Priestley and Taylor approach

The Priestley and Taylor approach is a simplification of Penman’s formulation of evapotranspiration ET, assuming that the equilibrium term λEeq is significantly larger than the aerodynamic term λEa. On the basis of this assumption, the Priestley–Taylor formulation for ET is expressed as λE = α λEeq where α is the so-called Priestley–Taylor coefficient.

Sources
Agam, Nurit, William Kustas, Martha Anderson, John Norman, Paul Colaizzi, Terry Howell, John Prueger, Tilden Meyers, and Tim Wilson. (02/2010AD) 2010. “Application Of The Priestley–Taylor Approach In A Two-Source Surface Energy Balance Model”. Journal Of Hydrometeorology 11. American Meteorological Society: 185-198. doi:https://doi.org/10.1175/2009JHM1124.1.