Spatio-Temporal Evaluation of Temperature-Based ET0 Estimation Methods in Northwestern Iran

Abstract

Agriculture aims for effective resource management techniques, such as calculating irrigation needs, to maximize agricultural productivity. Reference evapotranspiration (ET₀), an important component of the hydrological cycle, has important role in agricultural operations, particularly irrigation and drainage plans. This research aims to evaluate the accuracy of the Hargreaves-Samani (HS) model in the two stages of calibration and validation and comparing with gene expression programming (GEP) in daily ET₀ modeling. In addition, interpolation techniques, such as ordinary kriging (OK) and inverse distance weighting (IDW) for the spatial distribution of ET₀ in northwest Iran were utilized. The meteorological data of 43 synoptic stations in northwestern Iran were used. FAO Penman-Monteith (FAO56 PM) model was used as benchmark of assessing the rest of the models. Models were evaluated according to five performance indices such as the root mean square error (RMSE), the scatter index (SI), the Nash-Sutcliffe coefficient (NS), the coefficient of determination (R²) and the coefficient of residual mass (CRM). According to the obtained results, the accuracy of the HS model decreases with calibration. The GEP model has better performance than the HS model, which has high accuracy in estimating ET₀ at the Urmia station with a statistical index of R²=0.945, RMSE=0.543 mm, SI=0.149, NS=0.944 and CRM=0.003. The maps of the spatial distribution of ET₀ were produced with the IDW interpolation method, which provided the best estimates.