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Freak phenomenon along the southern coast of India

 T. NANDAKUMAR

U.N. recognises terminology borrowed from Kerala fishermen 

T. Peter vividly recalls the panic that gripped the coast for five days from May 17 in 2005. “The sea came surging in, inundating vast areas… It was an unprecedented phenomenon, occurring as it did in perfectly fair weather.”

With memories of the 2004 tsunami still fresh in the minds of people, the event sparked alarm all along the coast. As many as 12,000 people were affected as the tidal swell slammed the coastal belt, from Adimalathura to Pozhiyoor.

Residents fled their waterlogged houses; boats and fishing equipment were damaged. “It took several days for the situation to return to normality,” remembers Mr. Peter, president of the Kerala Swathantra Matsya Thozhilali Federation, who was at the forefront of relief operations.

Baffled by the freak phenomenon, scientists initially attributed it to an intensive pre-monsoon swell. The Centre for Earth Science Studies (CESS) later conducted a detailed study, which traced the origin of the swell to a cyclonic storm off the west coast of Australia.

The project, which involved tsunami expert Tad Murty of Canada, established that swells generated in the southern Indian Ocean by storms near Antarctica could propagate northward, to the Arabian Sea and the Bay of Bengal.

“Travelling thousands of kilometres across the entire ocean basins, the swell gets amplified when it encounters a coastal current directed southward, resulting in increased wave setup, a phenomenon referred to as remote forcing,” says Director of CESS N.P. Kurian, who was part of the study.

‘Kallakkadal,' the term used to name the freak flooding, was borrowed from the parlance of fishermen. “In local parlance, it means the sea that arrives like a thief, unannounced,” says Dr. Kurian.

In February this year, UNESCO formally accepted the term to explain the freak occurrence. Earlier, the World Meteorological Organisation and the Intergovernmental Oceanographic Commission too recognised the terminology. “The formal recognition could perhaps pave the way for the term to be included in subsequent editions of dictionaries,” Dr. Kurian says.

Mr. Peter said the adoption of the term by the U.N. represented a marriage of conventional wisdom and scientific endeavour. “It calls for further studies to be taken up for hazard assessment and disaster mitigation.”

‘Kallakkadal' is known to occur along the southern coast of India, mainly during the pre-monsoon period, in April and May, marked by clear weather. The flooding turns severe on the days of spring tide. Though not well documented in scientific literature, the swells occur almost every year with varying intensity. They are characterised by long-period waves, with frequency of more than 15 seconds.

http://www.thehindu.com/sci-tech/science/article3318196.ece?homepage=true