Hedieh Ahmadpari - M.Sc. Student of Irrigation and Drainage, University of Tehran
Maryam Barzgar - M.Sc. Student of Watershed Management, Faculty of Agriculture and Natural Resources, University of Tehran
Nasrollah Barzegar - Expert of the Natural Resources Administration in Bavanat City

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. In this study, Bavanat synoptic station data used for estimating monthly reference Evapotranspiration and ET was estimated with 16 different methods and each estimated result were compared with FAO-Penman-Montith ET result. The efficiency of all methods were evaluated with RMSE (Root Mean Square Error) and MAE (Mean Absolute Error) statistic parameters. The results showed that ASCE st PM, ASCE PM, ASCE PM, ASCE PMrs, 1972 K Pen, FAO 24Pen, FP 17 Pen, 1948Pen, 1996 KPen, 1985 Harg, FAO 24Rd, FAO 24BC, 1957 Makk, 1961 Turc, Prs -Tylr and FAO Pan methods, respectively, have less MAE and RMSE. So in situation of less data for FAO Penman Monteith method in Bavanat, it is possible to use of other methods that needs few hydrological parameters.

Evapotraspiration, meteorological data, Bavanat, FAO-penman-Montith