Explain the teleconnection between ENSO and the Indian summer monsoon. Why do El Niño years not always translate into droughts of the same severity?

ENSO (El Niño–Southern Oscillation) is the cyclical warming (El Niño) and cooling (La Niña) of the central-eastern equatorial Pacific, coupled with shifts in air pressure. Through a long-distance teleconnection it is the strongest external influence on India's monsoon, but its effect is probabilistic, not deterministic.

ENSO–monsoon teleconnection

• Normal/La Niña years: a strong Walker circulation, with air rising over the warm western Pacific and Indian Ocean, favours convection over India.
• El Niño years: warm water shifts east, the rising limb moves to the central Pacific and the sinking limb settles over India. This weakens monsoon winds and rainfall.
• 2026: Niño-3.4 crossed the El Niño threshold in May and reached about +2.08°C by August [2]. IMD gave a 60% probability of a 'deficient' season [1].

Warm central-east Pacific → Walker cell shifts east
→ sinking air over India → weak convection → rainfall deficit

Fig.: El Niño–monsoon teleconnection

Why severity varies

• Timing and strength: an El Niño that sets in before June, as in 2026 [2], hurts the whole season. A late onset mostly affects September.
• Flavour: central-Pacific ("Modoki") and east-Pacific warming place the sinking limb differently.
• Indian Ocean Dipole (IOD): a positive IOD can offset El Niño. In 1997, an extreme positive IOD accompanied a very strong El Niño [4], and the monsoon stayed near normal. In 2026 the IOD remained neutral, so there was no buffer [2].
• Other drivers: Eurasian snow cover and intraseasonal oscillations (MJO, monsoon depressions) redistribute rainfall.
• Weakening link: an IMD monograph notes the ENSO–summer monsoon relationship has weakened in recent decades [3].
• Impact side: a shortfall in the sowing month, or in poorly irrigated regions, causes more damage than the same all-India deficit spread evenly.

ENSO sets the odds of monsoon failure, while the IOD, onset timing and regional factors decide how severe it is. The National Monsoon Mission has already produced high-resolution dynamical and extended-range forecasts [5]. Turning those probabilities into district contingency plans can keep El Niño years from becoming food crises, advancing SDG 2 and SDG 13.