Effects Of Greenspace Landscape Pattern On Thermal Environments In Pearl River Delta Urban Agglomeration

Urban thermal environment is one of the most important contents of urban eco-environment research.Pearl River Delta?PRD?agglomeration is an important component of Guangdong-Hong Kong-Macao Greater Bay Area,and with rapid urbanization and global warming,thermal environment in this region has aroused great attention.Greenspace,regarded as a good recipe for improving urban livability,can mitigate urban heat island effect by photosynthetic,evapotranspiration and shading.Numerous researches indicate that vegetation composition and configuration have crucial influence on greenspace cooling effect.However,most of present researches on thermal environment are targeted on a single city,and few researches compare greenspace landscape pattern and thermal circumstance spatiotemporal evolution amongst different cities in the same urban agglomeration.Moreover,much concern has been paid to the lower temperature inside greenspaces,neglecting the external cooling effects of greenspace is also of great significance.Thus,conducting comparison analysis on greenspace landscape pattern and thermal environment among multiple cities,synthetically exploring both greenspace internal and external cooling effects and studying thermal environment responses to greenspace patterns is of double significant for thermal stress mitigation and greenspace refined management.Taking the PRD agglomeration as object,this article analyzes greenspace landscape pattern and evolution of PRD cities from 2000 to 2015 based on Landsat remote sensing data.Using MODIS land surface temperature?LST?data,the distribution characteristics and spatiotemporal dynamics of thermal environment are explored.Afterwards,combining the data of population and economic of each city as well as the ecological environment parameters,we study how greenspace landscape pattern affects thermal environment from aspects of scaling,cooling paths and influential factors.The main results are as follows.?1?Greenspace landscape pattern and spatiotemporal evolution vary among PRD cities.Greenspace proportion of the nine cities in 2015 is as follows:Zhaoqing?75.35%?>Huizhou?64.55%?>Jiangmen?52.33%?>Guangzhou?45.72%?>Shenzhen?34.98%?>Zhuhai?33.18%?>Foshan?22.66%?>Zhongshan?21.11%?>Dongguan?18.76%?.From 2000 to 2015,Dongguan and Zhongshan have experienced great decrease in greenspace proportion,separately 24.81%and 20.95%.The higher population density of a city,the lower greenspace proportion,the smaller average greenspace patch size,the simpler patch shape and the more disperse spatial distribution,which resulting in higher average land surface temperature.?2?Land surface temperature distribution has great diversity in the nine PRD municipalities.During 2000 and 2015,high LST value presents a tendency of diffuse from the southeast region,and then transfer and cluster in the central and east-wing zone of PRD agglomeration.?3?The relationship between urban thermal environment and greenspace composition depends on scale.As the scale of analysis increases,the negative correlation between tree proportion and LST strengthens,and the fitness of multivariate regression equation increases.?4?Evapotranspiration?ET?,Leaf Area Index?LAI?and Fraction of Photosynthetically Active Radiation?FPAR?can affect greenspace cooling effect.The correlation between ET and LST,LAI and LST are non-linear.When ET<1.6kg/m²/day,LST increases significantly as the increase of ET?P<0.001?.When ET>1.6 kg/m²/day,increasing ET continuously exerts no significant effects on LST.When LAI<1.7,increasing 0.1 LAI can decrease 0.24?LST.When 1.7<LAI<4.1,increasing 0.1 LAI can decrease 0.08?LST.FPAR is significantly negatively correlated with LST?P<0.001?,increase the FPAR of greenspace can benefit greenspace cooling effects.?5?Greenspace cooling effects behave differently inside and outside the patch,affected by vegetation composition and configuration.Increasing the patch size of greenspace can help to get a lower interior mean temperature inside the patch and obtain a broader cooling cover externally but decrease external cooling efficiency.Greenspace composition evenness is significantly negatively correlated with the interior mean temperature????_?????,external cooling efficiency?????and external radiant efficiency(?_????)?P<0.001?.Increase composition evenness is good for greenspace's interior cooling but go against its external cooling.The compactness of tree and shrub are both significantly positively correlated with???and?_?????P<0.001?.Each0.1 higher in both tree compactness and shrub compactness can increase 20%of???.This study provides a basic knowledge of greenspace pattern and thermal environment of PRD agglomeration.Suggestions are given that more attention should be paid to improving greenspace distribution evenness and integrality in this region and greenspace should be planned scientifically in the light of the population feature,original greenspace landscape pattern and local thermal condition of the target city.Meanwhile,the planning of local greenspace should be targeted on its intended use and balance its internal and external cooling effects by optimizing the vegetation composition and configuration such as evenness and compactness.