REFERENCE EVAPOTRANSPIRATION: CURRENT ANALYSIS OF DIFFERENT ESTIMATING METHODS

Abstract

The reference evapotranspiration (ETo), originally known as potential evapotranspiration (ETp), is an important agrometeorological parameter, mainly for planning and managing irrigation, besides being considered a climatic element of hydric demand, and that is the reason it is used in meteorological, climatological, and hydrological studies. There are several methods for estimating ETo, from the simpler ones, purely empiric, to those which present a consistent basis of the phenomenon, however, some empiricism is always present. This diversity of methods happens due to the complexity of the water transfering from the soil-plant system to the atmosphere, different climates around the world, and difficulties for obtaining the necessary meteorological data to make those methods work. The Penman-Monteith-FAO (PM-FAO) is internationally known as the most appropriate approach for estimating ETo, being adopted as standard two decades ago. Besides representing, in a consistent way, the evapotranspiration biophysical phenomenon, it makes use of almost all meteorological data observed in surface weather stations. However, when it is not possible to apply this method, it is necessary to investigate which method would be the most suitable for local conditions. Therefore, this study was carried out in order to present, discuss, and point out the most appropriate method(s) for each specific use.