Rainfall simulation data associated with JFSP Project 22-1-01-17

Mulch application following wildfire is increasingly being used to mitigate hillslope runoff and erosion. A mulch coverage of 70% has been proven to be effective in reducing sediment losses; however, most previous studies test only a single slope and rainfall regime when evaluating mulch type and coverage. Experimental studies across a wider range of slopes and rainfall intensities are needed to help identify hillslopes that will respond best to mulching at this coverage. The purpose of this study is to experimentally investigate the percent reduction of runoff and sediment yields with mulching for a wide range of slopes and rainfall intensities using slope-model rainfall simulations. We conducted experiments on a 1 m2 inclined plot with a full cone nozzle lifted 3 m above the plot. We tested two slopes (20% and 40%) at three different rainfall intensities (30, 60, 90 mm/h for 20 min) for 0% and 70% mulch coverage. Mulch was effective at all tested slopes and intensities, reducing 76-100% of the unmulched simulations’ sediment yields. Mulch reduced sediment losses 12% more on the higher slope (40%) compared to the lower slope (20%). Although there was not a large difference between sediment reduction percentages across rainfall intensities, mulch reduced sediment yields the most during the lowest rainfall intensity of 30 mm/h. Runoff was not reduced between the mulched and bare soil conditions, which we attribute to pre-wetting the plot to saturation. Our study supplements previous research demonstrating that mulch effectively reduces sediment yield at the plot scale across the range of rainfall intensities. We recommend prioritizing mulch on steep slopes (> 40%) expected to experience 20-minute rainfall intensities greater than 30 mm/h, along with shallower slopes where downstream values may be at risk.