Rainfall Thresholds for Postfire Debris-Flow Initiation Vary With Short-Duration Rainfall Climatology

IF 3.5 2区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY
David B. Cavagnaro, Scott W. McCoy, Donald N. Lindsay, Luke A. McGuire, Jason W. Kean, Daniel T. Trugman
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Abstract

The size, frequency, and geographic scope of severe wildfires are expanding across the globe, including in the Western United States. Recently burned steeplands have an increased likelihood of debris flows, which pose hazards to downstream communities. The conditions for postfire debris-flow initiation are commonly expressed as rainfall intensity-duration thresholds, which can be estimated given sufficient observational history. However, the spread of wildfire across diverse climates poses a challenge for accurate threshold prediction in areas with limited observations. Studies of mass-movement processes in unburned areas indicate that thresholds vary with local climate, such that higher rainfall rates are required for initiation in climates characterized by frequent intense rainfall. Here, we use three independent methods to test whether initiation of postfire runoff-generated debris flows across the Western United States varies similarly with climate. Through the compilation of observed thresholds at various fires, analysis of the spatial density of observed debris flows, and quantification of feature importance at different spatial scales, we show that postfire debris-flow initiation thresholds vary systematically with short-duration rainfall-intensity climatology. The predictive power of climatological data sets that are readily available before a fire occurs offers a much-needed tool for hazard management in regions that are facing increased wildfire activity, have sparse observational history, and/or have limited resources for field-based hazard assessment. Furthermore, if the observed variation in thresholds reflects long-term adjustment of the landscape to local climate, rapid shifts in rainfall intensity related to climate change will likely induce spatially variable shifts in postfire debris-flow likelihood.

Abstract Image

火灾后泥石流起始的降雨阈值随短时降水气候而变化
严重野火的规模、频率和地理范围正在全球范围内扩大,包括在美国西部。最近被烧毁的陡地发生泥石流的可能性增加,这对下游社区构成了危害。火灾后泥石流开始的条件通常表示为降雨强度-持续时间阈值,可以根据足够的观测历史来估计。然而,在观测有限的地区,野火在不同气候条件下的蔓延对准确的阈值预测提出了挑战。对未燃烧地区的物质运动过程的研究表明,阈值随当地气候的变化而变化,因此,在以频繁强降雨为特征的气候中,需要更高的降雨率才能启动。在这里,我们使用三种独立的方法来测试美国西部火灾后径流产生的泥石流的开始是否与气候相似。通过对不同火灾的观测阈值的编制、泥石流观测空间密度的分析以及不同空间尺度上特征重要性的量化,我们发现火灾后泥石流起始阈值随短时降雨强度气候学而有系统的变化。在火灾发生前随时可用的气候数据集的预测能力为面临野火活动增加、观测历史稀少和/或现场灾害评估资源有限的地区提供了急需的灾害管理工具。此外,如果观测到的阈值变化反映了景观对当地气候的长期调整,那么与气候变化相关的降雨强度的快速变化可能会导致火灾后泥石流可能性的空间变化。
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来源期刊
Journal of Geophysical Research: Earth Surface
Journal of Geophysical Research: Earth Surface Earth and Planetary Sciences-Earth-Surface Processes
CiteScore
6.30
自引率
10.30%
发文量
162
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