GS Paper I

News Excerpt

India may witness increased rainfall during the southwest monsoon season following a dry winter and predictions of intense heat.

More details on the news:

• Predictions about the increased rainfall in India come 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. 
• As per National Oceanic and Atmospheric Administration (NOAA) forecast, 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.
• The latest official probabilistic forecast issued by NOAA indicates a greater than 70 % chance of a La Nina event during September-November 2024.

La Nina

• Also known as ‘El Viejo’ or cold event, La Nina is observed when the water temperature in the Eastern Pacific gets comparatively colder than normal, as a consequence of which, there is a strong high pressure over the eastern equatorial Pacific.
• The difference in pressure between Eastern Pacific and Western Pacific/Asia causes a moisture-laden wind movement from East to West Pacific and Asia.
• As a result, La Nina causes drought in the South American countries of Peru and Ecuador, heavy floods in Australia, high temperatures in Western Pacific, Indian Ocean, off the Somalian coast and a comparatively better monsoon rains in India.
• Generally, El Nino and La Nina occur every 4 -5 years. El Nino is more frequent than La Nina.

El Nino

• El Nino is a natural climate pattern borne out of unusually warm waters in the eastern Pacific. It forms when the trade winds blowing east-to-west along the equatorial Pacific slow down or reverse as air pressure changes, although scientists are not entirely sure what kicks off the cycle.
• Because the trade winds affect the sun-warmed surface waters, a weakening causes these warm western Pacific waters to slosh back into the colder central and eastern Pacific basins.
• It is known to suppress monsoon rainfall. 

Forecast and historical Trends of La Nina in India

• 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.
• 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 6% 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. 

Conclusion

While the potential shift from El Nino to La Nina brings hope for increased rainfall during India's southwest monsoon, concerns linger over the possibility of extreme weather events. The nuanced outlook combines positive prospects with worries about heightened climatic extremes.

Prelims PYQ

Q. La Nina is suspected to have caused recent floods in Australia. How is La Nina different from El Nino? (UPSC 2011)

1) La Nina is characterized by unusually cold ocean temperature in the equatorial Indian Ocean, whereas El Nino is characterized by unusually warm ocean temperature in the equatorial Pacific Ocean.

2) El Nino has an adverse effect on the southwest monsoon of India, but La Nina has no effect on the monsoon climate.

Which of the statements given above is/are correct?

(a). 1 only

(b). 2 only

(c). Both 1 and 2

(d). Neither I nor 2