La Nina: Impacts, Mechanisms, and Predictions | 11 Jan 2025

Source: BS 

Why in News?

The long-anticipated La Nina has emerged, but the Pacific Ocean's cooling is mild and unlikely to cause as many weather problems as usual. 

• Its delayed arrival may have been influenced by the world's oceans being much warmer than the last few years. 
• La Nina conditions emerge in the tropical Pacific in December. 

What is La Nina? 

• About: La Niña, meaning "The Little Girl" in Spanish, is a cool phase of the El Nino Southern Oscillation (ENSO). 
  • It is characterized by colder-than-normal sea surface temperatures in the eastern Pacific Ocean. 
  • La Nina is one of the three phases of ENSO, alongside El Nino (the warm phase) and the neutral phase. 
• Mechanism: In La Nina, the trade winds strengthen, pushing warm water toward the western Pacific. 
  • Cooler waters from below rise in the eastern Pacific, causing a temperature drop in that region. 
• Cycles: La Niña occurs in irregular cycles, typically lasting from two to seven years, and often follows an El Nino event. 
• Recent Events: The most recent La Nina phase lasted from 2020 to 2023, before transitioning to an El Nino phase in mid-2023. 
• Climate Change: The intensity of La Nina's impacts, such as extreme temperatures and unusual weather patterns, is exacerbated by anthropogenic climate change. 

What are the Potential Regional Impacts of La Nina? 

• Asia: In India, La Nina is expected to lead to above-average monsoon rainfall from July to September, which may result in a decrease in the production of pulses in the Indo-Gangetic Plains, but rice production may see an increase. 
  • In Southeast Asia, including Indonesia, Malaysia, and the Philippine, La Nina brings above-average rainfall, causing flooding but boosting rice and palm oil production. 
• South America: In Southern Brazil, Uruguay, northern Argentina, and southern Bolivia, La Nina causes below-average rainfall, leading to drought and affecting soybeans and maize.  
  • In contrast, Northern Brazil, Colombia, Venezuela, and parts of Ecuador and Peru experience wetter conditions, leading to potential flooding. 
• Africa: In East Africa, La Nina brings drier conditions in December and January, negatively impacting crops harvested in February and March. 
  • In Southern Africa, La Nina causes above-average summer rainfall, benefiting agriculture with higher yields of maize, sorghum, wheat, and soybeans. 
• Oceania: In Australia, the region experiences above-average rainfall in the northern and eastern regions, often linked to severe flooding.  
• North America: In the US, La Nina causes drier conditions in the south and wetter, stormier weather in the north, including Alaska and Canada. 

What is El Nino-Southern Oscillation? 

• About: ENSO is a recurring climate pattern involving periodic changes in the temperature of waters in the central and eastern tropical Pacific Ocean, affecting global weather patterns. 
• Historical Context: The term El Nino was used by South American fishermen for warm Christmas waters. 
  • Sir Gilbert Walker discovered the Southern Oscillation, linking sea pressure changes to atmospheric conditions in the 1960s, leading to the ENSO term. 
  • La Nina and Neutral became widely used in the 1980s. 
• Phases of ENSO: 
  • El Nino: Warming ocean temperatures in the central/eastern Pacific, weakens easterly winds, reducing rainfall in Indonesia and increasing it in the central/eastern Pacific. 
  • La Nina: Cooling ocean temperatures in the central/eastern Pacific, strengthens easterly winds, increasing rainfall in Indonesia and decreasing it in the central/eastern Pacific. 
  • Neutral: Tropical Pacific sea surface temperatures are average, with atmospheric conditions showing signs of either El Nino or La Nina. 

• ENSO Cycle: The ENSO cycle oscillates every 3 to 7 years, with sea surface temperatures varying between 1°C to 3°C above or below average. 

How La Nina and El Nino are Predicted? 

• Climate and Observational Data: Scientists use climate models alongside observational data (such as sea surface temperatures, trade wind strength, and data from satellites and ocean buoys) to predict the onset of ENSO events (El Nino and La Nina). 
  • Ocean buoys are floating devices placed in the ocean for various purposes, including environmental monitoring, data collection, and navigation. 
• Oceanic Nino Index: ONI It compares the 3-month average sea surface temperatures in the East-Central Tropical Pacific with the 30-year average.  
  • When the difference between the two is 0.5º C or higher, it is an El Nino, and when it is –0.5º C or lower, it is a La Nina. 
• Nino-3.4 Index: This index helps to identify the thresholds that define El Nino and La Nina events.  
  • A value of 0.5°C or greater is indicative of the event's initiation, while a strong event requires a temperature anomaly of 1.5°C or more.  
• Lead Time for Predictions: La Nina events can be forecasted up to two years in advance if they follow a strong El Niño.  

Conclusion 

La Nina, the cool phase of the El Niño-Southern Oscillation (ENSO), influences global weather patterns, affecting rainfall, agriculture, and climate extremes. Accurate forecasting through models and indices like ONI and Nino-3.4 is vital for mitigating its impacts, especially as anthropogenic climate change amplifies its intensity and unpredictability.