Comment on the Reference to Makkink Potential Evaporation Equation

The Makkink evaporation equation has been applied worldwide to estimate potential evaporation based on measured or estimated radiation, and mean atmospheric temperature. The general form of the Makkink equation is similar to the well-known Priestley and Taylor (1972) evaporation, although Makkink proposed the equation nearly 2 decades earlier. The writers have examined 51 references that refer directly or through a secondary source to the Makkink equation, yet every reference the writers have sighted refers to Makkink (1957b) as the relevant reference. This reference is incorrect, as the Makkink equation is not mentioned therein. After an exhaustive library search and pursing other avenues through colleagues, the writers are convinced the correct reference is Makkink (1957a). de bruin (1981) cites Makkink (1960) in a discussion of methods to estimate reference crop evapotranspiration. Makkink (1957a) is written in the international language Esperanto, and researchers can use the Google Translate function to translate. The Makkink equation, as reported in Makkink (1957a), is