Why in the news?

  • Experts suggest that La Niña may lead to a colder winter in several parts of India, especially in the northern region. It may result in cold waves and increased snowfall in hilly regions.

La Nina

  • What is it?: La Niña (means The Little Girl in Spanish) is a climatic phenomenon characterized by cooler-than-average sea surface temperatures in the central and eastern equatorial Pacific Ocean, along with some changes in atmospheric circulation. It’s essentially the opposite of El Niño.
  • Mechanism of La Niña Formation:
    • Strengthening of Trade Winds: Easterly trade winds blow more strongly than usual from South America → Indonesia.
    • Warm-Water Displacement: These winds push warm surface water westwards, causing it to pile up near Australia and Indonesia.
    • Upwelling of Cold Water: To replace the displaced warm water, cold nutrient-rich water upwells from the deeper ocean along the Peruvian and Ecuadorian coasts.
    • Cooling of Eastern Pacific: The SSTs of the central and eastern tropical Pacific drop by ~0.5 °C or more below normal.
    • Enhanced Walker Circulation: Rising motion over the warm western Pacific and sinking motion over the eastern Pacific intensify rainfall in Asia–Australia and suppress it near the Americas.
    • Teleconnections: The altered circulation shifts the jet streams, influencing rainfall, temperature, and storm patterns worldwide.
  • Global Impacts of La Niña:
    • Generally leads to cooler global average temperatures than El Niño years.
    • Associated with heavy rainfall and floods in parts of Southeast Asia, Australia, and South America, and drier conditions in the US west coast and eastern Africa.
    • May increase Atlantic hurricane activity due to reduced vertical wind shear.
  • Impact on India:
    • Rainfall and Monsoon:
      • It usually brings above-normal monsoon rainfall in India.
      • Enhances southwest monsoon strength, leading to better kharif crop yields.
      • Reduces the likelihood of droughts (in contrast to El Niño years).
    • Temperature and Winter Conditions (2025–26):
      • Expected to bring a colder-than-usual winter, especially in North India.
      • Likely to cause cold waves and higher snowfall in Himalayan and hilly regions.
    • Agriculture and Water Availability:
      • Favors rabi sowing due to increased soil moisture from good monsoon rains.
      • Could improve reservoir storage and groundwater recharge.
    • However, Global Warming May Offset Cooling:
      • The World Meteorological Organization (WMO) notes that despite La Niña, global mean temperatures remain above normal.
      • Anthropogenic climate change is weakening traditional ENSO effects, altering expected rainfall and temperature patterns.