A probabilistic approach to modeling postfire erosion after the 2009 Australian bushfires

Major concerns after bushfires and wildfires include increased flooding, erosion and debris flows due to loss of the protective forest floor layer, loss of water storage, and creation of water repellent soil conditions. To assist postfire assessment teams in their efforts to evaluate fire effects and make postfire treatment decisions, a web-based Erosion Risk Management Tool (ERMiT) has been developed. ERMiT uses the Water Erosion Prediction Project (WEPP) model to predict postfire hillslope erosion and to evaluate the potential effectiveness of some common hillslope erosion mitigation practices. The model uses a probabilistic approach that incorporates variability in climate, soil properties, and burn severity for forests, rangeland, and chaparral hillslopes. For user specified climate, burn severity, and soil conditions, ERMiT produces a distribution of erosion rates with a likelihood of their occurrence for each of five years after the fire. ERMiT also provides single-event erosion rate distributions for hillslopes that have been treated with seed, straw mulch, and erosion barriers. ERMiT's outputs help managers establish the probability associated with a given level of sediment yield for a given location, and this information can be used along with information about the value of resources at risk and acceptable loss thresholds to make postfire erosion treatment decisions. The objectives of this paper are to describe: 1) the conceptual framework and components of the ERMiT model; and 2) an application of ERMiT from 2009 Victoria, Australia bushfires.