Abstract In the southwestern United States, post-fire debris flows commonly initiate during short bursts of intense rainfall. To date, the frequency of the rainfall rates has not been quantified. Here, we combine an existing database of debris-flow occurrences and corresponding peak storm intensities with a geospatial library of rainfall recurrence interval (RI) information and climate type to determine the distribution of the estimated frequencies of the rainfall associated with 316 observed post-fire debris flows in the southwestern United States. Our results indicate that a majority (77%) of the observed debris flows were triggered by rainfall intensities with RI less than 2 years. Climatic and geographic differences in RI were evident in our analysis. Debris flows in most of the analyzed climates within California, Colorado, and New Mexico were primarily associated with 1-year or less RI intensities, whereas debris flows in arid portions of Arizona, Colorado, and Utah tended to be generated during storms greater than 2-year RI. Event consequence, as defined by the impact on downstream communities and infrastructure, was not directly related to RI, as very destructive debris flows were initiated at a wide range of RI intensities. Our results highlight that post-fire debris-flow initiation can be expected during common rainstorms in the southwestern United States, therefore emergency management plans and risk mitigation efforts must focus on both extreme and frequent rainstorms.

中文翻译：

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美国西南部火灾后泥石流产生降雨的重现间隔

摘要 在美国西南部，火灾后泥石流通常在短时间的强降雨期间引发。迄今为止，降雨率的频率尚未量化。在这里，我们将现有的泥石流发生和相应峰值风暴强度数据库与降雨重现间隔 (RI) 信息和气候类型的地理空间库相结合，以确定与 316 次观察到的火灾后降雨相关的估计频率分布美国西南部的泥石流。我们的结果表明，大部分（77%）观测到的泥石流是由 RI 小于 2 年的降雨强度引发的。在我们的分析中，RI 的气候和地理差异很明显。在加利福尼亚州、科罗拉多州、和新墨西哥州主要与 1 年或更短的 RI 强度有关，而亚利桑那州、科罗拉多州和犹他州干旱地区的泥石流往往是在大于 2 年 RI 的风暴期间产生的。事件后果，定义为对下游社区和基础设施的影响，与 RI 没有直接关系，因为在各种 RI 强度下引发了极具破坏性的泥石流。我们的结果强调，火灾后泥石流在美国西南部的常见暴雨期间可能会发生，因此应急管理计划和风险缓解工作必须同时关注极端和频繁的暴雨。事件后果，定义为对下游社区和基础设施的影响，与 RI 没有直接关系，因为在各种 RI 强度下引发了极具破坏性的泥石流。我们的结果强调，火灾后泥石流在美国西南部的常见暴雨期间可能会发生，因此应急管理计划和风险缓解工作必须同时关注极端和频繁的暴雨。事件后果，定义为对下游社区和基础设施的影响，与 RI 没有直接关系，因为在各种 RI 强度下引发了极具破坏性的泥石流。我们的结果强调，火灾后泥石流在美国西南部的常见暴雨期间可能会发生，因此应急管理计划和风险缓解工作必须同时关注极端和频繁的暴雨。