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Regionalising Parameters of a Conceptual Rainfall-Runoff Model for Stream Flow Estimation in Ungauged Catchments
IHACRES, a lumped conceptual rainfall-runoff model, was calibrated to six catchments ranging in size from 49km2 to 600 km2 within the upper Tana River basin to obtain a set of model parameters that characterise the hydrological behaviour within the region. Physical catchment attributes indexing topography, soil and land use were derived from spatial data using GIS. Equations were developed which related the conceptual parameters to catchment characteristics and which enabled the estimation of model parameters from catchment characteristics. The estimated hydrological model parameters were used to simulate stream flows in two validation catchments within the same region. Although the results varied, the stream flows simulated using the derived regional parameter sets agreed well with the observed stream flow series. The R2 values were 0.21 and 0.67 while the Nash-Sutcliffe efficiency values were 0.21 and 0.68 respectively. The results indicated that the method is viable and can be used to extend existing stream flow data in ungauged catchments or to generate data where none exists.