Assessing the Potential Impact of the 2015-2016 El Niño on the California Rim Fire Burn Scar Through Debris Flow Hazard Mapping

Abstract:

Wildfires are a perennial issue for California, and the current record-breaking drought is exacerbating the potential problems for the state. Fires leave behind burn scars characterized by diminished vegetative cover and abundant bare soil, and these areas are especially susceptible to storm events that pose an elevated risk of debris flows and sediment-rich sheet wash. This study focused on the 2013 Rim Fire that devastated significant portions of Stanislaus National Forest and Yosemite National Park, and utilized readily available NASA JPL SRTM elevation data and AVIRIS spectral imaging data to construct a debris flow hazard map that assesses mass wasting risk for the Rim Fire burn scar. This study consisted entirely of remotely sensed data, which was processed in software programs such as ENVI, GRASS GIS, ArcMap, and Google Earth. Parameters that were taken into consideration when constructing this map include hill slope (greater than 30 percent rise), burn severity (assessed by calculating NDVI), and erodibility of the soil (by comparing spectral reflectance of AVIRIS images with the reference spectra of illite). By calculating percent of total burn area, 6% was classified as low risk, 55% as medium risk, and 39% as high risk. In addition, this study assessed the importance of the 2015-2016 El Niño, which is projected to be one of the strongest on record, by studying historic rainfall records and storm events of past El Niño's. Hydrological and infrastructural problems that could be caused by short-term convective or long-term synoptic storms and subsequent debris flows were explored as well.