Realism test of a topography driven conceptual model (FLEX-Topo) in nested catchments of the Heihe River Basins, China

Although elevation data are globally available and many models do take topographical information into account, here it is demonstrated that topography is still an under-exploiting source of information in hydrological models . Based on the recently proposed modelling approach (FLEX-Topo) a semi-distributed topographic driven conceptual model (FLEXT), has been developed and tested in two nested catchments of the Heihe river basin. The model uses four topographical properties (i.e. Height Above the Nearest Drainage (HAND), absolute elevation, slope and aspect) to make a hydrological landscape classification which correspond with the dominant rainfall-runoff processes of these landscapes, to which a conceptual model structure is attributed. To analyses the additional information provided by the landscape classification, the performance of the FLEXT model is compared to a completely lumped hydrological models (FLEXL) and a semi-distributed model (FLEXD). All models have been calibrated and validated at the catchment outlet. Additionally, the models were evaluated in two nested sub-catchments. FLEXT performs substantially better than the other two models especially in the two nested sub-catchments during validation. It is especially better equipped to represent rainfall-runoff events during the dry season, which supports the following hypotheses: (1) topography can be used to distinguish different landscape elements with different hydrological function; (2) the model structure of the FLEXT is much better equipped to represent hydrological signatures than a lumped or semi-distributed model, and hence has a more realistic model structure and parameterization. The hydrograph components of the calibration(a), split-sample validation(b) and nested sub-catchments validation(c,d), of the FLEXT model