THE LAND-SURFACE SCHEME ISBA WITHIN THE METEO-FRANCE CLIMATE MODEL ARPEGE .1. IMPLEMENTATION AND PRELIMINARY-RESULTS

This paper describes recent developments in climate modeling at Meteo- France related to land surface processes. The implementation of a simp le land surface parameterization, Interactions between Soil Biosphere Atmosphere (ISBA), has gained from previous validations and calibratio ns at local scale against field datasets and from aggregation procedur es devised to define effective land surface properties. Specific impro vements for climate purposes are introduced: spatial variability of co nvective rainfall in canopy drainage estimation and subsurface gravita tional percolation. The methodology used to derive climatological maps of land surface parameters at the grid-scale resolution of the model from existing databases for soil and vegetation types at global scale is described. A 3-yr integration for the present day climate with a T4 2L30 version of the climate model has been performed. Results obtained compare favorably with available observed climatologies related to th e various components of the continental surface energy and water budge ts. Differences are due mostly to a poor simulation of the precipitati on field. However, some differences suggest specific improvements in t he surface scheme concerning representation of the bare soil albedo, t he surface runoff, and the soil moisture initialization. As a first st ep prior to tropical deforestation experiments presented in Part II, r egional analyses over the Amazon forest indicate that the modeled evap oration and net radiation are in good agreement with data collected du ring the Amazon Region Micrometeorological Experiment campaign.