Mendenhall Fellow at the USGS Pacific Coastal and Marine Science Center
Dr. Helen Willemien Dow (maiden name: Beeson)
How has climate change and the associated changes in wildfire regime altered spatial and temporal patterns in erosion and sediment yield across California and how will this change in the future?
Global climate change is projected to have dramatic impacts on California’s hydroclimate. This includes compression of the rainy season into November-March, an increased frequency of both extremely wet and dry years as well as an increased frequency of precipitation whiplash, in which hydrology swings from one extreme to another. The western US has also seen a twofold increase in the number of fires and a fourfold increase in median annual area burned as fire regime has shifted in recent decades, and the number of days with extreme fire weather is predicted to increase even further with ongoing climate change. How these changes in hydroclimate and wildfire impact California’s landscapes through time is currently poorly understood. Post-wildfire studies reveal that wildfire greatly facilitates erosion via changes to vegetation and soil properties, with particularly extreme erosion observed when wet years follow wildfire. This suggests that the spatial and temporal patterns of post-wildfire erosion across the state may carry additional signatures of global climate change, with potential impact on water resources, aquatic and riparian ecosystems, and near-shore environments.
To quantify the potential impacts of post-wildfire erosion across California, I am applying two models to wildfire-affected regions for the first water year post-fire: 1) the Water Erosion Prediction Project (WEPP) model, which is a process-based model that simulates hillslope and channel erosion but does not simulate post-fire landslides or debris flows, and 2) an empirical model for debris flow probability and flow volume developed by the USGS Landslide Hazards Program. I am starting with fires in 2020 and working back in time, generating estimates of sediment yield for each wildfire as the sum of sediment yield predicted by WEPP and by debris flows for a range of debris flow probabilities.
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A second component of this research leverages existing climate forecasts to model erosion in small- to moderate-sized watersheds in coastal California to examine how terrestrial sediment supply to nearshore environments will change with changing hydroclimate over the coming decades.
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