Evaporation and Transpiration

For years, the principal objective of evapo-transpiration research has been to calculate the loss of water under varying conditions of climate, soil, and vegetation. The early simple empirical methods have generally been replaced by more detailed models which more closely represent the physical and biological processes involved. Monteith's modification of the original Penman This paper is not subject to U.S copyright. Published in 1979 by the American Geophysical Union. Paper number 9R0474 evapotranspiration equation to include a term for canopy resistance signaled a shift in emphasis in evapotranspiration research from a physically controlled process to one which can be physiologically controlled. This change in direction was acknowledged by Federer [1975] in his earlier review and has continued for the past four years. The scope of this review, as were the reviews of Ekern [1971] and Federer [1975], is, for the most part, limited to evaporation from terrestrial surfaces rather than from lake or ocean surfaces.