Understanding La Niña’s Effect on India’s Weather Patterns

La Niña, a phase of the El Niño Southern Oscillation (ENSO), has significant effects on global weather patterns. This climatic phenomenon is characterized by cooler-than-usual sea surface temperatures in the central and eastern Pacific Ocean. While La Niña typically leads to increased rainfall in India during the monsoon season, it can also cause disruptions in other parts of the world, such as droughts in Africa and intensified hurricanes in the Atlantic. The emergence of La Niña is a critical factor in determining India’s seasonal weather, including its monsoons and winters. However, the delay in La Niña’s expected onset in 2024 has raised questions about its eventual impact.

What is La Niña?

• La Niña is part of the El Niño Southern Oscillation (ENSO) and occurs when the central and eastern Pacific Ocean experiences cooler-than-normal sea surface temperatures.
• It often brings opposite weather effects compared to El Niño, which is marked by warmer sea surface temperatures.

Impact on India’s Climate

• Monsoons: La Niña typically leads to normal or above-normal rainfall during the monsoon season in India.
• Winter: La Niña winters tend to be colder, but not always uniformly across the country.
• Summer: La Niña generally mitigates extreme heat during the summer, contrasting with the hotter, drier conditions associated with El Niño.

Delayed La Niña in 2024

• The La Niña phase was expected to begin by July 2024, but it has not emerged as predicted.
• Forecasts suggest that La Niña may form by late 2024 or early 2025, but its strength may be weaker than usual.
• Historically, La Niña has formed more commonly in the monsoon or pre-monsoon periods. It has formed only twice between October and December since 1950.

Current Oceanic Niño Index (ONI) Values

• The ONI compares three-month average sea surface temperatures in the tropical Pacific to a 30-year average.
• For La Niña, ONI values must be below -0.5°C, and the current ONI value is around -0.3°C, indicating a weak La Niña.

La Niña Winter

• Southern India: Cities like Bengaluru and Hyderabad have experienced colder winters, though this may not be directly linked to La Niña, given the weak ONI values.
• Northern India: There has been a delay in the onset of winter, with above-normal temperatures observed.
• Air Quality: La Niña winters tend to have higher wind speeds, which help in dispersing pollutants and improving air quality. However, lower planetary boundary layer heights can trap pollutants near the ground.

Effects of La Niña on Air Pollution

• Faster wind speeds during La Niña winters help transport pollutants away, improving air quality.
• A lower planetary boundary layer height could potentially trap pollutants, worsening air quality, especially if people burn biomass for heating.

La Niña and Monsoon Outlook for 2025

• If La Niña persists into the summer of 2025, it could offer relief from extreme heat, unlike the intense heatwaves observed in El Niño years.
• La Niña generally supports a robust monsoon, leading to normal or above-normal rainfall in India.
• El Niño Impact: El Niño years, on the other hand, typically result in below-average rainfall during the monsoon, as seen in 2023.

Historical La Niña and El Niño Trends

• India has received less rainfall during intense El Niño events (e.g., 1980s, 1990s), with more pronounced effects in north and south India.
• In contrast, La Niña years (e.g., 2020, 2021, 2022) have generally provided normal or above-normal rainfall.

Potential Impact of La Niña in 2024-2025

If La Niña forms as expected, it could lead to,

• A milder winter, with cooler temperatures in southern India.
• A more moderate summer with less intense heat.
• A stronger monsoon season, with higher rainfall across India, benefiting agriculture and water resources.

Summary/Static	Details
Why in the news?	Understanding La Niña’s Effect on India’s Weather Patterns
What is La Niña?	A cooler phase of the El Niño Southern Oscillation (ENSO), characterized by lower sea surface temperatures in the central and eastern Pacific Ocean.
Impact on India’s Monsoon	Leads to normal or above-normal rainfall during the monsoon season, improving agricultural conditions.
Impact on Winter	Typically causes colder winters, especially in northern India. However, the impact may vary, as seen in the current year.
Impact on Summer	Mitigates extreme heat, providing relief from intense heatwaves often associated with El Niño events.
La Niña in 2024	Expected to form by late 2024 or early 2025, though currently weak with an Oceanic Niño Index (ONI) value of -0.3°C.
Oceanic Niño Index (ONI)	ONI values below -0.5°C indicate La Niña. Current ONI value is -0.3°C, suggesting a weak La Niña.
Winter in 2024	Southern India has experienced colder-than-usual winters, while northern India has seen delayed winters with above-normal temperatures.
Air Quality Impact	Higher wind speeds during La Niña winters help disperse pollutants, improving air quality. However, lower planetary boundary layer height can trap pollutants near the surface.
La Niña and the Monsoon	Expected to lead to a robust monsoon with above-normal rainfall, which benefits agriculture and water resources.
El Niño vs. La Niña	El Niño brings drier conditions and extreme heat, while La Niña promotes rainfall and moderate temperatures.
Potential Impact in 2024-2025	A milder winter, moderate summer temperatures, and a stronger monsoon with higher rainfall are expected if La Niña forms.