WILDLAND FIRE IMPACTS ON HILLSLOPE SURFACE RUNOFF GENERATION DURING AN EXTREME RAINFALL EVENT IN THE COLORADO FRONT RANGE

Fire-effects on hydrologic processes can result in substantial increases in surface runoff generation, which motivate post-wildfire soil-hydraulic property characterization and hydrologic modeling. Predicting wildfire disturbance impacts on runoff generation requires knowledge of the affected processes as well as the magnitude and duration of disturbance effects. Longer-term recovery and relaxation times of amplified hillslope hydrologic response after wildland fire are not as well characterized as immediate fire effects. Recovery times and conditions become especially important when extreme rainfall events affect landscapes that have partially recovered. A unique opportunity to capture such an event occurred when prolonged rainfall in September 2013 fell on a headwater catchment in Colorado, USA that had previously been burned by a wildfire in 2010 and instrumented soon after the wildfire containment. This study focuses on soil-hydraulic property effects on infiltration and indirectly-estimated peak runoff associated with the extreme rainfall. Catchment-scale simulations of runoff generation and subsurface hydrologic response during this event provide additional insight into runoff generation mechanisms. Despite over three years of recovery time since the wildfire, substantial surface runoff generation took place during the extreme rainfall event in the burned headwater hillslopes, whereas unburned headwater hillslopes had primarily subsurface runoff generation. These results suggest longer-term observations of 5-10 years following wildfire are needed to characterize the potential for disturbed hillslopes to generate enhanced surface runoff and associated sediment yields.