Comment on “Rescaling the complementary relationship for land surface evaporation” by R . C rago et al.

The generalized complementary relationship (GCR) model of Brutsaert (2015) has been widely applied to estimate land surface evapotranspiration ( E ) over Chinese eastern monsoon region, Loess Plateau and Australia. However, Crago et al . (2016, hereinafter C16) recently noted a deficiency in one of his boundary conditions and proposed a novel approach to improve it. The key of this approach is to determine the ratio ( x min ) of the potential evapotranspiration ( E po ) to the apparent potential evapotranspiration for an entirely dry surface ( E pads ) at which E tends to be vanishing. As seen, the physically reasonable range of x min should be between 0 and 1. The present comment reports that the x min in C16 may become invalid under conditions of relatively strong available energy but weak winds if E pads is calculated by the mass‐transfer‐based method, thereby causing unrealistic estimation of E . A more preferable way to determine E pads is still based on the traditional Penman‐based equation with consideration of the characteristics of dry air in which E pads occurs.