AKSHIT SANGOMLA
BARELY AN hour—that’s what saved the Sundarbans from being washed away on May 20 as Amphan made landfall in this densely populated, ecologically fragile delta of West Bengal. “Strong winds and heavy rains, accompanied by a surge in seawater, raged through the island even before the super cyclone made landfall at 2.30 pm. It continued till 3.30 pm,” recalls Joydeb Das, headmaster of a school at Sagar island. “After an hour’s lull, it started again as Amphan crossed us and headed towards Kolkata. The storm surge was more intense in the second phase,” he says. That was also the time when high tides start returning, causing waves as high as 4.5 m. People were dreading an Aila-like situation when, in 2009, the cyclone’s high intensity phase coincided with the peak tide, causing seawater to rise 6-7 m, flooding paddy fields with seawater and displacing 2.3 million people. But this time the intensity of Amphan reduced by 7.30 pm, just an hour before peak tide. And a head-on collision was averted.
“The combined effect of the high tide and Amphan pushed water levels to 5.45 m at Sagar island at 8.38
pm—about 0.7 m above the forecast level,” says a source associated with the Kolkata Port Trust. Yet, the devastation caused by the first super cyclone to form over Bay of Bengal in the past two decades is as severe as the 1999 super cyclone. In the Sundarbans alone, it has washed away about 90 km of embankments that guarded two-thirds of islands in the South 24 Parganas district. Seawater has swept 10 km inland, inundating 50,000 ha of land. At places, jetties that connect the islands to the mainland have collapsed. Initial estimates show that the super cyclone, which also hit other parts of West bengal and coastal Odisha, has damaged 2.5 million houses and affected 10 million people; close to 90 have lost their lives. As the authorities try to cope with the double emergency, providing food, shelter and other relief measures to the affected while ensuring that they maintain social distancing to avert any outbreak of COVID-19, the super cyclone, the first this year, underlines how cyclones are changing their behaviour and becoming more intense in a warming world. in a span of just 18 hours. On the night of May 18, the Joint Typhoon Centre of the US recorded wind speed of 270 km per hour and called it the strongest storm recorded in the Bay of Bengal in over a decade.
Weather scientists say this rapid intensification of Amphan might signal a warming Bay of Bengal. “It was because of many favourable conditions over the Bay of Bengal like high sea surface temperatures, low vertical shear winds and enough moisture in the middle layers of the atmosphere, all of which aid in the development of a cyclone,” says Mrutyunjay Mohapatra, director
WARM AIR, OCEAN SURFACE TEMPERATURES HAVE INTENSIFIED BAY OF BENGAL CYCLONES DURING PREMONSOON SEASON, IN MAY
air and ocean surface temperatures have significantly intensified the Bay of Bengal cyclones, especially during the pre-monsoon season and in May,” says Wang. His co-researcher Jin-Ho Yoon says the new environment with much less aerosols and greenhouse gases provides a new testbed for climate change impact studies.
Irrespective of the reason, there is no denying that cyclones are becoming more severe and frequent in recent decades. An analysis by
(DTE) shows from 2015 to 2017 five of the 11 cyclones that formed in the North Indian Ocean had turned severe. In the past two years, 12 of the 16 cyclones have turned severe, including 7 very severe cyclones, 3 extremely severe cyclones and two super cyclones. This is an increase from 45 per cent to 75 per cent.
To estimate the frequency with which these cyclones are forming, DTE analysed all the cyclones formed in the North Indian Ocean since 1981 (see ‘Unquiet times’). Between 2011 and 2019, as many as 28 cyclones have developed, the highest in last four decades. They are now occurring at times when they usually did not. For example, before 2011, cyclones never occurred in January, March and April. In the last decade, cyclones have occurred every month except February and August. The months with the maximum number of cyclones has also changed from December and November in the past decades to October and March. Since cyclones form over warm sea surfaces (above 27oC) the analysis shows seas are now warm throughout the year, leading to an increased possibility of cyclone formation at any time of the year.
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