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Explainer | What Is ‘La Nina’ And How It Can Lead To A Colder Winter In India This Year

'La Nina', a climate pattern that causes ocean temperature to drop drastically, has reportedly raised sea levels by 20cm. What is this climate pattern often called a 'cold event'?

Explainer | What Is ‘La Nina’ And How It Can Lead To A Colder Winter In India This Year

La Nina, a term that has been growing familiar to events related to climate change. The colder sister to El Nino, La Nina has reportedly raised the sea levels by 15 to 20 cm in some regions of the western Pacific regions. According to experts, the same sea-level rise is expected to occur globally by 2050.

The latest assessment report by the Intergovernmental Panel on Climate Change suggests that the average seal level across the world has risen by 20cm between 1901 and 2018.

Low-lying islands of the Pacific region are most susceptible to destruction to climate change-induced rise in sea levels as they are easily inundated. The exponential threat could uproot the homes of millions of people, forcing them to find new shelter in other countries.

This means climate change and La Nina could be a possible reason for increased floods this year. La Nina typically lasts for nine to 12 months, however, at times for a year.

What is La Nina?

La Nina (‘little girl’ in Spanish) is a climate phenomenon that cools the ocean surface on the tropical west coast of South America. It is opposite to what El Nino (‘little boy’ in Spanish) does, which is warming up the ocean surface in the equatorial region of the Pacific ocean.

La Nina and El Nino jointly cause the El Nino-Southern Oscillation (ELSO), which is a weather and ocean-related phenomenon, that is also characterised by atmospheric pressure, according to National Geography.

La Nina and El Nino occur at irregular intervals between two to seven years. With the impact opposite to each other in character, La Nina is often called Anti-El Nino, El Viejo or a ‘cold-event’.

La Nina is caused by the build-up of cold water on the ocean surface dropping the temperature. The event mostly occurs in the tropical Pacific region, between the Tropic of Cancer and the Tropic of Capricorn. The strong, east-moving trade winds move the cold water to the surface in a process called upwelling.

Upwelling causes ocean temperature to drop drastically and scientists by the means of the Oceanic Nino Index, are able to understand whether La Nina has been prevailing in the region. When ocean temperature drops below 0.5 degrees Celcius for five successive three-month seasons, scientists confirm the even of La Nina.

La Nina also affects the pattern of rainfall across areas. It brings high rainfall and tropical cyclones across countries in the Pacific region.

La Nina’s warning in India

Winter could be colder this season due to the prevailing La Nina conditions, India Meteorological Department (IMD) Director General Mrutunjay Mohapatra had warned in October, early this year.

"As weak La Nina condition is prevailing, we can expect more cold this year. The El Nino and La Nina conditions play a dominant role if you consider the large scale factor for the occurrence of cold wave conditions," Mohapatra had said.

(with inputs from PTI)