The Estimation Evaporation Pan Coefficient For Calculating Reference Evapotranspiration in Ahvaz

Estimation the exact amount of water that is used for evapotranspiration, is the major factor in planning for achieving higher production and its most important parameter of management of water in plants. In terms of lack of access to accurate data lysimeters may use the FAO- Penman-Monteith method as the standard method to evaluate the experimental results. In this study using 15 years of weather data of Ahvaz (1998-2012) evaporation pan coefficient has been calculated with the equations of Orang, Snyder, Cuenca, Allen and Pruitt and their results were compared with the FAO Penman-Monteith. Also for choosing the best model, between five coefficient of determination parameters, Root mean square error, the mean absolute error, the slope and width of the source rank test was performed and the results showed for daily and seasonal pan coefficient calculation is better to use Allen and Pruitt and in ten-day use Snyder in Ahvaz climate.