Use of the modified atmometer to estimate reference evapotranspiration in Mediterranean environments

Reference crop evapotranspiration (ET0) estimates on the basis of FAO recommended methodology require the knowledge of several meteorological data. An alternative approach is the use of the modified atmometer which reduces the work and the complexity associated with ET-based irrigation scheduling. To establish relationships between Penman Monteith (PM), atmometer and Class ‘A’ pan ET0 in Mediterranean environments, field tests were carried out during five irrigation seasons in different east and west coast sites of southern Italy. In all sites, high values of the correlation coefficient were found when comparing daily estimates of atmometer versus PM ET0. Scattering of experimental data was the result of atmometer readings taken manually. Linear regression models yielded intercept coefficients which did not differ from zero, in any of the sites. A unique relationship could be established between atmometer and PM when data from all sites were pooled, providing a slope coefficient of 1.034. When comparing with a high resolution weighing lysimeter across a complete irrigation season, a slope not different from unity was found. Comparisons with Class ‘A’ mean weekly ET0 during two consecutive irrigation season, indicated a slight underestimation of pan ET0 by the atmometer. On the basis of experimental evidence, atmometer may be used for reliable ET0 estimates under Mediterranean conditions, at both the farm and the extension level, whenever standard meteorological data are not available.