CLIMATE ANALYSIS FOR REGIONAL IRRIGATION PLANNING

Rainfall characteristics and potential evapotranspiration together determine the agro meteorological regime of a region and influence decisions concerning the magnitudes and timing of irrigation applications. In addition to rainfall input, an important aspect of the water balance model is the crop evapotranspiration (ETcrop), which is a main factor in determining irrigation schedule. The procedure for estimation of ET rates from agricultural crops is well established and involves as a first step, computation of reference crop evapotranspiration (ETcrop) using regular climatologically recorded data. ETcrop could be estimated by reference evapotranspiration (ET) and crop coefficient. ‘Moisture Availability Index’ (MAI), which is computed as the ratio of 75% dependable rainfall and potential evapotranspiration is used as an index to indicate dry and wet periods. An MAI value of 1.00 indicates that dependable precipitation equals potential evapotranspiration. A value of MAI of 0.33 or less for one month during the crop-growing season is considered to be a signal of water deficit, causing crop production to fall below an economic level. Obtained information on MAI is used to decide the selection of sowing period of crops so as to avoid water stress during crucial harvesting period.