El Niño Explained: Formation, Circulation, and Its Impact on the Indian Monsoon

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  • In our previous blog, we examined the far-reaching consequences of a deficient monsoon triggered by the "El Niño phenomenon", where-
  1. We explored in detail its agricultural, social, economic, and political implications, and 
  2. Why rainfall deficiency remains one of the most critical challenges for a monsoon-dependent economy like India.
  • The issue has become even more significant in 2026 as concerns over a weaker-than-normal monsoon have prompted the Union Agriculture Minister, "Shivraj Singh Chouhan," to review preparedness measures and advise states to formulate contingency plans for districts likely to face low or erratic rainfall. The government has also acknowledged the possibility of El Niño-related disruptions and has emphasized the need for advance planning to safeguard (primarily)-
  1. agricultural production and 
  2. food security.
  • Such concerns extend far beyond the agricultural sector in a country like India, where a substantial share of employment, rural income, consumption, and economic activity remains directly or indirectly linked to the monsoon, so any indication of rainfall deficiency can have wider economic, social, and political implications, when a weak monsoon can affect-
  1. farm incomes through the disturbing wealth creation cycle
  2. lowering rural demand, 
  3. inflated food prices, and 
  4. disappointing economic sentiment. 
  • Therefore, policymakers view monsoon preparedness not merely as an agricultural necessity but as a critical component of maintaining- 
  1. economic stability, 
  2. social cohesion, and 
  3. political resilience in the anticipation of uncertainties.

  • Now, as we have promised, in this blog, we are going to discuss-
  1. The formation of El Niño conditions, and 
  2. The operating mechanism through which it can cause a deficiency in the Indian monsoon. 
  • Understanding this mechanism will help us to connect ourselves to "climatic events" occurring thousands of kilometres away in the Pacific Ocean and affecting India negatively with respect to-
  1. rainfall variability, 
  2. agricultural productivity, 
  3. Concern related to food security in India, 
  4. India's economic stability through proportional wealth distribution,
  5. Economic Demand -& Supply combination 
So, with this understanding, when we start our discussion, it would be better to have a comparative analogy to develop our core understanding.


Party Event Analogy


  • Imagine that one day you receive an invitation to attend a party. Since there is only one invitation, your choice is simple—you attend that particular event. However, suppose that the very next time you receive invitations to several different parties. In that situation, you will naturally prefer the event that appears more attractive, whether because of its-
  1. atmosphere, 
  2. food, 
  3. beverages, or 
  4. overall experience.
  • In geographical terms, we can compare this attraction to a low-pressure area. The stronger the low pressure, the deeper the attraction. If you were not a person but a moving air mass in the form of wind, you would naturally move towards the region of relatively higher temperature (the charged atmosphere of food, beverages and overall experience), which means an area of lower pressure. Look at the following image-



  • A similar phenomenon occurs during El Niño years, when the Equatorial Pacific Ocean undergoes excessive warming, and a stronger zone of convection and lower pressure develops over the central and eastern Pacific. Consequently, a significant portion of the atmospheric circulation of the south-west monsoon winds that would normally support the Indian monsoon starts to attract towards the Pacific region instead.


Now, let us return to our party analogy.

  • Imagine that the Indian subcontinent is hosting a party. Under normal conditions, the atmosphere of this event is highly attractive, and therefore, a large number of guests arrive. In our analogy, these guests represent the moisture-laden monsoon winds.
  • However, suppose another party is being hosted elsewhere, in our case, the region of central and east pacific, where its environment becomes even more attractive. Naturally, a significant number of guests who were originally expected to attend the first party may now choose to attend the second one instead.
  • The same phenomenon occurs during El Niño conditions. The abnormal warming of the central and eastern Pacific Ocean creates a more attractive zone of low pressure and atmospheric convection. As a result, a substantial portion of the atmospheric circulation monsoonal winds that would normally support the Indian monsoon becomes associated with the Pacific region.
  • Consequently, fewer moisture-bearing winds reach the Indian subcontinent, weakening the monsoon circulation and increasing the likelihood of rainfall deficiency. 
  • This phenomenon is known as El Niño. The term "El Niño" is derived from the Spanish language and literally means "The Little Boy" or "Christ Child." Over time, climatologists and commentators have often described it as a "mischievous little boy" because of its ability to disrupt normal weather patterns across the world, particularly the Indian monsoon.


Temperature–Pressure Relationship

  • For this purpose of understanding, we first need to understand the intricate yet indispensable relationship between temperature and pressure—a relationship that is proportional in its operation but inverse in its consequences. 
  • As we have already discussed this fundamental concept in one of our previous blogs, it is essential to revisit it before proceeding further. Therefore, click here first to understand this intricate relationship, where it forms the very foundation for comprehending the formation and operating mechanism of El Niño and its subsequent influence on the Indian monsoon.


👉Indian Subcontinent Monsoon (2/16): The Dynamics of the Earth–Sun Relationship Behind Its Origin 👀


Earth's Geoid Shape and Differential Heating

  • Now, with an understanding of the indispensable and intricate relationship between temperature and pressure, we can discuss it in conjunction with the geoid shape of the Earth.
  • As we know, due to the geoid shape of the Earth, different regions receive different intensities of incoming solar radiation (insolation). Look at the following infographics


  • The Equatorial region receives the maximum insolation, while the intensity gradually decreases towards the poles. Furthermore, the Earth is slightly bulged around the Equator, approximately between 5° North and 5° South, whereas it becomes relatively flattened towards the poles. This geographical configuration contributes to a significant temperature gradient between the Equatorial and Polar regions.
  • After 21 March, when the apparent position of the Sun shifts from the Southern Hemisphere towards the Northern Hemisphere, the Equatorial Pacific continues to experience substantial heating. Simultaneously, the Indian Ocean also undergoes warming. Beginning in April, sea surface temperatures in the Indian Ocean rise steadily and often approach 30°C, generally reaching their peak during May.






Pressure Belts and Seasonal Shift of ITCZ
  • At this stage, it is important to recall the Earth's major pressure belts. 
Pressure Belts of Earth.

  1. First, we have the Equatorial Low-Pressure Belt, commonly known as the "Inter-Tropical Convergence Zone (ITCZ)." 
  2. Beyond this, between approximately 20° and 30° North and South latitudes, lie the "Subtropical High-Pressure Belts." 
  3. Around 60° to 70° North and South latitudes are "the Subpolar Low-Pressure Belts," while 
  4. "The Polar High-Pressure Belts" are situated at the North and South Poles.
  • Among all these pressure belts, the ITCZ is of utmost importance. We also know from geography perspective that the pressure belts migrate seasonally following the apparent movement of the Sun. 
  1. On 21 March, the Sun is positioned directly over the Equator at a 90-degree angle. 
  2. Thereafter, its apparent position shifts northward and reaches its maximum extent, at a 90-degree angle, over the Tropic of Cancer on 21 June and comes back over the equator on 23rd of september means in between 21 March and 23 September, the Northern Hemisphere receives greater insolation than the Southern Hemisphere.
  • We are already aware that whenever the temperature rises, pressure falls. Therefore, as the Northern Hemisphere receives increasing insolation after 21 March, temperatures rise, and atmospheric pressure proportionally falls. At the same time, the Southern Hemisphere remains relatively cooler and therefore maintains comparatively higher pressure. 
Now, look at this image. 
   


  • As we have already discussed, after 21 March, the apparent position of the Sun gradually shifts towards the Northern Hemisphere. As a result, temperatures rise and a stronger low-pressure area develops over the Northern Hemisphere. Consequently, all major pressure belts, including the Intertropical Convergence Zone (ITCZ), begin to shift northward following the apparent movement of the Sun.
  • By June, July, and August, when solar heating over the Northern Hemisphere reaches its peak, the ITCZ attains its northernmost position and lies over the Indian subcontinent. In other words, with respect to India, the ITCZ has shifted significantly northward from its equatorial position and has become firmly established within the Northern Hemisphere.
  • If this concept is clear, we can now move to the next infographic, where we will observe how the Southeast Trade Winds of the Southern Hemisphere are compelled to cross the Equator, enter the Northern Hemisphere, and converge at the ITCZ. 
        

  • Now, look at the above image. As we have already discussed, during June, July, and August, the ITCZ shifts significantly northward and becomes established over the Indian subcontinent. Since the ITCZ is a zone of convergence, it attracts winds from the surrounding regions, including Southern Hemisphere.
  • As a result of this northward shift, the Southeast Trade Winds are compelled to cross the Equator and enter the Northern Hemisphere in order to converge at the ITCZ. The moment these winds cross the Equator, they are deflected towards their right due to the Coriolis force. While moving northward, they pass over the warm waters of the Indian Ocean, absorbing large quantities of moisture.
  • These moisture-laden winds are then drawn towards the low-pressure conditions prevailing over the Indian subcontinent and eventually bring widespread rainfall across the region. This seasonal wind system, responsible for the majority of India's annual rainfall, is known as the Southwest Monsoon.
  • This process ultimately forms the foundation of the Southwest Monsoon system over the Indian subcontinent.

  • This mechanism forms the foundation of the Southwest Monsoon. The winds-
    1. Originating in the Southern Hemisphere,
    2. Cross the Equator, 
    3. acquire moisture from the Indian Ocean, and, 
    4. After being deflected by the Coriolis force, 
    5. Approach the Indian subcontinent as the Southwest Monsoon.
  • The geography of the Indian subcontinent further strengthens this process thats is why we are seeing a higher northward shifting of ITCZ over the Indian Subcontinent. From the Makran Coast (in Pakistan) and the Hindu Kush (In Afghanistan) in the northwest to the Himalayas and the Arakan Yoma in the east (Myanmar), the subcontinent is enclosed by extensive mountain barriers. These mountains act as a heat-trapping system, enhancing the heating of the landmass. Higher temperatures create deeper low-pressure conditions, and the stronger the pressure gradient, the stronger the monsoon winds become.
  • As a result, moisture-laden winds from the Indian Ocean are drawn towards the Indian subcontinent, where they produce the rainfall that characterises the monsoon season.



Formation Mechanism behind El Niño formation

  • Everything that we have discussed up to this point has been aimed at helping us understand the following infographics. 
  • We are already aware that during the pre-monsoon period, both the Indian Ocean and the Pacific Ocean undergo significant warming.
  • In a normal year, the warmest waters of the Pacific Ocean are concentrated along the eastern margins of Asia and Australia, particularly in the western Pacific region. This warm water creates a zone of low pressure and strong convection, which supports the normal atmospheric circulation pattern.
  • However, during an El Niño year, this condition undergoes a significant transformation. The warm waters and the associated low-pressure zone begin to shift eastward, extending from the western Pacific towards the central and eastern Pacific Ocean, reaching the western margins of South America. In other words, the centre of low pressure moves away from Asia and Australia and becomes established over the central and eastern Pacific.
  • As we have already learned, a low-pressure area acts as an attracting zone for winds. The deeper the low pressure, the stronger its ability to draw surrounding air towards itself. This is precisely the concept we understood through our party-event analogy, where the most attractive destination naturally draws the greatest attention.
  • Similarly, the newly established low-pressure zone over the central and eastern Pacific begins to attract a larger share of the atmospheric circulation. As a consequence, a portion of the moisture-bearing winds and monsoon-supporting circulation that would ordinarily contribute to rainfall over the Indian subcontinent becomes associated with the Pacific region instead.
  • This eastward shift of the low-pressure zone, along with the weakening and redirection of the monsoon-supporting circulation away from the Indian subcontinent, is the fundamental mechanism behind the El Niño phenomenon. As a result, the Indian monsoon weakens, increasing the likelihood of below-normal rainfall and monsoon deficiency over large parts of India. What could be the negative consequences of more information and conceptual understanding addressed to this link

Walker Circulation and Its Disruption- 

  • This is the concept associated with the formation mechanism of monsoon that we will discuss in the upcoming blog. Thanks.


Conclusion

  • In conclusion, El Niño can be understood as a climatic phenomenon in which the abnormal warming of the Equatorial Pacific Ocean alters the normal atmospheric circulation patterns, due to this a substantial portion of the atmospheric circulation that would ordinarily support the Indian monsoon becomes associated with the Pacific region, thereby weakening the Southwest Monsoon over the Indian subcontinent.
  • The intensity of El Niño depends upon the extent of warming that develops in the Equatorial Pacific Ocean as a result of enhanced insolation and ocean-atmosphere interactions. Generally, the stronger the warming, the greater its potential to adversely affect the Indian monsoon system. 
  • But it does not mean that every time Pacific water gets warmer, we have El Niño. Several factors that affectthe  its efficacy which listted in upcoming topics. 
  • Thus, we can conclude that El Niño represents a climatic condition that disrupts and weakens the normal monsoon circulation over the Indian subcontinent, often resulting in below-normal rainfall and associated agricultural, economic, and social consequences.
Thanks
Critical comments are welcome


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