Arctic sea ice loss causes extreme rainfalls in India, suggests research

New Delhi: A study by the National Centre for Polar and Ocean Research under the ministry of earth sciences reveals that the frequency of extreme rainfall events (daily rainfall >150 mm) in the month of September in central India shows an ascending trend with a decrease in summer sea ice extent during the Early Twentieth Century Warming (ETCW, 1920–1940) period and recent warming since the 1980s.

According to the paper published in the journal Nature on June 22, the satellite records in 1979 suggest that the Arctic Sea Ice Extent (SIE) has been declining at a rate of about 4.4% per decade in annual mean. 

According to researchers at NCPOR, very warm sea surface temperatures over the Arabian Sea and the changes in upper-level atmospheric circulation caused due to Arctic sea ice loss together contribute to an increase in extreme monsoon rain in central India, particularly in the month of September.

While the final links have not been established between the rapid sea ice decline and the extreme weather events in the tropics, or the extreme rainfall events during monsoon in India, NCPOR scientists suggest that it may be causing a high-pressure area over Northwest Europe. 

According to a report in an English daily, in 2015 TN Krishnamurti, a meteorologist at Florida State University in his paper proposed that the heat released in the atmosphere during extreme rainfall events over northwest India ultimately travels to the Canadian Arctic region and causes a significant sea ice loss in the Arctic.

“As the sea ice reduces in the Barents-Kara Sea region of the Arctic Ocean, it allows more convection and upward air motion over the open ocean during summer. This air then descends at a further south location over northwest Europe and intensifies a deep anticyclonic atmospheric circulation. The associated meandering of the jet stream also contributes to it. This abnormal upper atmospheric disturbance is then further propagated towards subtropical Asia extending over the Indian landmass. The upper-level atmospheric circulation change along with an above-normal Arabian Sea surface temperature help in enhanced convection and moisture supply - resulting in extreme rainfall events during August-September,” said Sourav Chatterjee, researcher and lead author from NCPOR.

As per a report in an English daily, the effects of Arctic Sea ice changes on the mid-latitudes are still debated but it is often proposed that an increase in mid-latitude extreme weather events is associated with Arctic Amplification induced loss in sea ice. Over the past 30 years, the Arctic has warmed at twice the rate as the entire globe — this phenomenon is known as Arctic Amplification, according to the US’s National Snow and Ice Data Center.

“In summary, our results indicate since the 1980s, rapidly declining summer sea ice extent in the Kara Sea region exhibits a more robust relationship with the frequency of Indian Summer Monsoon Rainfall extremes, compared to mean ISMR intensity; extreme precipitation events in central India during the late phase of ISMR season can be explained by the combined effect of the upper atmospheric circulation anomalies resulting from reduced sea ice extent and low-level circulation anomalies over west-central India supported by warm sea surface temperature anomalies in the north-western Arabian Sea,” the paper stated.

The changes in the sea-ice extent in the Arctic affect the atmospheric patterns. Although the mechanism of the phenomenon is not clear yet, it is evident that it caused the three-fold rise in extreme rainfall in recent decades.

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