The West Bengal government had announced that the strong cyclonic winds, which reached the speed of 135 km/hour, uprooted some 2,140 trees and 337 electric poles, particularly in southern West Bengal, including Kakdwip, Namkhana, Sagar Island, Diamond Harbour, Fraserganj, Bakkhali, and Mandarmani in the Sundarbans.
Year after year, the Bay of Bengal, the world’s largest bay, covering an area of 2,600,000 sq km, is one of the most cyclone-prone regions on Earth. According to research published by Dr Jeff Masters, hurricane scientist and meteorologist who documents extreme weather, in the Yale Climate Connections platform, 22 of the 30 deadliest tropical cyclones in world history have been recorded in the Bay of Bengal and during the past two centuries.
Storm surges caused the most severe damage in tropical cyclone-related disasters in the region. Floods caused by storm surges are a significant threat to the inhabitants of the Bay of Bengal and the Arabian Sea. A research paper published in 2009 noted that more tropical cyclones are formed in the Bay of Bengal than in the Arabian Sea, and the frequency of storm surges is also greater.
The Bay of Bengal is prone to large storm surges, in part because of its funnel-like shape and topography where it is shallow for a large distance from the coast. This unique geographical shape has contributed to the region witnessing some of the deadliest disasters in world history.
The northern part of the Bay of Bengal is very shallow, where the coast is landlocked on three sides. When a very severe cyclonic storm approaches the coast, the enormous storm surge generated by the wind pressure submerges the coastal belt when the storm passes through the region.
Another unique feature of this coast along the West Bengal-Bangladesh belt is that it is crisscrossed by several rivers and rivulets, where the elevation of the islands is 4 to 5 metres above sea level. The sea-dykes and embankments are not strong enough to resist strong wind-driven waves and cave in during a depression or a cyclonic storm. The frequency of storms crossing this belt is also high, all of which contributes to the severity of the impact of the cyclones that impact this region.
An academic paper titled ‘Effect of landfall location and coastal topography on surge response in the Northern Bay of Bengal’ published in 2020 mentions that in addition to the features of the cyclonic wind, the destruction caused by storm surges also depends on local features and the shape of the coastline. This is because a storm surge is highly dependent on local features and barriers that affect the flow of water. “The Bay of Bengal has a complex coastal geometry, including estuary deltas, pocket-like bays, and straight coasts. In recent years, infrastructure development such as the construction of coastal polders and road networks have acted to concentrate human populations along coasts, which will reduce the local resistance to storm surges and increase the vulnerability of local communities,” the paper says.
“The cyclones that we see now when compared to cyclones that occurred in the previous decades are more intense and they have more moisture. The frequency of cyclones has also increased,” says Rabindra Goenka, a weather expert based in Kolkata, and founder of Weather Ultima, a private weather research company.
One reason why the Bay of Bengal has been witnessing frequent cyclones over the past few years is because the sea surface temperature in the region is high, scientists say. “The sea surface temperature should typically be between 26 to 30 degrees centigrade, but recent measurements have recorded temperatures between 31 to 32 degrees centigrade, which is a significant increase. This high sea surface temperature is also helping cyclones gather moisture,” Goenka says.
Bangladesh-based climate expert Professor A K M Saiful Islam points to the 2023 Intergovernmental Panel on Climate Change (IPCC) report to which he contributed as lead author. It focuses on the warming of the oceans of the Earth. “The Indian Ocean is warming faster and it is already 1 degree warmer from the pre-industrial period. Overall, the land and ocean temperature has seen a 1.1-degree centigrade increase from the last IPCC report. But in the past year, we have observed a 1.5 degree centigrade rise in temperature, exceeding globally from April to May,” says Islam.
Researchers based in South Asia, focusing on extreme weather occurrences, had been expecting a cyclone in May this year due to the extreme heat conditions in the region, which was witnessed in the form of Cyclone Remal. The ocean is warmer and currently, the temperature in the Bay of Bengal is 31 degrees Celsius.
The oceans store 90 per cent of heat energy trapped in the Earth’s climate system by excess greenhouse gases, says Islam. “So there is a favourable condition that forms for tropical cyclones before the monsoons set in during the first week of June. We have seen many cyclones occur between May and June and it is not unusual. The only development now is that it rapidly intensifies,” he says.
While cyclones have been documented in this region since A.D. 1000 in what scientists call the pre-1890 North Indian Ocean cyclone seasons, scientists have become increasingly certain of human activity contributing to climate change, which in turn, impacts the way cyclones are occurring.
In addition to factors like storm surges and the increase in intensity of cyclones, scientists are also marking an intensification of rainfall and wind speed caused due to warmer air temperatures. Scientists have been documenting how cyclones now are stronger and last longer than what has been witnessed in the past, a development that they attribute to climate change.
While there are several different factors contributing to the way cyclones are occurring in this region, scientists who have focused on the South Asia region for years agree that this can largely be attributed to global warming and the warming of the oceans. “In the future, we are going to see more intense cyclones, more precipitation and the height of the storm will be higher because sea level will rise. This region will be vulnerable until we reduce greenhouse gases and keep the ocean temperature stable,” says Islam.
For the Bay of Bengal region, intense cyclones at a higher frequency can be devastating. The deltaic West Bengal in India and deltaic Bangladesh are densely populated regions, where local communities are highly exposed to the effects of cyclonic storms.
Just before Cyclone Remal made landfall in southern West Bengal, near the Sundarbans, the state government had shifted some 2.07 lakh people to the 1,438 safe shelters, with some 77,288 people in relief camps, according to a government statement.
Despite the disaster preparedness, in West Bengal’s North 24 Parganas, South 24 Parganas, Kolkata, and Howrah districts, the state government figures estimated that some 15,000 houses in 24 blocks and 79 municipal wards in the coastal areas were affected by the cyclone, in addition to the death of at least six people. The government believes that these numbers will only increase following ongoing surveys in the affected areas.
Deltaic West Bengal and Bangladesh, near the Sundarbans, are around zero to three metres above sea level, and the complex river system in the region, along with subsidence, makes it difficult to create embankments along the coastline to minimise damage from storms.
According to a research paper published in 2002 by Jadavpur University’s School of Oceanographic Studies titled ‘Sea Level and associated changes in the Sundarbans’, scientists had stated that the estimated rise of sea level would pose serious problems during the pre- and post-monsoon phase when most of the cyclonic storms occur in the next few decades, where the effect of the storm surge would be likely to be more devastating in areas which were not earlier vulnerable, including the city of Kolkata.
“This is the new normal. These are very unusual years and with global warming, we expect that these occurrences will be accelerated in the future,” says Islam.