Every monsoon season, news channels flash terms like El Niño, La Niña, and cyclone warnings — often in the same breath. Yet most aspirants study these as separate topics and miss the deeper ocean-atmosphere linkage that UPSC loves to test. I have seen this pattern across fifteen years of teaching geography, and once you see the connection, you never forget it.
Where This Topic Sits in the UPSC Syllabus
This topic straddles multiple papers and appears with surprising regularity. The examiner does not ask about El Niño in isolation anymore. Questions now demand that you connect ocean currents, pressure systems, and cyclone frequency in one coherent answer.
| Exam Stage | Paper | Syllabus Section |
|---|---|---|
| Prelims | General Studies | Physical Geography — Oceanography, Climatology |
| Mains | GS-I | Important Geophysical Phenomena — Cyclones, Earthquakes, Volcanic Activity |
| Mains | GS-III | Disaster Management — Cyclone Preparedness |
Related topics in the same syllabus zone include Indian monsoon mechanism, jet streams, Indian Ocean Dipole (IOD), and pressure belts. UPSC has asked direct or indirect questions on ENSO and cyclones at least eight to ten times between 2011 and 2026.
Understanding ENSO — The Engine Behind It All
ENSO stands for El Niño–Southern Oscillation. Think of it as the Pacific Ocean’s mood swing that affects weather across the planet. In normal conditions, trade winds blow from east to west across the tropical Pacific. Warm water piles up near Indonesia and Australia, while cool water upwells along the coast of Peru.
During an El Niño event, these trade winds weaken or reverse. Warm water shifts eastward toward South America. Sea surface temperatures (SSTs) in the central and eastern Pacific rise above normal. This seemingly distant change alters the Walker Circulation — the giant east-west atmospheric loop over the Pacific.
La Niña is the opposite phase. Trade winds strengthen. More warm water accumulates in the western Pacific. SSTs in the eastern Pacific drop below normal. The Walker Circulation intensifies. Both phases typically last 9 to 12 months, and they alternate irregularly every 2 to 7 years.
How El Niño Affects Cyclone Activity
Here is where the connection becomes exam-relevant. El Niño increases vertical wind shear over the Atlantic and the North Indian Ocean. Wind shear means winds at different altitudes blow at different speeds or directions. High wind shear tears apart the organised convection a cyclone needs to form. So during El Niño years, cyclone formation in the Bay of Bengal and the Arabian Sea often decreases.
However, El Niño boosts cyclone activity in the central and eastern Pacific. The warmer SSTs there provide more energy for storm development. This is a favourite UPSC trap — aspirants assume El Niño reduces cyclones everywhere, but it only shifts the zone of activity.
For India specifically, El Niño years tend to bring weaker monsoons and fewer but sometimes more intense late-season cyclones. The 2015 El Niño, for instance, coincided with Cyclone Chapala — an extremely rare cyclone that hit Yemen after forming in the Arabian Sea.
How La Niña Affects Cyclone Activity
La Niña generally favours more cyclone formation in the North Indian Ocean. The warmer western Pacific SSTs provide abundant moisture and heat energy. Reduced wind shear allows cyclonic systems to organise and intensify. India typically sees stronger monsoons and a higher frequency of cyclones during La Niña years.
The 2020–2023 triple-dip La Niña was a textbook example. India experienced Cyclone Amphan (2020), Cyclone Tauktae (2021), and several others in quick succession. The Bay of Bengal remained especially active. This correlation between La Niña and enhanced cyclone activity in the Indian Ocean basin is well-documented by the India Meteorological Department (IMD).
The Walker Circulation Link — Connecting the Dots
I always tell my students to visualise the Walker Circulation as a conveyor belt. During La Niña, the ascending limb of this circulation sits firmly over the western Pacific and the Indian Ocean region. Rising air means low pressure, moisture convergence, and favourable conditions for cyclone genesis.
During El Niño, this ascending limb shifts eastward. The Indian Ocean region falls under the descending limb — sinking air, high pressure, suppressed convection. Cyclone formation gets starved of the ingredients it needs.
The Indian Ocean Dipole (IOD) adds another layer. A positive IOD can partially offset El Niño’s drying effect on the Indian monsoon. UPSC has started testing this nuance, asking how IOD and ENSO interact to determine monsoon rainfall and cyclone tracks.
How UPSC Tests These Connections
From my experience analysing previous year papers, UPSC tests this cluster in three ways. First, direct factual questions — what happens to SSTs during El Niño, which direction do trade winds blow, etc. Second, analytical mains questions asking you to explain how Pacific Ocean phenomena affect Indian weather. Third, application-based questions linked to a recent cyclone or drought event.
The 2024 Prelims had a question testing whether aspirants understood the difference between ENSO and IOD. Mains 2023 GS-I asked about the increasing frequency of cyclones in the Arabian Sea — a question that demanded knowledge of warming SSTs, La Niña influence, and climate change together.
When writing mains answers on this topic, I recommend drawing a simple diagram showing the Walker Circulation in normal, El Niño, and La Niña phases. Examiners reward visual representation of atmospheric processes.
Previous Year UPSC Questions on This Topic
Q1. Consider the following statements about El Niño:
1. El Niño is characterised by unusually warm ocean temperatures in the equatorial Pacific.
2. It leads to increased monsoon rainfall in India.
Which of the above is/are correct?
(a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither
(UPSC Prelims 2014 — General Studies)
Answer: (a) 1 only. El Niño warms the central-eastern Pacific SSTs, but it generally weakens the Indian monsoon, leading to below-normal rainfall. Statement 2 is incorrect because the subsidence over the Indian Ocean during El Niño suppresses convective activity.
Q2. Discuss how ENSO and the Indian Ocean Dipole together influence the Indian monsoon. (150 words)
(UPSC Mains 2017 — GS-I)
Answer: ENSO and IOD are two coupled ocean-atmosphere phenomena that jointly modulate monsoon strength. During El Niño, the weakened Walker Circulation suppresses convection over India, reducing rainfall. However, a simultaneous positive IOD — where western Indian Ocean SSTs are warmer than eastern SSTs — can counterbalance this effect by enhancing moisture supply to the Indian subcontinent. The 1997 strong El Niño did not cause a severe drought partly because a strong positive IOD was active simultaneously. Conversely, a negative IOD during El Niño amplifies drought risk. La Niña with a positive IOD creates the most favourable conditions for above-normal monsoon rainfall. Understanding both phenomena together is essential for accurate seasonal forecasting by IMD.
Q3. Why has the Arabian Sea witnessed an increase in the frequency and intensity of tropical cyclones in recent years? Examine. (250 words)
(UPSC Mains 2023 — GS-I)
Answer: The Arabian Sea has traditionally been less cyclone-prone than the Bay of Bengal due to cooler SSTs and stronger wind shear. However, recent decades show a clear shift. Rising SSTs driven by climate change now provide sufficient thermal energy for cyclogenesis. La Niña phases further reduce wind shear over the Arabian Sea, allowing storms to organise. Declining aerosol emissions from South Asia — previously thought to have a cooling effect — may also contribute to SST warming. Cyclones Tauktae (2021) and Biparjoy (2023) were unusually intense Arabian Sea storms. This trend has implications for India’s western coastline, which has less cyclone-preparedness infrastructure compared to the east coast. Disaster management agencies must now factor in this changing cyclone geography when planning early warning systems and evacuation protocols.
Key Points to Remember for UPSC
- ENSO is the combined ocean-atmosphere system; El Niño and La Niña are its warm and cool phases respectively.
- El Niño weakens trade winds and shifts warm water eastward in the Pacific, generally reducing Indian monsoon rainfall and Bay of Bengal cyclone frequency.
- La Niña strengthens trade winds, enhances western Pacific warming, and increases cyclone potential in the North Indian Ocean basin.
- The Walker Circulation is the key atmospheric mechanism linking Pacific SST changes to Indian weather patterns.
- A positive IOD can offset El Niño’s drying effect on the monsoon — UPSC tests this interaction.
- Arabian Sea cyclone frequency is increasing due to rising SSTs and La Niña-related wind shear reduction.
- For mains answers, always connect the Pacific phenomenon to the Indian impact using the Walker Circulation as the bridge.
This topic rewards aspirants who study geography as a connected system rather than isolated chapters. My suggestion is to draw the Walker Circulation diagram three times from memory — normal, El Niño, and La Niña — until it becomes second nature. Once you master this one linkage, questions on monsoon variability, cyclone trends, and climate change all become easier to handle with depth and confidence.