones on an average in a year – four in the Bay of Bengal and one in the Arabian Sea.

However, from the past few years due to global warming the sea surface temperatures in the Arabian Sea continue to remain abnormally high, in the 30s, feeding cyclonic conditions.

Data from Indian Institute of Tropical Meteorology shows a 52 per cent increase in the number of cyclones in the Arabian Sea between 2001 and 2019. An 8 per cent decrease was observed in the number of cyclones in the Bay of Bengal during the same period.

In 2021, a research paper in Nature journal said there is a significant increasing trend in the intensity, frequency, and duration of cyclonic storms . And also very severe cyclonic storms were observed over the Arabian Sea during the study period of 1982 to 2019.

Further, there has been an 80% increase in the total duration of cyclones in the Arabian Sea during the last two decades.

The duration of very severe cyclones has increased by 260%.

In comparison to the Bay of Bengal, the proportion of Arabian sea cyclones was initially 1:4, but now it has become 2:4 from 2001-2020.

Recent evidences of increased cyclonic activity in Arabian Sea

Out of five cyclones in 2020, two were in the Arabian Sea. Five of the eight cyclones in 2019 were in the Arabian Sea, a marked shift from the eastern bay being the hub of cyclones.

The west coast of India has been hit with mutiple “severe intensity” and “very severe intensity” cyclones since the disastrous Cyclone Ockhi in 2017. Cyclone Ockhi took form in November 2017, and left a trail of destruction in the Lakshadweep archipelago and the southernmost districts of Tamil Nadu and Kerala.

Cyclone Ockhi was followed by Cyclone Vayu (June 2019), Cyclone Kyarr (Oct-Nov 2019), Cyclone Nisarga (June 2020) and Cyclone Tauktae (May 2021). Formed close to Lakshadweep, Tauktae travelled up to the Gujarat coast and retained its fury for 24 hours after landfall. It brought severe rains over parts of Rajasthan, Delhi and even Uttar Pradesh.

Why Arabian Sea is witnessing more cyclones?

According to a paper in Elsevier’s Earth Science Reviews published last year, the sea surface temperatures over the Arabian Sea increased by 1.2°C to 1.4°C in recent decades. The Arabian Sea is one of the fastest warming basins across the global oceans. The Arabian Sea is warming at the rate of 0.18 degree Celsius per decade which is much higher than the warming of the Pacific Ocean and Atlantic Ocean.

Rapid warming in the north Indian Ocean, associated with global warming, tends to enhance the heat flux from the ocean to the atmosphere and favour rapid intensification of cyclones.

The surface temperature in the Arabian Sea has been rising at an alarming rate since 1995. The Arabian Sea has two mechanisms to cool — upwelling and winter convection. This cooling system was sufficient to offset the excess heat in the Arabian Sea till 1995. But now the sea is trapping excess heat which has led to rapid warming of the water up to a depth of 300m. The excess heat trapped in the sea is the primary mechanism that stirs up cyclones. It will intensify evaporation. Warming of the atmosphere will increase the moisture-holding capacity. When there is excess moisture in the air, a cooling system can trigger intense rainfall like a cloud burst in a small area which can trigger floods.

Why the frequency of Arabian Sea cyclonic storms has increased inspite of a slight decrease in Bay of Bengal cyclonic storms?

Arabian Sea was always relatively cooler in comparison to the Bay of Bengal in the north Indian Ocean until it started undergoing a major change of character around four decades ago.

The Arabian Sea side of the north Indian Ocean, has seen a 52 per cent increase in cyclonic storms (63-88 km per hour) from 2001 -2019. The length, energy and intensity of these cyclones increased over the last 20 years.

In contrast, the frequency of Bay of Bengal cyclonic storms has slightly decreased but not to a significant extent. The reason is that there is a warming threshold for sea surface temperature (SST) over any ocean. It is generally between 26 degrees Celsius and 30 degrees Celsius, which has already been achieved in the Bay of Bengal. However, sea surface temperature is still gradually increasing over the Arabian sea,