We present the first description of summer stream thermal regimes in Alaska using metrics that represent the magnitude, variability, frequency, duration, and timing of temperature events related to salmon life histories. We used cluster analysis to characterize thermal regimes present in the Matanuska‐Susitna (Mat‐Su) Basin based on 10 nonredundant temperature metrics and identified the most important drivers of our thermal regimes using random forests. Our results indicated four distinct thermal regimes among the 248 site‐years in the Mat‐Su Basin. Over 41% of site‐years had cold‐stable temperatures. An additional 22% of site‐years had cold‐variable temperatures and the latest timing of maximum stream temperatures. Twenty‐eight percent of site‐years had warm‐variable temperatures that remained above 13°C for approximately two months. The remaining 9% of site‐years had the warmest and most variable daily maximum temperatures, exceeding 18°C for almost one month, indicating potential impacts to spawning and rearing salmon. Climate and landscape drivers differentiating thermal regimes included spring and summer air temperatures, spring snowpack, summer precipitation, wetlands, and lakes. Climate change projections for 2050–2069 indicated a future shift toward warm thermal regimes and a reduced portfolio of thermal diversity. These results portend negative impacts to some salmon populations and stress the importance of prioritizing actions that maintain thermal regime diversity.

中文翻译：

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阿拉斯加马塔努斯卡-苏西特纳盆地鲑鱼流的热多样性

我们使用表示鲑鱼生活史相关温度事件的大小，变异性，频率，持续时间和时间的度量标准，对阿拉斯加的夏季溪流热态进行首次描述。我们使用聚类分析基于10个非冗余温度指标来表征Matanuska-Susitna（Mat-Su）盆地中的热态，并使用随机森林确定了我们热态的最重要驱动因素。我们的结果表明，在Mat-Su盆地的248个站点年中，有四种不同的热态。超过41％的站点年温度为低温稳定。在现场使用年限中，另有22％的温度是冷变化的，并且是最高河流温度的最新时间。28％的站点年的温度可变温度大约在两个月内保持在13°C以上。剩余的9％的站点年份的每日最高温度最高，且变化最大，连续近一个月超过18°C，这表明可能对鲑鱼的产卵和饲养产生影响。区分热力状况的气候和景观驱动因素包括春季和夏季的气温，春季的积雪，夏季的降水，湿地和湖泊。对2050年至2069年的气候变化预测表明，未来将朝着温暖的热态转变，并减少了热多样性。这些结果预示了对一些鲑鱼种群的负面影响，并强调了优先采取措施维持热态多样性的重要性。区分热力状况的气候和景观驱动因素包括春季和夏季的气温，春季的积雪，夏季的降水，湿地和湖泊。对2050年至2069年的气候变化预测表明，未来将朝着温暖的热态转变，并减少了热多样性。这些结果预示了对一些鲑鱼种群的负面影响，并强调了优先采取措施维持热态多样性的重要性。区分热力状况的气候和景观驱动因素包括春季和夏季的气温，春季的积雪，夏季的降水，湿地和湖泊。对2050年至2069年的气候变化预测表明，未来将朝着温暖的热态转变，并减少了热多样性。这些结果预示了对一些鲑鱼种群的负面影响，并强调了优先采取措施维持热态多样性的重要性。