Investigating the relationship between a soils classification and the spatial parameters of a conceptual catchment-scale hydrological model

There are now many examples of hydrological models that utilise the capabil ities of Geographic Information Systems to generate spatially distributed p redictions of behaviour. However. the spatial variability of hydrological p arameters relating to distributions of soils and vegetation can be hard to establish. In this paper, the relationship between a soil hydrological clas sification Hydrology of Soil Types (HOST) and the spatial parameters of a c onceptual catchment-scale model is investigated. A procedure involving inve rse modelling using Monte-Carlo simulations on two catchments is developed to identify relative values for soil related parameters of the DIY model. T he relative values determine the internal variability of hydrological proce sses as a function of the soil type. For three out of the four soil parameters studied, the variability between HOST classes was found to be consistent across two catchments when tested i ndependently. Problems in identifying values for the fourth 'fast response distance' parameter have highlighted a potential limitation with the presen t structure of the model. The present assumption that this parameter can be related simply to soil type rather than topography appears to be inadequat e. With the exclusion of this parameter. calibrated parameter sets from one catchment can be converted into equivalent parameter sets for the alternat e catchment on the basis of their HOST distributions. to give a reasonable simulation of flow. Following further testing on different catchments, and modifications to the definition of the fast response distance parameter. the technique provides a methodology whereby it is possible to directly derive spatial soil param eters for new catchments. (C) 2001 Elsevier Science BN. All rights reserved .