Golabi, MR; Niksokhan, MH; Radmanesh, F (2020). Estimating reservoir evaporation: fusing Kohli and Frenken method and the FAO's WaPOR Product. ARABIAN JOURNAL OF GEOSCIENCES, 13(19), 992.

Given the limited fresh water resources available, evaporation from dam reservoirs and freshwater lakes whereby large amounts of water resources are lost is now becoming a serious challenge in hydrology and water resource management. In this study, Kohli and Frenken (KF) method and the KF modified (MKF) (for the modification of this method, level I (250 m) reference evapotranspiration (RET) data were obtained from the FAO's WaPOR Product (FWP) which is a ready product based on remote sensing (RS)) were utilized to estimate reservoir evaporation (RE) in seventeen stations in Iran for the period of 9 years: 2009-2018. The current study includes four distinct steps, as follows. In the first step, the KF method was evaluated with the ground data (measured), and the ready RS product was then validated in the second step. In the third step, we evaluated the MKF method. Finally, in the fourth step, a number of statistical indices were evaluated for each of the methods in order to examine its performance. The results indicated that there was no significant difference between the estimated evaporation values using KF method and the measured values based on the statistical indices. As such, the validation of the ready RS product was acceptable for all dam reservoirs. Moreover, it was found that coefficients of the MKF equation for all stations had a relatively high degree of reliability (R > 0.871). Also, these coefficients had a wide range of variations in different regions, so using a fixed coefficient for all stations will have a relatively large error. The findings also revealed that using the MKF method can improve the performance of the KF method from 0.11 to 9.28%.