Is La Nina in the offing? How the shift from El Nino may impact monsoon, summer in India this year

India may experience increased rainfall during the southwest monsoon season. This comes after a dry winter season for most of northwest, northeast and central India and a prediction for sweltering heat in the spring and summer season for these regions. 

The surge in precipitation is expected due to a La Nina event predicted to develop later in the year, while the heat may be because of the ongoing El Nino conditions and background warming from the greenhouse gas (GHG) emissions in the atmosphere. 

The El Nino and La Nina are the two phases of the El Nino Southern Oscillation (ENSO) phenomenon that occurs in the equatorial Pacific Ocean. 

During El Nino, temperatures higher than normal prevail mainly over eastern and central parts of the equatorial Pacific Ocean. During La Nina the exact opposite happens. 

While El Nino is mostly associated with hot summers and lack of rainfall during monsoon season in India, La Nina brings cooler temperatures and general increase in rainfall for the country. 

La Nina itself, however, may be changing in character. For instance, the early and intense heat waves across India from March to June 2022 occurred while a La Nina event was in place in the equatorial Pacific Ocean. 

The current El Nino phenomenon in the equatorial Pacific Ocean may end by April. After a brief phase of ENSO neutral conditions (neither El Nino nor La Nina) from April to June, the situation may shift to La Nina conditions from July, according to the latest ENSO update from the National Oceanic and Atmospheric Administration (NOAA) of the United States. 

“The latest official probabilistic forecast issued by NOAA indicates a greater than 70 per cent chance of a La Nina event during September-November 2024,” Akshay Deoras, a research scientist at the National Centre for Atmospheric Science and Department of Meteorology, University of Reading, United Kingdom, told Down To Earth (DTE).

“Observations from the sub-surface part of the equatorial Pacific Ocean indicate a developing and expanding patch of cooler than normal water, which will cause the termination of the ongoing El Nino event early summer, and push the system towards a La Nina-like state in late summer,” he added. 

Usually prediction of ENSO conditions for the summer and monsoon seasons is difficult because of the spring barrier. During the spring season in the northern hemisphere, the interaction between the ocean and atmosphere becomes weaker due to which prediction becomes challenging.

“La Nina is just an amplification of normal cold conditions in the eastern tropical Pacific. The spring barrier may not be so important since strong El Ninos tend to transition into La Ninas,” Raghu Murtugudde, a climate scientist at the Indian Institute of Technology, Bombay and University of Maryland, United States, told DTE.

“While the spring predictability barrier can’t be ignored at present, historical events show that big El Nino events (more specifically around 63 per cent of them since 1950) are generally followed by La Nina events,” said Deoras. 

One recent example of this is the 2016-17 La Nina event, which followed the big 2014-16 El Nino event. “If we include weak El Nino events, over half of them have been followed by La Nina events since 1950. So observations, model forecasts, and past statistics indicate a good possibility of witnessing La Nina in the second half of 2024,” said Deoras. 

“I expect a La Nina this year but the key question is how strong it will be. The El Nino may collapse suddenly around May and transition to a strong La Nina,” according to Murtugudde.

This could mean more than average rainfall for most of India during the latter part of the southwest monsoon season which starts in June and has been extending into October in the past few years. 

“There should be a positive impact on the all India mean rainfall but states like Uttar Pradesh, Jharkhand and Bihar may again face a deficit,” said Murtugudde. 

“It is not clear yet when La Nina will form, but current forecasts indicate that it can remain present during the second half of the southwest monsoon season. Statistics indicate that the performance of the southwest monsoon in India during La Niña years has been satisfactory in general,” said Deoras. 

The previous La Nina event which ended after three years in March 2023 had caused above normal and extended monsoon seasons. For instance, the monsoon season in 2022 ended up with an all India excess of six per cent and rains extended well into October. 

La Nina during the three years was also responsible for many extreme rainfall events and consequent floods, flash floods and landslides during the monsoons across many states of India, especially in the later part of the seasons. 

This may happen if La Nina develops during the later part of the monsoon season in 2024 as well. This is also at the back of general warming of the atmosphere and oceans that is also aiding the occurrence of such extreme weather events. 

“Most of what is happening in the northwest and over Pakistan are directly related to the Arabian Sea warming. The rest of India may see more extremes because of the La Nina,” said Murtugudde. 

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