In this work, we compare the rate of warming of summertime extreme temperatures (summer maximum value of daily maximum temperature; TXx) relative to the local mean (summer mean daily maximum temperature; TXm) over the Northern Hemisphere in observations and one set of large ensemble (LE) simulations. During the 1979–2021 historical period, observations and simulations show robust warming trends in both TXm and TXx almost everywhere in the Northern Hemisphere, except over the eastern U.S. where observations show a slight cooling trend in TXx, which may be a manifestation of internal variability. We find that the observed warming rate in TXx is significantly smaller than in TXm in North Africa, western North America, Siberia, and Eastern Asia, whereas the warming rate in TXx is significantly larger over the Eastern U.S., the U.K., and Northwestern Europe. This observed geographical pattern is successfully reproduced by the vast majority of the LE members over the historical period, and is persistent (although less intense) in future climate projections over the 2051–2100 period. We also find that these relative warming patterns are mostly driven by the local hydroclimate conditions. TXx warms slower than TXm in the hyper-arid, arid, semi-arid and moist regions, where trends in the partitioning of the turbulent surface fluxes between the latent and sensible heat flux are similar during regular and extreme hot days. In contrast, TXx warms faster than TXm in dry-subhumid regions where trends in the partitioning of the surface fluxes are significantly different between regular and extreme hot days, with a larger role of sensible heat flux during the extreme hot days.

中文翻译：

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当地水文气候导致北半球正常夏季和极端炎热天气之间的升温速度存在差异


在这项工作中，我们比较了北半球夏季极端气温（夏季每日最高温度的最大值；TXx）相对于当地平均值（夏季平均每日最高温度；TXm）的升温速率和一组大型观测数据。集成（LE）模拟。在1979-2021年的历史时期，观测和模拟显示北半球几乎所有地方的TXm和TXx都有强劲的变暖趋势，除了美国东部，观测显示TXx有轻微的降温趋势，这可能是内部变异的表现。我们发现，在北非、北美西部、西伯利亚和东亚，观测到的 TXx 的变暖速率明显小于 TXm，而美国东部、英国和西北欧的 TXx 的变暖速率明显更大。这种观察到的地理模式在历史时期被绝大多数 LE 成员成功复制，并且在 2051-2100 年期间的未来气候预测中持续存在（尽管不那么强烈）。我们还发现这些相对变暖模式主要是由当地的水文气候条件驱动的。在超干旱、干旱、半干旱和潮湿地区，TXx 的升温速度比 TXm 慢，在正常和极端炎热的日子里，表面湍流通量在潜热通量和感热通量之间的分配趋势相似。相比之下，在干燥半湿润地区，TXx 比 TXm 变暖得更快，这些地区的地表通量分配趋势在正常天气和极端炎热天气之间显着不同，在极端炎热天气期间，感热通量的作用更大。