The Hindu Business Line : `Hurricanes intensifying in Indian Ocean region'

THE North and South Indian Oceans are among the regions worldwide where the number of intense hurricanes (also known as typhoons or tropical cyclones) has nearly doubled over the past 35 years, says a study by researchers in the US.

Significantly, this is at odds with the number of overall hurricanes, which has dropped since the 1990s, the study by the Georgia Institute of Technology and the National Centre for Atmospheric Research (NCAR) revealed.

The anomaly has been attributed to the rise in global sea surface temperatures over the period. The number, duration and intensity of these weather systems occurring worldwide from 1970 to 2004 were analysed for the study.

In the 1970s, there was an average of ten Category 4 and 5 hurricanes (on the five-step Saffir-Simpson scale) per year globally. Since 1990, this number has almost doubled, averaging 18 per year.

Category 4 and Category 5 systems made up about 20 per cent of all hurricanes in the 1970s, but over the last decade, they accounted for about 35 per cent of these storms. The largest increases in the number occurred in the North Pacific, Southwest Pacific, and the North and South Indian Oceans, with slightly smaller increases in the North Atlantic Ocean.

The trend was more or less evident in the prevailing weather over the North Indian Ocean (Bay of Bengal) and the western and eastern Pacific on Monday. A remnant from a weather system in the western Pacific had intensified into a cyclonic storm over the Bay of Bengal and crossed the Andhra coast.

The eastern Pacific is currently hosting at least four active systems — two hurricanes, a tropical depression and a tropical storm. While Hurricane Jova and Hurricane Kenneth were churning their way across the warm waters, the Joint Typhoon Warning Centre (JTWC) had issued alerts for Tropical Depression Lidia (regenerating) and Tropical Storm Max.

The JTWC has notified the formation of a significant cyclonic circulation over the western Pacific during the next 24 hours. The system is expected to take shape off the Manila coast. The only region that is experiencing more hurricanes and tropical cyclones overall is the North Atlantic, where they have become more numerous and longer lasting, especially since 1995. The North Atlantic has averaged eight to nine hurricanes a year in the last decade, compared to six to seven a year before the increase.

But whether all of this is due to human-induced global warming is still uncertain. "We need a longer data record of hurricane statistics, and we need to understand more about the role hurricanes play in regulating the heat balance and circulation in the atmosphere and oceans," the researchers said.

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