秋冬季节广州城市绿地对热岛效应的调控作用差异分析

Thermal island regulation differences of urban green spaces between autumn and winter in Guangzhou,South China

城市绿地具备"冷岛"效应功能,其在调控城市热岛效应方面发挥着独特作用,是城市生态研究的重要领域。以Landsat 8多光谱和热红外波段遥感影像为基础,系统分析了秋冬季节广州市地表参数比如植被覆盖度、归一化湿度指数(NDMI)和减化比值植被指数(RSR)变化对地表温度的影响;并综合绿地地表参数信息,定量研究了城市绿地面积和周长变化对其热环境调控功能的影响及其季节性差异。结果表明:广州秋季热岛强度和范围大于冬季;相比冬季,秋季地表参数与地表温度间具有更好的相关性,即秋季植被有更好降温效应。但是RSR与地表温度间呈对数函数关系,说明在高植被覆盖区降温效应可能出现"饱和现象"。秋冬季节城市绿地降温效应的影响距离为300 m左右。城市绿地面积和周长与地表温度间显著负相关,但秋季相关性小于冬季。绿地属性参数与地表温度间显著负相关,秋季相关性更强。然而,相关分析发现,除秋季绿地NDMI与内外累积温差间显著负相关外,其它地表参数与秋冬季节内外累积温度差之间的显著性并不明显,这一定程度说明绿地地表参数可能并不直接影响外部环境温度。

Urban heat island(UHI)has been mostly reported as the consequence of accelerated urbanization and industrialization.UHI can be obviously regulated by the cooling-island effect of urban green spaces.Thus,growing attention has been paid to understanding the cooling regulation mechanism of urban green spaces.Land surface temperature(LST),vegetation cover,normalized difference moisture index(NDMI),reduced simple ratio(RSR),and urban green spaces in Guangzhou were retrieved using Landsat-8 images in autumn and winter.This study focused on the correlation relationships between LST and land surface attributes(such as vegetation cover,NDVI,and RSR)in autumn and winter,and also paid much attention to know how LST was affected by urban green spaces as urban green spaces varied in area and parameter and land surface attributes.The results showed that both UHI magnitude and area are much higher in autumn than in winter.Compared with winter,there was better correlation relationship between land surface attributes and LST in autumn,indicating that better cooling effect could be existed in autumn with higher temperature.However,logarithmic function relationship was existed between LST and RSR.It was indicated that cooling effect of vegetation could be at“saturation”as RSR used,when vegetation cover increased.LST exponentially decreased with buffer distance increased.Cooling effect of urban green spaces was gradually limited,when buffer distance continued to be increased as buffer distance is greater than 300 meters.Cooling effect of urban green spaces was much stronger in autumn than in winter.Furthermore,LST was also negatively correlated with both the area and parameter of urban green spaces and higher correlation coefficient occurred in winter.There was significant correlation relationship between internal LST and land surface attributes of urban green spaces and higher correlation coefficient occurred in autumn.LST difference between internal and external green spaces was not significantly correlated with vegetation cover and RSR in both autumn and winter,except for NDMI in autumn.LST was not directly affected by vegetation cover and RSR.Generally,cooling effect of urban green spaces was obviously better in autumn.