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).