Possible El Nino conditions this year could lead to deficit in monsoons: climate experts

El Nino and La Nina are climate patterns in the Pacific Ocean that can affect weather worldwide. Episodes of El Nino and La Nina typically last 9-12 months, but can sometimes last for years. El Nino and La Nina events occur every two to seven years, on average, but they don’t occur on a regular schedule, say experts. Generally, El Nino occurs more frequently than La Nina.

According to the latest forecast by National Oceanic and Atmospheric Administration (NOAA), a transition from La Niña to ENSO-neutral will occur mostly during the February-April 2023 season.

Climate models are predicting a potential return to El Niño by May-July, which coincides with the summer monsoon that spans from June- September.

The occurrence of three consecutive La Niña in the Northern Hemisphere is a relatively rare phenomenon and is known as the ‘triple dip’ La Niña. The latest triple dip La Nina occurred between 2021-23.

“During a La Niña, the tropical Pacific soaks up heat like a sponge and builds up the warm water volume. This is the warm water that 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,” said Raghu Murtugudde, Visiting Professor, Earth System Scientist at IITB, and Emeritus Professor at the University of Maryland.

El Niño is invariably linked with poor monsoon performance. According to statistics, about 60 per cent of the time there will be a probability of drought in India during an El Niño year, say experts. Chances of below-normal rain will be 30 per cent, while the prospect of normal rain remains very rare at 10 per cent, they add.

“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 per cent. This implies that the pre-monsoon and monsoon circulations tend to be weaker,” added Murtugudde.

However, El Niño conditions have been known to be unpredictable as well, climate experts admit. For instance, even the strongest El Niño has given normal Monsoon rains of 102 per cent in 1997, while weak El Niño conditions resulted in severe drought in 2004 to the tune of 86 per cent.

Statistics from the year 2000 till 2019 show that there have been four instances of drought years. In 2002 and 2009, the countrywide deficiency was 19 per cent and 22 per cent, respectively, which were considered severe drought years. While in 2004 and 2015 the deficiency stood at 14 per cent each, which was again a drought.

There has been only one instance in the last 25 years, since 1997, when the country saw surplus rain of 2 per cent despite El Niño.

G P Sharma, President, Meteorology and Climate Change, Skymet Weather says while the El Nino forecast is available for the next 9 months, model accuracy of more than 4 months is low.

“Yet, the past record of El Nino indicated around this time, is a testimony of spoiled southwest monsoon. ENSO forecasts for December 2013 and December 2017 were akin to December 2022. Both these years witnessed sub-par southwest monsoon rainfall leading to moderate drought in 2014 and near drought in 2018. Earlier, similar patterns in 2003 and 2008 also proved dreadful, defacing the Indian monsoon in 2004 and 2009, both drought years. The initial projections indicate ENSO building up sharply and El Nino getting augmented rapidly during monsoon. As of now, the principal indicator Nino 3.4 holds ground and negative anomalies still prevail,” said Sharma.

Recent research indicates that the frequency of extreme El Niño events increases linearly with the global mean temperature, and that the number of such events might double (one event every 10 years) under 1.5°C of global warming. This pattern is projected to persist for a century after stabilisation at 1.5°C, indicating continuing high risks.

Changes to the frequency of extreme El Niño and La Niña events may also increase the frequency of droughts and floods in South Pacific islands.

During and following El Niño, the global mean surface temperature increases as the ocean transfers heat to the atmosphere. Warming of the waters, such as during El Niño, eliminates the cloud deck and leads to further sea surface warming through solar radiation.

“We do get a mini-global warming during an El Niño since the warm water spreading across the Tropical Pacific releases massive amounts of heat to the atmosphere,” said Murtugudde adding that an El Niño this year could push global warming to rise past the 1.5° C level.

Several researchers have already raised an alarm citing an increase in the 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.