Assessment of Evapotranspiration Estimation Models for Use in Arsanjan County

Reference evapotranspiration (ETo) determination is a key factor for water balance and irrigation scheduling. Evapotranspiration can be measured directly by high-cost micrometeorological techniques, or estimated by mathematical models. The FAO Penman–Monteith method has been considered as a universal standard to estimate ETo for more than a decade. This method is also considered as a universal standard to estimate ETo for more than a decade. This method is also appropriate for the calibration of other ETo estimation equations. The utilization of these calibrated ETo equations is recommended in the absence of data of any of the meteorological parameters necessary for the application of FAO Penman–Monteith. In this study reference crop evapotranspiration calculated by Ref-ET software for Arsanjan county, Fars province in Iran, by using Arsanjan synoptic stations meteorological data during years 2004 to 2016. The results of methods evaluated 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 (ASCE stPM, ASCE PM, ASCE PMrs, 1972KPen, FAO 24Pn, 1948Pen, 1996KPen, FP 17 Pen), respectively, with the RMSE of about 0.011, 0.150, 0.150, 0.225, 0.275, 0.333, 0. 565, 0.601 and with the MAE of about, 0.007, 0.131, 0.131, 0.210, 0.233, 0.264, 0.470, 0.532 appropriate methods for estimating reference evapotranspiration are considered. FAO Pan, Prs –Tylr, 1957 Makk, FAO 24Rd, FAO 24BC, 1961 Turc, 1985 Harg methods, respectively, with the RMSE of about 2.580, 1.726, 1.710, 1.284, 1.064, 0,997, 0.772 and with the MAE of about 2.192, 1.649, 1.604, 1.023, 0.952, 0.876, 0.662 has the least compliance with the FAO Penman-Monteith method. So in situation of less data for FAO Penman-Monteith method in Arsanjan, it is possible to use of other methods that needs a little hydrological parameters.

Keywords:

Potential Evapotranspiration , Arsanjan County , Ref-ET Software , FAO-Penman Monteith