Tamil Nadu

T.N. not experiencing more cyclones now than before

With the Tamil Nadu coast bearing the impact of Cyclone Burevi within days of having been battered by Cyclone Nivar, the question that many ask is whether the State has been experiencing more tropical cyclones in recent years than in the past.

A firm ‘no’ is the response from veteran meteorologists Y.E.A. Raj and S. Balachandran. They say occurrences in a year or two should not be construed as a trend. Instead, the data for at least 10 years should be taken into account.

Average figure

Pointing out that the State on an average gets one cyclonic system or disturbance annually, Dr. Raj, former Deputy Director-General of Meteorology (DDGM), explains that going by the data for the period from 1965 to 2019, the average number of systems that affected the Bay of Bengal region during October-December was 3.6 a year.

In other words, there were 198 weather systems in total. Apart from Tamil Nadu, the region includes Andhra Pradesh, Odisha and West Bengal, and the neighbouring countries of Sri Lanka, Bangladesh and Myanmar.

Different stages

The term, ‘cyclonic system or disturbance’, covers different stages — depression, deep depression, cyclonic storm, severe cyclonic storm, very severe cyclonic storm, extremely severe cyclonic storm and super cyclonic storm, which are all graded on the basis of associated maximum wind speed.

There has not been any perceptible rise in the number of cyclonic systems that crossed the Tamil Nadu coast. This is evident from the fact that 39 systems had hit the State in the 54-year period (1965-2019), Dr. Raj says, adding that the use of satellites for weather forecasting started in the mid-1960s.

Factors at play

There were years when the Tamil Nadu coast did not have even a single severe cyclonic storm, as had happened during 2001-10. But the State did record heavy rainfall in the period. For example, in 2005, when Tamil Nadu had bountiful rainfall, it was Andhra Pradesh that bore the brunt of the systems, he says.

Dr. Balachandran, the present DDGM, says the recent data reveal that it is the Arabian Sea region that experiences the increase in the number of systems. This can be attributed to factors such as warming of the sea and reduction in vertical wind shear, which is characterised by changes in the speed or the direction, or in both.

The coastal belt between Tiruvallur and Pudukottai is hit by more number of cyclones than the region south of Pudukottai. Among the reasons is Sri Lanka acting as a shield for the southern belt. In this context, the official recalls that Cyclone Ockhi, which devastated Kanniyakumari three years ago, was one of the four systems that have crossed the place in the last 100 years.

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Printable version | Jan 21, 2021 2:34:37 AM | https://www.thehindu.com/news/national/tamil-nadu/tn-not-experiencing-more-cyclones-now-than-before/article33235481.ece

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