Regionalisation of the base flow index from dynamically simulated flow components — a case study in the Elbe River Basin

This study investigates possibilities for the regionalisation of flow components within large river basins. One main purpose is the derivation of an empirical relationship for the estimation of the average base flow index (i.e. the ratio of base flow to total flow, BFI), which can be included into simplified models in form of decision support systems aimed at rapid integrated water resources assessment. Based on results from the hydrological models ARC/EGMO and HBV in 25 mesoscale sub basins of the macroscale Elbe River Basin, the modelled BFI is regionalised for the whole German part of the Elbe Basin, divided into 114 subbasins. For regionalisation of the average BFI multiple regression (MREG) and two geostatistical approaches (ordinary kriging (OK) and external drift kriging (EDK)) are applied using different physical catchment attributes and observed climate data as independent variables. The average base flow index is strongly related to topographical, pedological, hydrogeological and precipitation characteristics and less influenced by land cover/land use properties of the catchments. As indicated by cross validations, both EDK and MREG are suitable for regionalising the BFI with coefficients of determination of 0.80 and 0.77, respectively. Furthermore, the plausibility of the estimated BFI values is shown by comparisons with parameters calculated from statistical and fractal analysis of daily flow time series, which represent a strong relation to the regionalised BFI values.