Mohawesh O. and Talozi  S. 2010.

Abstract

The objectives of this study are to compare ETo computed using different forms of the HG equation with the standard FAO56PM; and compare ETo computed using the FAO56PM with limited data with the standard FAO56PM complete data set method. For this purpose, climatic data from 12 weather stations covering an area of approximately 90 km2 of predominantly arid and semi arid conditions are used. The ratios of ETo estimated using updated HG equation were closer to 1 comparing with the HG equations and ET o -est. Also, the RMSE, ME and R2 ranged from 0.235 to 0.526 mm day-1, -0.526 to 0.383 mm day-1, and 0.945 to 0.989, respectively. Therefore, updated HG equation can be used for ETo estimates instead of using the FAO56PM method with acceptable accuracy. In addition, it was found that the standard FAO56PM can be used with estimated solar radiation and humidity from temperature data and estimates of mean wind speed. In conclusion, this study produced two accurate methods that can be used to calculate monthly ETo in conditions characterized by limited data, arid, and semi-arid environments.

 Accepted in Archive of agronomy and soil science.

Keywords: FAO56 Penman-Monteith; Hargreaves equations; Evapotranspiration; arid and semiarid; limited or missing data.