The India Meteorological Department (IMD) has kept its forecast of normal rainfall from June-September this year, unchanged from its prediction in April. At 96% of the Long Period Average (a 50-year mean) of 87 cm, this is at the lowest end of what is considered ‘normal.’ The chances of an El Nino forming are near certain, and this will likely mean that rainfall levels will be below normal in northwest India, the department said on May 26.
The key factor influencing the quantum of monsoon rains is the development of an El Nino, a cyclical phenomenon of warming in the central Pacific Ocean that is linked — in six out of ten years — to diminished rainfall in western and northwestern India, as well as the western parts of central India. Since 2019, India has been under the influence of the converse La Nina, which is a cooling in those regions, and therefore linked to substantial monsoon rains.
Compensating for El Nino
Another ocean-linked phenomenon, called the Indian Ocean Dipole (IOD), which is characterised by a difference in temperature between the western and eastern parts of the Indian Ocean, is also likely to play out during the monsoon. A positive dipole, characterised by a warming in the western half of the ocean relative to the eastern, is expected to compensate for some of the rain sucked out due to El Nino, said D.S. Pai of the IMD.
“In 1997, India had a strong El Nino but received 2% excess rain because of positive IOD. However, both haven’t appeared at the same time since that year. Also, the link between IOD and good monsoon rains isn’t as strong as the link between El Nino and diminished rains,” he added.
June rains below normal
IMD officials added that monsoon rains over most parts of India, including the rainfed-agriculture zones of the country, will be between 92% and 104% of the average. Southern India will receive above normal levels of rainfall.
The IMD has forecast that the monsoon will arrive over Kerala on June 4, three days after the usual due date. While onset dates have no link to the quantum of monsoon rainfall, IMD’s monsoon models say that June rainfall is likely to be “below normal” (<92% of the average of 16.54 cm). Except in some areas of southern peninsular India, northwest India, north India and pockets of northeast India, rainfall is likely to be “below normal” in June, a press statement from the agency noted.