Drought and Its Classification
Definition: A prolonged period of deficient rainfall leading to moisture stress for crops, livestock, and human activities.
Types of Drought
|
Type |
Description |
Example/Indicator |
|
Meteorological drought |
Rainfall deficiency >25% of normal |
Recorded by IMD |
|
Agricultural drought |
Insufficient soil moisture for crop growth |
Based on soil water status |
|
Hydrological drought |
Low water in reservoirs, rivers, wells |
Observed in water bodies |
|
Socio-economic drought |
Reduced agricultural production affects economy |
Food scarcity, unemployment |
Drought-Prone Areas in India: , Gujarat, Maharashtra, Karnataka, Madhya Pradesh, Andhra Pradesh, and Tamil Nadu.
Facts
- IMD declares meteorological drought if rainfall deficiency > 26% of Long Period Average (LPA).
- National Commission on Agriculture (1976) categorized drought-prone areas into severe and moderate.
- India Meteorological Department (IMD) monitors drought using Standardized Precipitation Index (SPI).
Fact: The National Rainfed Area Authority (NRAA) was established in 2006 for rainfed area management and drought-proofing.
Weather Hazards in Agriculture
|
Hazard |
Description |
Effect on Crops |
|
Flood |
Waterlogging due to heavy rains |
Root damage, pest outbreak |
|
Cyclone |
Strong wind system over sea |
Lodging, saline intrusion |
|
Hailstorm |
Ice pellets during thunderstorms |
Physical damage to fruits and flowers |
|
Frost |
Freezing of plant tissues |
Death of seedlings, damage to fruits |
|
Heat wave |
Temp >40°C for several days |
Flower drop, sterility |
|
Cold wave |
Temp below threshold |
Delayed germination |
Cyclones in India
- Occur mainly in Bay of Bengal (more frequent) and Arabian Sea.
- Season: April–June and October–December
- Cyclone Warning Centres: Kolkata, Chennai, Mumbai, Visakhapatnam, Ahmedabad
Fact:
- Super Cyclone of Odisha (1999) recorded winds > 250 km/h.
- IMD uses satellite-based systems (INSAT series) for real-time cyclone monitoring.
Agro-Advisory Services (AAS)
- IMD provides location-specific weather forecasts and advisories.
- Disseminated through:
- Krishi Vigyan Kendras (KVKs)
- Mobile Apps (Mausam, Meghdoot)
- Radio, TV, and farmer portals
Fact:
- IMD issues bi-weekly agromet advisories for all districts under DAMUs (District Agromet Units).
- Gramin Krishi Mausam Sewa (GKMS) launched in 2007 for farmer-level weather-based advisories.
Fact Highlights for Quick Revision
- IMD Headquarters: New Delhi (Established 1875)
- First Weather Observatory in India: Chennai (1793)
- Normal lapse rate: 6.5°C/km
- Tropopause height: 16–18 km at equator; 8–10 km at poles
- World Meteorological Day: March 23
- Evapotranspiration: Combined loss of water by evaporation + transpiration
- Agricultural drought = Moisture stress in soil affecting crops
- Optimum temp for photosynthesis: 25–30°C
- Relative humidity conducive for disease: >80%
- Instruments for Solar radiation: Pyranometer & Pyrheliometer
Crop–Weather Relationships: Definition: The study of how meteorological parameters affect the physiological processes and yield of crops.
B. Key Weather Elements Influencing Crops
|
Weather Element |
Effect on Crops |
|
Temperature |
Affects germination, flowering, pollination, maturity |
|
Rainfall |
Decides crop type, sowing time, irrigation |
|
Humidity |
Influences disease incidence and transpiration |
|
Solar Radiation |
Determines photosynthesis rate |
|
Wind |
Affects lodging, transpiration, pollination |
|
Frost/Heat |
Damages tender crops or causes sterility |
🌾 C. Critical Stages Sensitive to Weather
|
Crop |
Critical Stage |
Major Factor |
|
Rice |
Flowering & grain filling |
Temperature, humidity |
|
Wheat |
Heading & grain filling |
Temperature |
|
Maize |
Tasseling–silking |
Moisture stress |
|
Cotton |
Flowering–boll formation |
Rainfall |
|
Sugarcane |
Tillering & grand growth |
Temperature & moisture |
|
Groundnut |
Peg formation |
Soil moisture |
|
Mustard |
Flowering |
Temperature (frost damage risk) |
Phenology
- Definition: Study of periodic plant growth events in relation to weather (e.g., flowering, fruiting, maturity).
- Used to: Correlate crop stages with temperature and rainfall.
- Fact: Growing Degree Days (GDD) is a thermal index used to predict crop development.
