How does ENSO affect the two Indian monsoon seasons differently? What does this mean for agriculture and water security in South India?

The El Niño–Southern Oscillation (ENSO) is the periodic warming (El Niño) and cooling (La Niña) of the equatorial Pacific. It does not affect India's two monsoons in the same way. 2026 is a clear example: a strong El Niño came with a deficient southwest monsoon, and it now shapes the outlook for the northeast monsoon [2][3].

Differential impact of ENSO on the two seasons

• Southwest monsoon (SWM, Jun–Sep): El Niño suppresses it. In May 2026, IMD expected El Niño to develop and forecast 90% of LPA [1]. The season ended at 87% of LPA, and the South Peninsula received only 76% [2].
• Northeast monsoon (NEM, Oct–Dec): IMD says ENSO has a significant influence on year-to-year NEM variability [3]. El Niño is generally associated with normal-to-excess NEM rain. With a strong El Niño and a neutral IOD, IMD forecasts a normal 2026 NEM, at 88–112% of an LPA of about 334 mm [3].
• Extremes, not just totals: The El Niño year 2015 brought cloudburst-scale rain of 100–200 mm/hour over Chennai [4].
• Spatial unevenness: For 2026, IMD expects normal-to-above rain in south Kerala and Tamil Nadu and below-normal rain elsewhere [3].

El Niño year:  SWM ↓ (deficit)  ──►  NEM ↔/↑ (volatile, extreme spells)
               kharif stress          rabi relief  OR  floods

Fig: ENSO's opposite effects on the two monsoons

Implications for agriculture

• The NEM coincides with the second agricultural season. Oct–Dec brings about 30% of the South Peninsula's annual rain and 48% of Tamil Nadu's [3].
• After a weak SWM, the NEM has to make up for kharif losses and support rabi/samba crops.
• Where rain is below normal, IMD warns of soil-moisture stress and higher irrigation demand, made worse by above-normal temperatures [3].
• Excess rain also hurts crops. Intense NEM floods have repeatedly affected both rabi and kharif seasons in Tamil Nadu [4].

Implications for water security

• Reservoirs and aquifers depend on NEM recharge, and IMD flags the risk of reduced recharge where rain falls short [3].
• The same tank can cause both scarcity and floods. After a dry SWM, managers keep tanks full. In 2015, the CAG found that Chembarambakkam had no inflow-forecast system or Emergency Action Plan, so outflow exceeded inflow and caused unregulated releases into the Adyar river [5].
• Urban drainage gaps: The CAG also found inadequate storm-water drains and encroached water bodies [5].

ENSO thus links a dry summer to an unpredictable winter, so South India can face scarcity and floods in the same year. The way forward is to use IMD's extended-range and impact-based forecasts [3] for crop contingency plans, adopt forecast-based reservoir rules, and remove encroachments as the CAG recommended [5]. Together these build climate resilience in line with SDG 6 and SDG 13.