Amid reports from western US wildland fire managers that, compared to when many started their careers, fires are burning longer throughout the day before reducing in intensity overnight, we examined decadal changes in nighttime vapor pressure deficits over the western United States with a focus on the summer fire season. We calculated changes using a recently updated observation-assimilating reanalysis (ERA5) available at hourly resolution over the 1980–2019 period. Analysis identifies the proximate cause (atmospheric temperature vs. moisture content) of the observed changes and the extent to which they have been captured in climate model simulations. Increases in nighttime vapor pressure deficits of >50% in 40 years are evident over foothills of mountains ranges adjacent to arid plateaus. The largest observed increases greatly exceed the forced climate-model response. Correlation analysis reveals a broad link between the variability of western US summer-nighttime vapor pressure deficit and the Pacific Decadal Oscillation.

中文翻译：

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美国西部夜间蒸汽压差的多年变化

根据美国西部荒地火灾管理人员的报告，与许多人开始职业生涯时相比，火灾在一天中燃烧的时间更长，然后在一夜之间减弱，我们研究了美国西部夜间蒸汽压差的十年变化，重点是夏季火灾季节。我们使用最近更新的观测同化再分析 (ERA5) 计算了 1980-2019 年期间每小时分辨率的变化。分析确定了观察到的变化的近因（大气温度与水分含量）以及它们在气候模型模拟中被捕获的程度。40 年来夜间水汽压亏缺增加了 50% 以上，这在与干旱高原相邻的山脉山麓上很明显。观察到的最大增加大大超过了强制气候模型响应。相关性分析揭示了美国西部夏夜蒸汽压差的可变性与太平洋年代际振荡之间的广泛联系。