| In the context of rapid global urbanization,the rapid expansion of urban space is constantly squeezing ecological space,and the spatial structure of urban functions can directly reflect the composition and configuration of urban built-up areas,which is closely related to urban ecological problems.To understand the impact of the functional configuration of different regions in a city on the ecological environment of the corresponding region is an important condition for maintaining the ecological security of the city and ensuring its sustainable development.In recent years,urban Point-Of-Interest(POI)data,which can reflect the distribution of urban functions at the microscopic scale,has received wide attention from scholars.Combining urban POI data with remote sensing data can quantitatively analyze the impact of human activities and urban infrastructure on the urban surface ecological index.Therefore,the integrated application of multi-source data provides a new means for the impact of spatial differentiation of urban functions on urban ecological environment at fine scale.This study takes Shenzhen as the study area,integrates remote sensing data,land use data,urban POI data,socio-economic data and other multi-source data,and firstly analyzes the spatial and temporal changes of vegetation cover,urban heat island and land use in the study area in four periods of 1990,2000,2010 and 2020.And using spatial overlay analysis and geodetector models to reveal the effects of land use types on urban vegetation and surface temperature.Secondly,based on the POI data of urban functional facilities,this study used the kernel density estimation method and information entropy model to reveal the spatial aggregation and functional mixing degree of seven categories of functional facilities such as basic commercial facilities in Shenzhen,and analyzed the spatial differentiation of the two in Shenzhen.Then,based on the current situation of functional distribution and ecological environment in Shenzhen,this study explored the effects of changes in the nucleus density of urban functional facilities and changes in functional mix on NDVI and LST as remote sensing ecological indicators by using a geodetector model,and revealed the way of the spatial differentiation of urban functions affects the ecological environment.Finally,based on the city network model and the gravitational force model,this study calculated the accessibility and economic links between Shenzhen and the cities in the Guangdong-Hong Kong-Macao Greater Bay Area based on roads and railroads,analyzeed the advantages of Shenzhen.In addition,this study proposed relevant countermeasures for the sustainable development of Shenzhen city,with a view to providing reference for the sustainable construction of large cities.(1)From 1990 to 2020,the area share of very high vegetation cover in Shenzhen shows a trend of first decreasing and then recovering.Then,the high and higher vegetation cover areas shows a fluctuating trend of increasing,then decreasing and then increasing and the medium,low,low and very low vegetation cover areas shows an increasing and then a continuous decreasing trend.There are significant improvement in vegetation condition after 2010.The area change of both low and high temperature zones in the city showed a decreasing and then increasing trend and the change in the area of the low temperature zone shows an opposite trend.Over the past 30 years,the distribution of low vegetation cover areas is consistent with that of high temperature areas,mainly in the central and western areas with flat topography,high population density and industrial concentration.However,the medium to high vegetation cover locations are mainly in areas with relatively low urban construction and low population activities,such as Yantian,northeastern of Longgang,Pingshan and Dapeng,and vegetation cover in Midwestern cities recovered after 2010.Very high vegetation cover areas are consistent with the urban low-temperature area,mainly in the Paiya Mountain in the eastern part of the northern peninsula and Qiniang Mountain in the eastern part of the southern peninsula within the Dapeng,as well as the Yangtai Mountain,Fenghuang Mountain Forest Park and urban parks and green areas such as Xianhu Botanical Garden,Drinking Water Source Protection Zone,Dasha River Park,etc.(2)From 1990 to 2020,the impervious surface of Shenzhen expands dramatically,with a total increase of 511.11 km~2,and is mainly transferred from the area of forests,arable land,and water.Spatial and temporal changes in land use have significant effects on vegetation cover and surface temperature,especially impervious surfaces have the greatest impact.Within the four periods,the percentage of impervious surface to water body area is high and the percentage of forest,arable land,shrubland,wetland,and other land types is low in the very low-medium vegetation cover class,and the highest percentage of forest area in the very high vegetation cover class.From 1990 to 2010,impervious surfaces were mainly below the medium vegetation cover level,and after2010,the area share of impervious surfaces in the medium-very high vegetation cover level gradually increased,and the vegetation condition of urban areas improved.The percentage of impervious surface in the low-temperature zone was small and did not vary much during the four periods.However,the area of high-temperature areas above classⅣ accounts for a large proportion and maintained a continuous increase.In the low temperature zone,the area of forest,cropland,grassland and shrubland accounted for a large proportion of the area,and the proportion of forest is the highest.In the lowtemperature zone,the proportion of forests exceeded 50% in all four periods,and the change in the proportion showed a decrease followed by a recovery(3)The spatial differentiation of urban function distribution in Shenzhen is obvious,and there are significant differences in urban construction.The urban functional facilities in the central and western regions are perfect,forming the core of high density and high function mixing degree,and the comprehensive power of urban functions is strong,while the urban facilities in the north,northeast and southeast regions are significantly reduced and the functions are single.The basic business district is located at the junction of Futian and Luohu.The transportation core area is located in Bao’an,Luohu,Nanshan,Futian and Longhua,with perfect transportation functions.Among them,Bao’an has the most types of transportation facilities with high degree of function mixing,and is an important transportation hub in Shenzhen.The distribution of administrative institutions and social organizations in each district is relatively balanced,gathering areas are formed mainly in the residential and commercial areas.But there are significant differences in the distribution of educational facilities and medical and health care facilities: Nanshan District is the core area of educational resources,Bao’an,Longgang and Longhua are the gathering areas of medical and health care resources,while Yantian,Pingshan and Dapeng relatively lacking in education and healthcare resources.The living service area is located in Huaqiangbei-Naigang in Futian and Dongmen-Renmin South Road in Luohu,and is distributed around the center of the business district.The company business district spatial distribution polarization phenomenon is obvious,mainly located in Futian Huaqiang North-Futian CBD,Nanshan District Science and Technology Park.Factories and industrial parks are mainly located in the north of Baoan District,the west of Guangming District,the west of Longhua,and the middle and northeast of Longgang and Pingshan District.The green areas are mainly located near the Window of the World,Happy Valley and Overseas Chinese Town in Nanshan District and the Shenzhen Garden Expo in Futian District as well as various scenic spots.(4)Different functional facilities’ POI core density and functional mix degree have different explanatory power to NDVI and LST,and the explanatory power is higher under the interaction of two factors,while NDVI and LST have different responses to different types of urban facilities’ POI core density and functional mix degree.For NDVI,the influence of POI core density change of living service,administrative public service,road traffic and factory park facilities is significant and has higher explanatory power,and the influence of functional mix of living service,basic commercial and administrative public service facilities is significant and has higher explanatory power.For LST,the influence of POI core density of factory park,living service,administrative public service and road traffic facilities is significant and has higher explanatory power,and the influence of functional mix of living service,basic commercial,administrative public service and factory park facilities is significant and has higher explanatory power.NDVI decreased with the increase of POI density of basic commercial facilities,road traffic facilities,company business facilities and factory park facilities,while LST showed the opposite trend.The high-density areas of factory parks and road traffic POI are consistent with the high-temperature areas,and industrial land and traffic land are prone to form urban "heat islands".When attraction green space facilities reach a certain density level and mix level,it will lead to higher NDVI and lower LST,indicating that attraction green space with a certain density and functional mix can optimize urban vegetation conditions and suppress surface temperature increase.But the increase in the mix of POI functions of basic commerce,living services,road traffic,administrative and public services,and factory parks has a negative effect on NDVI and a positive effect on LST.(5)Shenzhen’s transportation and economic advantages in the Guangdong-Hong Kong-Macao Greater Bay Area city cluster are increasing,but the quality of ecological environment is significantly affected by urban construction,and the high-quality and sustainable development of the city is closely related to ecological environmental protection.In order to achieve sustainable development in Shenzhen,in terms of action,the government should strengthen the supervision and restoration of natural ecological protection,continue to promote the delineation of ecological protection red lines,strengthen the investigation and supervision of key ecological reserves,conduct key assessments and centralized treatment of pollution sources,make timely and focused rectification of ecological problems,and focus on modernizing the ecological and environmental governance process.In terms of policy and legislation,relevant departments should make more efforts to establish environmental legislation and environmental policies,so as to provide legal and policy protection for ecological protection.In addition,while protecting key areas,relevant departments should improve the construction of green space facilities in urban areas.Considering the limited land resources in Shenzhen,relevant departments can increase the use of some spaces,such as three-dimensional space,river space,coastline space,etc. |
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