There are excellent sources of information on general weather, and this information is readily available. Generalized forecasts have, however, limited use in farming. Weather information for agriculture needs to be tailored to meet the needs of farmers and graziers (see Figure 9.1). It should not be a repackaging of the general weather forecast of the national forecasting centers. It should be a tailored product that can be effectively used in growing crops, managing animals, and controlling pests and diseases. A comprehensive agroclimatological forecast or a farm advisory is an interpretation of how expected weather in the future and weather conditions accumulated to the present will affect crops, livestock, and farm operations.
An agroclimatological forecast usually has five components: weather synopsis, interpretation of weather for crops, interpretation of weather for farm operations, interpretation of weather for livestock, and interpretation of weather for crop pests and diseases.
• Weather synopsis: This is the description of locations and movements of low pressure systems, high pressure systems, upper air troughs, fronts, and associated weather with these systems. This information is derived from synoptic observations, prognostic charts, and visible and infrared imageries from meteorological satellites. For seasonal forecasts the inferences are drawn from historical data, sea-surface temperature, SOI values and phases, and other relevant tele-connections.
• Interpretation of weather on crops: Interpretation of weather conditions on crops takes into account the impact of weather on germination, growth rate, freeze protection, and irrigation demand. The cumulative effect of weather encountered and anticipated is used to determine dates of harvest, duration of harvest, and quality and storage capabilities of grains, fruits, and vegetables.
• Interpretation of weather on farm operations: Interpretation of weather on farm operations takes into account the drying rate of soil, evaporation losses, effect of heat, cold, and wind on applications of chemicals and fertilizers, and the drying rate of curing, wetting, and rewetting grains and hay.
• Interpretation of weather on livestock: Various combinations of heat and moisture in the atmosphere cause comfort or discomfort to animals. Indices are available that express the combined effects of temperature and humidity on animals. The indices provide indications of heat stress, cold stress, shelter requirements, and the effect of weather on meat, milk, and egg production. These indices are used to give timely warnings of anticipated weather dangerous to the health and safety of livestock.
• Interpretation of weather for crop pests and diseases: A close relationship exists between many animal and plant diseases, insect pests, and weather. The incidence of these diseases and pests is forecast in the light of accumulated and anticipated weather. Simulation, synoptic, and statistical techniques are used for forecasts which pertain to the probable development, intensity, spatial and temporal spread, or suppression of diseases.
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