DT Next Explains: What are El Nino and La Nina, how do they impact India

CHENNAI: Usually, warm water from South America is moved towards Australia by trade winds (easterlies) along the equator. Due to this, sea surface temperature in the Western Pacific (near the eastern coast of Australia) is higher than the waters off the Eastern Pacific (near the northwest coast of South America). This makes cold water from the deep of the sea to come up (upwelling) near South America to substitute the moved away warm water. This will keep the sea surface temperature and the weather patterns across the globe normal.

On the other hand, when trade winds weaken, they cannot move warm water from South America. This results in warm water piling up in the Eastern Pacific (near South America). As the distance between the cold water and the surface increases, cold water upwelling becomes nil or weaker. As cold water is prevented from reaching near the surface, the surface temperature increases. This causes El Nino (Little Boy in Spanish). This phenomenon occurs every two to seven years on average, and lasts for up to 12 months.

Impact of El Nino on India:

While the El Nino causes direct impact on rainfall or drought in other parts of the world, especially the Pacific region, it plays an intensification role in India.

Dr Kurian Joseph, director of Centre for Climate Change and Disaster Management (CCCDM) in Anna University, said that El Nino phenomenon can be related to intensification of temperature. "The previous year was an El Nino year. This year's El Nino has started to withdraw. After El Nino, La Nina would start, which may have a cooling effect - opposite to El Nino," he added.

However, S Balachandran, Head of Regional Meteorological Centre in Chennai, clarified that El Nino is not the only factor that decides weather conditions over India. "Various factors contribute to high temperature in India including local conditions apart from climate change," he explained.

It has been observed that monsoons in India have been poor during the El Nino years and better during La Nina years. The Meteorological department has also predicted good monsoon in 2024 as the present El Nino is set to withdraw by June this year.

Addressing the media recently, Dr Mrutyunjay Mohapatra, Director General of Meteorology, said that during El Nino, warm air increases near the tropical region and it pushes the cold air towards the north. Due to such a large-scale feature, minimum temperatures were also higher-than-normal.

What is La Nina

La Nina (Little Girl in Spanish) is a phenomenon exactly opposite to the El Nino. When the trade winds are stronger than normal, more warm water is moved towards Australia. This will result in strong upwelling, which will lower the sea surface temperature.

Apart from weather patterns of the globe, El Nino and La Nina play a vital role in marine life of the Pacific Ocean. During normal years, cold water from the deep sea would bring nutrients to the near surface. This helps phytoplankton (microscopic algae) to sustain. Small fishes feed on phytoplankton and large fishes eat small fishes. During the normal years, fishermen along the coast of northwest South America enjoy normal catch.

During the El Nino years, nutrient-rich cold water could not reach the near surface - which means less food for phytoplankton and less food for fishes. On the other hand, La Nina brings bounty to fishermen.

Around 40 to 50 million people are currently affected in 16 countries by the El Nino event, Reena Ghelani, the new Climate Crisis Coordinator for the El Niño/La Niña Response, told media recently.

The 2023-24 El Nino event was one of the five strongest on record, the WMO has said, adding that it contributed to extreme heat across the planet, culminating in the warmest year on record and unprecedented marine heatwaves, coupled with human-induced climate change.