IMD Cuts 2026 Monsoon to 90% of LPA: El Niño, IOD & "Below Normal" Rainfall Explained

• Definition and seasonal rhythm: The Southwest Monsoon is the four-month rainy season from June to September during which moisture-laden winds blow from the southwest (from the sea towards land) and deliver the bulk of India's annual rainfall. It normally sets in over Kerala around 1 June, advances across the country by mid-July, and begins withdrawing from Northwest India in September.

• The driving mechanism: The monsoon is essentially a giant sea-breeze on a sub-continental scale, created by the differential heating of land and ocean. In summer, the landmass of South Asia heats faster than the Indian Ocean, creating an intense low-pressure trough over Northwest India and the Tibetan Plateau. The apparent northward migration of the Inter-Tropical Convergence Tone (ITCZ) draws in the southeast trade winds from the Southern Hemisphere; after crossing the equator these are deflected by the Coriolis force to become the southwesterly monsoon winds. The Mascarene High (a high-pressure cell near Madagascar), the Somali Low-Level Jet, the heating of the Tibetan Plateau, and the Tropical Easterly Jet aloft all act together to strengthen the circulation. The monsoon then splits into the Arabian Sea branch and the Bay of Bengal branch.

• Why it matters: The Southwest Monsoon contributes around three-fourths of India's annual rainfall and is decisive for the kharif cropping season. A very large share of India's net sown area remains rain-fed and dependent directly on the monsoon, so rainfall feeds agriculture, replenishes reservoirs and groundwater, supports hydropower and drinking-water supply, and influences food inflation and rural demand. Even a 10% deviation from the seasonal mean can have outsized effects on output and prices.

• The headline number: In its second-stage long-range forecast, IMD said seasonal rainfall over the country as a whole is likely to be 90% of the LPA, with a model error of ±4%, putting the season in the "below normal" category. This was a cut from the 92% projected in the first forecast of 13 April 2026.

• The probabilities: IMD attached a 60% probability to a deficient season and 24% to a below-normal season, implying roughly an 84% chance of subdued rainfall overall. A separate ~92% probability was assigned to El Niño developing during the season.

• Regional and temporal detail: No region except the Northeast is expected to receive "normal" rainfall. June alone is forecast at about 92% of LPA — important because a weak start can delay sowing. IMD also flagged above-normal temperatures and heatwave days across the Indo-Gangetic plains and central India, with advisories for cooling shelters, drinking water and health surveillance.

• Meaning of LPA: The LPA is the long-term average of seasonal rainfall computed over a reference period (currently 1971–2020) and treated as "normal." The IMD's all-India LPA for the June–September season is about 868.6 mm (roughly 87 cm). Forecasts are expressed as a percentage of this baseline, which IMD updates roughly every decade as the climatological record advances (earlier baselines were marginally higher, around 88 cm).

• The five categories (as % of LPA): IMD groups the season into five bands:

• Deficient: below 90%

• Below Normal: 90% to 96%

• Normal: 96% to 104%

• Above Normal: 104% to 110%

• Excess: above 110%

A forecast of 90% therefore sits right at the boundary between "below normal" and "deficient," which is why a model error of ±4% is significant — it could pull the season either way.

• Historical context (Actual rainfall as % of LPA): Recent years illustrate monsoon variability — 2014: 88%, 2015: 86% (a strong El Niño drought year), 2018: 91%, 2019: 110%, 2020: 109%, 2023: ~94% (an El Niño year), 2024 and 2025: ~108% each. Against this backdrop, a 2026 outcome near 90% would mark the driest season since 2015.

• The ENSO phenomenon: El Niño–Southern Oscillation (ENSO) is a coupled ocean–atmosphere phenomenon in the equatorial Pacific with three phases — El Niño (warm), La Niña (cool) and Neutral. El Niño refers to abnormal warming of sea-surface temperatures in the central and eastern equatorial Pacific. The "Southern Oscillation" is the see-saw of atmospheric pressure between the eastern Pacific (Tahiti) and the western Pacific (Darwin), measured by the Southern Oscillation Index (SOI).

• The Walker Circulation link: Normally, warm waters in the western Pacific drive rising air and rainfall over Indonesia/Australia, while cool eastern Pacific water has descending air — this east-west loop is the Walker Circulation. During El Niño, the warm pool shifts eastward, the Walker Circulation weakens and reverses, and the zone of strong convection moves away from the Indian/maritime continent towards the central Pacific. This tends to suppress monsoon convection over India.

• The El Niño–monsoon relationship: El Niño years are statistically associated with weak or deficient Indian monsoons (e.g., 1972, 1987, 2002, 2009, 2015), which is why the developing 2026 El Niño triggered the IMD downgrade. However, the relationship is not deterministic — 1997 saw one of the strongest El Niños yet a near-normal monsoon, because other factors (like a strong positive IOD) can counteract it. La Niña years, by contrast, usually favour good monsoons.

• The IOD: The Indian Ocean Dipole is the equivalent of ENSO in the Indian Ocean — an oscillation of sea-surface temperatures between the western Indian Ocean (Arabian Sea region) and the eastern Indian Ocean (near Indonesia). In a positive IOD, the west is warmer than the east, which enhances moisture supply and strengthens the monsoon, often offsetting an El Niño. A negative IOD does the opposite. In 2026, the IOD is expected to remain neutral, so it is not providing the cushioning effect — one reason the outlook is gloomier.

• Other influences: The monsoon is also shaped by the Equatorial Indian Ocean Oscillation (EQUINOO), the Madden–Julian Oscillation (MJO) — an eastward-moving band of cloud and rainfall that modulates active and break spells — and Eurasian/Himalayan winter snow cover (more snow tends to delay/weaken the monsoon by reducing land-sea temperature contrast). The interplay of all these makes single-cause prediction difficult.

• The institution: The IMD, established in 1875 and headquartered in New Delhi, functions under the Ministry of Earth Sciences (MoES) and is the national authority for weather and climate forecasting.

• Two-stage forecasting: IMD issues its first long-range forecast in April and updates it in late May/early June (the second stage), with monthly and regional updates thereafter. It uses a combination of statistical models (based on historical correlations with predictors like sea-surface temperatures) and dynamical models, chiefly the Monsoon Mission Coupled Forecasting System (MMCFS) and a Multi-Model Ensemble that runs the physics of the ocean–atmosphere system on supercomputers.

• Accuracy and limitations: Forecasts come with a stated model error (here ±4%) precisely because the monsoon is a chaotic system. Historically, IMD's predictions have faltered most in El Niño years, and the all-India average can mask sharp regional and intra-seasonal (week-to-week) variability — which often matters more for crops than the headline number.

• Agricultural risk: The forecast of below-normal rain over the monsoon core zone (rain-fed central/western/eastern India) threatens kharif crops, especially pulses, oilseeds and sugarcane. A weak June can delay paddy and maize sowing, while heatwaves stress crops and raise irrigation demand. This is the main channel for potential food inflation and pressure on rural incomes.

• The silver lining — shock absorbers: India today is structurally more resilient to monsoon shocks than in past decades. Central pool foodgrain stocks were around 604 lakh tonnes on 1 April — several times the buffer norm. Reservoir storage is comfortable: about 41% of live capacity across 166 major reservoirs, well above the ten-year average. Irrigation coverage has expanded to roughly 56% of sown area (up from about 49% in 2014–15), reducing dependence on rainfall for staples. The government has also built a seed "war chest" (over 1.7 lakh quintals extra for resowing) and assured MSP procurement.

• Macroeconomic perspective: Agriculture's direct share in GDP has shrunk and the farm sector has grown steadily, so the historical link between a poor monsoon and an economic downturn has weakened. The risk now lies less in aggregate output and more in distribution — perishables like vegetables, pulses and dairy, and the recharge of aquifers for the following rabi (winter) crop.

• Climate change angle: A warming climate is increasing monsoon variability — fewer rainy days but more intense bursts, longer dry spells, and possibly more frequent and stronger El Niño events. This makes the monsoon less predictable and raises the importance of preparedness over reliance on a single seasonal average.

• Way forward: Priorities include strengthening micro-irrigation and watershed management, promoting climate-resilient and short-duration crop varieties, improving real-time and district-level forecasting, efficient reservoir and groundwater management, robust crop insurance (PMFBY), and ready buffer stocks with timely trade interventions to contain inflation. The 2026 episode underlines that managing where and when it rains is now as critical as how much it rains.