Delayed monsoon: How a possible El Nino can lead to failed rains in parts of India

A cyclone before onset, floods also not ruled out; farmers across the country need to be prepared, say experts

By Akshit Sangomla
Published: Tuesday 16 May 2023
Photo: iStock

The upcoming southwest monsoon season may be delayed and shortened with skewed distribution of rainfall among various regions. 

A link with a poor monsoon season and an El Nino event developing in the equatorial Pacific Ocean this year has been made by several experts recently, even as the possibility of the warming event grew stronger.

The event is 80 per cent likely in the May-June-July period and 90 per cent likely in the June-July-August period, according to the National Oceanic and Atmospheric Administration (NOAA) of the United States.

El Nino, the warmer-than-normal phase of the El Nino Southern Oscillation (ENSO) phenomenon, is generally associated with less intense rainfall than normal during the monsoon season for India. Delayed onset and drought conditions have also been observed during El Nino years.

The strength of an ENSO event is measured by the Ocean Nino Index (ONI), which is the departure of sea surface temperatures from the normal in the central equatorial Pacific Ocean, according to NOAA.

When the index is between 0.5 and 0.9, a weak El Nino event is said to prevail and when it is above 1, it indicates a moderate El Nino event. When the index crosses 1.5 but is less than 1.9, the event is strong and it is very strong when the index is above 1.9.

Many ENSO models are predicting an ONI of more than 1.5 for the current El Nino event, according to data from NOAA. Some models are even predicting an ONI of more than 2.

During the last major El Nino event from September 2014 to May 2016, the ONI was as high as 2.6, making it a very strong El Nino event.

“There is a huge potential for the El Nino to impact the monsoon season this year and farmers across the country need to be prepared for this,” Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology (IITM), Pune, told Down To Earth.

“Usually an El Nino event peaks during the winter season but the current event seems to be developing quite rapidly. The fact that there is going to be a delay in the onset of the monsoon season is indicative of this impact. Further, there may be widespread regional deficits in rainfall across the country,” said Koll.

The withdrawal of the monsoon is usually early in an El Nino year, according to Koll. The late onset and early withdrawal leads to shortening of the overall rainfall season, he added.

Also, there are no signs of any compensatory factors such as the development of a strong Indian Ocean Dipole, which usually makes up for a decline in rainfall during an El Nino period, the expert noted.

This doesn’t mean that there will be no extreme rainfall events or floods. “In fact we should prepare for a season of floods in the time of drought”, the expert added.

“If the transition from a La Niña winter to an El Nino summer plays out like it usually does, then the onset may be delayed with a deficient June rainfall,” Raghu Murtugudde, a climate scientist at the University of Maryland and Indian Institute of Technology, Bombay, said.

“The cross-equatorial flow is strong right now. So, we have to see how the trough moves over the Andaman-Nicobar and into the Bay of Bengal in the next week or two,” Murtugudde added.

Another factor could be the possibility of the development of another cyclone closer to the onset of the monsoon, predicted experts. This happens when the onset of the monsoon season is delayed or weak which creates atmospheric and oceanic conditions conducive for cyclone formation.

Such cyclones have been observed in the past few years, such as Cyclone Nisarga in 2020 and cyclones Yaas and Tauktae in 2021.

“If a cyclone develops towards the onset of the monsoon season, then it could further have an impact on the distribution of rainfall during the beginning of the season,” said Koll.

There is still a couple of weeks left for the monsoon onset and so, a cyclone may come along and throw a monkey wrench into the monsoon forecasts, Murtugudde noted.

The Bay of Bengal has already experienced Cyclone Mocha in the second week of May, 2023, which grew to become a super cyclone and made landfall along the Myanmar coast.

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