Central Idea

• Delay in Monsoon: Any discussion on Indian monsoon delay these days invariably has references to the El Nino phenomenon.
• Sudden rise of El Nino: This year’s monsoon is also progressing under the cloud of an El Nino in the Pacific Ocean.

Understanding El Nino and La Nina

• El Nino and La Nina are two opposite phases of the El Nino-Southern Oscillation (ENSO) cycle.
• ENSO is a naturally occurring phenomenon that involves the interaction between the ocean and atmosphere in the equatorial Pacific.

Here is a detailed comparison of El Nino and La Nina

Impact on India

El Nino and Indian Monsoon

• El Nino and its impact on Indian monsoon: El Nino refers to abnormal warming of surface waters in the equatorial Pacific Ocean, which tends to suppress monsoon rainfall in India.
• Phases of El Nino Southern Oscillation (ENSO): ENSO consists of three phases in the Pacific Ocean: El Nino, La Nina (abnormal cooling), and a neutral phase with sea surface temperatures close to long-term averages.
• Ocean and atmospheric conditions: ENSO involves not only temperature abnormalities of sea surface waters but also atmospheric conditions, including differences in sea-level air pressure and wind strength and direction.
• Southern oscillation and the role of winds: Southern Oscillation Index measures the difference in sea-level air pressure over the western and eastern sides of the Pacific Ocean, while wind patterns play a crucial role in ENSO.

Factors triggering El Nino

• Weakening trade winds: When the trade winds in the tropical Pacific weaken, it contributes to the occurrence of El Nino by reducing the movement of warm surface waters.
• Changes in ocean currents: Alterations in the normal patterns of ocean currents can trigger El Nino events as they affect the distribution and accumulation of warm water in the central and eastern Pacific.
• Variations in atmospheric pressure: Fluctuations in atmospheric pressure patterns disrupt the typical circulation associated with trade winds, which can initiate the onset of El Nino conditions.
• Influence of oceanic Kelvin waves: The presence and behavior of oceanic Kelvin waves, large-scale waves that transport warm water eastward, play a role in the development and intensification of El Nino events.
• Interactions with other climate modes: El Nino can be influenced by the interactions and connections with other climate phenomena such as the Indian Ocean Dipole and the Madden-Julian Oscillation, which can impact the oceanic and atmospheric conditions in the Pacific region.

Measuring the Cycle

(1) Oceanic Nino Index (ONI)

• Measures the oceanic component of El Nino Southern Oscillation (ENSO).
• Tracks the departure from average sea surface temperatures in the tropical Pacific Ocean.
• Helps quantify the intensity and duration of El Nino or La Nina events.
• Typically based on a rolling three-month average of sea surface temperature anomalies in specific regions.

(2) Southern Oscillation Index (SOI)

• Measures the atmospheric component of ENSO.
• Quantifies the difference in air pressure between two locations: Tahiti and Darwin.
• Positive SOI values indicate higher pressure in the eastern Pacific and lower pressure in the western Pacific.
• Negative SOI values indicate lower pressure in the eastern Pacific and higher pressure in the western Pacific.
• Reflects the strength and changes in the atmospheric circulation patterns associated with ENSO.
• Used to assess the phase and strength of ENSO and its impact on global weather and climate patterns.

Economic impact of El Nino on Indian Agriculture

• Drought and reduced rainfall: El Nino events often lead to below-average monsoon rainfall in India, resulting in drought conditions in various regions.
• Crop failure and lower yields: Lack of adequate water availability can lead to crop failure or lower yields for major crops such as rice, wheat, pulses, and oilseeds.
• Increased input costs: During El Nino-induced droughts, farmers may need to invest in additional irrigation, water management, and supplementary feeding for livestock, leading to increased input costs.
• Price fluctuations: Reduced crop production due to El Nino can affect market supply, leading to price fluctuations and potential inflation in food prices.
• Livestock and fisheries: Water scarcity and changes in marine ecosystems can negatively affect animal husbandry and fishing activities, disrupting the livelihoods of those dependent on these sectors.
• Rural livelihoods and migration: The economic stress created can impact rural livelihoods, leading to increased migration from rural to urban areas in search of alternative employment opportunities.

Try this PYQ:

La Nina is suspected to have caused recent floods in Australia. How is La Nina different from El Nino?

1. La Nina is characterized by unusually cold ocean temperature in equatorial Indian Ocean whereas El Nino is characterized by unusually warm ocean temperature in the equatorial Pacific Ocean.
2. El Nino has an adverse effect on south-west monsoon of India, but La Nina has no effect on monsoon climate.

Which of the statements given above is/are correct?

(a) Only 1

(b) Only 2

(c) Both 1 and 2

(d) Neither 1 nor 2

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