Comparison of different methods of estimating potential evapotranspiration by FAO Penman Monteith (Case Study: Sepidan Region)

Evapotranspiration is an important factor of hydrological cycle that must be estimated in irrigation and drainage projects. Studies have shown that in the absence of lysimeter, FAO Penman-Monteith method provide acceptable estimate of evapotranspiration values, but this method requires a lot of meteorological parameters. Therefore other hydrological evapotranspiration methods that needs few parameters should be evaluate for each region. In this study reference crop evapotranspiration calculated by Ref-ET software for Sepidan, Fars, by using Sepidan synoptic stations meteorological data during years 2004 to 2015. The results of methods compared with FAO Penman-Monteith standard method. The efficiency of all methods was evaluated using Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) statistic parameters. The results showed that Methods based on Penman-Monteith (ASCE st PM, ASCE PM rs, ASCE PM), respectively, with the RMSE of about 0.03, 0.079, 0.079 and with the MAE of about, 0.021, 0.068, 0.069 appropriate methods for estimating reference evapotranspiration are considered. FAO 24Rd Pan and FAO Pan Methods, respectively, with the RMSE of about 1.426, 2.338 and with the MAE of about 1.186, 2.072 has the least compliance with the Penman-Monteith FAO method. So in situation of less data for FAO Penman-Monteith method in Sepidan, it is possible to use of other methods that needs few hydrological parameters.