THE USE OF UPSCALING PROCEDURES IN THE APPLICATION OF SOIL ACIDIFICATION MODELS AT DIFFERENT SPATIAL SCALES

Different soil acidification models have been developed for use on dif ferent scales, i.e. NUCSAM for the local scale, RESAM for the regional (national) scale and SMART for the continental scale. This paper focu ses on the uncertainties associated with scale transfer by a simpler m odel description by (i) temporal aggregation of process descriptions, (ii) neglection of processes associated with vertical aggregation of s oil layers and (iii) the use of less detailed formulations of processe s (process aggregation) and by spatial aggregation of input data. Resu lts obtained for simulations in acid (sandy) soils indicate that (i) t emporal aggregation and process aggregation have a limited impact on t he long-term (decades) annual response of soil solution chemistry to a tmospheric deposition, (ii) vertical aggregation mainly affects predic tions of solutes which show a strong concentration gradient with depth and (iii) spatial aggregation hardly affects the average output for a given forest/soil combination. However, ignoring the variability in i nput parameters, largely affects the frequency distribution of model o utputs in a region. Results imply that model simplification is an adeq uate step in the upscaling of modelling results from a local to a regi onal scale.