What caused the deluge in Kerala? Experts analyse

Aranmula rain
Aerial view of flooded Aranmula

Madden-Julian oscillation

- Dr M G Manoj

The geographical location of Kerala as a slender strip of land vertically sandwiched between a sea and a mountain range along the annual route of monsoon winds makes it a heavy-rain state. This time, though, quite a few other natural and man-made factors contributed to the August deluge that has similarities with the ‘Great Flood of 99’ the region witnessed in 1924.

The Arabian Sea by the state’s west has been warming up, accentuating evaporation that leads to formation of rain clouds. To its east, Kerala has the Sahyadri Mountains. Its high ranges check monsoon winds from the Indian Ocean, trapping the humid air to condense in high altitudes and fall as rains. These are nothing new.

This year, pre-monsoon showers began drenching Kerala as early as from May, a month ahead of the usual June 1 tryst with rains. Added to that happened the intra-seasonal variability in tropical atmosphere called Madden-Julian oscillation that manifests as anomalous rainfall. What’s more, a low-pressure trough formed in the Bay of Bengal recently moved of Orissa westward, adding to the precipitation in Kerala.

Why in Kerala?

It’s a rise in sea temperatures that forms low-pressure troughs. It’s the nature’s way to regulate heat, because low pressure formation will bring in rains and cool the air. When, earlier this week, a low-pressure area was formed along the Odisha coast by the Bay of Bengal, the air above the land sucked in the humid air from around the state. That meant a vigorous eastward movement of monsoon winds in Kerala, which has the Western Ghats (Sahyadri) checking them. Result: massive formation of clouds on the Kerala side of the mountains, leading to rains.

Global warming

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Global warming and resultant climate change heat up seawaters, leading to low-pressure formations. Usually they develop in a time span of two weeks. This monsoon, they formed much more frequently and it rained far more heavily. That led to Kerala’s gravest deluge in almost a century’s time. More studies are required to learn the exactness of the rise in sea temperatures.

(The writer is a scientist, Radar Research Centre, CUSAT.)

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Low-pressure area in the Bay of Bengal

- Dr K Santhosh

A low-pressure trough formed on the Odisha coast of the Bay of Bengal has led to a spurt in the rains in Kerala this week. The result was high-speed winds carrying humidity. They brought 30 per cent surplus rains and created unusual levels of flooding across the state. Right now the trough is moving northeastward towards Chhattisgarh: this means that Kerala is through with the worst phase of this spell of rains by Saturday and the winds too would have stopped by then.

(The writer is director, Meteorology Department, Thiruvananthapuram.)

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Solar Minimum and weak El Nino

- Dr A Rajagopal Kamath

A once-in-eleven-year dip in the activity in the cycle of the sun, which is scientifically known as Solar Minimum, has added to the monsoon rains this month amid a low-pressure trough this week. It is a period marked by weakest solar radiation, resulting in its increased beaming of cosmic rays towards the earth. If the start of monsoon this time in end-May saw unusual spells of thunder and lightning, it was also because of Solar Minimum.

El Nino, which typically weakens the monsoon by veering its winds away from the Indian subcontinent by unusual warming of surface waters in the eastern tropical Pacific Ocean, has petered out. Instead that warm current from the tropical region of the ocean around Indonesia has drifted towards Indian seas. That too aided rains, which struck Kerala in a big way this week.

Let’s not forget that 1924 Kerala deluge, called the Great Flood of ’99, was also in a Solar Minimum year.

(The writer is an astronomer, cosmologist and author.)

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