The influence of physical catchment properties on baseflow in semi-arid environments S. Mwakalila % *, J. Feyen % & G. Wyseurew % Institute for Land and Water Management (ILWM), K.U. Leuven, Vital Decosterstraat 102, B-3000 Leuven, Belgium wFaculty of Agricultural and Applied Biological Sciences, K.U. Leuven, Vital Decosterstraat 102, B-3000 Leuven, Belgium (Received 11 December 2000, accepted 10 October 2001) The present paper examines the influence of physical catchment properties on baseflow in semi-arid environments. It relates the dimensionless quantity, baseflow index (BFI) derived from data-based mechanistic modelling approach to dimensionless indices representing topographic, geologic and climatic properties. The relationship is derived using a progression of techniques, from inspection and correlation analysis, through stepwise regression and finishing with multiple regression. The BFI has a strong relationship with climate and geology. Catchments with high rainfall or low evapo-transpiration underlain with granites or basalt tend to give high baseflow. Within the topographical parameters tested, drainage density index has strong relationship with BFI. The approach used in this paper provides a viable alternative for baseflow estimation on ungauged semi-arid catchments using drainage density, geology and climate indices as key factors. # 2002 Elsevier Science Ltd. Keywords: data-based mechanistic modelling; baseflow index; physical catchment indices; multiple regression; semi-arid environments Introduction Baseflow is one of the most important low-flow hydrological characteristics of a catchment in semi-arid environments. Knowledge of low-flow characteristics is important for a number of reasons, including the development of water management strategies, especially for drought conditions; the establishing of relationships between aquatic organisms and their environment; the estimation of small to medium water supplies; and the management of salinity, water quality and algal blooms. However, baseflow is a function of a large number of catchment properties that include topographic, geologic, soil and climatic properties. The effects of these properties on baseflow can be evaluated through relationships between catchment properties and baseflow. *Corresponding author. Fax: +32-16-329760. E-mail: mwakalila@hotmail.com 0140-1963/02/020245 + 14 $35.00/0 # 2002 Elsevier Science Ltd. Journal of Arid Environments (2002) 52: 245–258 doi:10.1006/jare.2001.0947, available online at http://www.idealibrary.com on