UCLA

Wildfires alter land surfaces and land-atmosphere interactions, causing enhanced runoff and debris flows. The current study evaluates hydrologic behavior and recovery for three watersheds in the burned in the 2010 Bull Fire in the southern Sequoia National Forest. One unburned watershed was selected outside the fire perimeter for a control. The effects of wildfires have been extensively analyzed, but these studies typically focus on debris flows immediately following the fire and vegetation recovery on a plot-scale. This study attempts to evaluate hydrologic recovery through in-situ instruments in areas analyzed by a United States Forest Service Burned Area Emergency Response team. Many agencies attempt to predict post-fire runoff peaks and volumes to identify values-at-risk and determine if protective measures must be implemented. The four study sites are instrumented with tipping buckets and pressure transducers to measure precipitation and discharge throughout the approximate two year study period. Stream discharge is measured at five-minute intervals, the tipping buckets are event-based to track storm duration and intensity, and channel cross-sections are measured every two months to detail sediment deposition or scour that accompany rainfall-runoff events. Precipitation was found to be consistent between the study areas, but a link between precipitation and cross-section area changes was not determined. Geomorphic parameters were evaluated with an area-normalized discharge to determine correlations. Aspect, soil type, and watershed shape were found to be the controlling factors in elevated discharge. To judge watershed recovery, the response lag, lag-to-peak, and runoff ratio were calculated for 13 selected storms across all study sites. Variability of each parameter was determined to depend on the precipitation tipping bucket location and the time between storms. Recovery was unable to be determined based on the three rainfall-runoff hydrograph parameters. Future work involves relating a remote sensing vegetation index with the storm parameters to couple vegetation recovery with hydrologic recovery and gain insight into watershed recovery on a storm-by-storm basis.