Fear floods loom over state as heavy rainfall continues due to Asani
Intense low pressure and atmospheric instability caused by rise in sea-surface temperature are leading to regular formation of cumulonimbus clouds on the Western Coast, according to climate scientists.
The Arabian Sea has been warming at an alarming rate in the last three decades, studies by the department of atmospheric sciences at Cochin University of Science and Research showed. The maximum sea surface temperature in the 1980s was 29 degrees Celsius. This has crossed 30°C now, according to the researchers. Experts have linked the phenomenon to climate change.
The cumulonimbus clouds formed due to the warming sea have high water-holding capacity and cause sudden, erratic rainfalls in states like Kerala, the department concluded.
These clouds are a relatively new phenomenon on the Western Coast, and they stretch over 1-14 kilometres, said S Abhilash, associate professor of the department.
Warming in the Arabian Sea is about 1.5 times higher than that of other seas across the world, the study pointed out. This temperature rise has enormous consequences in the form of increased frequency of deep (cumulonimbus) clouds even during monsoon, leading to very heavy to extreme rainfall and cloud-burst type events in the state.
Comparative studies of the rain patterns of the west coast done by the university indicated that cumulonimbus clouds became active in the Kerala state over the last five years. Earlier, they were not seen during the southwest monsoon.
But now, they are unexpected and occur at regular intervals throughout the year irrespective of monsoon season, the expert said.
It is difficult to predict the formation of these clouds much in advance, he added.
Abhilash told Down to Earth:
The rains lashing Kerala at present are not summer rains or the advance onset of the Southwest Monsoon, which is due for May 27. These are unconventional and unseasonal rains caused by climate change, and they may continue for a few more days.
Cyclone Asani might have contributed slightly to the current situation, he added.
Almost all parts of Kerala have received an average of 20 centimetres of rainfall in the last three days, according to the India Meteorological Department. This may have led to a general impression that the monsoon has arrived early, experts said.
Rainfall was accompanied by gales and thunderstorms, and many-low lying areas have been inundated, according to media reports.
In the past, only typical rain clouds stretching up to 7 km would form over the western coast. These would cause longer spells of moderate rainfall in Kerala, meteorologists said.
The southern state is currently threatened by enhanced deep convection and cloud-burst extreme events, according to Abhilash.
An enhanced deep atmospheric convection caused by the vertical transfer of heat and moisture is visible in the eastern Arabian Sea, he said.
Cloud bursts caused massive landslides in the state in 2019 and 2020.
Along with rains, cumulonimbus clouds bring seasonal winds. The high-velocity winds wreak havoc sometimes, uprooting trees and destroying crops. The average wind speed in Kerala during monsoon is 40 km per hour, while winds caused by cumulonimbus clouds are 60 km per hour, and it does not blow in a particular direction, according to experts.
These clouds also cause thunder and lightning, which used to be a rare occurrence in Kerala during monsoons. This is because the cumulonimbus clouds are thick and motionless and cover a wide area, the kind that tend to discharge electricity, said Abhilash.
Kerala has been battered by excess rain in summer this year and the showers have not subsided yet due to the continuing effect of Cyclone Asani. There is a widespread fear the successive spells of heavy rain may set off floods like in 2018 and 2019.
But IMD has predicted a normal southwest monsoon this year, highlighted Abhilash. The rainfall this season will be evenly distributed, the weather agency said.
“What the cumulonimbus clouds are prompting us is the need to enhance disaster management mechanisms against extreme weather events throughout the year,” said Abhilash.
So far, the state authorities have only focused on rescue measures post tragedies, and there was no advance preparedness, he pointed out. “Though there are limitations in predictions, we have to evolve decentralised disaster management mechanisms covering the whole state.”
Quick interventions are possible if we have a decentralised permanent mechanism for rescue, rehabilitation and even advance relocation, he added.
The increased frequency of intense precipitation and forming of deep convective clouds over the west coast must be taken into consideration while thinking about future development plans for the state, the expert said.
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