Validation and calibration of FAO WaPOR product (actual evapotranspiration) in Iran using in-situ measurements

Estimation of actual evapotranspiration (ETa) in the scales of basin and field is one of the essential information for water resources allocation. Although estimating actual evapotranspiration has encounter with several restrictions (e.g., spatially, temporally and costly), but satellite images data can overcome these limitations usually. In this regard, the objectives of present paper are: a) evaluation and validation of WaPOR ETa product using Scintillometer instrument and, b) estimation of ETa over several land use regions over the Zayanderoud basin. Based on obtained results, MAE, RMSE, MAPE and R are equal to 2.14 (mm for 10 days), 2.55 (mm for 10 days), and 5.50 and 0.97 respectively which represent the appropriateness of WaPOR ETa data in comparison with Scintillometer. Also, the analysis of WaPOR product in different land-used showed that, the maximum amount of actual ETa has occurred in dual crops (513 mm), orchards (387 mm), spring crops (272 mm), autumnal crops (271 mm), dry farming (112 mm) and rangelands (83 mm) respectively. Also the results show that in rice fields, 992 mm fresh water lost in the form of ETa which is considered dramatically due to the climate and water resources of selected basin and its relevance challenges.