The Urban Heat Island (UHI), the tendency for urban areas to be hotter than rural regions, represents a significant health concern in summer as urban populations are exposed to elevated temperatures. A number of studies suggest that the UHI increases during warmer conditions, however there has been no investigation of this for a large ensemble of cities. Here we compare urban and rural temperatures in 54 US cities for 2000-2015 and show that the intensity of the urban heat island, measured here as the differences in daily-minimum or daily-maximum temperatures between urban and rural stations or ΔT, in fact tends to decrease with increasing temperature in most cities (38/54). This holds when investigating daily variability, heat extremes, and variability across climate zones and is primarily driven by changes in rural areas. We relate this change to large-scale or synoptic weather conditions, and find that the lowest ΔT nights occur during moist weather conditions. We also find that warming cities have not experienced an increasing urban heat island effect.

中文翻译：

---

在温暖条件下降低城市热岛强度

城市热岛 (UHI) 是城市地区比农村地区更热的趋势，在夏季，由于城市人口暴露在高温下，这是一个重大的健康问题。许多研究表明，在温暖的条件下，UHI 会增加，但尚未对大型城市群进行调查。在这里，我们比较了 2000 年至 2015 年美国 54 个城市的城市和农村温度，并表明城市热岛的强度，这里衡量的是城市和农村站之间的每日最低或每日最高温度或 ΔT，实际上大多数城市（38/54）随着气温升高而降低。这适用于调查气候区的日常变化、极端高温和变化，并且主要是由农村地区的变化驱动的。我们将这种变化与大规模或天气条件联系起来，并发现最低的 ΔT 夜晚发生在潮湿的天气条件下。我们还发现，变暖的城市并没有经历日益加剧的城市热岛效应。