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A partial covering mulch of residue on the soil strongly affects runoff dynamics, which consequently substantially reduces runoff amount. Experiments were conducted in la Tinaja (Mexico) on runoff plots (RPs) (20m²) of four different treatments (bare, unplanted with 1.5tha⁻¹ of residue, planted with 1.5 and 4.5tha⁻¹ of residue), to characterize mulch effects. During one crop cycle, rainfall and runoff flow were recorded at a 20s time step. Soil moisture, crop leaf area index, saturated hydraulic conductivity and sorptivity were also measured. Mulch increased the infiltration rate of the topsoil layer, concentrated overland flow and slowed it down by increasing roughness and pathway tortuosity. The physically based model developed accounts for these mulch effects on runoff. The model consists of a production and a transfer module. Each RP is considered as a micro-catchment drained by a single channel. The production …