Numerical modeling of surface runoff and erosion due to moving rainstorms at the drainage basin scale J.P. Nunes a, * , J.L.M.P. de Lima b , V.P. Singh c , M.I.P. de Lima d , G.N. Vieira a a Environmental Systems Analysis Group (GASA), Faculty of Sciences and Technology, New University of Lisbon, Quinta da Torre, 2829-516 Caparica, Portugal b IMAR – Institute of Marine Research, Coimbra Interdisciplinary Centre, Department of Civil Engineering, Faculty of Science and Technology – Campus 2, University of Coimbra, 3030-290 Coimbra, Portugal c Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, LA 70803, USA d IMAR – Institute of Marine Research, Coimbra Interdisciplinary Centre, Department of Forestry, Agrarian Technical School, Polytechnic Institute of Coimbra, Bencanta, 3040-316 Coimbra, Portugal Received 27 August 2004; received in revised form 26 April 2006; accepted 27 April 2006 Summary A physically-based distributed erosion model (MEFIDIS) was applied to evaluate the consequences of storm movement on runoff and erosion from the Alenquer basin in Portugal. Controlled soil flume laboratory experiments were also used to test the model. Nine synthetic circular storms were used, combining three storm diameters (0.5, 1 and 2 times the Alenquer basin’s axial length) with three speeds of storm movement (0.5, 1 and 2 m/s); storm intensities were synthesized in order to maintain a constant rainfall depth of 50 mm. The model was applied to storms moving downstream as well as upstream along the basin’s axis. In all tests, downstream-moving storms caused significantly higher peak runoff (56.5%) and net erosion (9.1%) than did upstream-moving storms. The consequences for peak runoff were amplified as the storm intensity increased. The hydrograph shapes were also different: for down- stream-moving storms, runoff started later and the rising limb was steeper, whereas for upstream moving storms, runoff started early and the rising limb was less steep. Both labora- tory and model simulations on the Alenquer basin showed that the direction of storm move- ment, especially in case of extreme rainfall events, significantly affected runoff and soil loss.  c 2006 Elsevier B.V. All rights reserved. KEYWORDS Soil erosion; Storm movement; Drainage basin; Numerical modeling Introduction Quantifying water erosion is a complex task, due to the great variability (spatial and temporal) of rainfall, relief, 0022-1694/$ - see front matter  c 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jhydrol.2006.04.037 * Corresponding author. Tel./fax: +351 21 294 83 74. E-mail address: jpcn@fct.unl.pt (J.P. Nunes). Journal of Hydrology (2006) 330, 709– 720 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/jhydrol