India is likely to witness "below normal" monsoon rain from June to September 2023. This is because of the El Nino effect, according to Skymet Weather Services, a private Indian company that provides weather forecasting services. The upcoming monsoon rain is expected to be 94 per cent of the long average period (LPA) of 868.6 millimetres for the four-month-long period from June to September, Skymet said in a statement.
According to the Indian Meteorological Organisation (IMD), the long period average of rainfall is the average rainfall recorded over a particular region during a particular interval, say, 30 years or 50 years.
Rainfall is considered to be "below normal" in India when it is in the range of 90 to 95 per cent of the LPA.
Skymet had released a forecast on January 4, 2023, stating that monsoon in 2023 in India will be "sub-par".
What is El Nino?
When conditions in the Pacific Ocean are normal, trade winds blow west along the equator. Trade winds are steady winds which flow towards the equator from the north-east in the Northern Hemisphere or the south-east in the Southern Hemisphere, especially at sea. These winds take warm water towards Asia.
Cold water rises from the depths to replace the warm water. This process is called upwelling. However, there are two conditions which break these normal conditions — El Nino and La Nina. El Nino is also known as the El Nino-Southern Oscillation (ENSO) cycle and can impact weather patterns globally.
Both El Nino and La Nino typically last nine to 12 months, and can occur every two to seven years, on average.
El Nino is the phenomenon in which trade winds weaken, as a result of which warm water is pushed back east, toward the west coast of the Americas, where the Pacific Ocean is present.
Since trade winds have been pushed back east due to El Nino, the monsoon in India is likely to be affected.
In the Skymet statement, Jatin Singh, managing director of the company, said the key oceanic and atmospheric variables are consistent with ENSO-neutral conditions, the likelihood of El Nino is increasing, and there is a huge probability of the effect becoming a dominant category during the upcoming monsoon season in India. He said that the return of El Nino may be a warning sign for a weaker monsoon.
What other factors influence India’s monsoon?
Other factors influencing India's monsoon season include the Indian Ocean Dipole (IOD). The IOD is defined as sea surface temperature differences between poles or dipoles: a western pole in the Arabian Sea, and an eastern pole in the eastern Indian Ocean south of Indonesia. The western pole is located in the western Indian Ocean.
Due to the change in temperature gradients across the Indian Ocean, changes occur in the ascent and descent of moisture and air in certain regions.
When the IOD is sufficiently strong, it can negate the effects of El Nino, and steer the monsoon season in India. According to Skymet, El Nino and IOD are likely to be 'out of phase' this year, because of which there could be extreme variability in the monthly rainfall distribution. The second half of the monsoon season is likely to be more abnormal.
According to Skymet, northern and central parts of India are at risk of being rain-deficit.
During the core monsoon months of July and August, Gujarat, Madhya Pradesh and Maharashtra are likely to witness inadequate rain.
During the second half of the monsoon season, Punjab, Haryana, Rajasthan and Uttar Pradesh are likely to receive 'less than normal' rain.