The monsoon process begins in April-May with the formation of a deep band of cloud in the equatorial Indian Ocean which moves northwards. After reaching the Bay of Bengal, it mixes with local systems generated in the head bay and marches into the mainland bringing rain everywhere. However, this did not happen in June this year.
After an early onset over Kerala on May 23, further advance of the monsoon over the Indian region was restricted to the west coast and southern peninsula till June 24.
This resulted in a massive deficit of 54 per cent in all-India rainfall in the first three weeks of June. Though there were a little bit of rain in the last week, the overall deficit in June was 48 per cent.
The June shortage was close to the lowest ever recorded rainfall (50 per cent drop in June 1926) since 1871. It could not be made up in the rest of the season.
This severe shortage in June, contributed to the final 23 per cent deficiency in
all-India summer monsoon, which is comparable to the two most severe droughts in the last 100 years – 24 per cent shortfall in 1972 and 22 per cent deficiency in 2002.
“It happened because clouds behaved peculiarly in the Bay of Bengal. The cloud-bands formed and disappeared after every two-three day,” Sulochana Gadgil, from the centre for atmospheric and oceanic sciences at the Indian Institute of Science, Bangalolre, told Deccan Herald.
In a typical monsoon year, bay clouds sustain to bring out rain over the landmass. But this year they lost to their competitors in the eastern equatorial Indian Ocean.
The culprit, Gadgil said, was an “extraordinarily warm” equatorial Indian Ocean.
Since 1982, such a high sea surface temperature was observed only once in 1995.
Competition between bay and equatorial clouds is known. But it generally ended in Bay’s victory, resulting in copious rainfall.
“Dominance of equatorial Indian Ocean is a rare event seen this year. Bay is a fertile region (for cloud formation), which behaved very peculiarly,” Gadgil said.
Gadgil – a veteran in atmospheric sciences who studied the monsoon for three decades – admitted that scientists had not yet understood the reasons.
However, usual suspects like El Nino and Equatorial Indian Ocean Oscillation did not have any role in influencing the June rainfall. Any possible impact of global warming has also been ruled out.