不同地表覆盖类型对城市地表热环境的调节

Regulation Function of Different Surface Cover Types to Urban Surface Thermal Environment

以南宁市高速环道范围内的主城区为研究对象,通过Landsat TM遥感影像反演地表温度(LST),提取归一化差值植被指数(NDVI)、改进的归一化差异水体指数(MNDWI)、改进的归一化建筑指数(NDBI),用最大似然分类法将研究区地表覆盖类型分为水体、林地、园地和建筑用地。同时将研究区按照3km×3km规格分为47个统计小区域,利用ArcGIS中的空间分析功能,统计每个小区域各地表覆盖类型的面积比例及其平均地表温度,并对两者进行相关分析。从而在像元(30m×30m)和小区域(3km×3km)2个尺度上定量研究地表覆盖类型对地表温度的影响。结果表明,在像元尺度上,地表覆盖类型的地表温度排序,从高到低依次为建筑用地、园地、林地、水体;LST与NDBI呈显著线性正相关,LST与NDVI和MNDWI呈非线性关系;LST与正的NDVI和正的MNDWI均呈显著线性负相关;在小区域尺度上,平均地表温度最高的是以建筑用地为主的15号小区域达33.2℃,平均地表温度最低的是以绿地和水体为主的36号小区域仅27.8℃,小区域的水体、林地、园地的面积比例和小区域的平均地表温度呈负相关关系,建筑用地面积比例与小区域平均地表温度呈明显正相关关系。不同地表覆盖类型对地表温度的影响不同,绿地与水体均具有降温作用,且绿地比水体降温效果好。因此,在城市规划中,通过适当设置水体和绿地可以达到调节地表热环境,缓解热岛效应的目的。

Based on Landsat TM images,the main urban areas within the “High-speed Ring Road” in Nanning were used as the research objects,land surface temperature （LST） of Nanning was retrieved.Indices such as normalized difference vegetation index （NDVI）,modified normalized difference water index （MNDWI）,normalized difference built-up index （NDBI） were derived.The land cover types of the study area were divided into four types：waters,forest land,garden land,and construction land by maximum likelihood classification method.The area proportion of each land cover type in small area and average surface temperature of small area were counted by using the spatial analysis function of GIS,and the correlation analysis was investigated between area proportion of the four kinds of land cover types and average land surface temperature.Quantitative study on the relationship between the surface temperature and the type of land cover from the two scales of the pixel and the small area.The results showed that at the pixel scale,the average surface temperature was in the order of construction land〉garden land〉forest land〉water body.The LST had significant linear relationships with NDBI,and had nonlinear relationships with NDVI and MNDWI,but significant linear relationships with positive NDVI and positive MNDWI.In small regional scale,the average surface temperature could be as high as 33.2℃,which was mainly based on construction land,the average surface temperature was 27.8℃,which was mainly based on water body and green land.Area proportion of water body,forest land,and garden land all had negative correlation to the average surface temperature in small areas,and area proportion of construction land showed significantly positive correlation to average surface temperature in small areas.So it was concluded that different surface cover types had different effects on the surface temperature,green land and water body had the effect of cooling and the cooling effect of green land was better than that of the water body.Therefore,in order to achieve the purpose of regulating the surface thermal environment and the heat island effect could be alleviated by adding water and green land in the urban planning process.