Combining GIS with regional hydrological modelling using hydrological response units (HRUs): An application from Germany

The concept of hydrological response units (HRUs) and their delineation and application to the Brol catchment (A=216 km(2)) in Germany is presented. HRUs are object orientated physiographic entities and can be used as model entities within the MMS/PRMS hydrological catchment model. Applying the HRU concept to the Frill catchment altogether 23 different HRUs were delineated from a DEM (50x50 m grid size), three classified pedo-topo-geological associations and four dominant land-use classes by means of GIS-overlay analyses. MMS/PRMS was then run with these HRUs using a 20-year daily data hydrometeorological time series. The model parameterization was carried out in such a way that rainfall input not consumed by evapotranspiration was routed to a common conceptual subsurface storage. The latter was drained by interflow laterally towards the shallow groundwater aquifer in the valley floors, which in turn seeped into the drainage channel network. The model fit between simulated and observed discharge was good (r=0.91) and it was found that the model was sensitive to parameters related to the land-use controlling evapotranspiration and direct overland flow. Future research activities will concentrate on applying the HRU concept and MMS/PRMS model in drainage basins of different climates in an object oriented way. Special attention will be given to integrating the spatial distributed precipitation into the HRU delineation and the flow routing linkages of the HRU subcells within the catchment which must be included in the present holistic approach.