An attempt has been made to estimate evaporation from a water body by developing a new approach based on the energy balance model. For this purpose, a new energy balance method for two surfaces was established: water (evaporating surface) and dry bare soil (non-evaporating surface as reference). An identical aerodynamic resistance ratio was assumed for both surfaces due to their similar conditions. With this assumption, a new form of energy balance was obtained which only depends on net radiation and temperature. The derived reference and water surface energy balance (RWEB) method was applied to estimate evaporation from Doosti dam reservoir in Iran. In order to evaluate the performance of the RWEB, comparison was performed with Bowen ratio energy balance (BREB) method as well as some conventional methods. According to the evaluations, the evaporation results of RWEB from 2011 to 2012 were satisfactory with RMSD value of 1.026 mm month
1 and R2 ¼ 0.937. Furthermore, the RWEB sensitivity analysis showed the highest sensitivity to air temperature and the lower sensitivity to net radiation. Thus, evaporation from a water body can be estimated accurately by precise measurements of air temperature and relatively reasonable estimations of other parameters (reference, water temperature and net radiation).

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