Towards the upscaling of local surface flux models.

Estimation of regional latent and sensible heat fluxes requires the upscaling of local models. One approach is to develop soil-vegetation-atmosphere transfer (SVAT) schemes at different scales (field, catchment and regional scale; e.g. Famiglietti and Wood (1994)). SVAT schemes at larger scales try to aggregate latent and sensible heat fluxes based on knowledge about the spatial distribution (GIS based) or the statistical-dynamic description of atmospheric forcing and internal state variables. Before one can approach this important problem of upscaling, it is necessary to study the impact of the parameters of the field scale SVAT model on the prediction of local fluxes. In this paper, we show results of a Monte Carlo sensitivity analysis performed on a local SVAT model, with data retrieved during the Autumn of 1995 in an experimental catchment in Belgium. During this field campaign, several parameters of the energy and water balance were measured by means of a Bowen ratio system, while soil moisture data were retrieved on a regular basis using an automatic TDR system. The results of the performed sensitivity analysis are presented and evaluated; conclusions are drawn with respect to the upscaling of local SVAT models to the larger scale