成都市热岛效应与城市空间发展关系分析

Analysis of the Relationship between Urban Heat Island Effect and Urban Expansion in Chengdu, China

利用Landsat卫星影像反演成都市中心城区1992、2001和2009年的地表温度,建筑用地和植被等信息,计算其城市热岛比例指数(URI),对成都市中心城区热岛效应与城市空间发展关系进行了分析。结果表明,在1992-2009年期间成都市主城区范围从91.24km2扩展到403.8km2。成都市建成区的大面积扩展导致了城市热岛空间分布发生迁移,从单中心聚集分布转变为多中心环状分布。回归分析说明,建筑用地和植被都是影响地表温度的重要因素,其中建筑用地与地表温度呈指数型正相关关系,而植被与地表温度呈负相关关系。总的看来,成都市中心城区在这17年间的热岛效应有了明显的缓解,城市热岛比例指数从0.72下降到0.33。城市植被覆盖率的增加和合理的规划对缓解城市热岛效应起到了积极的作用。

To study the relationship between urban heat island （UHI） effect and urban expansion in Chengdu＇ s main urban area, three Landsat images in the years of 1992, 2001 and 2009 were used to retrieve land surface temperature （LST）, built-up land and vegetation coverage of the area. The three thermal images were normalized and scaled to several grades to reduce seasonal difference, then overlaid to produce a difference image by sub- tracting corresponding pixels in order to find out the change of the UHI among different dates. In the period of the 17-year study, the urban built-up area of Chengdu has increased significantly, which dramatically increased from 91.24 km^2 in 1992 to 403.8 km^2 in 2009. The extent of the UHI expansion through the study years was due to large scale urban sprawl and the pattern of the UHI has changed from single-center aggregation to polycentric annular distribution. The quantitative analysis of the UHI using Urban-Heat-Island Ratio Index （URI） reveals that the UHI effect in the area has been greatly mitigated in the past 17 years, as the URI has decreased from 0.72 in 1992 to 0.33 in 2009. Regression statistics indicate that the built-up land and vegetation coverage are crit-ical factors for influencing on LST. The built-up land has a positive exponential relationship with LST rather than a simple linear one, which suggests that high percent built-up land could accelerate the rise of LST. The study also demonstrated that the vegetation coverage plays a distinct role on mitigating the UHI effect, which re- duces the built-up land while increases vegetation covers, so as to reduce the LST effectively. The increase of vegetation coverage and reasonable planning are beneficial to the UHI mitigation of Chengdu＇ s main urban area.