Background
What is El Niño?
El Niño is the warm phase of the El Niño-Southern Oscillation (ENSO), a naturally occurring climate phenomenon in the tropical Pacific Ocean.
Under normal conditions, easterly trade winds push warm surface waters towards Indonesia and Australia, facilitating the formation of rain-bearing clouds.
During El Niño, these trade winds weaken, allowing warm water to move towards the central and eastern Pacific Ocean.
This shifts atmospheric convection and rainfall patterns, affecting global weather systems.
The altered atmospheric circulation can lead to descending, warmer and drier air over parts of the Indian subcontinent, suppressing cloud formation and weakening the southwest monsoon.
How does El Niño affect the Indian monsoon?
El Niño generally has an inverse relationship with Indian summer monsoon rainfall.
It can weaken the monsoon circulation and reduce moisture-bearing winds reaching India.
However, this relationship is not absolute. A strong El Niño does not necessarily result in a deficient monsoon because several oceanic and atmospheric factors influence rainfall distribution.
El Niño and Indian monsoon rainfall
Year | El Niño impact and monsoon performance |
1997 | Strong El Niño, but India received nearly normal rainfall. |
2015 | Strong El Niño accompanied by approximately 13% rainfall deficiency. |
2023 | El Niño year; rainfall remained below average, with a particularly dry August. |
2026 | Strong El Niño conditions; rainfall was nearly 13% below the long-term average. |
Why Does a Strong El Niño Not Always Lead to a Poor Indian Monsoon?
The impact of El Niño is moderated by several other oceanic and atmospheric phenomena.
Indian Ocean Dipole (IOD)
The Indian Ocean Dipole is an ocean-atmosphere phenomenon characterised by differences in sea surface temperatures between the western and eastern equatorial Indian Ocean.
It has two major phases:
Positive IOD:
The western Indian Ocean becomes warmer than usual, while the eastern Indian Ocean near Indonesia becomes cooler.
Warmer waters in the western Indian Ocean enhance atmospheric convection and influence moisture-bearing winds.
This can strengthen rainfall over parts of India and compensate for the adverse impact of El Niño.
Negative IOD:
The western Indian Ocean becomes relatively cooler, while the eastern Indian Ocean becomes warmer.
This can weaken favourable atmospheric conditions for the Indian monsoon.
Role in different El Niño years:
In 1997, a favourable positive IOD helped offset the negative impact of El Niño, resulting in nearly normal monsoon rainfall.
In 2015, the IOD was not sufficiently favourable to counter the strong El Niño, contributing to deficient rainfall.
In 2023, a positive IOD helped improve rainfall conditions towards the latter part of the monsoon season.
Madden-Julian Oscillation (MJO)
The MJO is an eastward-moving atmospheric disturbance characterised by alternating zones of enhanced and suppressed rainfall across the tropics.
It generally completes its global journey in approximately 30–60 days.
Its movement influences cloud formation, convection and rainfall distribution over the Indian Ocean and the Indian subcontinent.
When the favourable phase of the MJO moves over the Indian Ocean, it can enhance monsoon rainfall.
Conversely, when it remains over Africa or the Americas, it may suppress rainfall over India.
Location of Warmest Waters in the Pacific Ocean
The geographical location of the warmest sea surface temperatures during El Niño also influences its impact on the Indian monsoon.
When maximum warming occurs in the central Pacific, the associated atmospheric circulation can increase the likelihood of reduced rainfall over India.
When warming is concentrated further east towards South America, its influence on Indian monsoon circulation can differ.
Atmospheric Circulation and Regional Weather Systems
High-pressure systems, upper-atmospheric circulation and changes in wind patterns influence the movement of moisture towards India.
In 1997, an unusual high-pressure system over the Iranian plateau and additional moisture from the Arabian Sea contributed to favourable rainfall conditions.
Changes in the westerly wind belt around Antarctica can also influence circulation over the southern Indian Ocean and consequently affect the IOD.
Challenges
Monsoon Forecasting Uncertainty: Complex interactions between El Niño, IOD and MJO make accurate rainfall predictions difficult.
Regional Rainfall Imbalance: Uneven rainfall distribution can cause drought-like conditions in certain regions despite normal national rainfall.
Agricultural Vulnerability: Dependence on monsoon rainfall exposes farmers to crop losses, reduced productivity and income insecurity.
Food and Water Security: Deficient rainfall can increase food inflation, reduce reservoir levels and affect drinking water availability.
Climate Model Limitations: Variations in ocean-atmosphere interactions and model predictions create difficulties in estimating monsoon intensity and distribution.
Way Forward
Integrated Forecasting: Strengthen IMD's forecasting by combining ENSO, IOD, MJO and multiple global climate models.
Climate-Resilient Agriculture: Promote drought-resistant seeds, crop diversification and climate-smart farming practices.
Water Conservation: Expand rainwater harvesting, watershed development, groundwater recharge and micro-irrigation.
Early-Warning Systems: Develop district-level rainfall forecasts and timely weather-based agricultural advisories.
Institutional Preparedness: Strengthen crop insurance, disaster compensation and coordination among meteorological, agricultural and water management agencies.
Conclusion
The association of El Niño and the Indian monsoon is complicated and is determined by several interlinked processes at the oceanic and atmospheric level. It has been seen that despite having a severe El Niño, there may still be no deficient monsoon, as evident from the different experiences of 1997, 2015, 2023 and 2026. There can be other factors which can change the effect of El Niño, like the Indian Ocean Dipole, Madden-Julian Oscillation, Pacific warming patterns and atmospheric circulation.
