EL NINO AND LA NINA
1. Context
India Meteorological Department (IMD) forecast above-normal rain in the upcoming monsoon season in India, with “favourable” La Nina conditions expected to set in by August-September. Another recent bulletin from the IMD noted how the strength of El Niño conditions has weakened since the beginning of this year.
2.What are El Niño and La Nina?
- El Niño and La Niña, translating to “little boy” and “little girl” in Spanish, are climatic events arising from interactions between the ocean and atmosphere. They influence water temperatures in the central and eastern tropical Pacific Ocean, thereby affecting global weather patterns.
- The Earth's rotation from east to west causes winds between 30 degrees north and south of the equator to tilt in their paths. This results in winds flowing southwest in the northern hemisphere and northwest in the southern hemisphere, a phenomenon known as the Coriolis Effect.
- Consequently, trade winds blow westward on either side of the equator. Typically, these winds move west from South America towards Asia, leading to upwelling, where cold water from beneath the ocean surface rises, replacing warmer surface waters.
- Occasionally, weakened trade winds shift back towards South America, preventing upwelling. This leads to warmer-than-normal sea surface temperatures along the equatorial Pacific Ocean, marking the onset of El Niño conditions.
- In contrast, during La Niña, stronger trade winds push warm water towards Asia, enhancing upwelling and bringing cold, nutrient-rich water to South America.
- Thus, El Niño and La Niña represent opposite phases of the El Niño Southern Oscillation (ENSO) cycle, which also includes a neutral phase.
- El Niño events are more common than La Niña ones, occurring every two to seven years when neutral ENSO conditions are disrupted by either phase. Recently, La Niña conditions were observed from 2020 to 2023
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3.How could the incoming La Nina impact global weather?
- Due to ENSO and the associated changes in ocean temperatures, air circulation in the region is also influenced. This, in turn, affects precipitation levels in nearby areas and has an impact on the Indian monsoon.
- The current El Niño event, which started last June, has weakened considerably. It is anticipated that by June, neutral ENSO conditions will be in place. Following this, La Niña conditions are expected to develop, potentially starting to have an impact by August
4.La Nina’s impact on the world
- Like India, countries such as Indonesia, the Philippines, Malaysia, and their neighbors experience abundant rainfall during a La Niña year. This year, Indonesia has already experienced flooding.
- Conversely, droughts are common in the southern parts of North America, where winters tend to be warmer than usual.
- Canada and the northwestern coast of the United States face heavy rainfall and flooding. Southern Africa experiences above-average rainfall, while the eastern regions of the continent receive below-average rainfall.
- ENSO significantly influences hurricane activity over the Atlantic Ocean, with La Niña years typically seeing an increase in hurricanes. For example, in the La Niña year of 2021, the Atlantic Ocean saw a record 30 hurricanes
5.Is climate change affecting ENSO?
- In India, El Niño is known to reduce southwest monsoon rainfall, leading to higher temperatures and more intense heatwaves, as seen this summer.
- Historically, monsoon seasons following an El Niño, such as in 1982-1983 and 1987-1988, saw abundant rainfall in 1983 and 1988. A similar pattern may occur this year.
- From 2020 to 2023, the longest La Niña event of the century took place. This was followed by ENSO neutral conditions, which transitioned to El Niño by June 2023.
- However, El Niño has been weakening since last December. According to Rajeevan, this rapid shift to La Niña is a natural occurrence and has happened many times in the past.
- Scientists suggest that climate change will impact the ENSO cycle. Various studies indicate that global warming may alter the average oceanic conditions in the Pacific Ocean, leading to more frequent El Niño events.
- The World Meteorological Organization (WMO) also predicts that climate change will likely affect the intensity and frequency of extreme weather and climate events associated with El Niño and La Niña
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For Prelims: Indian and World Geography
For Mains: GS-I, GS-III: Important Geophysical phenomena and environment
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Source: Indianexpress
