This study attempts to examine if catchment variability favours regionalisation by principles of catchment similarity. Our work combines calibration of a simple conceptual model for multiple objectives and multi-regression analyses to establish a regional model between model sensitive parameters and physical catchment characteristics (PCCs). The objective is to test robustness of regionalisation by assessing if generalisation of a wide range of climatic, topographic and physiographic settings in a regional model favours simulation of stream flow at ungauged catchments. Constraints in this work are very stringent performance measures for selection of catchments to establish the regional model and the selection of only PCCs that are available through the database of the National River Flow Archive in the United Kingdom. As such some PCCs have been ignored that have proven to be effective in other studies. For this study 56 well-gauged catchments in England and Wales are used. For model calibration and runoff simulation of ungauged catchments the HBV model is applied. Optimum parameter sets are derived for 48 catchments through Monte Carlo Simulation using an 8-year simulation period. This study aims to adequately simulate all aspects of the hydrograph at the ungauged catchment and therefore four single objective functions are combined in a multi-objective function. After calibration, 17 catchments that are widely spread over England and Wales are selected to establish relationships for seven selected model parameters using 14 PCCs (area, mean elevation, hypsometric integral, catchment shape, standard average annual rainfall, five types of land use and four classes of hydrogeology). Single and multiple regression analysis are applied to identify these relationships. For six model parameters statistically significant relationships could be established three of which are plausible on the basis of hydrologic interpretation. The established relationships are validated at eight gauged catchments that are spread over the UK and cover a large range of values of catchment descriptors. These catchments are assumed ungauged and results revealed that, in general, model parameters determined by the established regional relationships do not perform better as compared to default parameter values. Similar results are obtained for additional validation runs using catchments that are not used in the regionalisation procedure. Since these parameters are based on model performance assessments in a wide range of catchment settings, this suggests that large variability in settings of PCCs does not favour regionalisation. Therefore, for selected catchments the applicability of regionalisation by principles of catchment similarity for HBV model parameters may be questioned.
- England and Wales - HBV model - Multi-objective calibration - Physical catchment characteristics - Regionalisation - Ungauged catchment