Despite the recent prevalence of severe drought, California faces a broadly underappreciated risk of severe floods. Here, we investigate the physical characteristics of “plausible worst case scenario” extreme storm sequences capable of giving rise to “megaflood” conditions using a combination of climate model data and high-resolution weather modeling. Using the data from the Community Earth System Model Large Ensemble, we find that climate change has already doubled the likelihood of an event capable of producing catastrophic flooding, but larger future increases are likely due to continued warming. We further find that runoff in the future extreme storm scenario is 200 to 400% greater than historical values in the Sierra Nevada because of increased precipitation rates and decreased snow fraction. These findings have direct implications for flood and emergency management, as well as broader implications for hazard mitigation and climate adaptation activities.

中文翻译：

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气候变化正在增加加州特大洪水的风险

尽管最近发生了严重干旱，但加利福尼亚面临严重洪水的风险被广泛低估。在这里，我们结合气候模型数据和高分辨率天气模型，研究能够引发“特大洪水”条件的“可能的最坏情况”极端风暴序列的物理特征。使用来自社区地球系统模型大型集合的数据，我们发现气候变化已经使能够产生灾难性洪水的事件的可能性增加了一倍，但未来更大的增长可能是由于持续变暖。我们进一步发现，由于降水率增加和降雪量减少，未来极端风暴情景中的径流比内华达山脉的历史值高 200% 到 400%。