Evaluation of Different Determination Methods of Class A Pan Evaporation Coefficient For Estimation daily Evapotranspiration In Islamabad-Gharb Area

Thermal energy in the air, causing the evaporation of water in the hydrosphere Tremblay and This action continues until saturation the air from the water vapor. evaporate maybe accur from surface water or from wet soil or transpiration from the plants. a common method to estimate ( ) is using class A pan Evaporation, In this case, multiplying of evaporation from class A pan Evaporation in pan coefficient (Kp) can be achieved (ET0). Pan coefficient (Kp) depends on the location and weather conditions. There are several ways to estimate evaporation pan Coefficient that in all of them is used from daily mean of wind speed (U), relative humidity (H) and the cover (F). The purpose of this research is to find the best evaporation pan coefficient method in Islamabad-Gharb Area, between empirical methods Doorenbos And Pruitt (1977), the Cuenca (1989), the Allen and Pruitt (1991), Model Schneider (1992), model Pereira et al. (1995), the Orang (1998) and the FAO 56 (Allen et al. (1998)) according to the data of meteorological stations Islamabad-Gharb and Compare them with Kp values obtained by dividing the . The values of ET0 are extracted from the lysimetric data from 1395. The results showed that Orang model with a correlation coefficient of 0.99, the root mean square difference of 0.008, efficiency or performance of 0.98 and the mean percentage error (0.003) is much less than other methods shows better and The coefficient of determination show the suitability of the Orang method (0.98).