The surface resistance in an explicit single big leaf can be considered as a direct function of parameter values either from a PG file or from a parameter table, or it may be calculated as a function of leaf area index, Al, global radiation, Ris, and vapour pressure deficit, es -ea, i.e. the “Lohammar equation” option (see switch RSMethod). The latter option is always used for multiple plants i.e.:
where gris, gmax and gvpd are parameter values. See viewing functions Air and canopy resistances, Lohammar equation, function of global radiation, Lohammar equation, function of vapour pressure deficit and Lohammar equation surface resistance, canopy.
The Lohammar equation can optionally be used only during the growing season. In this case the maximum conductivity after and before the growing season (i.e. during winter) is given by the parameter gmaxwin. This forth alternative is only valid for explicit single leaf simulations.