بررسي اعتبار مدل هاي رياضي و رايانه اي تخمين تبخير غيرماندگار از سطح خاك تحت توسط عمليات ميداني سنجش تبخير

The validity of mathematical and computer models for estimating the non-steady evaporation from bare soil surface using evaporation evaluation field operations

The main problem for the exact estimation of evaporation in field conditions is the lack of basic relations with the least amount of information needed for considering water loss in water balance models. The main goal of this study is to examine the available methods of evaporation calculation from bare soil surface and to suggest the best method. Most of these relations are empirical; to deduce them, simplifying hypotheses have been used to analytically solve the Richardʹs equation with relatively constant border and initial conditions which donʹt have a physical basis. In regions where the ground water surface is low, the results of these relations do not coincide with reality. Evaporation from bare soil area was calculated through the numerical solution of Richardʹs equation in a one- dimension, non-steady form with border and initial conditions different from those of other methods using computer LEACHM model. There is a strong relationship between the results of the computer model and the water balance model carried out using field experiments in certain time intervals and specific areas.