Szilagyi, Jozsef. 2015. Water Balance Validation of a Temperature-Dependent Parameter Value of the Priestley-Taylor Equation of Evapotranspiration. Journal of Hydrology and Environment Research. 3(1): 1-5.
New research suggests that the Priestley-Taylor (PT) parameter, a, displays a temperature dependency with a significant increase
in its generally accepted constant value of 1.26 as air temperature (T) drops. Multi-year water-balance data from two humid, cool climate
experimental watersheds –Hubbard Brook in New Hampshire and Lookout Creek in Oregon, USA— and from a warm, humid catchment at
the border of Mississippi and Louisiana as a control, support a temperature-dependent a(T) value. Mean annual evapotranspiration rates
obtained with a(T) were superior to those of a=1.26 and fell within 3% of the water-balance derived (precipitation minus runoff) values. As a
consequence, humid, cold-region evaporation/evapotranspiration may be significantly underestimated via the PT equation when the classical
value of 1.26 is employed in place of a temperature-modulated a(T).
Keywords: Evapotranspiration, evaporation, Priestley-Taylor equation, Priestley-Taylor parameter.