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Kerala must be alerted of low-pressure areas in August

Vinson Kurian Thiruvananthapuram | Updated on August 07, 2020 Published on August 07, 2020

A man wades through a flood affected area during heavy rainfall, in Kochi on Friday   -  PTI

IMD study shows that whenever a low-pressure system forms near Odisha, rainfall scale up over Kerala

The heavy monsoon precipitation, flooding and landslides in Kerala are of a piece with its well-documented vulnerability to global warming as represented in the enhanced frequency of sudden and extreme monsoon rainfall events even when the overall rainfall in the State is on a declining trend.

Analysing the ongoing heavy to heavy rainfall over the State, Mrutyunjay Mohapatra, Director-General, India Meteorological Department (IMD), told BusinessLine that the mutually contrasting trend during the past 30 years is a linear one and embedded with year-to-year variation of the rainfall data. “But one can see that the intensity of rainfall this year is not comparable with that of 2018. This is because the rain-driving low-pressure area system moved across much faster this year. For one, frequency of low-pressure events is the most in August. For another, most of the systems form in the Bay of Bengal and move into land from the coast of Odisha,” Mohapatra said.

Another IMD study shows that whenever a low-pressure system forms near Odisha, rainfall scale up over Kerala. The mechanism here is very simple, Mohapatra said. “The air rotating anticlock-wise goes up, encounters cold air and condenses to form cloud and rain. The capacity of air to hold moisture is what decides the rainfall amount.”

Changes in troposphere

Global warming is raising the temperature not only at the surface but also in the troposphere. Warmth adds to its capacity of the air to hold moisture. This is what leads to heavy rains from global warming which impacts even the higher levels of the atmosphere (troposphere). The raised capacity to hold moisture allows deep convective clouds to form.

It is these convective clouds which let down extremely heavy rainfall. This link has been proved scientifically. “Everything in the monsoon paradigm remains the same. The only major differentiator is the enhanced moisture-holding capacity of the air. The trend is visible in Central India also.”

The contribution of June, July and September rainfall to annual rainfall is decreasing for a few regions while that of August is increasing in few others, Mohapatra said. July rainfall is decreasing for most parts of Central India while it is decreasing for the North-East. However, both June and August rainfall is increasing over Central and South-West of the country.

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Published on August 07, 2020
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