福州市地表温度热点及时空变化分析

The Hot Spot and Spatiotemporal Changes of the Land Surface Temperature in Fuzhou

中国作为世界第一大发展中国家,近年来城镇化发展迅速,大量自然地表转化为人工地表,从而引起了一系列环境问题,其中以城市热岛问题最为显著。因此如何缓解因城市化进程的加快引起的城市热岛效应已成为热门研究方向。为精确分析城市空间格局对热集聚的影响,本研究利用2000年5月4日的Landsat ETM+和2016年7月27日获取的Landsat OLI两期遥感影像,获取福州市的土地覆盖信息并进行精度验证。在地表温度(Land Surface Temperature,LST)反演基础上通过热点分析(Getis-Ord Gi*),并结合不透水面(Impervious Surface Area,ISA)信息来研究城市化进程中福州市16年来LST的变化特性,空间集聚特性及其产生的尺度效应。热点分析结果显示:①通过分析福州市内各地和热点中心的距离与LST的关系可较好地反映空间热聚集。2000年在距热点中心0.97、1.03、0.95 km范围内热聚集明显;2016年则增长到分别在距热点中心半径1.89、2.01、2.10、2.05、2.13 km范围内热集聚显著且热点区数量也从3个增加至5个。热集聚区(热点区和较热区)总面积在此期间从15.7%增至47.3%;②由于热点图中的热点区和冷点区的形成不单取决于LST的高低,因此热点分析与空间自相关分析方法相比,能更直观地分析土地覆盖变化对LST的影响,了解城市内部热强度变化的细节。本研究采用的热点分析方法可用于城市环境保护与规划,将来还可作为城市土地规划与热环境影响的分析依据。同时可利用热点分析图模拟城市微气候,估算城市绿地降温程度等。此外,未来还可基于此进一步探讨更多时相以及不同城市的对比分析,特别是对不同城市类型如带状城市,多中心城市及中心城市等的研究。

As the largest developing country in the world, China has witnessed rapid urbanization in the recent years. A large amount of natural land surface has been transformed into artificial land surface, leading to a series of environmental problems, among which the most prominent is urban heat island.Therefore, how to mitigate the urban heat island effect caused by the acceleration of urbanization process has become a hot research direction.To accurately analyze the influence of urban spatial pattern on thermal concentration, this article used two periods of remote sensing imagery, Landsat ETM+ on May 4, 2000 and Landsat OLI on July 27, 2016, to obtain the land cover information of Fuzhou and verified the accuracy. The hot spot analysis of the retrieved land surface temperature(LST) and impervious surface area(ISA) of Fuzhou were used to study the change characteristics,spatial concentration characteristics, and scale effect of LST in the past sixteen years of urbanization. The hot spot results show the following two findings.(1) The spatial thermal concentration could be better illustrated through analyzing the relationship between the distance from city center and LST. In 2000, the urban heat island effect was significant within a 1.03 km distance from the city center;however, in 2016 the distance increased to2.1 km and the number of hot spots increased from three to five. During this period, the hot concentrated area(the hot and less hot areas) also increased from 15.7% to 47.3%.(2) Compared with other spatial autocorrelation analysis methods, Getis-Ord Gi* can help more directly analyze the impact of land cover change on LST and understand the details of the change of urban internal thermal intensity, because the formation of hot and cold spots depends on not only the level of LST. The hot spot method adopted in this study can be used for urban environmental protection and planning, and can also be used as a basis for urban land planning and thermal environmental impact analysis in the future. Meanwhile, the hot spot chart can be used to simulate urban microclimate and estimate the cooling effect of urban green space. In addition, comparative analyses of more multi-temporal and different cities can be further discussed in the future, especially studies on different types of cities, such as strip cities, polycentric cities and central cities.