
Recently, the Union Ministry of Home Affairs announced that Cyclone Fengal which hit Tamil Nadu in December 2024 would be considered a “disaster of severe nature” for financial assistance, in view of the damage it caused.
“In the coastal districts of Nagapattinam and some parts of Mayiladuthurai, Thiruvarur and Thanjavur, Cyclone Fengal flattened crops across 75,000 acres,” said Cauvery Dhanapalan, president of Collective of Tamil Nadu Farmers’ Associations. “We had good rains and the crops grew taller than usual. So when the cyclone hit us, the plants just slumped to the ground.”
Further north of Nagapattinam in Chennai, many residents feel that Cyclone Fengal has been kind to them, compared to some previous cyclones.
Aaron Das, a Chennai-based businessman in the travel industry, was among those who were relieved that the festival season and celebrations went without a hitch.
“Ever since that dreadful tsunami, December seems bad for us, with cyclones hitting us every other year,” he said, listing some of the weather events that happened in December over the years.
However, in particular, Dhanapalan and Das remember Cyclone Gaja which left a trail of destruction, with toppled transmission towers, uprooted trees and flattened crops in agricultural fields.
“For those of us on the east coast facing the Bay of Bengal, cyclones have become a part of life,” Dhanapalan said.
Tropical cyclones
The oceans around the earth, lying between the Tropic of Cancer and the Tropic of Capricorn, are known as tropical oceans. As the North Indian Ocean basin – which includes the Arabian Sea and the Bay of Bengal – lies in this region, the cyclones that develop here are called tropical cyclones.
The North Indian Ocean has two cyclone seasons in a year: The pre-monsoon season from April to early June and the post-monsoon season from October to December. Due to the presence of strong wind shear – a sudden change in the speed and direction of wind over a short distance – during the monsoon season, cyclones are absent.
Tropical cyclones are low pressure systems or storms caused by winds that swirl around a central low pressure area called the eye. They move along the surface of the sea at the speed of 300–500 km a day.
In India, there are eight classifications of these low pressure systems, varying from low pressure area and depression to super cyclonic storm, depending on the wind speed.
“Cyclones are a resultant of depressions. Depressions are a cyclic, regular phenomenon without which we won’t get southwest and northeast monsoons,” says Abinash Mohanty, global sector head of climate change and sustainability at IPE Global – an organisation working towards sustainable development – and an expert reviewer for the sixth assessment report (AR6) of Intergovernmental Panel on Climate Change (IPCC).
“However, because of climate change, these depressions become deep depressions, and deep depressions become cyclonic storms. Historically the east coast has been a hub of cyclones and continues to be so.”
Why does the Bay of Bengal get more cyclones?
For every cyclone forming over the Arabian Sea, four cyclones develop over Bay of Bengal, according to Regional Specialised Meteorological Centre (RSMC) – Tropical Cyclones, India Meteorological Department (IMD).
Between 1990 and 2020, the number of tropical cyclones over the Arabian Sea was 73, whereas it was 190 over Bay of Bengal, according to Climatology of Tropical Cyclones over North Indian Ocean, a report by Ananda Kumar Das of IMD.
But why does the east coast of India experience more cyclones compared to the west coast?
A meteorological expert with Vagaries of the Weather, a weather blog covering the Indian subcontinent, cites three reasons for the Bay of Bengal getting more cyclones.
“Warm waters and moist air fuel a cyclone. Bay of Bengal is land-locked; so it does not get any cold water. This results in higher sea surface temperatures (SSTs), generally more than 28°C. Tropical cyclones form over warm waters, when the temperature is more than 27°C. Whether it’s pre-monsoon or post-monsoon, Bay of Bengal’s SST is around 29°C or 30°C,” explained the expert.
“In Arabian Sea, SST is generally low compared to Bay of Bengal because of evaporation caused by strong winds. Since the temperature is cooler during most of the year, not many cyclones develop in the Arabian Sea.”
Some of these coastal regions are getting highly urbanised, leading to carbon emissions. So heat is generated from the land and flows to the ocean, warming the seas further,” Mohanty added.
The second most important reason for a cyclone to develop is the difference in humidity.
“Arabian Sea gets a lot of dry air from desert countries like Oman and Yemen. So the atmospheric moisture is less. Since moist air is required for a cyclone to form and there’s atmospheric moisture in the Bay od Bengal, more cyclones develop there,” said the expert.
The other factor, he said, is the pulses. “Typhoons that form over the Pacific travel westward and enter Bay of Bengal as a low pressure or depression. Because of Bay of Bengal’s favourable conditions, the remnants of these typhoons intensify into cyclones. But the Arabian Sea does not get these pulses. So, there is no external factor to trigger cyclones.”
Though Bay of Bengal continues to have more cyclones, experts are quick to add that the number of cyclones in the Arabian Sea has been increasing in the last two decades.
The impact
Cyclones over Bay of Bengal and Arabian Sea make up only six percent of the global annual average. Of the six percent, Bay of Bengal accounts for four percent and the Arabian Sea accounts for two percent, according to research by Vineet Kumar Singh and Roxy Matthew Koll, scientists at the Pune-based Indian Institute of Tropical Meteorology.
Even though the number is less, these account for more than 80 percent of global fatalities.
The majority of the devastating cyclones formed in the Bay of Bengal caused extensive casualties and damage in India and Bangladesh, such as the Odisha super cyclone of 1999 and Cyclone Bhola of 1970.
“Whether it’s Bulbul or Amphan or Remal, Bay of Bengal cyclones affect people in the Sundarbans badly, leading to embankment erosion and brackish water entering villages, thus affecting their livelihood of fishing and farming,” said Arunabha Das, of Sabuj Sangha, a development organisation.
Although some farmers in the coastal districts of Tamil Nadu have switched to traditional, hardy varieties of paddy, the crops are often not able to withstand the intense cyclones.
Early warning systems have helped in reducing casualties. But can the impact be reduced?
Improving resilience
“The vagaries of weather are beyond our control. Cyclones bring associated disasters like urban flooding and landslides. Places like Tamil Nadu, Odisha and West Bengal are prone to cyclones but are not fully equipped to handle the unsustainable urbanisation and the extreme weather events,” said Mohanty.
He suggested mapping the carrying capacity of these regions, fixing the natural landscapes, doing hyper granular risk assessment – similar to the multi-hazard risk assessment being done by them for Mumbai.
“We should have nature-based solutions that are environmentally and climatologically strategic, and an innovative climate risk financing to implement such solutions,” he added.
Until such solutions are in place, farmers like Dhanapalan have learnt to take it in their stride.
With a sardonic laugh, he said, “We may have lost the crops to Cyclone Fengal. But there is a brighter side to it. The pests disappeared because of the heavy rains. So there was no sale of pesticides. And that is very good for the environment.”