PROBLEMS AND PROGRESS IN MACROSCALE HYDROLOGICAL MODELLING

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Abstract
One of the major problems in macroscale hydrological modelling is the assessment of areal heterogeneity in important land surface characteristics, such as topography, land use, land cover, soil, vegetation and hydrological characteristics. After a brief discussion of spatial scales to be covered and related categories of models to be applied two examples are presented which underline the problems involved in the application of lumped models for large areas, like grid areas of general atmospheric circulation models (GCMs). A strategy for a more appropriate hydrologically sound structuring of macroscale hydrological models is then outlined which takes into account the following facts and features: (1) zones of ‘uniform’ atmospheric forcing, (2) landscape patchiness, (3) intra-patch heterogeneity, (4) a ‘Two-Domains-Modelling’ concept, which is essential for the coupling of atmospheric and land-surface hydrological models. INTRODUCTION Global modelling is the subject of two of the most challenging recent international programmes: – The World Climate Research Programme (WCRP), and – The International Geosphere-Biosphere Programme (IGBP) – a Study of Global Change. A main objective in both programmes is to improve land surface process descriptions (parameterisations) to be applied at large scales, up to the scale of grid areas of global atmospheric circulation models (GCMs) which cover about 104–105km2. Problems in large scale land-surface process modelling and some improvements achieved during the last years are briefly discussed in the following and suggestions are made for further progress.
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