An evaluation of two models for estimation of the roughness height for heat transfer between the land surface and the atmosphere

Roughness height for heat transfer is a crucial parameter in estimation of heat transfer between the land surface and the atmosphere. Although many empirical formulations have been proposed over the past few decades, the uncertainties associated with these formulations are shown to be large, especially over sparse canopies. In this contribution, a simple physically based model is derived for the estimation of the roughness height for heat transfer. This model is derived from a complex physical model based on the "localized near-field" Lagrangian theory. This model (called Massman's model) and another recently proposed model derived by fitting simulation results of a simple multisource bulk transfer model (termed Blümel's model) are evaluated using three experimental datasets. The results of the model performances are judged by using the derived roughness values to compute sensible heat fluxes with the bulk transfer formulation and comparing these computed fluxes to the observed sensible heat fluxes. It is concluded, on the basis of comparison of calculated versus observed sensible heat fluxes, that both the current model and Blümel's model provide reliable estimates of the roughness heights for heat transfer. The current model is further shown to be able to explain the diurnal variation in the roughness height for heat transfer. On the basis of a sensitivity analysis, it is suggested that, although demanding, most of the information needed for both models is amendable by satellite remote sensing such that their global incorporation into large-scale atmospheric models for both numerical weather prediction and climate research merits further investigation