An interactive vegetation SVAT model tested against data from six contrasting sites

The interactions between soil, biosphere, and atmosphere scheme (ISBA) is modified in order to account for the atmospheric carbon dioxide concentration on the stomatal aperture. The physiological stomatal resistance scheme proposed by Jacobs (1994) is employed to describe photosynthesis and its coupling with stomatal resistance at leaf level. In addition, the plant response to soil water stress is driven by a normalized soil moisture factor applied to the mesophyll conductance. The computed vegetation net assimilation can be used to feed a simple growth submodel, and to predict the density of vegetation cover. Only two parameters are needed to calibrate the growth model: the leaf life expectancy and the effective biomass per unit leaf area. The new soil-vegetation-atmosphere transfer (SVAT) scheme, called ISBA-A-g(s), is tested against data from six micrometeorological databases for vegetation ranging from temperate grassland to tropical forest. It is shown that ISBA-A-g(s) is able to simulate the water budget and the CO2 flux correctly. Also, the leaf area index predicted by the calibrated model agrees well with observations over canopy types ranging from shortcycled crops to evergreen grasslands or forests. Once calibrated, the model is able to adapt the vegetation density in response to changes in the precipitation distribution. (C) 1998 Elsevier Science B.V. All rights reserved.