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Six reference evapotranspiration (ETo) methods are compared, based on their daily performances under the given climatic condition in the western region of Fukuoka City. The Penman-Monteith equation st...andardized by the Food and Agriculture Organization (FAO56-PM) is used to compare with the Thornthwaite, Hargreaves, and Hamon methods. The FAO56-PM method has also been used as an index for two equations: the solar radiation (Rs) based and net radiation (Rn) based equations, which are the simplified versions of FAO56-PM. Performance analysis for the calculated values using meteorological data for 7 years (Jan 1996 – Dec 2002) was made. The standard error of estimates (SEE) was calculated on monthly basis. The estimated values by the Thornthwaite, Hargreaves, Hamon, and the Rs-based and Rn-based radiation methods were all correlated with FAO56-PM having correlation (r2) values calculated by Pearson’s correlation of 0.80, 0.69, 0.48, 0.71 and 0.45 and their standard error estimates were 0.25 , 0.25, 0.25, 0.28 and 0.24 mm mon-1, respectively. Proximity in ETo estimates by the Hargreaves and the Rs-based methods showed that the solar radiation as input variable was important as the FAO56-PM method. Also, the Thornthwaite method, which uses only temperature as input variable, has been found to have highly correlated with the FAO56-PM method. Thus, when considering the availability and reliability of the input data, the use of all these methods are suggested as practical methods for estimating ETo if the standard FAO56-PM equation is not applicable due to the complexity of its input parameters.続きを見る
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