北京夏季高温变化特征及对城市热岛强度的影响

Characteristics and Amplified Effect of Summer High Temperature on Urban Heat Islands in Beijing

随着全球气候变暖和快速城市化,城市夏季高温及热浪出现频次和强度明显增加,但人口高度集聚的特大城市中夏季高温长期变化特征对城市热岛的影响程度和作用机制仍不甚明了。本文选择京津冀特大型城市群的核心城市北京为研究对象,基于长期气象观测数据计算夏季高温和城市热岛强度,阐明5—8月夏季高温长期变化特征及对城市热岛强度的影响。研究发现,1978—2020年北京城区夏季高温日数、强度和极端高温均呈现显著增加趋势,相伴随的是高温起始时间明显提前,结束时间显著推迟;高温天最高气温热岛强度呈显著降低趋势,而平均气温和最低气温热岛强度则呈轻微下降趋势;5—8月高温天最高、平均和最低气温多年平均热岛强度分别为0.73℃、1.61℃和2.40℃,明显高于非高温天的0.09℃、0.80℃和1.40℃,高温和非高温天热岛强度差值均在0.6℃以上,表明夏季高温放大城市热岛强度。预估未来全球变暖和快速城市化背景下北京城市热岛效应将进一步加剧,会形成更频繁和持续更长的夏季高温,给城市居民带来严重的健康风险。

Global climate warming and rapid urbanization have caused significant increases in the frequency, intensity, and duration of urban summer high temperature and heat waves. However, the knowledge of long-term characteristics, affecting degree, and driving mechanism of summer high temperatures on urban heat islands in highly populated megalopolises still need to be discovered. Beijing is the centre of the Beijing-Tianjin-Hebei metropolitan area and has experienced rapid urbanization in the past few decades. This study aims to elucidate the long-term trends of summer(May-August) high temperatures and explore the affecting mechanism of summer high temperatures on urban heat islands based on 43 years(1978-2020) daily meteorological observation data from the urban station(Beijing Station) and rural station(Miyun and Yanqing Stations). In the past four decades, the summer high-temperature days, intensity, and the yearly extreme maximal air temperature have shown significant increasing trends. Correspondingly, the initial time of summer high-temperature day was markedly advanced, and the end time of summer high-temperature day was significantly delayed. The urban heat island intensity of maximal air temperature significantly decreased, but the urban heat island intensities of mean and minimal air temperature slightly decreased during the summer high-temperature period from 1978 to 2020. The urban heat island intensities of maximal, mean and minimal air temperature during the summer high-temperature period were 0.73 ℃, 1.61 ℃, and 2.40 ℃, which were significantly higher than 0.09 ℃, 0.80 ℃, and 140 ℃ during the summer non-high temperature period from 1978 to 2020. The urban heat island intensity was significantly aggravated(more than 0.6 ℃) during the period with high-temperature compared to the period without high temperature, indicating that the urban heat island effect was amplified by summer high temperature. It is projected that summer high temperatures would become more frequent, and urban heat islands in Beijing would markedly increase under the background of future climate warming and rapid urbanization. These findings underline the serious heat-related health risks facing urban residents.