Explainer: Will the El Nino factor affect India monsoon rain prospects?

Tribune Web Desk

Chandigarh, February 15

The La Nina phase is about to pass and with it the anomalies of cool temperatures in the Pacific waters. According to the latest forecast by NOAA, a transition from La Niña to ENSO-neutral will occur mostly during the February-April 2023 season.

By February-April 2023, most models indicate the return of ENSO-neutral, with a probability of 82%. What is more concerning is the arrival of dreaded phenomenon of El Nino. Climate models are predicting potential return to El Niño by May-July, which coincides with summer, say experts.

El Niño is invariably linked to poor monsoon performance and has been considered as a threat

“During a La Niña, the tropical Pacific soaks up heat like a sponge and builds up the warm water volume. This warm water then spills across from the western Pacific to the eastern Pacific during an El Niño.

“Three consecutive years of La Niña means that the warm water volume is fully loaded and it is likely that the system is ready to give birth to an El Niño. Will it be a strong El Niño like the one during 2015-16? We may get some indications in spring itself,” says Raghu Murtugudde, Emeritus Professor at University of Maryland.

Relation between El Nino and Southwest Monsoon

El Niño is invariably linked to poor monsoon performance.

According to statistics, about 60% of the time there will be a probability of drought in the country during an El Niño year. Chances of below-normal rain will be 30%, while the prospect of normal rain remains very rare at 10%.

“As for the monsoon itself, if an El Niño state does emerge by summer, then we are more than likely to see a deficit monsoon. A transition from a La Niña winter (which we are in now) to a summer El Niño state tends to produce the largest deficit in the monsoon – of the order of 15%. This implies that the pre-monsoon and monsoon circulations tend to be weaker,” adds Murtugudde.

However, El Niño is not defined by any set rule book that shows the pattern of how it behaves and progresses.

“For instance, even the strongest El Niño has given normal monsoon rain of 102% in 1997, while weak El Niño conditions resulted in severe drought in 2004 to the tune of 86%.

“If we look back at the statistics from the year 2000 till 2019, there have been four instances of drought years,” say experts.  

In 2002 and 2009, the countrywide deficiency was 19% and 22%, respectively, which were considered severe drought years. While in 2004 and 2015, the deficiency stood at 14% each, which was again a drought.

There has been only one instance in the last 25 years (1997) that the country saw surplus rain of 2% despite El Niño.

According to GP Sharma from Skymet Weather, in an El Nino year, MJO and IOD can be the two saviours for monsoon.

“Under the gloomy scenario of El Nino, the oceanic parameters — MJO (Madden-Julian Oscillation) and IOD (Indian Ocean Dipole) are the two knights in shining armour for the Southwest Monsoon. Both the weather phenomena, if in a positive phase, are variably related to good monsoon rain over the country and are known for negating the effect of El Niño up to large extent. However, it is unclear whether that is a robust relation. It is also unclear if an IOD will evolve this year,” he says.

Several researchers have already raised an alarm citing an increase in frequency of extreme El Niño and La Niña events from about one every 20 years to one every 10 years by the end of the 21st century under aggressive greenhouse gas emission scenarios.

In a warming climate, rainfall extremes are projected to shift eastward along the equator in the Pacific Ocean during El Niño events and westward during extreme La Niña events. Less clear is the potential evolution of rainfall patterns in mid-latitudes, but extremes may be more pronounced if strong El Niños and La Niñas increase in frequency and amplitude.