The impact of drought on water resources in arid and semiarid regions can be buffered by water supplies from different source regions. Simultaneous drought in all major source regions — or perfect drought — poses the most serious challenge to water management. We examine perfect droughts relevant to Southern California (SoCal) water resources with instrumental records and tree‐ring reconstructions for the Sacramento and Colorado Rivers, and SoCal. Perfect droughts have occurred five times since 1906, lasting two to three years, except for the most recent event, 2012–2015. This number and duration of perfect droughts is not unusual in the context of the past six centuries. The modern period stands out for the relatively even distribution of perfect droughts and lacks the clusters of perfect drought documented in prior centuries. In comparison, perfect droughts of the 12th Century were both longer (up to nine years) and more widespread. Perfect droughts of the 20th and 21st Centuries have occurred under different oceanic/atmospheric patterns, zonal and meridional flow, and ENSO or non‐ENSO conditions. Multidecadal coherence across the three regions exists, but it has varied over the past six centuries, resulting in irregular intervals of perfect drought. Although the causes of perfect droughts are not clear, given the long‐term natural variability along with projected changes in climate, it is reasonable to expect more frequent and longer perfect droughts in the future.

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对南加州供水的远景：再遇完美干旱

干旱和半干旱地区干旱对水资源的影响可以通过来自不同水源地区的供水来缓解。所有主要水源地区的同时干旱（或完全干旱）对水资源管理构成了最严重的挑战。我们通过仪器记录和萨克拉曼多和科罗拉多河以及SoCal的树轮重建研究了与南加州（SoCal）水资源有关的完美干旱。自1906年以来，完全干旱发生了五次，持续了两到三年，最近的一次干旱是2012-2015年。在过去的六个世纪中，完全干旱的次数和持续时间并不罕见。现代时期以完美干旱的相对均匀分布而著称，并且缺乏前几个世纪记载的完美干旱集群。相比下，12世纪的完美干旱既更长（长达9年），也更加广泛​​。在不同的海洋/大气模式，纬向和经向流量以及ENSO或非ENSO条件下，发生了20世纪和21世纪的完美干旱。在这三个地区都存在多年代的连贯性，但在过去的六个世纪中它一直在变化，从而导致不规则的完美干旱间隔。尽管尚无完全干旱的原因尚不清楚，但考虑到长期的自然变异性以及预计的气候变化，合理的预期是未来会出现更频繁，更长的完全干旱。纬向和经向流动，以及ENSO或非ENSO条件。在这三个地区都存在多年代的连贯性，但在过去的六个世纪中它一直在变化，导致不规则的完美干旱间隔。尽管尚无完全干旱的原因尚不清楚，但考虑到长期的自然变异性以及预计的气候变化，合理的预期是未来会出现更频繁，更长的完全干旱。纬向和经向流动，以及ENSO或非ENSO条件。在这三个地区都存在多年代的连贯性，但在过去的六个世纪中它一直在变化，从而导致不规则的完美干旱间隔。尽管尚无完全干旱的原因尚不清楚，但考虑到长期的自然变异性以及预计的气候变化，合理的预期是未来会出现更频繁，更长的完全干旱。