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Science & Technology May 13, 2026 6 min read Daily brief · #50 of 90

IMD unveils weather model to provide ‘block level’ forecast of monsoon journey

The India Meteorological Department (IMD) unveiled a new block-level monsoon onset forecasting model that will generate probabilistic forecasts of the monsoo...

GS Paper 1 (Geography/Climate) GS Paper 3 (S&T Agriculture)

What Happened

  • The India Meteorological Department (IMD) unveiled a new block-level monsoon onset forecasting model that will generate probabilistic forecasts of the monsoon's progression across 3,196 revenue blocks in 15 states and one Union Territory covering India's "monsoon core zone" of rainfed agriculture.
  • The model is updated every Wednesday and generates forecasts up to four weeks in advance, with an error margin of approximately four days, enabling farmers and district administrations to plan ahead.
  • The system combines existing Numerical Weather Prediction (NWP) models with AI/ML techniques to produce probabilistic — rather than deterministic — forecasts of monsoon onset at the sub-district level.
  • Outputs will be shared with farmers through APIs developed by the Ministry of Agriculture and Farmers Welfare and through the Agri Stack digital public infrastructure platform.
  • IMD's network of Doppler weather radars, which underpins improved prediction accuracy, has grown from 15 in 2013 to 50 in 2026.

Static Topic Bridges

Numerical Weather Prediction (NWP) — Principles and India's NWP Architecture

Numerical Weather Prediction (NWP) is the method of using mathematical models of the atmosphere and ocean to predict the weather based on current conditions. NWP uses a set of differential equations (the primitive equations of atmospheric dynamics) solved numerically on global or regional grids. India's NWP history began in 1958 with pioneering work led by Prof. P. K. Das for predicting Bay of Bengal monsoon depressions. The National Centre for Medium-Range Weather Forecasting (NCMRWF) was established in 1988 as the dedicated NWP centre, initially powered by Cray supercomputers.

  • Two primary NWP centres in India: IMD (short-range, 0–3 days) and NCMRWF (medium-range, 3–10 days), both under the Ministry of Earth Sciences (MoES).
  • Global NWP models used: ECMWF (European Centre for Medium-Range Weather Forecasts), GFS (Global Forecast System, USA), NCMRWF's own Unified Model (UM).
  • India's operational NWP uses the Global Forecast System (GFS) and the Unified Model with horizontal resolutions progressively improving from ~50 km in the 1990s to ~12 km today.
  • NWP output includes temperature, wind, humidity, and precipitation at grid points; "direct model output" from NWP models forms the basis of block-level weather forecasts.
  • Limitations: NWP skill degrades beyond 10–14 days for weather; beyond 3–4 weeks, probabilistic ensemble approaches become essential.

Connection to this news: The new block-level monsoon model uses NWP model output as its physical backbone, then applies AI to downscale these outputs to the sub-district (block) level, overcoming NWP's inherent spatial resolution limitations.

Ensemble Weather Forecasting — Probabilistic Prediction for Uncertainty Quantification

Ensemble forecasting is a method where multiple model runs are initiated with slightly perturbed initial conditions or different model configurations to capture the range of possible atmospheric outcomes. Rather than a single deterministic forecast ("rain on Tuesday"), ensemble systems produce probability distributions ("60% chance of rain on Tuesday"). This approach is essential for extended-range prediction (beyond 5–7 days) where small errors in initial conditions grow significantly.

  • Extended Range Prediction System (ERPS): IMD operates an ensemble-based ERPS that provides probabilistic forecasts for 2–4 weeks ahead, focusing on active/break monsoon spells.
  • ECMWF's ensemble system (50 members) is globally regarded as the benchmark for medium- and extended-range probabilistic forecasting.
  • IMD's block-level monsoon model specifically produces a probabilistic onset forecast — meaning it estimates the likelihood distribution of monsoon arrival at each block, not a single date.
  • The ~4-day error margin stated for the new model reflects the spread of the ensemble distribution, not a fixed deterministic error.

Connection to this news: The block-level forecast is inherently probabilistic, making it a practical application of ensemble forecasting methodology — a key advancement from the earlier deterministic district-level advisories.

India Meteorological Department (IMD) — Institutional Role and Policy Context

IMD, established on 15 January 1875, is India's principal meteorological authority functioning under the Ministry of Earth Sciences (MoES). IMD's mandate covers meteorological observations, weather forecasting, seismology, and agro-meteorological advisory services. It operates a nationwide network of surface observatories, upper-air stations, Doppler weather radars, and satellite receiving systems.

  • IMD headquarters: Mausam Bhawan, Lodhi Road, New Delhi; established originally in Calcutta (now Kolkata).
  • Ministry of Earth Sciences (MoES) was carved out of the erstwhile Ministry of Science and Technology in 2006 to give dedicated focus to earth and atmospheric sciences.
  • IMD uses data from INSAT series satellites (INSAT-3D, INSAT-3DR, EOS-06) and RISAT radar satellites for real-time atmospheric monitoring.
  • Monsoon core zone: the belt of rain-fed agriculture across central and peninsular India (roughly 15 states + 1 UT) most sensitive to monsoon timing, where forecast uncertainty most directly affects farmer livelihoods.
  • Agro-meteorological Advisory Services (AAS): IMD already issues district-level advisories twice weekly during the Kharif season in collaboration with the Indian Council of Agricultural Research (ICAR) — the block-level system is a finer step within this framework.

Connection to this news: The block-level monsoon forecast model represents a strategic upgrade of IMD's agro-meteorological advisory infrastructure, motivated by the Ministry of Agriculture's data needs and the policy push under the Digital Agriculture Mission.

Monsoon Onset — Definition, Progression, and Agricultural Significance

The onset of the Southwest Monsoon is formally declared by IMD when specific criteria are met: sustained rainfall over Kerala and surrounding area, specific wind patterns at 925 hPa, and Outgoing Longwave Radiation (OLR) values below a threshold. Normal onset date over Kerala is 1 June (±7 days). The monsoon then progresses northward, completing coverage of the entire country by approximately 8 July under normal conditions.

  • Kharif crop sowing is critically dependent on monsoon onset timing; a late onset of even 10–14 days can shift sowing windows and reduce yields for crops like paddy, soybean, and cotton.
  • The monsoon accounts for approximately 75% of India's annual rainfall; ~50% of India's cultivated area remains rain-fed.
  • Block is the administrative unit below the district (taluka/tehsil equivalent); India has approximately 6,500 blocks in total; the 3,196 blocks targeted are in the monsoon core zone.
  • Four-week advance block-level forecasts could allow kharif farmers to optimize sowing decisions, reduce crop losses, and improve insurance uptake under the Pradhan Mantri Fasal Bima Yojana (PMFBY).

Connection to this news: By providing probabilistic monsoon onset forecasts at block resolution with a four-week lead time, this model directly addresses the "last-mile" gap in agricultural weather services — the biggest actionable frontier for reducing climate risk to smallholder farmers.

Key Facts & Data

  • New model covers: 3,196 revenue blocks across 15 states + 1 UT (monsoon core zone of rainfed India)
  • Forecast lead time: up to 4 weeks in advance; updated every Wednesday
  • Error margin: approximately 4 days (probabilistic distribution)
  • IMD Doppler radar network: 15 in 2013 → 50 in 2026
  • IMD established: 15 January 1875 (150 years old in 2025)
  • IMD under: Ministry of Earth Sciences (MoES)
  • NCMRWF established: 1988 (first NWP centre with supercomputing)
  • India's first NWP research: 1958, led by Prof. P. K. Das
  • Normal SW Monsoon onset over Kerala: 1 June (±7 days)
  • India's rain-fed cultivated area: approximately 50% of total cropped area
  • Output dissemination: Ministry of Agriculture APIs + Agri Stack digital platform
On this page
  1. What Happened
  2. Static Topic Bridges
  3. Numerical Weather Prediction (NWP) — Principles and India's NWP Architecture
  4. Ensemble Weather Forecasting — Probabilistic Prediction for Uncertainty Quantification
  5. India Meteorological Department (IMD) — Institutional Role and Policy Context
  6. Monsoon Onset — Definition, Progression, and Agricultural Significance
  7. Key Facts & Data
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