Comparison of different determining methods of reference eto based on limited weather conditions in gap region

Abstract

Reference crop evapotranspiration (ETo) is among the most important components of the hydrologic cycle. Standard FAO-Penman-Monteith method is the most frequently used equation to estimate of ETo. However, the usability of this method is limited due to its complexity Hargreaveas-Samani (HS) and Turc methods that can be operated with limited data such as temperature and solar radiation are used as an alternative to the standard method. In the present study, the reference ETo values estimated with FAO-PM as the standard method, Hargreaveas-Samani and Turc methods were compared at semi-arid climate conditions. Based on the acquired results; highest R2 value at the GAP region with semi-arid climate conditions was determined as 0.9872 from the monthly averages of ETo-PM and ETo-HS comparison, whereas the lowest RMSE value was also obtained from the same monthly comparison (0.08). ETo-Turc method yielded a monthly average comparison of 0.981 for the R2 values comparison. While ETo-CAP put forth the lowest values for all three intervals. It is suggested that HS method can be used instead of Standart Penman-Monteith method (FAO-PM) under GAP region semi arid climate conditions for reference ETo estimation if Penman-Monteith can not be calculated. The Turc method is also can be a good alternative to estimate potential evapotranspiration that can be measured by Class A pan. And that ETo estimation should be made by determining the Kp value in case CAP based ETo estimation is carried out.