Interactions between Cyclone Biparjoy, Typhoon Mawar, Bay of Bengal winds and the blocking of the monsoon trough for a couple of weeks likely to blame, experts say
Even Kerala, one of the rainiest states in India, has received very less rain in some districts. Photo: iStock South India has received its lowest June rainfall in 122 years according to the India Meteorological Department (IMD) due to extremely severe cyclone Biparjoy and other interactions of wind systems that led to a unique progress of the monsoon winds.
The region received 88.6 millimetres (mm) rainfall in the month of June which was 45 per cent less than the normal between 1971 and 2020, according to the IMD.
Many southern Indian states have huge deficits in rainfall despite the rapid progress of the monsoon in the past 10 days and the country-wide rainfall deficit being 10 per cent at the end of June.
As of July 4, four of the states have deficient rainfall. These are Telangana (53 per cent deficit), Kerala (52 per cent deficit), Karnataka (44 per cent deficit) and Andhra Pradesh (26 per cent deficit).
In Telangana, 12 districts have received large deficient rainfall (more than 60 per cent deficit rainfall) and 17 have received deficient rainfall (20-59 per cent deficit rainfall). Only four districts have received normal rainfall (19 per cent deficit to 19 per cent excess rainfall).
In Kerala, four districts have large deficient rainfall, while nine have deficient rainfall, only one district received normal rainfall. Kerala had a 34 per cent deficit rainfall in the pre-monsoon period as well, which means that one of the most rain-rich states in India, home to pristine rainforests of the Western Ghats, hasn’t received much rainfall since March.
The IMD has not cited any reasons for this lack of rainfall.
“The monsoon has been strikingly anomalous in its onset and progress because of the unusual interactions between Typhoon Mawar, Bay of Bengal winds and the blocking of the monsoon trough for a couple of weeks,” Raghu Murtugudde, a climate scientist at the University of Maryland and Indian Institute of Technology, Bombay, told Down To Earth.
The southwest monsoon arrived a week later than its normal date and after a few days of rapid progress, it stalled over the southern peninsula. It then made rapid progress again after June 21-22 and covered the entire country on July 2, six days earlier than its normal date of July 8.
“Biparjoy formed late because of this (interactions between Bay of Bengal winds and typhoons in the western Pacific Ocean) and this affected the arrival of the monsoon over the Western Ghats and peninsular India,” said Murtugudde.
The Arabian Sea has warmed by over 1.5 degrees Celsius since January which allowed Biparjoy to last for almost 10 days. This long life cycle of the cyclone allowed the monsoon trough to arrive at the same time over Mumbai and Delhi, according to Murtugudde.
“The configuration of the trough is rather unique as well and this allowed a faster progress of monsoon over the whole country and now the warm Arabian Sea is able to feed the monsoon,” he added.
Going forward, the situation may not improve much and even if it does, there may be flooding in the Western Ghats. In its July monthly outlook, IMD has shown (through a probabilistic rainfall map) that there is a chance of below normal rainfall in large parts of Tamil Nadu and southern Karnataka.
Another spectre looming over the prospects for good rainfall is the El Nino weather phenomenon which has already been declared by the World Meteorological Organization on July 4 and by the National Oceanic and Atmospheric Administration on June 8.
El Nino is the warmer than normal phase of the El Nino Southern Oscillation phenomenon and generally leads to suppressed monsoon rainfall.
The IMD has not declared El Nino conditions as yet but has highlighted in its monthly outlook for July that El Nino may develop in the month.
“The El Nino effects are subdued so far because of these weird confluences of natural variabilities like typhoons and cyclones which were affected by warming oceans, especially over the northern Arabian Sea,” said Murtugudde.
But there is always the possibility of the impacts showing up in July and later. “I expect to see more extremes over the northern Western Ghats, Northwest India and even over Pakistan,” Murtugudde added.
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