Identification of basin characteristics influencing spatial variation of river flows Dominic Mazvimavi a, * , Saskia L.G.E. Burgers b , Alfred Stein b,c a Department of Geography & Environmental Science, University of Zimbabwe, P.O. Box MP167, Mt. Pleasant, Harare, Zimbabwe b Biometris, P.O. Box 100, 6700 AC, Wageningen, The Netherlands c International Institute for Geo-Information Science and Earth Observation, Hengelosestraat 99, P.O. Box 6, 7500AA, Enschede, The Netherlands Received 31 January 2004; accepted 12 August 2005 Abstract The selection of basin characteristics that explain spatial variation of river flows is important for hydrological regionalization as this enables estimation of flow statistics of ungauged basins. A direct gradient analysis method, redundancy analysis, is used to identify basin characteristics, which explain the variation of river flows among 52 selected basins in Zimbabwe. Flow statistics considered are mean annual runoff, coefficient of variation of annual runoff, average number of days per year without flow and selected percentile flows. Basin characteristics investigated are those likely to reflect climatological, topographical and hydro- geological influences including that of land cover on river flows. The first ordination axis of flow statistics is strongly correlated with mean annual precipitation, mean annual potential evaporation and median slope. This ordination axis explains 64% of the variation of selected flow statistics among the selected drainage basins. The proportions of a basin under cultivation, and that with grasslands are correlated with the second ordination axis, which explains 6% of the variation of selected flow statistics. Mean annual precipitation is the most important basin characteristic, and this alone explains 50% of the variation of flow statistics. Median slope is the second most important basin characteristic. Proportions of a basin underlain by different lithological types had no effect on flow characteristics of selected basins. The paper has demonstrated the ability of redundancy analysis to identify basin characteristics that explain the variation of river flows among basins, including estimating the relative importance of these basin characteristics. # 2005 Published by Elsevier B.V. Keywords: Redundancy analysis; Ungauged basins; Regionalization 1. Introduction The identification of basin characteristics that influence river flows is a priority issue for hydrological regionalization studies (Simmers, 1975; Nathan and McMahon, 1990; Riggs, 1990). Knowledge of basin characteristics which significantly affect hydrological responses at various scales and in different environmental settings will improve the understanding of hydrological processes. This will also enhance our ability to solve water resources planning and management problems. The improvement of both the science and applied aspects of predicting in ungauged basins has been recognized as a major scientific challenge. Hence, the International Association of Hydrological Sciences adopted in 2002 Prediction in Ungauged Basins (PUB) as a decadal research programme (Sivapalan, 2003). www.elsevier.com/locate/jag International Journal of Applied Earth Observation and Geoinformation 8 (2006) 165–172 * Corresponding author. E-mail addresses: dmazvimavi@orc.ub.bw (D. Mazvimavi), saskia.burgers@wur.nl (Saskia L.G.E. Burgers), stein@itc.nl (A. Stein). 0303-2434/$ – see front matter # 2005 Published by Elsevier B.V. doi:10.1016/j.jag.2005.08.006