绿地景观对城市热环境的影响——以长春市建成区为例

The impacts of green landscape on urban thermal environment:A case study in Changchun city

绿地景观作为城市生态网络中的自然要素,在缓解城市热岛、调节城市气候中发挥着极其重要的作用。以绿地景观为研究对象,基于SPOT5影像提取长春市建成区绿地景观数据,基于TM影像估算地表温度,分析城市绿地景观与地表温度的相关关系,将"植被—不透水面—土壤"模型与具有明确物理意义的线性光谱混合模型相结合估算城市地表植被覆盖度,进一步剖析绿地景观的植被覆盖对城市热环境的影响。结果表明:绿地面积与该块绿地的最低温度负相关性较大,当绿地的面积达到50 hm2之后,面积的增大会使其地表温度显著降低;生产绿地和农业用地的地表温度最低,居住绿地地表温度最高,公园绿地温度受植被状况的影响与其他类型相比更剧烈,常绿树和落叶树的降温效果更好;增加公园绿地、常绿树和落叶树的植被覆盖,对于减缓城市热岛效应具有更好的调节作用。

As the main natural productivity in urban structure, the green landscape plays an important role in mitigating the urban heat island, and regulating urban climate. In the perspective of interactive human- environment system, a case study was carried on green landscape of a typical garden city in Northeast China. SPOT5 image was selected for extraction of urban green landscape, and TM image was chosen to retrieve land surface temperature(LST). Correlation analysis was investigated between green landscape(size and area of urban green patches) and LST. The 'vegetation- impervious surfaces- soil' model and the physically explicit linear spectral mixing model was combined for mapping the fractional coverage of vegetation, and the vegetation cover of green landscape on LST was further analyzed. Results showed that:(1) the area of green lands has stronger negative correlation with the lowest temperature. It was found that the LST decreased with increasing green lands when the coverage area was over 50 ha. Thus, if green land area was too small, it would have little impact on urban thermal environment;(2) the corresponding LST was low in the productive plantation area and cultivated land, and it was the highest in the residential green space. The vegetation coverage and the LST of green patches was quantitatively analyzed for the whole study area,the result revealed that the impact of vegetation growing conditions on LST of green lands in park green space was more severe than that of other green- land types. Thus, the increase of vegetation coverage in parks could be helpful for regulating the LST;(3) the LST of evergreen and deciduous forest lands was the lowest, followed by the cultivated land, while the cooling effect of grasslands was not obvious, so the LST of evergreen and deciduous forest lands was more sensitive than that of grasslands and cultivated lands, that is, the evergreen and deciduous forest lands could be helpful for alleviating the urban heat island effect.