Which type of soil–vegetation–atmosphere transfer scheme is needed for general circulation models: a proposal for a higher–order scheme

Abstract

Recent investigations on various aspects of land–atmosphere interactions at the microscale and the mesoscale are summarized, for the purpose of reflecting on the type of Soil–Vegetation–Atmosphere Transfer (SVAT) schemes, needed for General Circulation Models (GCMs). It appears that, among all land–surface characteristics considered in advanced SVAT schemes, only stomatal conductance, soil–surface wetness, leaf area index, surface roughness, and albedo play a major role inthe redistribution of energy at the ground surface. However, the relationship between these characteristics and the surface heat and momentum fluxes is strongly nonlinear. Furthermore, landscape discontinuities resulting from spatial heterogeneity of these characteristics, can induce atmospheric mesoscale circulations, which have a strong impact on the structure of the planetary boundary layer, clouds, and precipitation. These findings imply that appropriate SVAT schemes for GCMs need to provide higher statistical moments and characteristic length scales of the spatial distribution of the above mentioned five land–surface characteristics. The conceptual features and equations of a higher–order SVAT scheme are described here. This new SVAT scheme will probably not be able to mimic diurnal variations of land–surface fluxes at a precise location, but is expected to provide appropriate surface forcings, which trigger nonlinear atmospheric responses (including clouds and precipitation) at the microscale and the mesoscale. Furthermore, this new SVAT scheme is designed to directly use remotely–sensed parameters, which are not converted into pseudo plant and soil characteristics. Thus, this scheme is particularly convenient for data assimilation.