Evaluation of FAO Penman-Monteith method for estimating reference evapotranspiration with air temperature data in a semi-arid environment.

摘要

The Penman-Monteith equation is widely recommended because of its detailed theoretical base. This method is recommended by FAO as the sole method to calculate reference evapotranspiration (ET₀) and for evaluating other methods. However, the detailed climatological data required by the FAO Penman Monteith (FAO-PM) method are not often available especially in developing nations. Hargreaves equation (HG) has been successfully used in some locations for estimating ET₀ where sufficient data were not available to use FAO-PM method. The HG equation requires only maximum and minimum air temperature data that are usually available at most weather stations worldwide. Another method used to estimate ET₀ is to estimate the parameters of the FAO-PM equation, as recommended by FAO Irrigation and Drainage Paper 56. The objective of this study was to compare HG and FAO-PM methods for estimating ET₀ only on the basis of the temperature data. The 12 weather stations selected for this study are located in Khuzestan plain (southwest of Iran). The HG method mostly underestimated or overestimated ET₀. The FAO-PM method based on air temperature data predicted ET₀ better than HG method at all sites.