The impacts of heat waves in a warming climate depend not only on changing temperatures but also on changing humidity. Using 35 simulations from the Community Earth System Model Large Ensemble (CESM LENS), we investigate the long‐term evolution of the joint distribution of summer relative humidity (RH) and daily maximum temperature (Tmax) near four U.S. cities (New York City, Chicago, Phoenix, and New Orleans) under the high‐emissions Representative Concentration Pathway (RCP) 8.5. We estimate the conditional quantiles of RH given Tmax with quantile regression models, using functions of temperature for each city in July for three time periods (1990–2005, 2026–2035, and 2071–2080). Quality‐of‐fit diagnostics indicate that these models accurately estimate conditional quantiles for each city. As expected, each quantile of Tmax increases from 1990–2005 to 2071–2080, while mean RH decreases modestly. Conditional upon a fixed quantile of Tmax, the median and high quantiles of RH decrease, while those of the Heat Index (HI) and dew point both increase. This result suggests that, despite a modest decrease in median relative humidity, heat stress measured by metrics considering both humidity and temperature in a warming climate will increase faster than that measured by temperatures alone would indicate. For a fixed Tmax, the high quantiles of RH (and thus of HI and dew point) increase from 1990–2005 to 2071–2080 in all four cities. This result suggests that the heat stress of a day at a given Tmax will increase in a warming climate due to the increase of RH.

中文翻译：

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变暖条件下以每日最高温度为条件的相对湿度的演变分布

热浪在气候变暖中的影响不仅取决于温度变化，而且取决于湿度变化。使用35个模拟来自社区的地球系统模式大合奏（CESM LENS），我们研究了夏季相对湿度的联合分布（RH）和日最高气温（的长期演进最高温度）附近的四个美国城市（纽约，芝加哥，凤凰城和新奥尔良）下的高排放代表浓度途径（RCP）8.5。在给定Tmax的情况下，我们估计RH的条件分位数使用分位数回归模型，使用三个月份（1990–2005、2026–2035和2071–2080）中每个城市在7月的温度函数。拟合度诊断表明，这些模型可以准确估算每个城市的条件分位数。不出所料，从1990–2005年到2071–2080年，每个Tmax分位数都增加，而平均RH则适度下降。以Tmax的固定分位数为条件，RH的中位数和高位数降低，而热指数（HI）和露点的位数和高位数均增加。该结果表明，尽管中值相对湿度略有下降，但在考虑到气候变暖的情况下通过考虑湿度和温度的指标测得的热应力将比仅通过温度测得的热应力增加更快。对于固定Tmax，在四个城市中，从RH（以及HI和露点）的高分位数从1990-2005年增加到2071-2080。该结果表明，由于RH的增加，在给定的Tmax下一天的热应激将在气候变暖的情况下增加。