Effective parameters for surface heat fluxes in heterogeneous terrain

Abstract

The relations between most land-surface characteristics and surface heat fluxes are typicallynon-linear. Because the ground surface is heterogeneous at all scales, it is important to accountfor these non-linear relations. EVective parameters are often applied for that purpose. Steady-state simulations were used in this paper to thoroughly analyse the eVective parameters impactunder a broad range of atmospheric conditions. The eVect of diVerent types of aggregatingfunctions on the accuracy of various eVective parameters is also examined. The authors foundthat linear averaging of leaf area index and soil water content gives higher latent and lowersensible heat fluxes than the corresponding flux averaging over all surface types existing in onesquare grid. Linear averaging of roughness length under unstable conditions provides higherlatent and lower sensible heat fluxes than flux averaging, whereas under stable conditions giveshigher sensible and lower latent heat fluxes. Non-linear functions result to be more useful thanlinear functions to compute the eVective value of those parameters which aVect the surface heatfluxes independently of the atmospheric stability (e.g., leaf area index and soil water content,and unlike roughness length).