ABSTRACT
The methods of determining or estimating potential evapotranspiration fall into five categories: (1) direct measurements by lysimeters, (2) empirical formulae using one or more common climatic factors, (3) the aerodynamic approach, (4) the energy budget approach, and (5) the use of evaporimeters. Both the empirical formulae and the simple energy budget approach do not make sufficient allowance for the influence of advection; hence, they must be modified when used to estimate the potential maximum evapotranspiration in arid climates.
