An Evaluation of the Hargreaves-Samani Method for Estimating Evapotranspiration Under Semi-Arid Conditions

It is suggested by the Food and Agriculture Organization of the United Nations (FAO) to use the FA056-Penman-Monteith (FA056-PM) model as the standard model in reference crop water consumption studies. However, the climate parameters required by the standard model cannot be fully and reliably obtained in under developed or developing countries. Hence, the Hargreaves-Samani (HS) equation is used as an alternative to the FA056-PM model since it can be used for calculations with less climate data. In the present study, ETo-PM and ETo-HS values calculated at 8 provinces in Southeastern Turkey using the IAM-ETo software were evaluated and compared in order to examine whether the HS equation can be alternative to the FAO-PM equation or not. It was observed at the end of the study that the daily calculated ETo-HS values yielded 16% overestimation on average compared with ETo-PM. Statistically highest (RMSE: 1.32, MAE: 1.10, MR: 1.37, and PE: 36.86) and lowest (RMSE: 0.33, MAE: 0.24, MR: 0.96, and PE: 5.32) values were calculated for Batman and Mardin respectively. The mean values for the Southeastern Anatolia Region were calculated as RMSE: 0.64, MAE: 0.52, MR: 1.17, and PE: 16.04. It was identified in the light of these findings that the HS equation can be used as an alternative to FA056-PM for the studied provinces.