Changes and trends in Indian cyclones
The cyclonic disturbances over the North Indian Ocean, which includes the Arabian Sea, the Bay of Bengal and the land area in between, have gone through many significant changes in recent decades.
The number of cyclonic disturbances in the North Indian Ocean has declined considerably over the past four decades.
This decline was mostly due to a rapid decrease in the number of cyclonic disturbances originating from the Bay of Bengal, the source of most past cyclones to have made landfall in south-east and west Asia.
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In contrast, the number of such disturbances originating from the Arabian Sea has been steadily increasing in recent years, though the count is still relatively low.
While the frequency of disturbances has decreased, the intensity of cyclones has increased in recent decades.
After a gap of almost three decades, the average number of Cyclones went slightly above 10 cyclonic disturbances in 2023 (Chart 1).
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The number of cyclonic disturbances originating from the Bay of Bengal has rapidly declined since the 1970s.
In contrast, those originating from the Arabian Sea have considerably increased.
Global warming is causing the Arabian Sea to heat up, which is resulting in more, stronger cyclones.
Data show that about 34% of all disturbances that originated in the Arabian Sea have become severe cyclonic storms (a top speed of >48 knots).
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Only 19% of disturbances which originated from the Bay of Bengal and become severe cyclonic storms.
Indian Meteorological Department finds it tougher to forecast cyclones originating from the Arabian Sea as the models have to be adjusted given the oceanographic differences it has with the Bay of Bengal.
As can be observed from the chart, between 2019 and 2023 (latest five years), the share of severe cyclonic storms (>48 knots) in all cyclonic disturbances increased to 32%, the highest for any five-year period since 2004.
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In the last five years, 55% and 17% of the cyclonic disturbances were depressions (<33 knots) and cyclonic storms (34-47 knots), respectively
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Reasons for changes Indian cyclones
The north Indian Ocean is rapidly warming and has contributed to more than a quarter of the total increase in the ocean heat content globally in the last two decades.
In a global warming scenario, an increase in ocean temperatures at a faster rate in the Arabian Sea as compared to the Bay of Bengal.
Rapid warming in the north Indian Ocean, associated with global warming, tends to enhance the heat flux from the ocean to the atmosphere and favor the rapid intensification of cyclones.
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Cyclones have been intensifying at a faster pace in the recent past. The reason for this is increased sea-surface temperatures and rising ocean heat content.
Earlier, the system used to take 2-3 days before forming into a tropical storm, but nowadays, the change from depression into cyclonic storm takes just a day.
The atmosphere not only interacts with sea-surface temperatures but also with the entire ocean.
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