THE IMPACT OF WILDFIRES ON HILLSLOPE HYDROLOGY IN THE BLUE RIDGE MOUNTAINS OF NORTH CAROLINA, USA

Wildfires in mountainous regions have been documented to create hydrophobic soils which can increase runoff during subsequent rain events. This exceptional discharge can impact downstream communities and ecosystems with flooding and debris flows. However, the extent of soil hydrophobicity varies significantly with burn severity and between ecosystems. Here we examine the impact of low intensity wildfires on soils and runoff in the Blue Ridge of North Carolina. To examine these impacts, we installed crest-stage gauges in burned and unburned colluvial hollows after the Chestnut Knob Fire which occurred in South Mountains State Park in the fall of 2016. Results from the 2017 field season indicated that burned locations were producing much greater maximum runoff discharges than comparable unburned sites. From July to November 2019, we repeated the experiment using similar methods and found that burned areas had recovered and now produce runoff similar to unburned areas. In fact, many hollows never produced runoff discharge at all, even during rain storms with high intensity and magnitude. Our examinations of soil morphology suggest that increased hydrophobicity and decreased soil moisture capacity in upper horizons are likely the cause but decreased evapotranspiration may also play a role. The relatively fast recovery highlighted in this study is important in understanding the duration of increased debris flow risk in the Blue Ridge.