Agricultural Meteorology
Comprehensive Study Notes
General Introduction
| Particular | Information |
|---|---|
| Subject | Agricultural Meteorology (Agrometeorology) |
| Definition | Science dealing with the interaction of weather and climate with agriculture. |
| Objective | To maximize crop production by efficient use of weather and climate information. |
| Father of Agrometeorology (World) | G. S. Callendar |
| Father of Indian Agrometeorology | Dr. L. A. Ramdas |
| Applied Science | Yes |
✨ Core Definition Distinction
Meteorology: Science of the atmosphere and weather.
Agroclimatology: Study of climate in relation to agriculture.
Atmospheric Structure & Composition
Gaseous Composition
| Gas | Percentage (%) |
|---|---|
| Nitrogen (N2) | 78.08% |
| Oxygen (O2) | 20.95% |
| Argon (Ar) | 0.93% |
| Carbon Dioxide (CO2) | 0.04% |
Structural Layers
| Layer | Height | Key Feature |
|---|---|---|
| Troposphere | 0–12 km | All weather phenomena occur here; temperature decreases with altitude. |
| Stratosphere | 12–50 km | Contains the Ozone Layer; ideal for flying aircraft. |
| Mesosphere | 50–80 km | Meteors burn up upon entry; coldest layer. |
| Thermosphere | 80–700 km | Contains the Ionosphere; Auroras occur here. |
| Exosphere | >700 km | Outermost layer merging with space. |
Weather vs Climate
| Weather | Climate |
|---|---|
| Short-term atmospheric condition | Long-term average condition (WMO standard: 30+ years) |
| Changes hourly or daily | Changes over large periods (decades) |
| Local phenomenon | Regional or global phenomenon |
| Forecasted for days | Studied over many years |
Weather Elements & Instruments
| Element | Measuring Instrument | Unit |
|---|---|---|
| Temperature | Maximum & Minimum Thermometers | °C / °F / K |
| Rainfall | Rain Gauge | mm |
| Humidity | Hygrometer / Psychrometer | % |
| Wind Speed | Anemometer | km/h or m/s |
| Wind Direction | Wind Vane | Compass points |
| Sunshine Hours | Campbell-Stokes Sunshine Recorder | Hours |
| Solar Radiation | Pyranometer / Actinometer | W/m² |
| Atmospheric Pressure | Barometer | mb / hPa |
| Evaporation | Class-A Pan Evaporimeter | mm |
🛡️ Instrument Protection
Standard meteorological thermometers and relative humidity sensors are housed within a well-ventilated wooden structure called a Stevenson Screen.
Radiation & Thermodynamics
| Solar Constant | ≈ 1361 W/m² |
| Visible Light Spectrum | 400–700 nm |
| PAR Range | 400–700 nm (Photosynthetically Active Radiation) |
| Ultraviolet (UV) | < 400 nm |
| Infrared (IR) | > 700 nm |
| Albedo | Percentage of solar radiation reflected back by a surface |
Heat Transfer Mechanics
| Conduction | Heat transfer via direct physical contact. |
| Convection | Vertical heat transfer through fluid/air movement. |
| Advection | Horizontal heat transfer through air masses. |
Moisture, Humidity & ET
Relative Humidity Crop Dynamics
| High Relative Humidity | Low Relative Humidity |
|---|---|
| Fungal disease incidence increases rapidly | High transpiration rates occur |
| Poor crop pollination properties | Induces crop wilting tendencies |
Evapotranspiration (ET) Metrics
| Term | Agronomic Context |
|---|---|
| ET Formula | Evaporation + Transpiration |
| PET | Potential Evapotranspiration (Maximum possible under optimum conditions) |
| AET | Actual Evapotranspiration (Observed field crop dynamics) |
| Dew Point | Temperature at which condensation processes begin |
Agrometeorological Indices
| Index Name | Calculation Formula / Context |
|---|---|
| Growing Degree Days (GDD) | GDD = [(Tmax + Tmin) / 2] – Tb Tb = Base Temperature |
| Heliothermal Units (HTU) | GDD × Bright Sunshine Hours |
| Photothermal Units (PTU) | GDD × Day Length |
| Hydrothermal Units (HYTU) | GDD × Relative Humidity |
| Phenothermal Index (PTI) | GDD / Number of Growth Days |
| Heat Use Efficiency (HUE) | Yield / GDD |
⏱️ GDD Application
Growing Degree Days (GDD) units are measured in °C day and are utilized to systematically predict crop growth stages, flowering window intervals, and final maturity dates.
Monsoon & Synoptic Systems
| Monsoon Origin | Arabic word “Mausim” (meaning season) |
| India Average Rainfall | ≈ 1170 mm annually |
| South-West Monsoon | June–September; contributes 75–80% of total rainfall |
| North-East Monsoon | October–December; targets SE India (Tamil Nadu) |
| Kerala Onset Window | Around 1st June |
| Western Disturbances | Mediterranean origins; brings vital winter rains for Wheat |
Pressure Systems Comparison
| Feature | Cyclone | Anticyclone |
|---|---|---|
| Core Pressure | Low Pressure | High Pressure |
| NH Wind Direction | Anticlockwise | Clockwise |
| Associated Sky | Cloudy, Heavy Rain | Clear and Dry |
Climate Anomalies & Zones
| Phenomenon | Impact Matrix on Indian Farming |
|---|---|
| El Niño | Warming of Pacific waters; causes weak monsoons and severe droughts. |
| La Niña | Cooling of Pacific waters; triggers heavy monsoons and high yields. |
Agro-Climatic Classification Systems
| Organizing Authority | Zone Count |
|---|---|
| Planning Commission Agro-Climatic Zones | 15 Zones |
| NBSS & LUP Agro-Ecological Regions | 20 Regions |
| ICAR Agro-Climatic Zones (NARP Setup) | 127 Zones |
Weather Forecasting Framework
| Forecast Classification | Valid Duration |
|---|---|
| Nowcasting | Up to 6 hours |
| Very Short Range | Up to 12 hours |
| Short Range Forecast (SRF) | 1–3 days |
| Medium Range Forecast (MRF) | 3–10 days (Best for tactical farming changes) |
| Extended Range Forecast | 10 days–4 weeks |
| Long Range Forecast (LRF) | > 4 weeks (Seasonal outlook models) |
Historical Scientists Matrix
| Scientist Name | Pioneering Research & Breakthrough Contribution |
|---|---|
| Dr. L. A. Ramdas | Established Agrometeorology foundations in India. |
| Luke Howard | Developed modern cloud morphology and classification standard lists. |
| Vilhelm Bjerknes | Introduced data-driven scientific numerical weather forecasting models. |
| Wladimir Köppen | Engineered empirical climate system classification using vegetative indicators. |
Meteorological Organizations
| Organization | HQ Location | Major Operational Focus |
|---|---|---|
| IMD | New Delhi | National weather forecasting and operational agrometeorological advisories. |
| WMO | Geneva, Switzerland | International coordination body for atmospheric and hydrology services. |
| NCMRWF | Noida, U.P. | Numerical weather prediction using supercomputing clusters. |
| IITM | Pune, Maharashtra | Advanced research on monsoon mechanics and climate variation. |
| CRIDA | Hyderabad, Telangana | Dryland agro-ecosystem structural design and climate resilience research. |
Competitive Exams Q&A
Q: Who is acknowledged as the Father of Indian Agricultural Meteorology?
A: Dr. L. A. Ramdas
Q: Which atmospheric layer contains the vital protective ozone layer?
A: Stratosphere
Q: Most convective, active weather changes take place in which layer?
A: Troposphere
Q: What specific wavelength range defines Photosynthetically Active Radiation?
A: 400–700 nm
Q: Which unique cloud form is directly responsible for violent thunderstorms and hail events?
A: Cumulonimbus
Q: What structural parameter changes occur during severe El Niño years over India?
A: Weakened monsoon circulation leading to widespread agricultural drought.
Q: How many distinct agro-climatic zones were demarcated by the Planning Commission?
A: 15 Zones
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