Estimation of evapotranspiration by Hargreaves formula and remotely sensed data in semi-arid Mediterranean areas

A methodology is proposed for estimating evapotranspiration by Hargreaves formula and image analysis of remotely sensed data. At first, for a large sicilian basin (Belice basin), the actual evapotranspiration values are estimated by the energy balance equation, spectral data of two Landsat TM images and ground agrometereological measurements, Then these actual evapotranspiration estimates and the I reference evapotranspiration values obtained by a slightly modified Hargreaves formula, which incorporates the outgoing short-wave radiation and an albedo coefficient equal to 0.23, are used for calculating suitable crop coefficients, Finally, the minimum area of each land-use map unit, obtained by aggregating an increasing number of image pixels, is determined that is useful to enable a stable estimate of crop coefficient (k(c),), (C) 1997 Silsoe Research Institute.