Agronomy - Agrometeorolgy module 5


Type of weather forecast

Types of forecast
Validity period
Short range
Up to 72 hours
Rainfall distribution, heavy rainfall, heat and cold wave conditions, thunder storms etc.
Scheduling of irrigation
Adjusting of time of agricultural operations
Protection of plants from frost

Medium range
Beyond 3 days and upto 10 days.
Occurrence of rainfall, Temperature.
Useful to determine sowing time
Useful to determine depth of sowing
Planning of irrigation
Decision on harvesting
Decision on time of spraying to get higher efficiency
Management of labour and equipment

Long range
Beyond 10 days upto a month and a season.
This forecasting is provided for Indian monsoon rainfall. The out looks are usually expressed in the form of expected deviation from normal condition.
To decide on soil moisture management
to decide on irrigation scheduling
decision on selection of crops
decision to manage irrigation with limited water supply
decide on cropping pattern and
to determine crop yield


            The earths atmosphere has never been free of change ( in its composition, temperature, self-cleaning ability).  Due to change in atmosphere the world is warming, climatic zones are shifting; glaciers are melting and sea level is rising. We anticipate these changes to accelerate over the next few years to come.

Greenhouse effect: The theory of "greenhouse effects" was conceived by the French Mathematician J.B. Fourler over a century ago.  It was supported by Tyndall's studies on the absorption of heat by gases. 
            Increased human activities increase carbon dioxide, methane, nitous oxide, chloro flurorocarbons (CFC) etc., which lead to increase in temperature and sea level rise.  These gases which are in traces cause environmental parturbations ( distrubances) such as green house effect ( global warming), stratospheric ozone depletion , acid deposition, smog and corrosion.

Environmental Perturbations                                  Responsible  gases

1. Green house effect                                      Co2,CH4(Methane, N2, CFCS, Ozone
2. Ozone depletion in the stratosphere           Chloro-fluoro carbons (CFCS)
3. Acid deposition                                           SO2, NO, NO2, S, O3
4. Smog corrosion                                           SO2


            Season is a period in a year comprising few months during which the prevailing climate does  not very much.  Growing season for a crop is more important for its yield and other management practices to be followed.
Indian Meteorological Department has divided the year into four seasons.

i. Summer                                : March- May
ii. Monsoon                             : June- September
iii. Post Monsoon                    : October- November
iv. Winter                                : December - February

            The monsoon season is designated as Kharif, whereas the post monsoon and winter seasons are together designated as "Rabi" throughout India.

            Based on temperature ranges three distinct crop season have been identified in India.

i.                    Hot weather ( Mid February-Mid June)
ii.                  Kharif or  rainy season ( Mid June-Mid October)
iii.                Rabi ( Mid October to Mid February)

In Southern states ( Tamil Nadu, Andhara Pradesh and Karnataka) there is slight variation  in the season based on rainfall duration as

1.      Winter                   - January and February
2.      Summer                 - March to May
3.      Rainy season         - a. South West monsoon - June to September
  b. North East  monsoon - October- December

            Based on the criteria, monthly precipitation and temperature, the growing season is broadly divided as follows:-

i.          Hot month                              - if the average temperature is above 20oC
ii.         Cold month                             - if the mean temperature is between 0-10oC
iii.        Warm month                           - if the mean temperature is between 15-20oC