Even then monsoon rainfall would end up below normal; overall deficit of 7% in India at present
The withdrawal of the monsoon this year is delayed for the 13th consecutive time. The winds of the southwest monsoon should have started retreating from northwestern India by September 17, but the withdrawal is nowhere in sight and the rainfall may extend well into October, according to experts.
Even then, the season (June 1 to September 30) could end up below normal, which is 90-95 per cent of the long period average of 868.8 millimetres.
Rains in October would go unaccounted for as monsoon rainfall by the India Meteorological Department (IMD). On September 21, the IMD indicated that monsoon withdrawal conditions may begin around the end of the forecasting period of September 21 to September 27.
There are numerous local and global reasons for the monsoon’s anticipated late withdrawal.
As of September 21, the country has an overall deficit of seven per cent, with 36 per cent of the districts having received either deficient (20 to 59 per cent less rainfall than normal) or large deficient (above 59 per cent less rainfall than normal) rains, according to data from the IMD.
The withdrawal of the monsoon from northwest India may begin between September 30 and October 9, according to a forecast by Elena Surovyatkina, a climate scientist at the Potsdam Institute for Climate Impact Research in Germany.
This means that the monsoon retreat will be delayed by 13 to 22 days in the northwest of the country.
Surovyatkina generates forecasts for the onset and withdrawal of the monsoon from three different places in India 40 days and 70 days in advance, respectively. These places are Delhi in northwest India, central India and northern Telangana. Her forecasts are based on temperature tipping elements for the monsoon in northern Pakistan and central India.
Due to the instability of the monsoon system over India in the current season and long break periods in August, she postponed her forecast for withdrawal and generated it 40 to 50 days in advance.
“The withdrawal from western Rajasthan will commence around September 25,” Akshay Deoras, a research scientist at the National Centre for Atmospheric Science and the Department of Meteorology, University of Reading, United Kingdom, told Down To Earth (DTE).
“After the withdrawal commences, it is expected to be rapid in the northern and north-central parts of India,” added Deoras.
However, the retreat may not be abrupt from the Eastern Ghats, said Surovyatkina. It would start in the first week of October, with the last rains between October 7 and October 17. In North Telangana, the monsoon season could bid adieu anytime from October 10 to October 20.
Other experts concurred with her assessment.
The Intertropical Convergence Zone (ITCZ) is a band of winds and rainfall that circulates the Earth and connects the trade winds from north and south of the Equator. Monsoon season begins over the Indian subcontinent when the ITCZ shifts northward.
“The Arctic sea ice loss is high and the northern hemisphere was warm — especially the tropical Atlantic. The ITCZ is pulled north and the El Nino pattern has a global warming signature in it in the western Pacific,” Raghu Murtugudde, professor of climate studies at the Indian Institute of Technology, Bombay and an emeritus professor at the University of Maryland, told DTE.
All of these factors interact to influence the movement of the monsoon trough and monsoon depressions with forcing from the upper atmosphere and moisture supply from the Arabian Sea, according to Murtugudde.
“I would expect the monsoon to continue into October and the deficits to drop. Especially over Uttar Pradesh, Bihar, Chhattisgarh, Odisha and the northeast,” concluded Murtugudde.
“The rainfall pattern during the rest of September will be dominated by thunderstorms over east, central and southern parts of the country. The daily all-India average rainfall in this period is not expected to be significantly above the normal,” said Deoras.
“As a result, the expected June 1 to September 30 total rainfall will be below the long-period average, with the largest possibility of it being below the normal,” he added.
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