The intensity of cyclones in the Arabian Sea has increased by 20–40% in the recent decades, a review study of the Indian Institute of Tropical Meteorology, Pune, has revealed.
The study stated that during the past four decades, the maximum intensity of cyclones has increased by 40% (from 100 km per hour to 140 km per hour) in the Arabian Sea, during the pre-monsoon season (April–May).
“During the post-monsoon season (October–December), the Arabian Sea has witnessed a 20% increase in the cyclones’ intensity (from 100 km per hour to 120 km per hour). In the north Indian Ocean, every 4th cyclone in the pre-monsoon season intensifies to a severe cyclone of category 3 or more (wind speed over 175 km per hour) and every 7th cyclone in post-monsoon season intensifies to a severe cyclone of category 3 or more,” IITM scientist Roxy Mathew Koll said.
Koll said that the sea surface temperatures leading to cyclogenesis (the development or strengthening of an area of low pressure in the atmosphere, resulting in the formation of a cyclone) in the Arabian Sea were 1. 2–1. 4°C higher in the recent decades, compared to the SSTs four decades ago.
“Rapid warming in the north Indian Ocean, associated with global warming, tends to enhance the heat flux from the ocean to the atmosphere and favour the rapid intensification of cyclones. For example, Cyclone Amphan intensified from a category 1 cyclone (about 100 km per hour) to a category 5 cyclone (about 250 km per hour) in less than 24 hours,” Koll said.
Quick intensification means that it does not provide sufficient time for evacuation and disaster management on the ground.
Scientists involved in the study said changes in the ocean-cyclone interactions were emerging in recent decades in response to the Indian Ocean warming.
“These should be closely monitored with improved observations since future climate projections demonstrate continued warming of the Indian Ocean at a rapid pace, along with an increase in the intensity of cyclones in this basin,” he said.
As per authors Koll and Vineet Kumar Singh, 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 the ocean temperatures at a faster rate in the Arabian Sea as compared to the Bay of Bengal is one of the major parameters. As a result, the models are projecting an increase in the frequency of the cyclones in the Arabian Sea.
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