Sigmoid generalized complementary equation for evaporation over wet
surfaces: A nonlinear modification of the Priestley-Taylor equation
Abstract
The deviations of the Priestley–Taylor (PT) coefficient from a fixed
value around 1.26 indicate a nonlinear dependence of wet surface
evaporation (E) on the equilibrium evaporation
(Erad, which is the radiation term in Penman
potential evaporation (EPen)). The linear PT
equation with a fixed coefficient underestimates E for small E_rad but
overestimates E for large Erad. In this study, the
sigmoid generalized complementary (SGC) equation by Han and Tian (2018)
was applied to estimate the wet surface evaporation by setting its
asymmetric parameter to infinity. The SGC equation with one parameter
captures the nonlinear dependence of E on Erad
over the wet surface by including the aerodynamic component of
EPen and amends the shortage of the linear PT
equation. By using datasets over open water surfaces of lakes and ocean,
wetlands, and paddy fields, the validation results indicate that the wet
surface SGC equation performed better than the linear PT equation on
evaporation estimation, especially over open water surfaces, where
advections or large-scale synoptic changes are more substantial. The
success of the wet surface SGC equation has implications for the
extension of the complementary principle to consider above processes.