2003—2011年夏季北京城市热景观变化特征

自北京城市总体规划(2004—2020年)以来,城市化快速发展,强烈的人类活动改变了城市的热环境。基于2003年、2007年和2011年夏季同时期的TM遥感卫星影像,采用遥感反演地温的方法,运用RS、GIS以及景观分析工具,对北京城市六环内的热场和热岛变化特征进行了分析。分析结果表明,2003—2011年北京城市六环内的热场分布特征发生了很大变化,2003年城市各环线内的植被覆盖度最低,但是夏季城市的地表辐射亮温分布差异相对较小,热岛特征也并不十分明显,随着城市建设规模扩大和用能的增加,到2011年,尽管城市植被覆盖度提高很快,但城市和城郊的温差达到最大,城市热岛在不断增强,热场向城市中心集聚趋势明显。通过城市热岛等级类型的景观指数分析表明,2011年的高等级的热岛斑块分布范围和强度都明显提高,而且城市五环内高等级的热岛范围基本连成一片。由于城市人类活动的加剧各热岛等级斑块的形状更加复杂。在景观水平上的分析显示,2007年的热景观斑块类型多,在六环内的分布均匀,破碎化程度高,至2011年,景观斑块的蔓延度逐渐下降,低等级的热岛斑块优势度逐渐降低。研究结论可以为城市管理决策部门制定有效的热岛效应缓解措施提供理论依据。

Characteristic change and analysis of urban heat island in Beijing, China, Summer, 2003-2011

Urban heat island phenomenon describes the excess warmth of the urban atmosphere and surfaces compared to the non-urbanized rural surroundings. Urbanization process occupied amounts of open spaces, especially agricultural land and green space, which changes the natural land surface features into impervious lands such as buildings and paved lands. In addition, the population increases due to urbanization resulted in the increases of energy consumption. These factors impacted the urban thermal environment. Since the last City's Master Planning (2004-2020), Beijing experienced rapid urbanization, and the city expanded in larger-scale and population increased so much, which had effects on the pattern of urban heat island. Based on the landsat TM images of 2003, 2007 and 2011, we are trying to analysis the urban thermal environmental characteristics during these years. The results will support the city environmental management. Applying the method of retrieval of land surface temperature and using the tools of RS, GIS and Fragstats, The thermal environment and heat island changes in Beijing was analyzed. The results showed that at the extent of inner city sixth ring road in 2003, although the urban plant cover is the lowest among the three years, the urban heat island is not apparent because of the thermal differences between urban and rural are little. The high temperature areas are mainly distributed outside of southern third ring road and northern fifth ring road. The Fengtai and Daxin districts, and the Changpin and Shunyi districts, and inner old city core around Tiananmen Square. is also featured by high temperature. With the urban sprawling and and increases of city's energy consumption, urban heat island intensity increases. In 2007, the mean temperature is highest at every ring road among three years, and the high thermal areas was located evenly inside the study area. In 2011, within sixth ring road, the plant cover is 38.9%. In spite of the urban plant cover was improved much more than ever, the thermal differences between urban and rural areas is magnified, the maximum and minimum land surface temperature difference reaches to 29.1K, and in the centre of city, the heat island is very apparent. The analysis results of landscape metrics showed that in 2007, there is a high degree of heat island landscape fragmentation. In 2011, the patches number and extent of high-level heat island increased much more than before. Furthermore, within inner fifth ring road, the high level heat island patches connected each other. Because of urban expanded, the shape of heat island patches become more complicated, the dominance of low-level heat island patches decreased, which are important for mitigating urban heat island. Some suggestions for urban planners and natural resources managers were given on mitigating the impact of urban development on heat island.