By Hera Rizwan
Originating in the Arabian Sea, Cyclone Biparjoy is expected to make a landfall in the Saurashtra-Kutch coast on June 15 and in southwest Rajasthan on June 16.
India’s Regional Specialised Meteorological Centre has warned that the cyclone could result in storm surges of two to three metres, the destruction of thatched homes, flooding, widespread damage to plantations, orchards, and standing crops, as well as the disruption of railways, power lines in Gujarat's northern and western coastal districts.
Biparjoy, which formed into a cyclonic storm on June 6 and will finally make a landfall on June 15, is one of the longest lasting cyclones to have impacted in the recent past. However, this is not the first time that a prolonged intense cyclone has developed in the Arabian Sea.
According to a research by Centre for Climate Change Research (CCCR), Pune, “The frequency, duration, and intensity of cyclones in the Arabian Sea have increased significantly, while there is a slight decrease in frequency in the Bay of Bengal.”
BOOM spoke to experts to know the reason behind this change in trend.
Why have the instances of cyclones increased in the Arabian Sea?
According to the research, there is a 52% increase in the number of cyclones in the Arabian Sea, while very severe cyclones have increased by 150%.
Speaking to BOOM, Trishant Dev from Centre of Science and Environment, said that traditionally, the Arabian Sea has comparatively been less prone to intense cyclones compared to the Bay of Bengal. “One of the reasons is the less warm sea surface temperatures and higher air pressure over the sea compared to the Bay of Bengal,” he said.
However, in the recent past the Arabian Sea has witnessed some of the most severe and prolonged cyclones. “Cyclone Tauktae, originating in the Arabian Sea was categorised as an extremely severe cyclone back in 2021, one of the strongest in over a century. Before this, Vayu in 2019 and Nisarga in 2020 were classified as severe or very severe,” he said.
Dev attributed it to the increasing temperatures of the Arabian Sea, which may be related to increasing greenhouse gas concentrations in the atmosphere and the resulting global warming.
“High sea surface temperatures are known to trigger severe cyclones. Moreover, higher temperature also means a higher energy available to help intensify the cyclone in a short duration,” he said.
But how does the warming of sea surface temperatures lead to the intensifying of cyclones?
Akshay Deoras, a UK-based research scientist, told BOOM that as tropical cyclones derive energy from the influx of heat and moisture from the upper layers of a sea, “higher sea surface temperature would increase the intensification of a pre-existing low-pressure system in the sea into a tropical cyclone if other conditions are favourable”.
Does global warming also affect the duration of cyclones?
The CCCR research notes that there has been an 80% increase in the total duration of cyclones in the Arabian Sea, during the last four decades. The duration of very severe cyclones has also increased by 260%.
Deoras said that a tropical cyclone keeps growing if it gets more heat and moisture. The current scenario due to global warming is also very conducive for cyclones. However, he notes, that the duration of the tropical cyclones also depends on multiple factors, such as low-pressure area, and small variations in vertical wind speed, apart from the increase in the sea surface temperatures.
Deoras said, “There is some evidence that global warming prolongs the duration of cyclones, in certain regions of the world such as the continental US, but it hasn't been linked to anthropogenic climate change with a high confidence.”
According to Dev, global warming does contribute to the longer-lasting cyclones. Explaining the phenomenon, he said, “Warmer ocean waters provide the necessary energy for cyclones to form and intensify, while increased moisture content in the atmosphere supports their development and sustenance.”
Can we attribute the prolonged cyclones to the weak monsoon?
Dev explained that this is scientifically possible. Monsoon circulations can affect the track and intensity of a cyclone, and this is also true vice versa. “A weaker monsoon favours the formation of severe cyclones, among other factors, such as favourable temperature conditions,” he said.
This year the monsoon season is expected to have a delayed onset as well as reduced rainfall, since it is an El Nino year. El Nino and its counterpart La Nina are ocean-borne phenomena which affect the incidence of heatwaves and rainfall worldwide.
Alluding to the prolonging of the Cyclone Biparjoy, Dev said, “As far as Biporjoy is concerned, a weak monsoon may have enabled an extremely severe cyclone and not the other way round. However, going forward, the monsoon winds will likely be under the influence of the cyclone.”
Tropical cyclones over the Bay of Bengal and Arabian Sea are capable of modulating the monsoon's onset and progression. Citing the example of Cyclone Biparjoy, Deoras said, “The cyclone helped in the onset of the monsoon over Kerala and also caused its further progression up to the south coast of Maharashtra.”
However, the cyclone can also weaken the onset of monsoon if it's very strong enough to pull away the moisture from the monsoon circulation and also disrupt the wind pattern.
