城市地表热力景观格局时空演变——以长春市为例

Spatial and temporal changes to urban surface thermal landscape patterns: a case study of Changchun City

城市热环境问题是城市气候和区域气候研究中的热点,其对城市空气质量和公共健康等有着深远影响,严重威胁城市的可持续发展。以长春市为例,基于3期Landsat ETM+影像数据(2006、2010和2014),应用覃志豪单窗算法和线性光谱混合模型获取长春市区夏季地表温度、长春市不透水面盖度和植被覆盖率,构建热力景观动态度指数,分析了2006—2014年长春市热力景观格局的时空变化特征,并探讨地表温度与不透水面盖度和植被覆盖率的关系。结果表明:研究区城市热环境整体呈恶化趋势,地表平均温度年均增长0.15℃;热力景观整体变化更为剧烈,2006—2010年热力景观综合动态度为45.39%,2010—2014年热力景观综合动态度为52.64%;城市地表高温等级热力斑块面积和数量都增大,并向郊区扩张,热力景观整体呈现破碎化;低温等级为长春市变化最为剧烈的地表温度等级,城市地表热力性质复杂化。此外,统计分析表明:长春市的不透水面每增加1%,地表温度上升0.06—0.07℃;植被覆盖率每增加1%,地表温度下降0.07—0.08℃,植被对地表温度的影响力大于不透水面。

Urban expansion has caused many more environmental problems to emerge. In particular, the urban thermal environment issue, which has mainly been caused by the concentration of populations in downtown areas, has caused an increase in heat emissions. Today, it poses potential threats to factors that affect urban sustainable development, such as urban air quality and public health. Therefore, a considerable amount of research has focused on urban thermal issues. In this study, three Landsat ETM ＋ image data sets （2006, 2010 and 2014） were used to derive urban land surface temperature （LST） during the summer. The analysis was based on Qin＇s mono-window algorithm. The impervious surface area （ISA） percentage and the amount of land covered by vegetation （FV） in Changchun City were obtained from the data using the linear spectral mixture model. A thermal landscape dynamic degree （TLDD） index was proposed for the first time which was based on the land use dynamic degree （LUDD） concept. Then, TLDD was used to describe the spatial and temporal changes to the urban surface thermal landscape pattern in Changchun City. Finally, the relationships between LST and the ISA and FV percentage were investigated in order to determine the effects of the different underlying surfaces on temperature. The results showed that the urban thermal environment in Changchun City declined between 2006 and 2014. The average land surface temperature was 34.14℃ in 2006 and 35.3℃ in 2014, which meant that the annual rise in land surface temperature was 0.15℃. This may increase energy consumption and lead to a cycle of environmental decline. The urban thermal landscape has changed very rapidly, especially in low-temperature patches, which means that human activity has been high. The total thermal landscape dynamic degree （TTLDD） reached 52.46% between 2010 and 2014 as against 45.39% between 2006 and 2010. This suggested that there was a greater change in LST between 2010 and 2014 than between 2006 and 2010, which may have negatively affected land surface thermal properties. The area and number of high temperature patches increased and expanded from downtown towards the suburbs, which has caused thermal landscape fragmentation. Large changes to the urban thermal landscape occurred in the low temperature patches and this aggravated the thermal environmental problem. The thermal distribution for Changchun City showed that, the thermal center was not located in downtown area, but was centered near the Dongda Bridge and the Xixin Economic and Technological Development Zone where many industrial companies were to be found. The results obtained by the regression models for ISA and LST, and FV and LST showed that LST would increase by 0.06-0.07℃ with each one percentage point increase in ISA, and decrease by 0.07-0.08℃ with each one percentage point increase in FV. This suggests that the influence of the area covered by vegetation on LST was much stronger than the influence of ISA on LST. The conclusions in this paper will have guiding significance on urban land use and heat island mitigation.