快速城市化进程中扬州城市热环境与景观格局的动态关联

Dynamic relationships between the urban thermal environment and the pattern of landscape development in Yangzhou city

剖析城市扩张过程中热环境的时空演变特征及其与景观格局的动态关联,有助于缓解城市热岛问题,促进城市人居环境建设。以快速发展的中型城市--扬州为例,基于多期(1995、2000、2005、2010和2015年) Landsat卫星影像,运用景观格局分析、增强回归树等方法,探讨城市热环境的时空演变特征,定量探究景观组成与配置对热环境的影响。结果表明:1995-2015年,扬州整体升温,市中心和西南地区尤其明显,北部则有一定降温趋势,热力学中心逐渐向东南移动。随着城市的发展,景观组成对热环境的相对影响呈现先减少后增加的变化态势,并始终高于景观配置的影响。景观组成方面,建设用地面积比例的增加促使地表升温,耕地面积比例的增加对热环境的作用表现为先促进后抑制,水体则为明显的冷源;景观配置方面,斑块密度的增加促使地表升温,聚合度表现为先促进后抑制的作用,边缘密度和香农多样性指数的影响则随城市的发展而发生改变,如边缘密度对热环境既有促进(2000年)又有抑制(2015年)。

Understanding spatio-temporal changes in urban thermal environments and their correlation with urban landscape patterns not only helps alleviate urban heat island problems,but also promotes construction of urban habitats.Here,multi-period Landsat images with a resolution of 30 m were used to analyze spatio-temporal evolution characteristics of the thermal environment in Yangzhou,a rapidly-urbanized and medium-sized city in Jiangsu Province.We employed a boosted regression tree method to quantify effects of landscape composition and configuration on the urban thermal environment.Results showed that Yangzhou was relatively warmer with urban sprawl in the center and southwest,while a cooling trend in the north from 1995 to 2015.Moreover,the thermodynamic center gradually moved southeast.With urban development,landscape composition initially had a relatively small impact on the thermal environment before increasing;however,was always greater than that of configuration.In terms of composition,an increasing proportion of built-up land area increase land-surface temperature.Arable land first promoted a higher land-surface temperature and then inhibited it;while water bodies were an obvious source of cooler temperatures.For landscape configuration,patch density promoted a higher land-surface temperature while the initially increasing aggregation-index ended with an inhibiting effect.However,effects of edge-density and Shannon’s diversity-index varied with urban development,e.g.,edge-density promoted a thermal environment in 2000 and inhibited it in 2015.