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La Niña’s Impact on Global Weather and India’s Climate in 2024-2025
Context:
La Niña, a phase of the El Niño Southern Oscillation (ENSO), occurs when the Pacific Ocean region between Indonesia and South America cools down, impacting global weather patterns.
- Its counterpart, El Niño, represents a warming of the same region, and the interplay between these two phases significantly affects atmospheric circulation and weather worldwide.
Effects Across the Globe:
- La Niña effects: It generally leads to normal or above-normal rainfall in India during the monsoon season but causes droughts in Africa and intensifies hurricanes in the Atlantic.
- El Niño effects: It brings extreme heat and droughts to India while increasing rainfall in the southern U.S.
La Niña Delayed in 2024:
- Current Scenario: La Niña was expected to emerge by July 2024 but has been delayed.
- The India Meteorological Department (IMD) now forecasts La Niña to develop by late 2024 or early 2025. A delayed La Niña may also result in a milder winter this year.
- Historical Perspective: From 2020 to 2022, the world witnessed three consecutive La Niña events, known as the Triple Dip La Niña – a rare occurrence. 2023, however, saw the return of El Niño.
- Rising global temperatures due to climate change may increase the frequency and intensity of both El Niño and La Niña events.
- Likelihood of La Niña Formation in 2024: Historically, La Niña tends to form during the monsoon or pre-monsoon period.
- It has emerged between October and December only twice since 1950.
- Forecasts in December suggest a 57% chance of La Niña forming this year, but it is expected to be weak.
- Currently, the Oceanic Niño Index (ONI) stands at –0.3ºC.
Meteorology of a La Niña Winter:
- Temperature Trends Across India: Southern cities like Bengaluru and Hyderabad are experiencing colder-than-usual winters. Northern India, however, is seeing delayed winter with above-normal temperatures.
- Role of ONI: The ONI compares three-month average sea surface temperatures in the East-Central Pacific with a 30-year average. A full-fledged La Niña occurs only when the ONI value is –0.5ºC or lower for at least five consecutive months.
- 35-Year Meteorological Analysis: Research by the Council on Energy, Environment, and Water highlights the following trends during La Niña winters:
- Night temperatures tend to be colder compared to El Niño.
- Daytime temperatures are often higher.
- Wind Speed: Average wind speed is higher throughout the day during La Niña winters, aiding in pollutant dispersal.
- Planetary Boundary Layer Height (PBLH): Slightly lower during La Niña winters, which can trap pollutants closer to the ground.
- Impact on Air Quality: If La Niña sets in, lower temperatures in north India may lead to increased biomass burning for heating, worsening air pollution. However, higher wind speeds could help disperse pollutants, potentially improving air quality.
Broader Implications:
- Agricultural Impact: The variability in weather patterns can affect agricultural output and economic activities dependent on stable weather conditions.
- Economic Impact: The extreme weather events associated with La Niña can lead to economic losses due to damage to infrastructure, agriculture, and increased disaster response costs.
What Lies Ahead?
- If La Niña forms by early 2025 and persists into the summer, India could experience:
- A less intense summer.
- More robust monsoon rainfall.
- This would be a welcome development for India, offering relief from extreme summer heat and potential drought conditions.
