Geological evidence from the last millennium indicates that multidecadal megadroughts may have occurred simultaneously in California and Patagonia at least once. However, it is unclear whether or not megadroughts were common in South America, whether or not simultaneous megadroughts in North and South America occurred repeatedly, and what would cause their simultaneous occurrence. Here we use a data-assimilation-based global hydroclimate reconstruction, which integrates palaeoclimate records with constraints from a climate model, to show that there were about a dozen megadroughts in the South American Southwest over the last millennium. Using dynamical variables from the hydroclimate reconstruction, we show that these megadroughts were driven by the El Niño/Southern Oscillation (ENSO). We also find that North American Southwest and South American Southwest megadroughts have occurred simultaneously more often than expected by chance. These coincident megadroughts were driven by an increased frequency of cold ENSO states relative to the last millennium-average frequency. Our results establish the substantial risk that exists for ENSO-driven, coupled megadroughts in two critical agricultural regions.

上个千年的地质证据表明，加州和巴塔哥尼亚可能至少同时发生了一次多十年的特大干旱。然而，目前尚不清楚特大干旱在南美洲是否普遍，北美和南美同时发生的特大干旱是否反复发生，以及是什么导致它们同时发生。在这里，我们使用基于数据同化的全球水文气候重建，将古气候记录与气候模型的限制相结合，以表明在过去的一千年中，南美西南部发生了大约十几个特大干旱。使用来自水文气候重建的动态变量，我们表明这些特大干旱是由厄尔尼诺/南方涛动 (ENSO) 驱动的。我们还发现，北美西南地区和南美西南地区的特大干旱同时发生的频率比偶然预期的要高。这些同时发生的特大干旱是由相对于上个千年平均频率增加的冷 ENSO 状态频率驱动的。我们的研究结果确定了在两个关键农业地区 ENSO 驱动的耦合特大干旱存在的重大风险。