Many studies have demonstrated that G is strongly correlated with net radiation (Rn). However, methods to parameterize G based on this relationship typically do not account for the dependency of G on soil properties and ignore the phase shift in the timing of peak G relative to Rn. Here, a method is described to parameterize G as a function of Rn for sparse cover or bare soil conditions that takes into account the diurnal variation in this relationship, as well as the effects of soil moisture and soil type. This approach combines information from field data and simulations from a multi-layer, diffusion-based soil model, (SHAW; Simultaneous Heat and Water model), over a range of soil types and conditions. A critical factor controlling the relationship between G and Rn is the relative soil moisture and the transition from stage-one (atmosphere limited) to stage-two (soil limited) evaporation. As part of this analysis the effect of vegetation density is also considered. The resulting parameterizations for G/Rn provide a robust representation of this ratio on hourly time scales for varying soil conditions. This method provides improvement over previous simplified treatments for G in energy balance modeling in the absence of a physically-based soil model, and where diurnal energy balance closure is required.