How does La Niña affect India’s climate?

The Hindu 17-Dec-2024

La Niña, a cooling phase of the Pacific Ocean, plays a critical role in India’s weather patterns, bringing favorable monsoons and cooler winters. Its delayed formation this year raises concerns about its impact on Indian winters, summers, and monsoons in 2025. While La Niña generally ensures robust rainfall, climate change may amplify its effects, causing unpredictable and extreme weather globally. Understanding La Niña’s patterns is essential for managing its impact on agriculture, air quality, and regional economies.

India’s weather patterns are deeply tied to global climatic phenomena, particularly the El Niño Southern Oscillation (ENSO), which consists of two opposite phases: El Niño and La Niña. While El Niño often brings drought and extreme heat, La Niña is generally associated with normal to above-normal rainfall, offering relief during monsoons. However, this year, La Niña’s delayed emergence has sparked discussions on its potential impact on India’s winter, summer, and the upcoming monsoon seasons.


Understanding La Niña and El Niño

La Niña occurs when sea surface temperatures in the Central and Eastern Pacific Ocean (between Indonesia and South America) drop below average. This cooling disrupts atmospheric circulation and weather patterns worldwide. Its counterpart, El Niño, involves warming of the same region, leading to opposing effects.

  • La Niña and El Niño influence:
    • La Niña: Causes robust monsoons in India, cooler winters, and intense hurricanes over the Atlantic. However, it may cause droughts in parts of Africa and the Americas.
    • El Niño: Often disrupts Indian monsoons, bringing lower rainfall, extreme summer heat, and drought conditions.

Current Situation: Delay in La Niña Formation

The India Meteorological Department (IMD) had initially predicted the onset of La Niña by July 2024. However, it is now likely to form late this year or early 2025. To classify as a full-fledged La Niña, oceanic indices like the Oceanic Niño Index (ONI) must show consistently low sea surface temperatures. Currently, ONI is around -0.3ºC, which is insufficient for declaring La Niña.

Historically, La Niña usually develops during the monsoon or pre-monsoon periods. It has only twice formed between October and December since 1950, making the current delay unusual.


Impact on Indian Winter

This year’s winter has displayed mixed signals:

  • Southern cities like Bengaluru and Hyderabad are experiencing colder temperatures.
  • Northern India, however, is witnessing a delayed and warmer winter.

Had a La Niña already developed, north India would likely experience a colder winter due to its association with extreme winters in the subcontinent.


La Niña and Monsoons

The Indian monsoon is heavily influenced by ENSO cycles. El Niño summers are typically harsh, as seen in 2023, when India recorded intense heat waves and below-normal monsoon rains. In contrast, La Niña years are generally favorable for Indian monsoons.

  • Historical Patterns:
    • La Niña years (2020, 2021, 2022): India recorded normal or above-normal rainfall during the monsoon season.
    • El Niño year (2023): India witnessed below-average rainfall, especially in north and south India.

If La Niña develops by early 2025 and persists into the summer, it could bring:

  1. Relief from extreme heat waves in the summer.
  2. Normal to above-normal monsoon rainfall, which is crucial for agriculture, water supply, and the economy.

La Niña’s Broader Meteorological Effects

La Niña also influences atmospheric parameters such as wind speeds and the Planetary Boundary Layer Height (PBLH) — the lowest layer of the atmosphere that interacts with the Earth’s surface:

  1. Higher wind speeds during La Niña winters help disperse pollutants, improving air quality.
  2. A lower PBLH can trap pollutants near the ground, worsening air pollution, particularly in north India, where burning biomass for heating is common.

Thus, La Niña’s effects on air quality can be mixed, depending on how these factors interact.


Triple Dip La Niña and Climate Change

A Triple Dip La Niña refers to three consecutive La Niña years, a rare phenomenon observed between 2020-2022. This was followed by El Niño in 2023.

  • Climate change may amplify the frequency and intensity of La Niña and El Niño events. Rising sea and land temperatures disrupt the Pacific Ocean’s natural balance, making extreme La Niña episodes more likely. These, in turn, can lead to harsher winters, more hurricanes, and other unpredictable weather.

Global Implications of La Niña

La Niña does not affect India alone. Its global impacts include:

  1. Droughts in East Africa and parts of South America.
  2. Hurricanes in the Atlantic Ocean becoming more intense.
  3. Relief from heat in the southern U.S., which experiences heavier rainfall.

These opposing effects demonstrate the complex and far-reaching consequences of La Niña, which can disrupt weather systems worldwide.


Why La Niña Matters for India

For India, where agriculture is largely dependent on monsoons, La Niña is often viewed positively. Normal rainfall during La Niña supports crop production, replenishes reservoirs, and stabilizes the rural economy. However, the effects of La Niña must be monitored carefully, as it can also bring extreme cold spells, increase air pollution in winter, and cause regional imbalances.


Conclusion

La Niña plays a crucial role in shaping India’s climate, particularly influencing winters, summers, and monsoons. While it often brings relief from the extreme heat and dry conditions associated with El Niño, its delayed emergence this year highlights the unpredictable nature of climate systems. As climate change accelerates, the frequency and intensity of such events may increase, making it essential for India to prepare for their far-reaching consequences.

Summary
  • What is La Niña?: A cooling of the Pacific Ocean, part of ENSO, influencing global and Indian weather.
  • Current Status: Delayed formation; expected by late 2024 or early 2025.
  • Impact on Winter:
    • Southern India: Colder-than-normal temperatures.
    • Northern India: Delayed winter with above-normal temperatures.
  • Monsoon Impact: La Niña supports normal to above-normal rainfall, unlike El Niño, which disrupts monsoons.
  • Global Effects: Causes droughts in Africa, intensifies Atlantic hurricanes, and brings rain to the southern U.S.
  • Climate Change: Increasing frequency and intensity of La Niña and El Niño events.

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