Study On The Temporal And Spatial Changes Of Urban Green Space And Land Surface Temperature In Main Urban Areas Of Beijing

The spatial pattern,especially its configuration and composition of urban greenspace have long been considered to have a significant effect on LST(land surface temperature),which in turn affects UHI(urban heat island).Therefore,understanding how green space affects city temperature is critical to assess the thermal benefits of landscape planning.This study investigated the dynamics of green areas and surface temperatures within the metropolitan area of Beijing(within the five rings).To ensure data consistency,land use classification and surface temperature inversion are all obtained from Landsat TM images.The study time was selected in 1999 when Beijing had not yet undergone rapid urbanization and in 2011 after rapid urbanization.The research area is generally divided into five types of land use(landscape):construction land,forest land,urban green space,water body and bare land.The expansion of green space shows that the landscape has changed from construction land and bare land to forest land and urban green space.The loss of green space indicates that the landscape has changed from woodland and urban green space to construction land.Finally,the exchange of green spaces indicates the exchange of landscapes between forest lands and urban green spaces.In order to facilitate the comparison of the two periods of data,the concept that the relative temperature RLST value of the temperature pixel minus the temperature average is also proposed.Research indicates:(1)Changes in land types lead to changes in LST,especially changes between changing and unchanged landscape types.2011 compared to the expansion of green space in 1999.(2)The area of dynamic change of green space accounts for 13.22%of the total area of the study area.The loss of green space is 16.14 km~2,green space expansion is70.65 km~2,and green space exchange is 1.56 km~2.(3)The change of RLST of invariant(0-0.17)and exchanged green space(0.30-1.31)is not significant.However,the RLST in the greenbelt expansion zone(-1.21 to-2.34)decreased slightly,while the RLST in the greenbelt loss zone(-3.31 to-0.97)increased significantly.In summary,the number of green spaces should not be the only criterion for assessing the effect of temperature mitigation.The cooling effect of newly planted green land may not be as high as we expected.In the future,we should focus on improving the quality of green space landscapes rather than just increasing the number of green space landscapes.