Mohawesh O. (2009).

Abstract

The FAO-56 Penman-Monteith model (FAO56PM)  is the most desirable for estimating reference Evapotranspiration (ETo). However, this method need full weather data. On the other hand, other models are simpler for estimation ETo, and some new types of these models have been proposed recently. In this study, daily output from eight evapotranspiration models (PE, Har, HarM1, HarM2, FAO24RD, Priestly-Taylor,  Makkink , and FAO24P)  have been tested against ETo computed by FAO56PM. Models were compared at eight stations across Jordan. Results showed that the eight evapotranspiration models (PE, Har, HarM1, HarM2, FAO24RD, Priestly-Taylor, Makkink , and FAO24P) need local calibration. Among these models, Hargreaves modified models exhibited the best. The mean biased error (MBE), root mean square error (RMSE), and (mean absolute error) MAE values ranged from -1.47 to 0.81, 3.87 to 1.14 and 0.87 to 3.15 mm day-1 for HarM1, and from -1.45 to 0.89, 1.08 to 3.91, and 0.85 to 3.16 mm day-1 for HarM2, respectively. Comparisons were also made using three composite regions: countrywide, semiarid, and arid regions. Hargreaves modified models (HarM1 and HarM2) also were relatively better agreed with FAO56PM based MBE, RMSE and MAE which ranged from -1.47 to 0.89 mm day-1, 1.39 to 2.38 and 0.86 to 3.15 mm day-1, respectively. Hence, these models  can be used for irrigation scheduling and water resources management were full data set is not available for FAO56M model. These results also provide basic guidance to the agricultural community in Jordan as to which models will give a better estimate of ETo, in light of data availability, for use in irrigation scheduling.

 Submitted to Water International.

Key words: Evapotranspiration, Semiarid and arid, FAO56 Penman-Monteith,