Meteorologists Warn of Strong El Niño Event and Potential Impact on Indian Weather
Worth reading — 1 past UPSC question on this theme (Prelims GS-1 2017).
2-minute summary
The US National Oceanic and Atmospheric Administration (NOAA) has warned of a potentially historic El Niño event developing in the equatorial Pacific Ocean, with climate models projecting it could peak during the Northern Hemisphere winter. El Niño represents the warm phase of the El Niño-Southern Oscillation (ENSO), marked by anomalous warming of central and eastern tropical Pacific waters and the weakening of easterly trade winds. For India, El Niño conditions are traditionally associated with weakened southwest monsoon rainfall and warmer winter temperatures. However, meteorologists highlight that the atmospheric and oceanic teleconnections to the Indian subcontinent typically manifest with a 40 to 45-day lag. Consequently, the direct impact on the ongoing summer monsoon is mitigated by timing, as the monsoon withdrawal begins in late September. Furthermore, a developing positive Indian Ocean Dipole (IOD)—characterized by warmer western Indian Ocean waters relative to the east—can offset some of the drying effects of El Niño by feeding moisture into the monsoon trough.
Why it's in the news
NOAA and global climate agencies projected a 69% probability that the developing El Niño could become one of the strongest events since 1950, raising concerns regarding rainfall deficits, agricultural productivity, and winter temperature anomalies across India.
Background and context
The El Niño-Southern Oscillation (ENSO) is a coupled ocean-atmosphere phenomenon occurring across the tropical Pacific. Under normal conditions, trade winds blow westwards, pushing warm surface water toward the western Pacific (creating the Western Pacific Warm Pool) and causing upwelling of nutrient-rich cold water along the South American coast (Walker Circulation). During an El Niño event, trade winds weaken or reverse, allowing warm waters to migrate eastward. This shifts atmospheric convection zones, altering global jet streams and precipitation patterns. Early 20th-century studies by Sir Gilbert Walker first established the relationship between atmospheric pressure swings across the Pacific/Indian Oceans and Indian monsoon failures. While historically over 60% of major drought years in India coincided with El Niño, the correlation is not absolute due to other atmospheric-oceanic drivers such as the Indian Ocean Dipole (IOD) and the Madden-Julian Oscillation (MJO).
Government schemes
- Pradhan Mantri Fasal Bima Yojana (PMFBY) — Provides comprehensive insurance coverage against crop failure caused by weather anomalies such as El Niño-induced drought.
- Mission Mausam — Aims to enhance India's weather and climate forecasting capabilities, monsoon predictability, and observational infrastructure.
International organisations
- National Oceanic and Atmospheric Administration (NOAA) — United States scientific agency providing global climate monitoring, ENSO diagnostic bulletins, and ocean temperature analyses.
- World Meteorological Organization (WMO) — United Nations specialized agency coordinating international meteorological observations and standardizing climate forecasts.
Previous UPSC questions on this theme
- Prelims GS-1 2017 — With reference to 'Indian Ocean Dipole (IOD)' sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct? 1. IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean. 2. An IOD phenomenon can influence an El Nino's impact on the monsoon. (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2
Mains practice: Explain the phenomenon of El Niño and evaluate how it influences the Indian Southwest Monsoon. What role does the Indian Ocean Dipole (IOD) play in modulating this impact?
El Niño is the oceanic component of ENSO, characterized by the periodic warming of Sea Surface Temperatures (SST) in the central and east-central equatorial Pacific Ocean. This warming weakens the easterly trade winds and displaces the atmospheric Walker Circulation eastward.
• Impact on the Indian Southwest Monsoon:
- Convection Shift: Convective rainfall shifts towards the central Pacific, creating descending dry air over the Indonesian-Australian region and the Indian subcontinent, which weakens the monsoon trough.
- Historical Drought Correlation: A majority of historic drought years in India have coincided with El Niño phases due to suppressed cloud formation and delayed or deficient precipitation.
- Teleconnection Lag: El Niño impacts over the Indian Ocean typically emerge with a lag of 40–45 days, meaning late-forming events often impact the post-monsoon or winter season rather than the primary summer monsoon.
• Modulating Role of the Indian Ocean Dipole (IOD):
- Counter-mechanism: The IOD refers to the SST gradient between the western tropical Indian Ocean (Arabian Sea) and the eastern tropical Indian Ocean (south of Indonesia).
- Positive IOD Offset: During a positive IOD phase, the western Indian Ocean becomes unusually warm, generating strong convection and easterly winds that pump abundant moisture into the Indian landmass. This helps neutralize the subsidence and moisture deficit caused by El Niño.
- Conversely, a negative IOD exacerbates El Niño-induced rainfall deficits.
Conclusion:
While El Niño poses a major downside risk to Indian agriculture and water security, monsoon performance is determined by a complex interplay of global and regional factors, including the IOD, Eurasian snow cover, and MJO, necessitating integrated, dynamic forecasting models.
Prelims practice questions
Q1. During an El Niño event, which of the following atmospheric and oceanic conditions typically occur in the equatorial Pacific?
- Shift of atmospheric convective ascending motion entirely over the Indian Ocean basin
- Strengthening of easterly trade winds and enhanced upwelling along the Peruvian coast
- Intense cooling of central and eastern Pacific sea surface temperatures
- Weakening or reversal of easterly trade winds and suppression of Peruvian coastal upwelling
Answer: D. During El Niño, trade winds weaken or reverse to westerlies, warm water moves eastward, and the cold, nutrient-rich upwelling along the western coast of South America (Peru) is suppressed.
Q2. Consider the following statements regarding the Indian Ocean Dipole (IOD): 1. A positive IOD is characterized by warmer sea surface temperatures in the western Indian Ocean compared to the eastern Indian Ocean. 2. A positive IOD typically brings deficient rainfall over the Indian subcontinent. 3. The IOD can develop independently of the ENSO cycle. Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Answer: C. Statement 1 is correct (positive IOD = warmer western Indian Ocean). Statement 2 is incorrect because a positive IOD generally enhances rainfall over India and can mitigate El Niño drying effects. Statement 3 is correct as the IOD is an independent coupled ocean-atmosphere phenomenon within the Indian Ocean basin.
Q3. Why does a late-developing El Niño in August-September have a limited impact on that year's Indian Southwest Monsoon?
- Because the Coriolis force reverses completely during September.
- Because El Niño completely dissipates upon reaching the International Date Line.
- Due to a typical 40 to 45-day lag for teleconnections to manifest over the Indian Ocean, coinciding with monsoon withdrawal.
- Because El Niño only influences weather in the Southern Hemisphere.
Answer: C. Atmospheric-oceanic teleconnections connecting Pacific SST anomalies to the Indian Ocean system exhibit a lag of approximately 40 to 45 days. By the time these effects manifest, the southwest monsoon has already begun its seasonal withdrawal (around mid-September).
Revision flashcards
- What is the El Niño-Southern Oscillation (ENSO)? A recurring climate pattern involving coupled oceanic (SST warming/cooling) and atmospheric (Southern Oscillation pressure changes) variations across the tropical Pacific Ocean.
- How does Walker Circulation change during an El Niño event? The normal east-to-west atmospheric circulation weakens or breaks down as warm water shifts east, causing the ascending (convective) limb to move to the central/eastern Pacific and descending dry air over the western Pacific and South Asia.
- What defines a 'Positive Indian Ocean Dipole' (+IOD)? Anomalous warming of the western equatorial Indian Ocean (near Arabian Sea/East Africa) and anomalous cooling of the eastern Indian Ocean (near Indonesia), typically boosting Indian monsoon rains.
- Why is there no 1:1 direct correlation between El Niño and Indian monsoon drought? Because the Indian monsoon is governed by multiple concurrent factors, including the Indian Ocean Dipole (IOD), Madden-Julian Oscillation (MJO), and Eurasian snow cover.
- What is the typical teleconnection lag of El Niño over the Indian Ocean? Approximately 40 to 45 days, meaning Pacific SST anomalies take several weeks to alter atmospheric circulation over South Asia.