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Will the Indian Ocean Dipole save the monsoon?

GS Paper 1

 Syllabus: Indian Geography: Monsoon


Source: TOI, IE

 Context: The Indian Meteorological Department (IMD) predicts a normal monsoon despite the possibility of an El Nino event.


What is Monsoon and El Nino?

  • Monsoon: A seasonal reversal of wind system that brings heavy rainfall, especially in the Indian subcontinent. The Indian summer monsoon affects a vast region spanning 25 countries and covering a distance of 18,000 kilometres from east to west and 6,000 kilometres from south to north.
  • El Nino: A climate pattern characterized by warmer-than-average sea surface temperatures in the central and eastern equatorial Pacific Ocean, which can have widespread impacts on weather patterns around the world.


Factors that can impact the monsoon rains:

Factors Impact on Monsoon
El Nino/La Nina El Nino can lead to weaker monsoons, while La Nina can enhance it.
Dateline El Nino or a Central Pacific El Nino It is considered to have a larger negative impact on the monsoon, but an exception was the 2005 El Nino.
Atlantic Nino It is the east-west anomaly pattern in the tropical Atlantic Ocean. It also influences the monsoon.
Indian Ocean Dipole (IOD) Positive IOD can enhance monsoon, while negative IOD can weaken it.
Sea Surface Temperatures Warmer sea surface temperatures can enhance monsoon, while cooler temperatures can weaken it.
Atmospheric Pressure Changes in atmospheric pressure patterns can affect monsoon circulation and rainfall patterns.
Land-Sea Temperature Contrast Greater contrast between land and sea temperatures can influence monsoon strength and rainfall distribution.
Himalayan Mountain Range The presence of the Himalayas can influence monsoon winds and rainfall patterns in the Indian subcontinent.
Topography The shape and elevation of landforms can impact local wind patterns and rainfall distribution.
Tropical Cyclones The occurrence and track of tropical cyclones can influence monsoon rainfall, especially in coastal regions.
Global Climate Patterns Variations in global climate patterns, such as the Madden-Julian Oscillation (MJO), can affect monsoon dynamics.
Local Factors Factors like local vegetation, soil moisture, and land use changes can also impact monsoon conditions at a regional level.


What is the Indian Ocean Dipole (IOD)?

IOD is a climate phenomenon in the Indian Ocean characterized by the fluctuation of sea surface temperatures and atmospheric pressure between its eastern and western parts. The IOD is similar in nature to the El Nino-Southern Oscillation (ENSO) phenomenon in the Pacific Ocean but on a smaller scale.


How the Indian Ocean Dipole (IOD) can affect the monsoon:

Indian Ocean Dipole (IOD) Phase Impact on Monsoon Example
Positive IOD Enhances monsoon rainfall over the Indian subcontinent In 1997, a positive IOD offset the impact of El Nino, resulting in above-normal monsoon rainfall.
Negative IOD Weakens monsoon rainfall over the Indian subcontinent In 2019, a negative IOD contributed to deficient monsoon rainfall, particularly during the first month of the monsoon season.
Neutral IOD Minimal or neutral impact on the monsoon A neutral IOD does not significantly influence the monsoon and allows other factors to play a more dominant role.


The Earth System Science Organisation (ESSO) and the IMD take into account five conditions while making forecasts about the monsoon in April every year.

1) The Sea Surface Temperature (SST) gradient between the North Atlantic and the North Pacific (conditions during December of the previous year and January of the present year)
2) SST of the equatorial south Indian Ocean (conditions during February and March of the present year)
3) Mean Sea Level pressure in East Asia (conditions during February and March of the present year)
4) The surface air temperature over northwest Europe (conditions during January of the present year)
5) The warm water volume of the equatorial Pacific Ocean (conditions during February and March of the present year)



What are the limitations of forecasting El Nino and IOD?

  • For the IOD and Atlantic Nino, forecasting models currently lack the reliability to accurately predict their occurrence and behaviour. As a result, their specific role in influencing monsoon patterns in a particular season remains uncertain.
  • When it comes to forecasting El Nino events, models face challenges in precisely predicting the location and intensity of warming during the early stages.


Insta Links:

El Nino


Prelims Links: (UPSC 2017)

With reference to the ‘Indian Ocean Dipole (IOD)’ sometimes mentioned in the news while forecasting the Indian monsoon, which of the following statements is/are correct?

  1. The IOD phenomenon is characterised by a difference in sea surface temperature between the tropical Western Indian Ocean and the tropical Eastern Pacific Ocean.
  2. An IOD phenomenon can influence El Nino’s impact on the monsoon.


Select the correct answer using the code given below:

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2


Ans: 2