Progress of monsoon

1. At a Glance

• The Southwest Monsoon (SWM) is a seasonal wind-reversal system delivering ~75–80% of India's annual rainfall between June–September, making it the lifeline of Indian agriculture and economy. [3]
• It advances in two branches: Arabian Sea branch (western coast, central India) and Bay of Bengal branch (northeast, east India), both deflected by the Coriolis Force to blow SW→NE. [3]
• The India Meteorological Department (IMD) under the Ministry of Earth Sciences (MoES) issues forecasts, onset dates, and advance bulletins — all high-yield Prelims material.
• Historical monitoring of monsoon progress dates back to at least 1926 (evidenced by contemporaneous Simla weather office bulletins), underscoring the deep administrative priority placed on this phenomenon. [1]

2. Why in the News

• 2026 Monsoon onset: SWM onset over Kerala occurred on 4 June 2026, three days later than its normal date of 1 June and nine days later than IMD's forecast of 26 May 2026. [2]
• El Niño Shadow: IMD forecast below-normal rainfall at ~90–92% of Long Period Average (LPA) for June–September 2026, with ~60% probability of a deficient season, attributable to El Niño influence. [4]
• Early Andaman onset: SWM arrived over Andaman & Nicobar Islands on 16 May 2026, six days ahead of IMD's forecast. [2]
• The 2026 monsoon season is being closely tracked for its implications on Kharif crop sowing, reservoir levels, and food inflation.

3. Background & Evolution

• Ancient understanding: Indian classical texts and Kautilya's Arthashastra recorded monsoon patterns for agricultural planning.
• Colonial-era monitoring (1875): IMD was established in 1875 as a formal meteorological service; Simla (Shimla) served as the summer headquarters for issuing monsoon bulletins — as seen in the 8 June 1926 bulletin noting "feeble advance of the Arabian Sea monsoon" over Malabar and Bombay Deccan. [1]
• 1926 forecast paradigm: Even in 1926, IMD issued seasonal outlooks distinguishing Peninsula, north-east, and north-west India — the same geographical framework used today. [1]
• Post-independence consolidation: IMD headquarters shifted to New Delhi (Lodhi Road); regional meteorological centres were established across India.
• Dynamical modelling era (2000s–present): IMD adopted coupled ocean-atmosphere models, seasonal prediction systems, and ensemble forecasting; introduced colour-coded warning systems (Green/Yellow/Orange/Red).
• ESSO-IMD (2006): IMD placed under the Earth Sciences Ministry (MoES), formed in 2006, for integrated weather-ocean-climate services.

4. Core Static Facts

5. Multi-Dimensional Analysis

Economic

• Agriculture contributes ~15–18% of GDP; ~50% of India's net sown area is rain-fed and entirely dependent on SWM. [3]
• Below-normal monsoon (as forecast for 2026) raises risks of Kharif crop failure (rice, pulses, oilseeds), food inflation, and rural distress. [4]
• Reservoir storage — critical for hydropower and irrigation — depends directly on SWM progress; a deficient season stresses power generation.
• RBI's monetary policy is sensitive to monsoon outcomes given their impact on rural demand, food CPI, and overall growth projections.

Environmental

• SWM replenishes groundwater aquifers, rivers, and wetlands; its failure is the primary driver of seasonal droughts. [3]
• Western Ghats act as an orographic barrier, intensifying rainfall on the windward (western) side and creating a rain shadow on the eastern (leeward) side.
• Climate change is altering monsoon variability — increasing frequency of extreme rainfall events while reducing overall seasonal totals in some regions.
• Rising Arabian Sea Sea Surface Temperatures (SSTs) are intensifying pre-monsoon cyclones, which can either accelerate or stall monsoon onset.

Scientific / Technological

• Two major branches depend on distinct physical mechanisms: orographic lifting (Western Ghats for Arabian Sea branch) vs. convergence zones (Bay of Bengal branch). [3]
• Madden-Julian Oscillation (MJO), Indian Ocean Dipole (IOD), and ENSO are the three principal large-scale climate drivers modulating SWM. [4]
• IMD uses Coupled Forecast System Model (CFS) and Global Forecast System (GFS) for real-time advance tracking.
• Doppler Weather Radars (DWR): IMD network of ~37 DWRs provides real-time rainfall mapping.
• ISRO satellites (INSAT, Megha-Tropiques) provide cloud-top temperatures and OLR data essential for onset declaration. [5]

Administrative

• Monsoon advance bulletins issued by IMD guide state governments on agricultural advisories, flood preparedness, and NDRF pre-positioning.
• The 1926 Simla bulletin model — tracking district-level rainfall, temperatures, and providing seasonal forecasts — remains the institutional template. [1]
• District-wise crop weather watch groups coordinate between IMD, state agriculture departments, and district collectors.

Historical

• The 1926 bulletin noted "feeble advance of the Arabian Sea monsoon" over Malabar and Bombay Deccan on 8 June 1926, with Bay monsoon "strengthening" — language and geographic divisions nearly identical to modern bulletins, evidencing institutional continuity over a century. [1]
• Historic droughts (1877, 1899, 1918, 1972, 1987, 2002, 2009) are benchmark events studied for socioeconomic impact.

Social

• Small and marginal farmers (>85% of farm holdings) bear disproportionate risk from monsoon failure due to limited irrigation access.
• Deficient monsoon triggers rural to urban distress migration, strains MGNREGS demand, and widens agrarian indebtedness.

6. Recent Developments (Last 12–18 Months)

• May 16, 2026: SWM arrived over Andaman & Nicobar Islands, six days ahead of IMD's forecast. [2]
• May 2026 (IMD Press Release, 15 May 2026): IMD issued the long-range forecast for SWM 2026, predicting 90–92% of LPA rainfall — categorized as below normal, with El Niño as the primary driver. [6]
• June 4, 2026: SWM onset over Kerala — 3 days behind the normal date (1 June) and 9 days behind IMD's forecast date of 26 May. [2] [4]
• ~June 12, 2026: SWM advanced into parts of West Bengal, Bihar, Sikkim, Sub-Himalayan West Bengal, and remaining NE states. [2]
• June 23, 2026 (projected): IMD projected further advance into Telangana, Odisha, Jharkhand, Bihar, and parts of Chhattisgarh. [2]
• 2025 PIB document (July 2025): PIB published a comprehensive background brief titled "The Indian Monsoon: Nature's Pulse and Nation's Lifeline" — indicating elevated public communication around monsoon science. [3]
• Downtoearth.org, 2026: Analysis noted early-onset cyclonic systems posed a stalling risk to monsoon advance — illustrating the non-linear relationship between cyclones and monsoon progress. [7]

7. Prelims Hooks

1. Normal date of SWM onset over Kerala: 1 June (±7 days).
2. Implementing/forecasting body for Indian monsoon: India Meteorological Department (IMD), under the Ministry of Earth Sciences (MoES).
3. IMD was established in: 1875.
4. LPA for Indian monsoon: Calculated over a 50-year base period; ~880 mm.
5. "Deficient" monsoon classification: Seasonal rainfall <90% of LPA.
6. Two branches of SWM: Arabian Sea branch and Bay of Bengal branch; both deflected SW→NE by the Coriolis Force. [3]
7. El Niño effect on SWM: Typically leads to below-normal / deficient rainfall in India (inverse relationship).
8. Western disturbance: An extra-tropical cyclonic system originating in the Mediterranean; influences north India but can also interact with the monsoon.
9. IMD seasonal forecast release: April (first stage) and June (updated second stage).
10. Onset criteria: Not just rainfall — also requires specific wind speed, depth of westerlies, and OLR thresholds over Kerala.
11. Andaman & Nicobar SWM onset 2026: 16 May 2026, six days ahead of forecast. [2]
12. Kerala SWM onset 2026: 4 June 2026 — behind normal (1 June) and behind IMD forecast (26 May). [2]
13. IMD 2026 seasonal forecast: 90–92% of LPA — categorized as below normal, under El Niño shadow. [4] [6]
14. Orographic rainfall mechanism: Moist SWM winds rise over the Western Ghats, cool, and precipitate on the windward (western) side; eastern side receives much less (rain shadow). [3]
15. 1926 historical bulletin: Issued from Simla (Shimla); noted "feeble Arabian Sea monsoon advance" over Malabar and Bombay Deccan on 8 June 1926, and forecast normal rainfall for Peninsula and NE India. [1]

8. Mains Relevance

GS Paper Mapping:

• GS-I: Geography of India — Physical geography; Monsoon as a unifying climatic factor.
• GS-III: Agriculture — Monsoon dependence of Indian agriculture; food security; El Niño and food inflation.
• GS-III: Disaster management — Drought/flood risk from monsoon variability.

Specific syllabus headings:

• Important geophysical phenomena: cyclones, earthquakes, tsunamis, volcanoes — monsoon is explicitly listed.
• Agriculture: Issues related to direct and indirect farm subsidies and minimum support prices; food processing.
• Disaster and Disaster Management.

Plausible Mains Question Stems:

1. "Discuss the factors that determine the onset, progress, and withdrawal of the Southwest Monsoon over India. How do El Niño and the Indian Ocean Dipole (IOD) modulate its behaviour?" (GS-I)
2. "A deficient Southwest Monsoon has cascading consequences for the Indian economy and food security. Critically analyse the policy mechanisms in place to mitigate these impacts." (GS-III)
3. "Examine the role of the India Meteorological Department (IMD) in disaster preparedness and agricultural planning. How has the evolution of forecasting technology improved monsoon prediction accuracy?" (GS-III / GS-II)

9. Related Topics to Study Next

10. Common Errors / Trap Areas

1. Wrong ministry: IMD is under Ministry of Earth Sciences (MoES) — NOT Ministry of Agriculture, NOT Ministry of Environment. This is a frequent trap in Prelims.
2. Normal onset date confusion: SWM onset over Kerala is 1 June — not May 31, not June 5. Some questions use "end of May" as a distractor.
3. Arabian Sea vs. Bay of Bengal branch roles: Students often reverse them — the Arabian Sea branch hits the western coast (Kerala, Karnataka, Maharashtra); the Bay of Bengal branch enters through Andaman → Myanmar → NE India. The BoB branch is NOT the primary branch for Maharashtra.
4. Western Disturbance ≠ SWM: Western Disturbances are extra-tropical systems from the Mediterranean, operative mainly in winter/pre-monsoon over north India. Confusing them with the SWM trough is a classic error.
5. LPA classification thresholds: Many aspirants remember "below normal = less than 90%" but forget the full classification — Normal is 96–104%, not "around 100%". Excess is >110%, not ">100%".