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River flow measurements are important data for water resource planning, pollution control, conservation and even recreational use. However, availability of such data in the most cases is either insufficient or not available at all. This then may become a hindrance to efficient utilisation of hydrologic input to river basin management projects. This paper examined the relationships between the physical properties of a catchment and hydrological model parameters which describes efficiently the hydrological response of the semi-arid catchment. A hydrological model was calibrated to 19 semi-arid catchments of the Great Ruaha basin in south-western Tanzania to obtain a set of parameters that efficiently characterise the hydrological response of a catchment. Physical catchment properties indexing topography, geology, climate and land use were collated using Geographical Information System and linked to the calibrated parameter values. The resulting quantitative relationships were assessed with respect to their value for estimating the parameter values of the model and the streamflow. The relationships indicated to be robust enough to reproduce hydrological response of the catchment. Hydrological model parameters were satisfactorily estimated for four validation catchments within the region using physical catchment properties. The results indicated that the technique is likely to offer a viable method for estimating flows of ungauged semi-arid catchments and the impact of land use and climate change on water resources. (C) 2003 Elsevier Ltd. All rights reserved.