KOCHI: Biparjoy, the cyclone that left a trail of destruction in Gujarat, has demonstrated the increasing intensity, duration and track length of cyclones in the Arabian Sea, said S Prasannakumar, emeritus scientist and former director of National Institute of Oceanography (NIO). The NIO has done two studies on the changing characteristics of tropical cyclones in the Indian Ocean region, analysing data from 1960 to 2021.
It found that cyclones’ lifetime and total track length show an increasing trend in both Bay of Bengal and Arabian Sea. While the cyclones in Bay of Bengal intensify much faster and travel a short distance, those in Arabian Sea show a slight increase in both parameters.
“Arabian Sea never witnessed Category 4 cyclones before 2000. But recently, the frequency and intensity of cyclones have increased. There have been more pre-monsoon cyclones in Arabian Sea recently, and these cyclones progress in a north-northeast track.
This will transport the moisture to the north and delay the progress of monsoon over the Indian subcontinent,” Prasannakumar said. He said the monsoon delay changes the water and agricultural cycles. The west coast is witnessing a decrease in rainfall duration, and the region has been receiving short-duration intense rainfall in recent times. This will have a wide range of implications.
“Biparjoy, which lasted 10 days and 18 hours, is the longest-duration cyclone in North Indian Ocean region. We can expect more such cyclones. The increase in cyclone duration would imply their strength will increase. The more time a cyclone stays over the sea, the more thermal energy it will absorb,” said Prasannakumar.
The NIO has done two studies on the subject, “Is warming of the North Indian Ocean generating more tropical cyclones?” and “Changes in the cyclone characteristics over the Arabian Sea and the Bay of Bengal”, which are under review.
The studies found that the sea surface temperature, relative humidity and vorticity are showing an increasing trend, while the wind shear is showing a decreasing trend. These aspects are congenial for cyclone generation.