长沙市热力景观空间格局演变分析

城市热环境是城市生态环境效应研究的热点之一,其演变规律的研究为缓解城市热岛带来的负效应、促进城市可持续发展提供依据。以2004年和2010年Landsat7 ETM+遥感影像数据和土地利用现状数据为数据源,在地表亮度温度反演的基础上,运用景观指数并结合GIS空间分析技术,采用移动窗口和梯度分析结合的方法,分析2004—2010年长沙市中心城区热环境的空间格局动态变化,通过分区统计法分析了不同热力景观等级下不同城市景观的空间格局变化,从景观尺度上阐明城市景观类型组成和空间格局与地表温度空间分异之间的关系。研究结果表明:2010年热岛区域扩大且更加分散,面积比2004年增加15.01km2,新增区域主要分布在金霞、岳麓和星沙的新兴工业园区;中心城区热力景观格局在景观水平上具有明显的空间分异特征,在从中心位置到偏北、偏东和偏南方向上,热力景观从市区向周边郊区呈现破碎化、多样性递增、形状复杂化,而从中心位置到偏西方向上与之相反;景观类型组成和空间布局对地表热环境产生不同影响,耕地、林地在热力景观内的优势度越大、分布越集中,地表降温效果越显著;反之,建设用地斑块越大、凝聚程度越高、形状越规整,地表温度越高,热岛效应显著。

Spatiotemporal changes of thermal environment landscape pattern in Changsha

The urban thermal environment has become the subject of considerable attention in the field of researchinto the eco-environmental effects of cities. Research into the laws governing the evolution of the urban thermal environment could contribute to the mitigation of the negative effects of the urban heat island (UHI) and promote the sustainable development of cities. This paper analyzed the spatiotemporal changes of the urban thermal landscape in Changsha, China. Four Enhanced Thematic Mapper Plus thermal images of the urban center of Changsha, taken in the same month in 2004 and 2010, were used to retrieve the brightness temperature, which was then classified into five temperature regions: low, sub-middle, middle, sub-high, and high. The landscape types of the urban center of Changsha in both 2004 and 2010 were classified based on land use data. Landscape metrics were used to quantify the spatiotemporal changes of the urban thermal landscape and the underlying surface pattern. By combining moving window and gradient analyses, the spatial changes of the urban thermal landscape pattern in Changsha from 2004 to 2010 were established and the evolution of the thermal landscape was analyzed from 16 directions. Zonal statistics were applied to investigate the changes of various urban landscape patterns under different thermal landscape ranks, which clarified the relationship between the spatial pattern and composition of the urban landscape and the spatial variation of surface temperature on a landscape scale. Based on this work, a number of conclusions were drawn. 1) Following the rapid urbanization of Changsha, the districts of the UHI expanded and became increasingly decentralized. The area of the UHI increased by 15.01 km² in 2010 in comparison with 2004; the increase was largely distributed in new industrial parks such as Jinxia, Yuelu, and Xinsha. 2) There was an obvious spatial variation of thermal landscape pattern on the landscape scale in the center of Changsha. From the center to the north, east, and south, the Patch Density, Shannon''s Diversity Index, and Perimeter-Area Fractal Dimension of the thermal landscape increased gradually, coupled with fluctuations of different amplitudes. In the other words, the thermal landscape has tended to become more fragmented and diversified, and the landscape shape has become more complex from the downtown area to the suburbs. However, the converse is true of the landscape pattern in the west. 3) Different shapes and spatial arrangements of landscape types exhibited different influences on the surface thermal environment; thus, the characteristics of the thermal landscape were changed. The greater the concentration of cropland and forested land in the thermal landscape, the more significant the surface cooling effect. Conversely, the higher surface temperatures were observed when the dominance of urban land was greater, degree of cohesion higher, and landscape shape simpler. Furthermore, the UHI effect of the study area is expected to become more remarkable. The changes of the underlying surface pattern exhibited remarkable influence on the local thermal environment and therefore, greater attention should be paid to the rational distribution of cropland and forested land in order to relieve the effects of the urban heat environment.