Science

The flash floods in Kerala come from a distance

The origin of the flash floods lay in the southern Indian Ocean.   | Photo Credit: H_Vibhu

The flash floods (Kallakadal) that wrecked havoc in the coastal areas of Kerala come furtively from a distance, nearly 6,000 km away from the Southern Indian Ocean, scientists have concluded.

Kallakadal, as they are locally known, or flash floods that swept across the Kerala coast in 2005 caught the scientific community and local communities off-guard. There were no apparent oceanographic reasons or scientific explanations for the process.

During the event, the sea surges into the land and inundates vast areas to leave a trail of destruction. In 2012, UNESCO formally accepted the term for scientific use.

While locally visible weather features like cyclones or storm surges could account for the usual coastal flooding, it is the absence of such elements that baffled the scientists.

Locals termed the process Kallakkadal, to suggest that the sea came in stealthily to steal away all their belongings. The failure of the ocean forecast systems to predict the process added mystery to it.

Studies carried out by the scientists of the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, revealed that the flash-flooding reported along the south-west coast was caused by the swell waves coming from the Southern Ocean.

The researchers — P.G Remya, T. M. Balakrishnan Nair S. Vishnu, B. Praveen Kumar and B. Rohith — recently published a paper in the Journal of Geophysical Research (Oceans) explaining the process.

Assessing the 2005 events and the generation mechanism and environmental conditions that caused the flooding, researchers suggested the “meteorological conditions in the Southern Indian Ocean creates helpful conditions for the generation of long period swells. These oceanic regimes are marked by strong westerly jet streams in the atmosphere. Sometimes, low-pressure cyclonic circulations (clockwise circulation) will be formed within these westerlies, and very slowly they move northward...”

These anomalous wind patterns, they say, have a strong northward component, and sustain over the ocean for a long period, typically around two to three days. These strong winds and the availability of large ocean area create helpful conditions for the generation of swells. According to the paper, these swells travel northward and reach the Indian coasts within three to five days creating havoc in the coastal areas.

It was also found that all the 10 high-wave incidents that were reported along the coast in 2005 were driven by a surge in swell waves coming from the Southern Ocean.

The proper monitoring of the oceanic-atmospheric conditions in the Southern Ocean should give a clue on the possible development of the events, and the subsequent generation and propagation of swells in the Indian Ocean, said Dr. Nair, the co-author of the paper and Head, Information Services and Ocean Sciences Group of the Centre.

The intensity and direction of the swells can be predicted, and with advance knowledge about the tidal conditions in the Northern Indian Ocean forecasters would be able to predict the high wave activity/Kallakkadal events in the NIO coastal regions at least to two to three days in advance, he said.


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Printable version | Jul 25, 2021 5:49:49 AM | https://www.thehindu.com/sci-tech/science/The-flash-floods-in-Kerala-come-from-a-distance/article16706744.ece

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