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Crop evapotranspiration is calculated using the single crop coefficient approach described in FAO-56 (Equation 6). For further information on how this approach is implemented in Source see the Irrigation Demand Model Crop Factors SRG entry. Source also offers sufficient flexibility to apply daily crop factors if they are known for a particular crop based on a different source or method.
The effects of soil water stress on crop ET are calculated by multiplying the crop coefficient by the water stress coefficient (Ks). The Ks value is evaluated based on soil water depletion at the start of the time-step.
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Kc = Single crop coefficient on growth day i j of the crop
Ks = water stress coefficient describes the effect of water stress on crop transpiration
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