Post-fire erosion and debris flows in the western Pacific Northwest, United States: recent science and opportunities

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Most research into post-fire geomorphology has been conducted in regions with frequent fire, such as in dry Mediterranean and temperate climates and less has been conducted in wet forests where wildfire is now expanding with climate change. Because climate, soils, topography, vegetation, management legacies and fire history influence post-fire geomorphic processes, research into post-fire erosion and debris flow hazards across a broader set of climatologies is needed. The western Pacific Northwest (wPNW) of the United States is susceptible to multiple types of post-fire debris flows (i.e. shallow landslide-initiated and runoff-generated) that can be initiated by longer-duration lower-intensity rainfall compared to other regions in the western US. Therefore, knowledge of how wildfire impacts geomorphic processes in drier, more frequently burned regions does not necessarily apply to the wetter wPNW climate. Significant gaps in data coverage remain a key limitation for predictive modeling and empirical studies in this region. This review synthesizes the current state of post-fire geomorphic knowledge and identifies gaps in data and understanding for the wPNW. These gaps and opportunities for future work can help expand knowledge and evaluate assumptions about post-fire geomorphology in other regions, such as those with similar pyro-climatology and others not yet well represented by current post-fire geomorphology research.