Measurement and estimation of actual evapotranspiration in the field under Mediterranean climate: a review

The Mediterranean regions are submitted to a large variety of climates. In general, the environments are arid and semi-arid with summers characterised by high temperatures and small precipitation. Due to the scarcity of mater resources, the correct evaluation of water losses by the crops as evapotranspiration (ET) is very important in these regions. In this paper, we initially present the most known ET measurement methods classified according to the used approach: hydrological, micrometeorological and plant physiological. In the following, we describe the methods to estimate ET, distinguishing the methods based on analytical approaches from the methods based on empirical approaches. Ten methods are reviewed: soil water balance, weighing lysimeter, energy balance/Bowen ratio, aerodynamic method, eddy covariance, sap flow method, chambers system, Penman-Monteith model, crop coefficient approach and soil water balance modelling approach. In the presentation of each method, we have recalled the basic principles, underlined the time and space scale of its application and analysed its accuracy and suitability for use in arid and semi-arid environments. A specific section is dedicated to advection. Finally, the specific problems of each method for comet use in the Mediterranean region are underlined. In conclusion, we focus attention on the most interesting new guidelines for research on the measurement and estimation of actual crop evapotranspiration. (C) 2000 Elsevier Science B.V. All rights reserved.