Interactive vegetation modelling at a regional scale: Application to the Adour Basin

The ISBA (Interactions between Soil Biosphere and Atmosphere) SVAT model wa s modified to include a representation of interactive vegetation. A paramet erization of CO2 assimilation was introduced, the photosynthesis process wa s parameterized as a unction of vegetation physiological properties and env ironmental conditions. Thereby, the canopy stomatal resistance is described in a more realistic way than in;the initial version. A growth model was us ed to compute Leaf Area Index (LAI) evolution instead of prescribing it fro m satellite data without taking: into account possible climate changes and their consequences on plant development. In this paper, the "ISBA-A-gs" mod ified model is tested at the regional scale in the Adour basin. For this pu rpose it was necessary to calibrate three parameters for each land cover ty pe (mainly coniferous forest, summer and winter crops): the mesophyll condu ctanse, the maximum turnover time of leaves and an effective biomass per LA I ratio. This work has been followed by a long term simulation (1986-1995) where the surface scheme was coupled with a distributed hy drological model . The results were compared to those obtained with the "standard version", i.e ISBA without A-gs. For the whole period, the simulated LAI was lower th an the prescribed one, which decreased evaporation (10 to 15 % less with A- gs) and led to a better simulation of streamflow on both crop and forest ar eas. (C) 2001 Elsevier Science Ltd. All rights reserved.