Evaluation of pan coefficient equations in a semi-arid Mediterranean environment using the ASCE-standardized Penman-Monteith method

Abstract

Reference crop evapotranspiration ( ET o ) is essential for irrigation, water resources management and environmental assessment. The indirect estimation of ET o is based a) on energy budget approach using meteorological data and b) pan evaporation measurements ( E pan ) multiplied by pan coefficients ( k p ) adapted to the surrounding environmental conditions. Significant interest is shown for the k p equations, which have to be tested before their use. The purpose of this study is to evaluate six different k p equations, such as those of Cuenca, Allen and Puitt, Snyder, Pereira et al ., Orang, Raghuwanshi and Wallender for the summer growing season (April to October) of Thessaloniki plain in Greece, which is characterized by a semi-arid Mediterranean environment. The evaluation of the k p equations is performed by two years E pan measurements, using as reference the daily ET o values estimated by the ASCE-standardized Penman-Monteith equation (ASCE-PM) in hourly time step. The results of this study showed that Cuenca’s equation provided more accurate daily estimations. Additional analysis is performed in other methods such as those of FAO-56 and Hargreaves based on the calculation time step (hourly or daily) and their correspondence to the ASCE-PM.