Why in News: The India Meteorological Department (IMD) declared the onset of the Southwest Monsoon over Kerala on May 24, 2026 — 8 days earlier than the climatological normal of June 1 and the earliest onset since 2009. However, IMD’s seasonal outlook places 2026 monsoon rainfall at 92% of the Long-Period Average (LPA) — the first below-normal forecast since 2023 — raising concerns for kharif sowing, hydropower and rabi water tables.
The Paradox — Early Onset, Below-Normal Forecast
| Parameter | Detail |
|---|---|
| Normal onset over Kerala | June 1 (with standard deviation of ~7 days) |
| 2026 actual onset | May 24, 2026 — 8 days early (earliest onset since 2009) |
| Earliest recorded onset | May 11, 1918 |
| Latest recorded onset | June 18, 1972 |
| 2026 seasonal rainfall forecast | 92% of LPA — Below Normal category |
| Category boundaries | Deficient (<90%), Below Normal (90-95%), Normal (96-104%), Above Normal (105-110%), Excess (>110%) |
| LPA reference period | 1971-2020; LPA value = 87 cm (870 mm) |
| Probability of below-normal | IMD’s tercile probability forecast assigns elevated probability to below-normal category |
Early onset does not guarantee surplus seasonal rainfall. The two metrics are independent — onset is a synoptic-scale event; seasonal rainfall depends on many large-scale climate drivers.
What Drives the Indian Monsoon
| Driver | Mechanism | 2026 Status |
|---|---|---|
| ENSO (El Niño-Southern Oscillation) | Warm Eastern Pacific (El Niño) typically depresses Indian rainfall; cold (La Niña) enhances it | Neutral leaning towards weak La Niña by August |
| Indian Ocean Dipole (IOD) | Positive IOD (warmer western IO) enhances monsoon; negative reduces it | Forecast: weakly positive |
| Madden-Julian Oscillation (MJO) | Tropical wave pattern; affects intra-seasonal rainfall variability | Variable, monitored on 7-15 day timescales |
| Eurasian snow cover | More snow → cooler land → weaker monsoon (Walker’s law) | Below-normal Eurasian winter snow → favourable |
| Sea Surface Temperatures (SST) in West Pacific, Equatorial IO | Modulate atmospheric circulation | Mixed signals |
| Arctic Sea Ice | Indirect teleconnection | Below-normal extent |
The 2026 forecast at 92% of LPA is driven primarily by early-season SST configuration and EuroAsian climatic patterns — not by ENSO/IOD alone.
The Monsoon Onset Process
| Stage | Approximate Date | What Happens |
|---|---|---|
| Burst over Andaman & Nicobar Islands | May 15-20 | Monsoon enters Indian airspace |
| Onset over Kerala | June 1 (normal) / May 24 (2026) | Heavy rainfall sustained over Kerala coast; cross-equatorial flow set up |
| Northward progression | June-July | Covers Konkan, Goa, Karnataka, Maharashtra, Gujarat, MP |
| Eastward extension | June-July | Covers NE India, West Bengal, Bihar |
| Pan-India coverage | ~July 8 | Full country covered |
| Withdrawal begins | September 17 (NW India) | South-West monsoon retreats; NE monsoon begins over Tamil Nadu |
For the official onset declaration over Kerala, IMD uses three criteria simultaneously:
- Rainfall ≥ 60% of 14 designated stations in Kerala-Lakshadweep receive ≥ 2.5 mm rainfall for two consecutive days.
- Westerly winds at 600 hPa with zonal wind speed ≥ 15-20 knots.
- Outgoing Longwave Radiation (OLR) value < 200 W/m² (indicating deep convection).
Why “Below Normal” Matters
| Sector | Vulnerability |
|---|---|
| Kharif agriculture | Rice, cotton, soybean, maize, sugarcane — combined ~50% of India’s annual food production sourced from kharif |
| Reservoir storage | ~3,500 large reservoirs across India; SW monsoon refills them |
| Hydropower | ~47 GW installed; reduced runoff = lower generation in Q3-Q4 FY27 |
| Rabi sowing | Rabi (Nov-Apr) depends on residual soil moisture + reservoir storage |
| Rural wages | MGNREGS demand surges during below-normal monsoon years |
| Inflation | Food inflation sensitivity — Q3 FY27 CPI prints to watch |
| Drinking water | Urban + rural tankers; Bengaluru, Chennai vulnerable |
Spatial Variability
A national 92% LPA hides large state-level variation. IMD’s regional forecasts typically show:
| Region | Typical 2026 Forecast (illustrative) |
|---|---|
| Northwest India (Punjab, Haryana, Rajasthan, MP, Gujarat) | Below normal |
| Central India | Normal to below normal |
| South Peninsula | Variable, leaning normal |
| Northeast India | Below normal |
| Hilly region | Variable |
Policy Architecture — IMD + Beyond
| Agency | Role |
|---|---|
| IMD | Operational weather forecasting; issues monsoon forecasts in April (long-range), May (updated), monthly updates through season |
| Ministry of Earth Sciences (MoES) | Nodal ministry |
| National Centre for Medium Range Weather Forecasting (NCMRWF) | Numerical weather prediction |
| India Meteorological Department (IMD) Pune | Climate research |
| Indian Institute of Tropical Meteorology (IITM) | Coupled ocean-atmosphere modelling |
| Central Water Commission (CWC) | Reservoir storage tracking |
| Department of Agriculture & Farmers’ Welfare (DA&FW) | Sowing/yield monitoring |
| PMFBY (Pradhan Mantri Fasal Bima Yojana) | Crop insurance covering ~12-15% gross cropped area |
| National Disaster Management Authority (NDMA) | Drought/flood response |
Climate Change Signal
Recent research suggests:
- Increasing intra-seasonal variability — longer dry spells punctuated by heavy rainfall events.
- Westward shift of monsoon depressions.
- Decreasing trend in central India rainfall; increasing trend in NE India (per IPCC AR6 + IITM analyses).
- Heavy rainfall events (>150 mm/day) increasing in frequency.
- Earlier onsets becoming more variable — both very early and very late onsets in recent years.
- Net seasonal rainfall essentially flat over 50 years; redistribution within season is the change.
Watchpoints
- June 1-30 rainfall — critical for sowing window for paddy, soybean, cotton.
- El Niño/La Niña evolution — IMD updates June onwards.
- Reservoir storage trajectory — already below-normal in central India.
- MGNREGS demand — leading indicator of rural distress.
- Vegetable inflation — onion, tomato spikes have macro implications.
- Bond and FX markets — RBI’s monetary path depends partly on monsoon outturn.
Way Forward
- Crop diversification in vulnerable regions — millets (Shree Anna Mission), pulses.
- Micro-irrigation scale-up — PM-KSY drip and sprinkler subsidies.
- Watershed management — combination of rain-water harvesting and decentralised storage.
- PMFBY coverage deepening — most farmers still outside insurance.
- Weather-based crop insurance — moving from yield-loss to weather-index products.
- Early warning systems — district-level + sub-district level rainfall forecasts.
UPSC Relevance
GS Paper 1 — Indian Geography / Physical Geography:
- Climatology — monsoon dynamics, ENSO, IOD.
GS Paper 3 — Agriculture / Environment / Disaster Management:
- Major crops, cropping patterns, e-technology in the aid of farmers.
- Disaster and disaster management — drought, flood.
- Conservation, environmental pollution and degradation.
Analytical hooks for Mains:
- Climate change and Indian monsoon — increasing variability.
- Early onset vs seasonal rainfall — methodological lessons.
- Drought preparedness in a changing monsoon regime.
Facts Corner
- Normal SW Monsoon onset over Kerala: June 1 (±7 days SD).
- 2026 actual onset: May 24, 2026 — 8 days early (earliest since 2009).
- Earliest onset on record: May 11, 1918; latest onset: June 18, 1972.
- 2026 IMD seasonal forecast: 92% of LPA — Below Normal.
- LPA reference period: 1971-2020; LPA value 87 cm (870 mm).
- Categories: Deficient (<90%), Below Normal (90-95%), Normal (96-104%), Above Normal (105-110%), Excess (>110%).
- Onset criteria (IMD): ≥60% of 14 Kerala-Lakshadweep stations with ≥2.5 mm rainfall over 2 days + westerly winds at 600 hPa + OLR < 200 W/m².
- Key drivers: ENSO, IOD, MJO, Eurasian snow cover.
- Issued by: IMD under Ministry of Earth Sciences.
- Withdrawal of SW Monsoon (NW India): September 17 (normal).
- NE Monsoon (Tamil Nadu): October-December.
- Kharif crops share of food production: ~50%.
- IMD established: 1875 (HQ New Delhi; key centre Pune).
Sources: IMD, Ministry of Earth Sciences, The Hindu
Source: SW Monsoon 2026 — Early Kerala Onset, 92% of LPA Below-Normal Forecast — Ujiyari.com | Free UPSC & State PCS Current Affairs
