ABSTRACT
Accurate estimates of actual evapotranspiration (ET) are costly to obtain. An inexpensive alternative is to estimate actual evapotranspiration by multiplying a potential or reference evapotranspiration [1, 2, 3] by a crop coefficient (Kc) [4, 5]. This approach has been promoted by the United Nations Food and Agriculture Organization (FAO) for more than 30 years through their Irrigation and Drainage Paper No. 24 [1] and more recently in Paper No. 56 [6]. Even though they have reported values for Kc for numerous crops, many crops grown in the world are not included in their lists, and coefficients for mixed natural vegetation are generally not available. Although crop coefficients derived in other parts of the world can be used to provide approximate estimates of evapotranspiration, the crop coefficient in fact depends upon the specific crop variety and other local conditions [7].
