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Relevance: GS Paper I & III — Geography, Climatology & Agriculture Source: The Hindu / IMD, 2026

1 · What happened

The India Meteorological Department (IMD) has revised the onset of the Southwest Monsoon over Kerala from May 26 to around June 4, 2026 — the first overshoot beyond the model’s ±4-day error window since 2015.

An upper-air cyclonic circulation off the southern Kerala coast is now providing the final atmospheric push for landfall. The delay is attributed to a building El Niño phase in the equatorial Pacific suppressing convection over the subcontinent.

2 · IMD’s Three-Criteria Onset Test & Why 2026 Stalled

Monsoon Onset over Kerala (MOK) is declared only when three meteorological conditions — rainfall, wind depth, and outgoing radiation — are simultaneously satisfied on any day after May 10.

Criterion 1 — Rainfall
60% of 14 Stations
At least 60% of 14 designated stations across Kerala and adjoining coast (Thiruvananthapuram, Kochi, Kozhikode, Mangaluru) must record ≥2.5 mm rainfall for two consecutive days.
Criterion 2 — Wind Depth
Westerlies up to 600 hPa
Lower-tropospheric westerlies must extend up to the 600 hPa pressure level (~4.5 km altitude) over the southeast Arabian Sea — proof of a structural, deep wind system.
Criterion 3 — Mechanism
OLR below 200 W/m²
Outgoing Longwave Radiation over the southeast Arabian Sea must drop below 200 W/m² — a proxy for deep, thick cloud tops blocking heat escape, distinguishing monsoon convection from pre-monsoon showers.
Threat — Why 2026 Stalled
El Niño & Walker Disruption
Abnormal warming of the eastern tropical Pacific disrupts the Walker Circulation, altering upper-air winds and suppressing convection over India. Season forecast: 90% of LPA — “Below Normal”.

  • Driver of the monsoon: Differential heating creates a low-pressure trough over Tibet/Central Asia while the southern Indian Ocean stays cool — drawing moisture-laden trade winds that the Coriolis force deflects into Southwest winds.
  • Agriculture exposure: Over 50% of India’s net sown area is rain-fed, with no irrigation backup — a delayed onset shortens the Kharif cycle for rice, pulses, oilseeds, cotton.
  • Inflation linkage: Below-normal rainfall directly spikes prices of vegetables, pulses and sugar — complicating RBI monetary policy.
  • Hydrological stress: Reservoir depletion hits rural drinking water security and hydroelectric generation at peak summer demand.

Image : Depicting El -Nino & La-Nina Phenomenon

UPSC Value Box
IMD India Meteorological Department — national weather agency under the Ministry of Earth Sciences (MoES); HQ at New Delhi, est. 1875.
LPA Long Period Average — average all-India seasonal rainfall over a 50-year reference period. Categories: ≥104% Above Normal · 96–104% Normal · 90–96% Below Normal · <90% Deficient.
OLR Outgoing Longwave Radiation — infrared energy radiated by Earth to space. Low OLR ⇒ thick high cloud tops ⇒ deep convection ⇒ active monsoon.
El Niño / ENSO Warm phase of El Niño–Southern Oscillation — abnormal warming of the eastern equatorial Pacific; historically correlated with weaker Indian monsoons.
Walker Circulation East–west atmospheric loop over the tropical Pacific — rising air over warm Indo-Pacific, sinking over cool eastern Pacific. Weakens/reverses during El Niño.
National Monsoon Mission Launched by MoES to build a dynamic mathematical forecasting system for seasonal and intra-seasonal monsoon prediction via high-performance computing.
PMKSY Pradhan Mantri Krishi Sinchayee Yojana — motto “Har Khet Ko Pani”; component “Per Drop More Crop” promotes micro-irrigation.
Amrit Sarovar Mission Mission to develop and rejuvenate 75 water bodies per district to strengthen decentralised rainwater harvesting.

MCQ Practice Question
Q. With reference to the Southwest Monsoon and its onset over Kerala, consider the following statements:

  1. The IMD declares monsoon onset over Kerala only when at least 60% of 14 designated weather stations record 2.5 mm or more rainfall for two consecutive days, along with specified wind and radiation criteria.
  2. El Niño refers to the abnormal cooling of surface waters in the eastern equatorial Pacific Ocean, which typically strengthens the Indian Southwest Monsoon.
  3. Outgoing Longwave Radiation (OLR) values below 200 W/m² over the southeast Arabian Sea indicate deep convective cloud cover and are used by IMD as one of the onset criteria.

Which of the statements given above is/are correct?
(a) 1 and 2 only    (b) 2 and 3 only    (c) 1 and 3 only    (d) 1, 2 and 3

Answer: (c) 1 and 3 only

  • Statement 1 — Correct: The rainfall criterion requires ≥60% of 14 designated stations (Thiruvananthapuram, Kochi, Kozhikode, Mangaluru and others) to record ≥2.5 mm for two consecutive days, alongside the wind and OLR criteria.
  • Statement 2 — Incorrect (the trap): El Niño is the abnormal warming (not cooling) of surface waters in the eastern equatorial Pacific, and it typically weakens (not strengthens) the Indian Southwest Monsoon by disrupting the Walker Circulation. The cooling counterpart is La Niña.
  • Statement 3 — Correct: OLR below 200 W/m² over the southeast Arabian Sea indicates thick, cold cloud tops and deep convection — the third pillar of IMD’s onset declaration.

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