Rainfall redistribution by plant canopy, notably the water flow down the plant stem (stemflow), modifies
the incident rainfall rate at the soil surface and may affect runoff generation. To test this hypothesis, we
observed and measured runoff at the plant scale with banana cultivated on tropical Andosol. Observation
of runoff by video and matrix potential monitoring showed that, during a runoff event, the matrix potential
increased mainly downstream from the pseudostem in line with the slope, delimiting a saturated
zone of runoff propagation that appeared on video monitoring. The results indicate that rainfall redistribution
by plant canopy, i.e. stemflow and dripping areas, enhances runoff even on soil with a high infiltration
rate (mean hydraulic conductivity at saturation Ks of 67 mm h1
). Data analysis of 40 runoff
events showed that events were composed of at least two runoff phases characterized by an abrupt
increase in runoff coefficient (RC) from 0.16 to 0.65 between the first and the second phase. The change
in RC was related to rainfall rate. Also, between the first and the second runoff phase, the apparent infiltration
rate at the plot scale decreased from 30 to 10 mm h1
. This was related to an increase in runoff
contributing areas (RCA), from an estimated 18% to 93% of the plot surface. However, data analysis and
model simulations showed that the increase in mean rainfall rate in RCA due to stemflow was not suffi-
cient to account for large runoff volumes. Hence, one must also take into account the spatial variation of
hydraulic conductivity at saturation with low values relative to RCA (estimation for the second runoff
phase was 7.6 mm h1
). Moreover, simulation results implied Ks decreases with time. Finally, rainfall
redistribution may have an impact at a larger scale. In banana plantations, the hydraulic connectivity
of runoff areas can enhance the stemflow effect up to the plot scale. From this point of view, the twocompartment
scheme we chose for modeling could be applied at a larger scale: one compartment including
stemflow and the relative water pathways and one compartment for the rest of the plot.