Soil erosion before and after wildfire
The long-term simulation revealed that nearly 99 percent of the study area experienced an estimated average annual erosion rate less than 0.25 Mg ha-1 before the fire. When burned, erosion risk increased considerably (Figure 2). 77.6 percent of the burned area had predicted sediment yields greater than 4 Mg ha-1yr-1 (Table 2). After the fire, only 19 percent of the area had estimated sediment yields less than 0.25 Mg ha-1. Table 2 shows the distribution of predicted post-fire sediment yield for different burn severities. The high and moderate severity categories account for 46 percent and 29 percent respectively of the total study area, but accounted for 86.8 percent of the highest erosion class. 56.3 percent of the highest sediment yield pixels (> 4 Mg ha-1y-1) were associated with the high burn severity. The low burn severity and unburned land account for 25 percent of the total area but only 13.2 percent of the area with a predicted erosion rates greater than 4 Mg ha-1 yr-1. The low and unburned areas accounted for 67.8 percent of the total lowest sediment yield category (<0.25 Mg ha-1y-1) in the study area.
The underlying topography also influences the predicted soil erosion rates. (Figure 2) On long hillslopes the high erosion rates were predicted to extended beyond the fire boundary in some cases. Road segments intercepted the flow, constraining areas of high sediment yields. In some cases, the sediment yield levels in the patches below a road were lower than that of the adjacent hillslope segment above the road (Figure 2).