An increase in winter air temperature can amplify snowmelt and sublimation in mountain regions with implications to water resources and ecological systems. Winter Warm Spells (WWS) are defined as a winter period (December to February, DJF) of at least 3 consecutive days with daily maximum temperature anomaly above the 90th percentile (using a moving-average of 15 days between 2001 and 2013). We calculate WWS for every 4-km grid cell within an atmospheric model over western North America to characterize WWS and analyze snow ablation and their changes in a warmer climate. We find that days with ablation during WWS represent a small fraction of winter days (0.6 days), however, 49% of total winter ablation (33.4 mm/DJF) occurs during WWS. Greater extreme ablation rates (99th percentile) occur 18% more frequently during WWS than during non-WWS days. Ablation rates during WWS in humid regions are larger (9 mm d⁻¹) than in dry regions (7 mm d⁻¹) in a warmer climate, which can be explained by differences in the energy balance and the snowpack's cold content. We find that warmer (0.8°C), longer (1.8 days) and more frequent (3.7 more events) WWS increase total winter ablation (on average 109% or 18 mm/DJF) in a warmer climate. Winter melt during WWS in warm and humid places is expected to increase about 3 times more than in the cold and dry region. This study provides a comprehensive description of WWS and their impact on snowpack dynamics, which is relevant to reservoir operations and water security.

中文翻译：

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冬季暖期变化对北美西部积雪消融的影响

冬季气温升高会加剧山区的融雪和升华，对水资源和生态系统产生影响。冬季暖流 (WWS) 被定义为至少连续 3 天每日最高气温距平超过 90% 的冬季（12 月至 2 月，DJF）（使用 2001 年至 2013 年 15 天的移动平均值）。我们计算北美西部大气模型中每个 4 公里网格单元的 WWS，以表征 WWS 并分析在温暖气候下的积雪消融及其变化。我们发现 WWS 期间发生消融的天数只占冬季日数的一小部分（0.6 天），然而，冬季总消融的 49% (33.4 mm/DJF) 发生在 WWS 期间。 WWS 期间发生的极端消融率（第 99 个百分位）比非 WWS 期间发生的频率高 18%。在气候温暖的情况下，潮湿地区WWS期间的消融率（9 mm d ^-1）比干燥地区（7 mm d ^-1）大，这可以通过能量平衡和积雪冷量的差异来解释。我们发现，在温暖的气候下，更温暖（0.8°C）、更长（1.8 天）和更频繁（3.7 个事件）的 WWS 会增加冬季总消融（平均 109% 或 18 毫米/DJF）。预计温暖湿润地区冬季融化量将比寒冷干燥地区增加约 3 倍。这项研究全面描述了 WWS 及其对积雪动态的影响，这与水库运行和水安全相关。