Effective parameters for surface heat fluxes in heterogeneous terrain

The relations between most land-surface characteristics and surface heat fl uxes are typically non-linear. Because the ground surface is heterogeneous at all scales, it is important to account for these non-linear relations. E ffective parameters are often applied for that purpose. Steady-state simula tions were used in this paper to thoroughly analyse the effective parameter s impact under a broad range of atmospheric conditions. The effect of diffe rent types of aggregating functions on the accuracy of various effective pa rameters is also examined. The authors found that linear averaging of leaf area index and soil water content gives higher latent and lower sensible he at fluxes than the corresponding flux averaging over all surface types exis ting in one square grid. Linear averaging of roughness length under unstabl e conditions provides higher latent and lower sensible heat fluxes than flu x averaging, whereas under stable conditions gives higher sensible and lowe r latent heat fluxes. Non-linear functions result to be more useful than li near functions to compute the effective value of those parameters which aff ect the surface heat fluxes independently of the atmospheric stability (e.g ., leaf area index and soil water content, and unlike roughness length).