Duration and intensity of rainfall events with the same erosivity change sediment yield and runoff rates

The effect of different rainfall patterns on surface runoff, infiltration and thus soil losses and sediment concentrations are still in the focus of current research. In most simulated rainfall experiments, precipitation is applied at a fixed intensity for a fixed time. However, the impact of rainfall patterns on soil erosion processes may be different varying the rainfall duration and intensity that produces an event with similar rainfall erosivity values. Twenty-five rainfall events were applied on micro-scale runoff plots in a soil covered with corn straw to evaluate the sediment yield and runoff rates. The different rainfall types were composed by association of duration (Dur) and intensity (IP) with the same erosivity value. The Dur varied from 38 to 106 min and the IP varied from 75.0 to 44.6 mm h-1. The sediment yield varied from 1.89 ± 1.26 g m-2 to 4.02 ± 2.66 g m-2 and runoff ranged from 16.9 ± 8.74 mm to 32.63 ± 10.67 mm with highest rates occurring with high intensity and low duration. The highest rainfall intensity provides the maximum sediment yield (0.138 g m-2 min-1) and runoff rates (0.87 mm min-1). The time to start surface runoff varied from 14 to 19.2 min and it was longer in treatments with longer durations and low precipitation intensity. No difference was found in the amount of sediments applying rain with the same erosivity and different associations of duration and intensity. However, the intensity and duration of the rain, with the same erosivity, altered the amount and time of runoff. In rainfall experiments with constant intensity and fixed time, the erosion rates depend on the duration of the applied rain. Therefore, the results of this study can contribute to the development of new perspectives in the design of water erosion experiments with simulated rain considering the duration, intensity and also the association of these variables to produce rainfall that delivery the same soil erosion capacity.