【摘要】 快速城市化形成超大城市导致地表覆盖快速变化,改变地表热平衡,使得城市热环境剧烈变化。以1990s, 2000s和2015年这3个时期为研究时相,选取中外6个典型超大城市(北京、上海、广州、伦敦、纽约和东京)为研究对象,多时相Landsat遥感影像为主要数据源,进行城市热环境变化对比及成因分析。利用普适性单通道算法反演各城市地表温度,计算城市热岛比例指数(urban heat island ratio index, URI)来定量对比研究期间各城市热岛效应时空变化。城市热岛效应对比研究结果表明,1990s—2015年间,北京、上海和东京的URI呈总体上升趋势,广州、伦敦和纽约的URI呈总体下降趋势。到2015年,东京城市热岛效应最严重(URI=0.630),其次是北京、上海、纽约和广州,分别为0.617,0.594,0.555和0.530,伦敦的URI指数最小为0.433。整个研究期间,北京、上海、广州和东京等超大城市均有较大幅度扩张,建成区面积均增加500 km~2以上,不透水面面积增加370 km~2以上,不断向外蔓延并占用生态用地,加上城市组团间无法形成良好的绿化分隔带,造成城市地表温度等级大幅上升,尤其是新城区热岛效应增强显著;而在老城区通过旧城改造,热环境得到显著改善。伦敦和纽约城市无明显扩张,地表温度变化幅度较小。在今后城市建设中,需注重生态理念,优化城市地表空间格局,提高生态用地效益。更多还原

【Abstract】 Megacities have formed due to rapid urbanization. As a result, the surface cover has rapidly changed, which changes the heat balance of Earth’s surface and induces drastic changes in the thermal environment in megacities. With six typical megacities(Beijing, Shanghai, Guangzhou, London, New York, and Tokyo) across the world as study objects and multi-temporal Landsat remote-sensing images of the 1990 s, the 2000 s, and 2015 as the main data sources, this study compares the changes in the thermal environment among the six megacities and analyzes their causes. For each of the megacities, the surface temperature was determined through reversion using the universal single-channel algorithm and the urban heat island ratio index(URI) was calculated to quantitatively compare the spatial-temporal changes in the heat island effect during the study period. The results are as follows. From the 1990 s to 2015, the URI values of Beijing, Shanghai, and Tokyo showed an overall upward trend, and while that of Guangzhou, London, and New York showed an overall downward trend. In 2015, Tokyo suffered the most serious urban heat island effect(URI=0.630), followed by Beijing, Shanghai, New York, and Guangzhou successively, of which the URI values were 0.617, 0.594, 0.555, and 0.530, respectively. In contrast, London had the smallest URI of 0.433. The megacities such as Beijing, Shanghai, Guangzhou, and Tokyo all considerably expanded throughout the study period. In these cities, the built-up areas and impervious surfaces increased by more than 500 km~2 and more than 370 km~2 on average, respectively in terms of area. They continuously spread outwards and occupied ecological land. Furthermore, green belts can not be formed between urban clusters. All these caused a significant increase in urban surface temperature and especially the significant aggravation of the heat island effect in new urban areas. In comparison, the thermal environment in the old urban areas was significantly improved through urban reconstruction. London and New York were not significantly expanded, where the surface temperature slightly changed. Therefore, it is necessary to pay attention to ecological philosophy, optimize the pattern of urban surface space, and improve the efficiency of ecological land in future urban construction.更多还原