Indian monsoon system

Monsoon: Definition: The term Monsoon is derived from the Arabic word “Mausim”, meaning season.

It refers to seasonal reversal of winds caused by differential heating of land and sea.

Types of Monsoon in India

1. South-West (SW) Monsoon – Summer Monsoon
   • Period: June to September
   • Brings about 75–80% of India’s total annual rainfall.
   • Divided into:
     • Arabian Sea Branch
     • Bay of Bengal Branch

Onset: Kerala – around June 1
Withdrawal: From northwest India by mid-September

Rainfall distribution:

1. • Heavy rainfall in Western Ghats, NE states
   • Moderate in Indo-Gangetic plains
   • Scanty in Rajasthan and parts of Ladakh

North-East (NE) Monsoon – Retreating or Winter Monsoon

1. • Period: October to December
   • Brings rainfall mainly to Tamil Nadu, South Andhra Pradesh, SE Karnataka, and Kerala.
   • Also called Post-Monsoon Season.

Monsoon Forecasting in India

• Managed by India Meteorological Department (IMD).
• Models used: Statistical and Dynamical models.
• IMD issues:
  • Long-range forecast (Seasonal)
  • Quantitative rainfall forecast
  • Weekly and district-level advisory.

Droughts and floods: Drought; A period of abnormal dry weather leading to water shortage affecting crops and livestock.

Types of Drought

• Meteorological drought: Rainfall less than 75% of normal.
• Agricultural drought: Soil moisture insufficient for crops.
• Hydrological drought: Depletion of surface/ground water.
• Socio-economic drought: Scarcity affects economy and livelihoods.

Drought Indices

• Palmer Drought Severity Index (PDSI)
• Standardized Precipitation Index (SPI)
• Aridity Index (AI):
  1. AI < 25% → Humid
  2. 25–50% → Moist
  3. >75% → Arid

Flood: Occurs when rainfall exceeds infiltration and storage capacity. Flood-prone areas: Indo-Gangetic plains, Brahmaputra valley.

Microclimate and crop environment

Definition: Microclimate is the climate of a small area near the surface (e.g., crop canopy).

Modification of Microclimate

• Windbreaks/shelterbelts: reduce wind speed.
• Mulching: conserves soil moisture and moderates temperature.
• Greenhouses/polyhouses: provide controlled microclimate.
• Intercropping: modifies radiation and temperature near soil.

Agro-climatic zones of india (icar classification)

India has 127 Agro-climatic Zones, grouped under 15 Major Agro-climatic Regions based on soil, rainfall, temperature, and cropping patterns.

Weather-based crop management

Weather hazards in agriculture

Agro-meteorological advisory services (aas)

Objective: To provide weather-based agro-advisories that help farmers make informed decisions on:

• Sowing, irrigation, and fertilizer application
• Pest and disease management
• Harvesting and post-harvest operations

Organisations Involved

• IMD (India Meteorological Department) – main coordinating agency under Ministry of Earth Sciences.
• ICAR – provides research support through Agrometeorological Research Centres.
• Agricultural Universities & Krishi Vigyan Kendras (KVKs) – act as local dissemination centres.
• Doordarshan, All India Radio, Kisan Call Centres, and mobile apps – used for dissemination.

Structure of AAS

Types of Agromet Services

1. Weather Forecasts
   • Short range (1–3 days)
   • Medium range (3–10 days)
   • Long range (seasonal)
2. Agro-Advisories
   • Prepared twice a week (Tuesday & Friday).
   • Translated into local language.
   • Broadcast through radio, SMS, WhatsApp groups, and TV.