Spatiotemporal Quantitative Analysis Of Local Climate Zones And Surface Temperature In Shanghai

Urbanization is a distinctive feature of the development of human society at this stage.Rapid urbanization is accompanied by drastic changes in land cover,resulting in a rapid increase in buildings and impervious surfaces,which in turn lead to urban thermal environmental problems.Urban heat island will accelerate urban energy consumption and air pollution,and greatly affect the comfort and health of urban residents.Solving the thermal environment problem in the process of urban development is an inevitable requirement for sustainable urban development.Obtaining urban land cover information efficiently and accurately,analyzing the temporal and spatial variation characteristics and correlation between urban land cover types and surface temperature,can provide reference for urban planning and construction,coordinate the contradiction between urbanization and thermal environment issues,and promote the sustainable development of the city.The Local Climate Zone(LCZ)classification system is well suited to meet the needs of urban thermal environment research and urban planning.Urban heat island under the LCZ framework has become a hot research topic in recent years,but most of the studies focus on LCZ and urban heat island research under a single time scale,and the surface spectral information of urban building types is complex,and there is a certain difficulty in high precision LCZ mapping.The focus of this research is to improve the accuracy of LCZ mapping at medium resolution,and to conduct quantitative research on the spatiotemporal changes of urban LCZ and surface temperature at long time scales,and to analyze the distribution characteristics and spatiotemporal changes of various types of surface temperature in LCZ at different time.This study takes Shanghai as the research area.Firstly,this study combined Landsat-5 TM optical imagery and dual-polarized PALSAR data in 2008,and combined Sentinel-2 multispectral optical images and dual-polarized PALSAR-2 data in 2020,the LCZ classification system and random forest classifier were used to generate two LCZ classification maps of Shanghai,and its classification accuracy was evaluated,and then analyzed the spatiotemporal changes of LCZ in Shanghai from 2008 to 2020.Secondly,the atmospheric correction method is used to retrieve the surface temperature of Landsat 5 TM in 2008 and landsat-8 OLI/TIRS image data in 2020,and the daytime surface temperature maps of Shanghai in 2008 and 2020 are obtained.The daytime and nighttime surface temperatures of Shanghai in different months were obtained through Landsat surface temperature products and ASTER data.The temporal and spatial distribution and correlation between Shanghai LCZ and surface temperature were analyzed.The results show that:(1)The overall accuracy of LCZ classification results in Shanghai in 2008 and2020 were 80.4% and 75.35%,respectively.Confusion was low between natural cover types and building types,high-rise building and low-rise building,but higher between building types of equal height and between low vegetation and shrubs and trees.Combining spectral images and SAR data can effectively improve the classification accuracy of building types,and the improvement of image resolution can improve the classification accuracy of exposed rocks or roads.(2)From 2008 to 2020,the area of various types of LCZ in Shanghai changed significantly,among which open high-rise buildings and bare soil or sand increased most significantly,and low vegetation decreased significantly.Dense high-rise buildings,open mid-rise buildings,dense trees,shrubs and water body have increased,while dense middle-rise buildings,dense low-rise buildings,open low-rise buildings and industrial plants have decreased.From 2008 to 2020,the transfer of various types of Shanghai LCZ is mainly manifested as the transfer between building types,the transfer between vegetation types,the conversion of vegetation types into building types,bare soil or sand,and exposed rocks or roads.Roads converted to building types.(3)The average daytime surface temperature of Shanghai building types is generally higher than that of natural covering types,dense building types are generally higher than open building types.The distribution characteristics of the average surface temperature in the Shanghai LCZ in 2008 and 2020 are generally consistent,but the temperature difference between the various types in the LCZ in 2020 is greater than that in 2008.The surface temperature changes significantly in different months.The heat island effect is obvious in the central urban area of Shanghai in spring and summer,and the surface temperature is significantly higher than that in the suburbs.The surface temperature difference between various types of LCZ in spring and summer is greater than that in autumn and winter.The distribution characteristics of the average daytime surface temperature of different types of Shanghai LCZ in different months are generally consistent.The average daytime surface temperature of building types is always higher than that of natural covering types.The average surface temperature of dense buildings and industrial plants is higher,and the water body and vegetation types are lower.The nighttime surface temperature in the central urban area of Shanghai is higher than that in the suburbs.The nighttime average surface temperature of building types is generally higher than that of natural cover types,but the overall temperature difference becomes smaller compared with that in the daytime.Among the building types,dense high-rise buildings have the highest average surface temperature at night,and medium and high-rise buildings are higher than low-rise buildings.Among the natural types,the average nighttime surface temperature of the water body is the highest,and the vegetation type is the lowest surface temperature among all types.Compared with the daytime,the average surface temperature of the three vegetation types shows the opposite distribution characteristics at night.The differences and changes of various types of surface temperature in the Shanghai LCZ in different time are affected by various factors such as vegetation coverage,land cover changes,and human life and production behaviors.