关键词: 不透水地表盖度, 地表温度, 城市热环境, CART算法, 相关分析

Abstract:

Classification and regression tree (CART) algorithm was used to extract the impervious surface percentage (ISP) of Beijing six ring within the city in 2001 and 2011 based on QuickBird high-resolution images, Landsat TM and night light data. The method is suitable for typical temperate semi-arid climate area. We classified the ISP as three groups. The ISP region for 10%~60% is defined as a low-density region, 60%~80% is defined as a medium-density area and for the rest area which the ISP is more than 80% is high-density area. Meanwhile, based on the Landsat TM, the land surface temperature of 2001 and 2011 were retrieved by using the single window algorithm. The study area has been designated as a region within six rings of Beijing. According to the characteristic of Beijing urban layout, this paper analyzed the development trend of ISP in different ring road and its correlation with land surface temperature from 2001 to 2011. In order to seek an effective way to improve the ecological environment in Beijing and mitigate the urban heat island effect. The results are as follows: (1) The change of ISP in Beijing urban area mainly concentrate in the low-density area. In comparison with the low-density area, the ISP of middle-densitiy area and high-density area does not change so much. Due to the vigorous city construction within the fifth ring road from 2001 to 2011, the whole change of ISP is not obvious. The variation mainly concentrates in the region between the fifth ring road and the sixth ring road, in which the growth of low density area was significant, while the growth in the middle and high density area was mainly in the east part. From the above results, it can be concluded that the development within the fifth ring road and sixth ring road develops rapidly and the range of city construction continued in recent years. (2) Compared with 2001, the land surface temperature of the central areas in Beijing in 2011 increased dramatically, and the aggregation extent of high-temperature region is more evident. The temperature difference increased significantly between the region within the fourth ring road and the surrounding areas. (3) By comparing the average surface temperature of each density area in 2001 and 2011 we find that compared with 2001, the differences in land surface temperature in 2001 also increased between different ISP categories and the urban heat island effect was more and more remarkable. (4) In both 2001 and 2011, there is a positive correlation between the land surface temperature and the ISP in every ring road region of Beijing urban areas. In the regions between the fourth and sixth ring road, the land surface temperature and the ISP shares a similar change trend. In the regions with ISP between 10% and 20%, the rising rate of land surface temperature is obviously higher than other regions. In the regions with ISP higher than 20%, the rising rate of surface temperature decreases, and the change tends is uniform.

Key words: impervious surface percentage, land surface temperature, urban thermal environment, CART algorithm, correlation analysis