Evaluation of reference evapotranspiration by empirical-physical models using weight lysimeter (Case study: Tabriz)

The use of measured data to evaluate reference evapotranspiration (ET0) estimation models in various studies has been limited due to the problems in the measurements. The types of grass and soil textures used in lysimeters differ in different studies, while these factors affect the amount of lysimetric measurements. This study evaluated 19 physical-experimental and experimental models in the combined, radiation, temperature, and mass transfer groups for three consecutive years (2017-2019) by lysimetric measurements in the Tabriz region with a semi-arid climate located in northwestern Iran. Also, to investigate the effect of reference plant species and soil texture on ET0, two grass species including Festuca Arundianacea Schreb and Lolium perenne were applied in three soil textures of sandy loam, clay, and silty loam in weight lysimeters. The Kimberly Penman-1996 (KP), Penman-1963, FAO.ppp.17 Penman (FAO.ppp.17), FAO24 Blaney Criddle (FAO24 BC), and FAO56 Penman-Monteith (FAO 56 PM) had the best performance among used models. Group comparison of models showed that the combination models had the best performance among the studied groups. The ET0 values estimated by the models were more consistent with the lysimeters filled with sandy loam soil than the ones filled with silt and clay lysimeters. The study of the effect of grass species on the performance of the models showed that the accuracy of the experimental models in lysimeters planted with grass Lolium was higher than the Festuca grass.