Abstract:

The continuous expansion of impervious surfaces in the rapid urbanization process is the leading cause of the change in the urban thermal environment. Research on the relationship between impervious surfaces and urban heat islands can provide a basis for effective and appropriate urban planning. Based on the Landsat images of the central metropolitan area in Nanning city during 2003-2019, we extracted the land use data using an object-oriented method and retrieved the land surface temperature of the study area by the radiative transfer equation method. Then, spatial-temporal characteristics of impervious surfaces and urban heat islands were quantitatively analyzed. Finally, we employed the bivariate spatial autocorrelation method to explore the spatial relations between urban impervious surfaces and the thermal environment. The results showed that the impervious surface of the central metropolitan area in Nanning City displayed a rapid increase trend, and the new growth expanded along the old city area and main roads. The urban thermal field was dominated by the medium temperature region, and the area of low or low-medium temperature regions had been decreasing in a fluctuated fashion. At the same time, the medium-high and high temperature regions had gradually expanded. The urban heat island pattern changed from single to multiple centers, and the heat island effect of the new development zone was noticeably enhanced. The study area had a significant positive correlation between urban impervious surface and the thermal environment, and the correlation coefficient had gradually increased from 2003 to 2019. The spatial correlation types were dominated by High-High agglomeration and Low-Low agglomeration. The High-High area was mainly distributed in the urban center, and the Low-Low area was located in the regions covered by vegetation and water. This study explored spatial relations between urban impervious surfaces and the thermal environment. It clarifies their spatial agglomeration types, which helps identify the key areas to improve the urban thermal environment. Planners concerned can optimize the allocation of urban blue-green space in these crucial areas by increasing green space and water patches and constructing green space network to alleviate the urban heat island effect. The research results provide guidance for urban landscape pattern optimization and ecologically livable city construction in Nanning City.

Key words: impervious surface, thermal environment, thermal field intensity, spatiotemporal evolution characteristics, bivariate spatial autocorrelation analysis, Nanning City

摘要：

快速城市化过程中不透水面持续扩张是影响城市热环境变化的重要原因。科学测度城市不透水面变化及其与热环境之间的关系，可以为有效制定合理的城市蓝绿空间规划提供依据。基于南宁市主城区2003-2019年间Landsat遥感影像，利用面向对象分类方法获取城市土地利用数据，借助辐射传输方程反演地表温度，定量分析城市不透水面与热环境效应的时空格局演变特征，运用双变量空间自相关方法探索城市不透水面与热环境效应的空间关系和集聚规律。研究结果显示，近15年来南宁市主城区不透水面的面积显著增加，城市主要沿环路以内的老城区和主要交通要道不断向外扩展，主要扩张方向为向东和向南。城市热场由中温区占主导，低温区和次低温区的面积波动下降，高温区与次高温区的范围逐渐蔓延，城市热岛效应有所加剧。南宁市热岛分布格局由单中心转变为多中心，新开发区的热岛效应明显增强。南宁市主城区不透水面与热环境效应之间呈现明显正相关关系，从2003-2019年相关性逐渐增强。空间集聚类型以高-高聚集和低-低集聚为主，高-高聚集区主要分布于城市中心，低-低聚集区位于东部绿地比例较高及河流分布集中的地区。该研究通过探讨南宁市主城区不透水面与热环境的空间关系，明确二者空间集聚与分异特征，有助于识别城市热环境亟需优化改善的区域，进而通过增加城市绿地和水体斑块，加强城市绿地生态网络建设等方式实现城市蓝绿空间优化配置以缓解热岛效应。研究结果可以为城市景观格局优化和生态宜居城市建设提供指导。

关键词: 不透水面, 热环境, 热场强度, 时空演变特征, 双变量空间自相关, 南宁市