Landscapes following wildfire commonly have significant increases in sediment yield and debris flows that pose major hazards and are difficult to predict. Ultimately, post-wildfire sediment yield is governed by processes that deliver sediment from hillslopes to channels, but it is commonly unclear the degree to which hillslope sediment delivery is driven by wet versus dry processes, which limits the ability to predict debris-flow occurrence and response to climate change. Here we use repeat airborne lidar topography to track sediment movement following the 2009 CE Station Fire in southern California, USA, and show that post-wildfire debris flows initiated in channels filled by dry sediment transport, rather than on hillsides during rainfall as typically assumed. We found widespread patterns of 1–3 m of dry sediment loading in headwater channels immediately following wildfire and before rainfall, followed by sediment excavation during subsequent storms. In catchments where post-wildfire dry sediment loading was absent, possibly due to differences in lithology, channel scour during storms did not occur. Our results support a fire-flood model in bedrock landscapes whereby debris-flow occurrence depends on dry sediment loading rather than hillslope-runoff erosion, shallow landslides, or burn severity, indicating that sediment supply can limit debris-flow occurrence in bedrock landscapes with more-frequent fires.

中文翻译：

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上游水道的干沉积物负荷为基岩景观中的野火后泥石流提供了燃料

野火之后的景观通常会大大增加沉积物产量和泥石流，这构成了重大危害，难以预测。最终，野火后的泥沙产量受将泥沙从山坡输送到河道的过程控制，但通常尚不清楚湿法与干法驱动山坡泥沙输送的程度，这限制了预测泥石流发生和破坏的能力。应对气候变化。在这里，我们使用重复的机载激光雷达地形来追踪美国南部加利福尼亚州在2009年CE站大火之后的泥沙运动，并显示野火后的泥石流始于由干燥的泥沙输送填充的河道，而不是通常假定的降雨期间的山坡。我们发现在野火之后和降雨之前，在源头河道中有1-3 m的干燥沉积物普遍分布，随后在随后的暴风雨中挖掘了沉积物。在野火过后的干流域，由于岩性的差异，干沉积物不存在，在暴风雨中没有发生河道冲刷。我们的结果支持基岩景观中的洪水模型，其中泥石流的发生取决于干燥的沉积物负荷，而不是山坡径流侵蚀，浅层滑坡或烧伤严重程度，这表明泥沙供应可以限制基岩景观中泥石流的发生，而更多-频繁发生火灾。可能由于岩性的差异，没有在暴风雨期间发生冲刷。我们的结果支持基岩景观中的洪水模型，其中泥石流的发生取决于干燥的沉积物负荷，而不是山坡径流侵蚀，浅层滑坡或烧伤严重程度，这表明泥沙供应可以限制基岩景观中泥石流的发生，而更多-频繁发生火灾。可能由于岩性的差异，没有在暴风雨期间发生冲刷。我们的结果支持基岩景观中的洪水模型，其中泥石流的发生取决于干燥的沉积物负荷，而不是山坡径流侵蚀，浅层滑坡或烧伤严重程度，这表明泥沙供应可以限制基岩景观中泥石流的发生，而更多-频繁发生火灾。