“Kallakadal” Freak phenomenon along the southern coast of India T. Nandakumar

Freak phenomenon along the southern coast of India
T. Nandakumar
http://www.thehindu.com/todays-paper/tp-national/article3318683.ece

THIRUVANANTHAPURAM, April 16, 2012
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.

Detailed study

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.

“The study highlights need for regular monitoring of Antarctic storms.
A global database on storm surges will be a critical input for a
numerical model that could help to predict the swell waves and coastal
flooding,” says Dr. Kurian.