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Critical Topics and Their Significance for the UPSC CSE Examination on December 17, 2024

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How does La Niña affect India’s climate?

For Preliminary Examination:  El Nino, La Nina, Southern Oscillations

For Mains Examination: GS I - World Geography

Context:

While the La Niña was expected to emerge by July this year, it is yet to. The India Meteorological Department now expects a La Niña to set in by late 2024 or early 2025, plus a milder winter due to this delay.

Read about:

La Nina

El Nino

Key takeaways:

What is La Niña?

• La Niña is one phase of the El Niño Southern Oscillation (ENSO) phenomenon, characterized by cooler-than-average sea surface temperatures in the Pacific Ocean between Indonesia and South America.
• Its opposite phase, El Niño, involves warming of this same region. Both phases play a major role in influencing global weather systems and atmospheric circulation.
• During La Niña years, India typically experiences normal to above-normal monsoon rainfall, while it triggers droughts in Africa and intensifies hurricanes in the Atlantic. In contrast, El Niño leads to extreme heat and droughts in India but causes increased rainfall in parts of the southern United States.
• The current decade began with an unusual sequence of three consecutive La Niña events (2020–2022), known as the Triple Dip La Niña, which was followed by an El Niño in 2023. Scientists suggest that climate change might increase the frequency and severity of both La Niña and El Niño events, as rising sea and land temperatures disturb the Pacific Ocean’s equilibrium. This could also amplify extreme La Niña conditions, potentially resulting in harsher winters in India.

Will La Niña develop this winter?

• The situation in 2024 is unusual, as La Niña has not materialized as expected. Historically, La Niña tends to develop during the pre-monsoon or monsoon seasons and has only formed twice between October and December since 1950.
• While global forecasts had anticipated its arrival during the recent monsoon season, current predictions indicate only a 57% chance of it forming by December 2024. Even if it develops, it is likely to remain weak, though it could still influence global weather conditions.
• The declaration of La Niña or El Niño relies on various meteorological indices. One key measure, the Oceanic Niño Index (ONI), compares the three-month average sea surface temperature in the East-Central Tropical Pacific against a 30-year average.
• When the temperature deviation is +0.5°C or above, it indicates El Niño; a deviation of –0.5°C or below signals La Niña.
• Currently, the ONI stands at approximately –0.3°C. For an event to be officially recognized, these thresholds must be consistently exceeded for at least five consecutive months.

What is the meteorological situation?

• Southern Indian cities like Bengaluru and Hyderabad are experiencing colder-than-usual winters this year, while northern India is facing a delayed winter accompanied by above-normal temperatures.
• Although some reports attribute the southern chill to La Niña, current ONI values do not confirm this. If La Niña had already set in, northern India would likely be experiencing significantly colder weather.
• A 35-year analysis by the Council on Energy, Environment, and Water in New Delhi found that La Niña w