Impact of La Niña on India’s Climate

  • December 17, 2024
  • Posted by: OptimizeIAS Team
  • Category: DPN Topics
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Impact of La Niña on India’s Climate

Sub: Geo

Sec: Climatology

Why in News

  • The India Meteorological Department (IMD) anticipates the emergence of a La Niña phase by late 2024 or early 2025. A delay in the La Niña onset is expected to influence India’s winters, summers, and subsequent monsoon patterns.

What is La Niña?

  • La Niña is a phase of the El Niño Southern Oscillation (ENSO), a climate phenomenon that involves variations in sea surface temperatures and atmospheric pressure in the tropical Pacific Ocean.
  • It can influence weather patterns globally, affecting rainfall, temperatures, and storm systems.
  • The ENSO has three phases, which occur in irregular cycles of two to seven years.:
    • El Niño (warm phase),
    • La Niña (cool phase),
    • Neutral phase.

What happens during La Nina:

  • In La Niña, the trade winds (winds blowing from east to west across the Pacific) are stronger than usual, pushing warm surface waters to the western Pacific.
  • This allows cooler waters from below the surface to upwell along the eastern Pacific, leading to lower-than-normal sea surface temperatures in this region.
  • In India, El Niño is associated with decreased rainfall and higher temperatures, while La Niña is associated with increased rainfall and hence lower temperatures.

Global Impacts

  • La Niña Effects:
    • Normal or above-normal rainfall during Indian monsoons.
    • Droughts in Africa.
    • Intensified hurricanes in the Atlantic Ocean.
  • El Niño Effects:
    • Extreme summers and droughts in India.
    • Increased rainfall in the southern United States.

El Niño:

  • In the El Niño phase, the trade winds weaken, leading to lesser displacement of warmer waters off the South American coast.
  • Consequently, the eastern Pacific becomes warmer than usual.

Neutral phase:

  • In the neutral phase, the eastern side of the Pacific Ocean (near the northwestern coast of South America) is cooler than the western side (near the Philippines and Indonesia).
  • This is due to the prevailing wind systems that move from east to west, sweeping the warmer surface waters towards the Indonesian coast.
  • The relatively cooler waters from below come up to replace the displaced water.

What is a Triple Dip La Niña?

  • A Triple Dip La Niña refers to the rare occurrence of three consecutive La Niña events over three years.
  • It happens when La Niña conditions persist or re-emerge for three successive winters.
  • The most recent Triple Dip La Niña occurred from 2020 to 2022.
  • This phenomenon is unusual as most ENSO phases (El Niño or La Niña) last for one or two years.

About Oceanic Niño Index (ONI):

  • The Oceanic Niño Index (ONI) measures sea surface temperature (SST) anomalies in the East-Central Tropical Pacific Ocean over a rolling three-month period.
  • Classification:
    • El Niño: ONI value is +0.5°C or higher.
    • La Niña: ONI value is –0.5°C or lower.
    • Neutral Phase: ONI values fall between –0.4°C and +0.4°C.
  • ONI values must persist above or below the thresholds for at least five consecutive overlapping three-month periods to declare a full-fledged El Niño or La Niña.
  • Current Status (2024): The ONI value is around –0.3°C, indicating a neutral phase and no active La Niña.
  • Importance of ONI: Used as a key indicator for monitoring ENSO phases. Provides insights into global climate patterns, such as monsoon rainfall in India or hurricane activity in the Atlantic.

About Planetary Boundary Layer Height (PBLH):

  • The Planetary Boundary Layer Height (PBLH) refers to the lowest layer of the atmosphere directly influenced by interactions between the Earth’s surface and the atmosphere.
  • It is where surface heating, moisture exchange, and wind interactions
  • Characteristics of PBLH: The height varies diurnally and seasonally:
    • Daytime: PBLH is higher due to surface heating and convection.
    • Nighttime: PBLH decreases as cooling sets in, creating a more stable atmosphere.
  • Role in Meteorology:
    • A higher PBLH allows pollutants to disperse, improving air quality.
    • A lower PBLH traps pollutant near the surface, worsening air quality.
    • Affects cloud formation, wind dynamics, and surface temperatures.
  • PBLH During ENSO Events:
    • La Niña Winters:
      • Typically associated with slightly lower PBLH in India, especially in winter.
      • This could lead to higher pollution levels as pollutants are trapped closer to the ground.
    • El Niño Winters:
      • Tend to have a higher PBLH, facilitating pollutant dispersion.
    • Current Implications: If a La Niña develops, northern India could see increased biomass burning for heating, worsening air pollution. However, higher wind speeds typical of La Niña may counteract this by dispersing pollutants.
Geography Impact of La Niña on India's Climate