Hydroclimatic swings between dry and wet spells are increasing globally, raising concerns due to their severe impacts on society, agriculture, infrastructure systems, and water resource management. These extremes and their projected changes are traditionally assessed in isolation, which can underestimate associated risks and future resilience and adaptation plans. This study investigates climate change projections of such lagged compound dry and wet spells across North America using a single model initial-condition large ensemble (SMILE). Three dry-wet spell indices are merged into an integrated indicator to provide a comprehensive perspective on changing risks. We apply an ensemble pooling approach using the Canadian Regional Climate Model version 4 Large Ensemble (CanRCM4-LE) to enhance sample size for index estimation. Results suggest that hydroclimatic swings across North America are expected to become more frequent and intensified in a warmer climate. Trends of spatial fraction and aggregation during transitions between dry and wet spells indicate future water resource management challenges. Hot spots for intensified transitions with higher frequency, such as Northern Central America, and the southern part of Eastern and Western North America, including Mexico and the state of California, overlap with larger spatial extent and higher aggregation during transitions. The seasonal analysis of spatial characteristics indicates winter may become wetter and summer drier at higher warming levels, potentially intensifying transitions between dry and wet extremes. Clustered hydroclimatic swings may lead to severe environmental, hydrological, and socio-economic consequences, necessitating appropriate mitigation and adaptation measures.

中文翻译：

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水文气候波动的风险上升：北美干湿期转变的大型整体研究


全球干湿期之间的水文气候波动正在加剧，因其对社会、农业、基础设施系统和水资源管理的严重影响而引起人们的关注。传统上，这些极端情况及其预计的变化是孤立评估的，这可能会低估相关风险以及未来的恢复力和适应计划。这项研究使用单一模型初始条件大集合 (SMILE) 调查了北美地区此类滞后复合干湿期的气候变化预测。三个干湿期指数合并为一个综合指标，为不断变化的风险提供全面的视角。我们采用加拿大区域气候模型第 4 版大型集合 (CanRCM4-LE) 的集合池方法来增强指数估计的样本量。结果表明，在气候变暖的情况下，整个北美的水文气候波动预计将变得更加频繁和加剧。干湿交替期间的空间分数和聚集趋势表明了未来水资源管理的挑战。转变频率较高的强化热点地区，如中美洲北部、北美东西部南部地区，包括墨西哥和加利福尼亚州，在转变过程中重叠空间范围更大、聚集程度更高。空间特征的季节性分析表明，在较高的变暖水平下，冬季可能会变得更加潮湿，夏季可能会变得更加干燥，这可能会加剧极端干旱和极端潮湿之间的转变。集中的水文气候波动可能会导致严重的环境、水文和社会经济后果，需要采取适当的缓解和适应措施。