El Nino and its impact on Indian monsoon

CHENNAI: With the Indian Meteorological Department (IMD) issuing heatwave warnings, and the El Nino phenomenon over the Pacific Ocean playing an intensification role, DT NEXT explains what the El Nino is and how it affects Indian summer and monsoon.

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 deep in the sea come up (upwelling) near South America to substitute the moved away warm water. This will keep the sea surface temperature and weather pattern across the globe normal.

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

Impact of El Nino on India

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

Explaining that El Nino is not the only factor that decides weather conditions in India, S Balachandran, head of the Regional Meteorological Centre in Chennai said, “Various factors contribute to high temperature in India including local conditions apart from climate change.”

Dr Kurian Joseph, director of the Centre for Climate Change and Disaster Management (CCCDM) at Anna University said that the El Nino phenomenon can be related to the 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.

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

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

La Nina is a phenomenon exactly opposite to the El Nino. When the trade winds are stronger than normal, more warm water is moved towards Australia which will result in strong upwelling, eventually lowering the sea surface temperature.

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

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

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 — Dr Kurian Joseph, Director, Climate Change and Disaster Management