Why in news?
Climate agencies have forecast that after a prolonged La Niña phase, El Niño conditions may return later in 2026. Understanding the El Niño–Southern Oscillation (ENSO) cycle is essential because it influences monsoons, droughts and extreme weather in India and around the world. ENSO has two opposite phases: the warm El Niño and the cool La Niña.
Background
ENSO refers to periodic fluctuations in sea‑surface temperatures and atmospheric pressure across the tropical Pacific Ocean. El Niño — meaning “the little boy” in Spanish — describes the warming of surface waters in the eastern tropical Pacific. Fishermen in Peru noticed this phenomenon around Christmas and named it after the Christ Child. La Niña (“little girl”) is the opposite phase, characterised by cooler‑than‑normal waters along the same region. These oceanic changes are linked with an atmospheric component called the Southern Oscillation, involving shifts in air pressure between the western and eastern Pacific.
El Niño
- Mechanism: During El Niño, westward‑blowing trade winds weaken, allowing warm surface water to move eastward toward South America. The warm layer thickens and suppresses upwelling of cold, nutrient‑rich water.
- Impacts: The lack of upwelling disrupts fisheries along Peru and Ecuador and brings heavy rainfall and flooding to western South America. Conversely, Indonesia and Australia often experience droughts and wildfires. El Niño’s influence can extend worldwide, altering the jet stream and causing extreme winters in North America.
- Frequency: El Niño events occur irregularly every two to seven years and typically last 9–12 months.
La Niña
- Mechanism: Stronger‑than‑usual trade winds push warm surface water westwards, causing a build‑up of cold water in the eastern Pacific. Upwelling brings nutrient‑rich water to the surface, cooling the ocean by more than 0.5 °C for at least five three‑month periods.
- Impacts: La Niña generally enhances monsoon rainfall in South and Southeast Asia, including northwest India. However, it can trigger floods in Australia and parts of Africa and cause droughts along the west coast of South America and the southern United States.
- Duration: La Niña events often last longer than El Niño, sometimes persisting for one to three years.
Significance for India
- Monsoon influence: El Niño tends to suppress the Indian summer monsoon, leading to droughts and poor harvests. La Niña generally enhances rainfall, benefiting agriculture but sometimes causing floods.
- Forecasting: Understanding ENSO helps meteorological agencies predict seasonal rainfall and prepare for extreme events. For example, early warnings can inform drought‑mitigation measures or flood preparedness.
- Global climate: ENSO influences cyclone activity, temperature anomalies and rainfall patterns around the world, making it a key factor in climate variability.
Source: TH
