近30年北京市ISP-LST空间特征及其变化

本文聚焦长时序地表的不透水与温度特征,利用Landsat影像数据,获取1991—2015年北京市的不透水地表盖度（Impervious Surface Percentage, ISP）与地表温度（Land Surface Temperature, LST）数据,构建不透水地表盖度-地表温度（ISP-LST）二维空间。结合标准差椭圆法,对ISP-LST空间密度分布的聚集特性进行分析,定量化表述各时期的特征与变化。研究发现：① ISP-LST二维空间特征表现为三种类型：弱相关、非完全正相关和显著正相关。② ISP-LST标准差椭圆的方向性和离散性均值为11.26和2.87,空间聚集性良好。随时间推移,高温现象受不透水地表的影响过程趋于复杂化。③ ISP-LST聚集区是城市热环境的重要表征,其在各功能区年际增长率为：功能扩展区（2.97%）>核心功能区（1.75%）>发展新区（1.63%）>生态涵养区（0.18%）。聚集区在东南方向增长明显,研究时段内累计增长14.77%。④ ISP-LST聚集区的斑块密度及形状复杂度的景观格局变化不大,但斑块连接性随时间推移有所降低。本文研究结果可为缓解城市热岛效应、制定生态环境调控政策提供相应参考。

The spatial characteristics and changes of ISP-LST of Beijing in recent 30 years

The construction and development of the city have caused the transformation of the natural surface to the impervious surface. At the same time, high-density impervious surface percentage (ISP) areas lead to the rise of the land surface temperature (LST), and form the thermal field in urban areas. It is of important research value to express the correlation between ISP and LST in the urban areas. This study focuses on the impervious properties and temperature properties of the underlying surface, attempts to establish a two-dimensional space about impervious surface percentage-land surface temperature (ISP-LST), and analyzes distribution relationship quantitatively. The two-dimensional spatial distribution of ISP-LST was constructed based on the multi-period Landsat image data in Beijing during 1991-2015 (the approaches to get ISP and LST are classification and regression tree model and radiative transfer equation method). Combined with the standard deviation ellipse method, the agglomeration characteristics of ISP-LST spatial density distribution were analyzed, and the characteristics and changes of ISP-LST in different times were quantitatively expressed. The study revealed that the spatial characteristics of ISP-LST in Beijing are manifested in three forms. The first type shows that there is no significant correlation between ISP and LST. This appears in the middle and early stages. The second one indicates that the high temperature appears in the medium-high coverage of the impervious surface and gradually decreases toward both ends. This appears in the middle stage. And the third type shows that ISP and LST perform the significant positive correlation. This appears in the late stage. The density core of the ISP-LST agglomeration is situated in areas with medium-high ISP and high LST. The mean directionality and dispersion of the ISP-LST standard ellipse are 11.26 and 2.87. It means that the directivity of spatial aggregation is good. The phenomenon of high temperature is complicated by the influence of the impervious surface over time. The aggregate areas of ISP-LST are important representation of the urban thermal environment, mostly located in the core functional areas and functional extended area of Beijing, and the growth rate is obvious in the southeast, with an accumulated growth of 14.77% in recent 30 years. The inter-annual growth rate of ISP-LST in each functional area is: functional expansion zone (2.97%) > core functional zone (1.75%) > development new zone (1.63%) > ecological conservation zone (0.18%). The change of ISP-LST landscape pattern like patch density and shape complexity is not significant, but patch connectivity decreased over time. The research results can help to provide a feasible ecological environment control policy for long-term urban planning.