The ground heat flux and its underlying model is closely linked to the way the surface energy balance is solved. The choice of the equations used to represent the thermodynamics of the ground and/or the vegetation will determine the heat capacity and the physical meaning of the surface temperature. The only input needed to solve the ground model is the surface temperature. As a consequence the ground thermodynamics are internal to the land surface scheme and it does not need to be considered for the interface with the atmosphere.