Pages: 56-66

Abstract

The base of irrigation system design is the estimation of Evapotraspiration (ETo) more correctly. According to need to determine of ET correctly in water balance calculations and the lack of suitable meteorological data, collecting ET method or model for simulating Evapotranspiration is essential. The Penman-Monteith FAO is a valid method, which has been presented by Food and Agriculture Organization of the United Nations, for estimating reference evapotranspiration and it provides the precise results in comparison with direct measurements. The mentioned method needs different parameters such as wind speed, air temperature, net radiation and sunshine hours for estimation of reference evapotranspiration. Also, the Penman-Monteith FAO is a suitable method for evaluating empirical methods. In this study reference crop evapotranspiration calculated by Ref-ET software for Fasa, by using Fasa synoptic stations meteorological data during years 2004 to 2018. The results of methods evaluated with Penman-Monteith FAO standard method. The efficiency of all methods were evaluated with Root mean square Error (RMSE), Mean Absolute Error (MAE) statistic parameters. The results showed that ASCE st PM, ASCE PM, ASCE PM, ASCE PMrs, 1972 K Pen, FAO 24Pen, FP 17 Pen, 1996KPen, 1948Pen, 1985 Harg, 1961Turc, FAO 24BC, FAO Pan, Prs -Tylr and 1957Makk methods, respectively, have less MAE and RMSE. So in situation of less data for Penman Monteith FAO method in Fasa, it is possible to use of other methods that needs few hydrological parameters.