Research On Spatial-temporal Changes Of Surface Elements And Its Thermal Environmental Effects In Nanchang

With the rapid development of cities,the process of urbanization has caused huge changes in the composition of the surface and global warming.As a result,the accompanying urban ecological problems have become increasingly prominent,and the thermal environment problem has become more serious.The change of urban thermal environment has a relationship with land use or cover type and surface landscape that cannot be ignored.A systematic study of urban surface elements,landscape patterns,and thermal environments is of great significance for the healthy development of cities and the construction of regional ecological environments.This article is based on RS and GIS technology,combined with landscape ecology ideas.Taking Nanchang City as an example,the data of 2000,2005,2011and 2017 are selected.The main tasks are as follows:(1)By comparing the three impervious surface extraction methods,the optimal method is used to extract impervious surfaces and other surface elements in each year.The single-window algorithm was used to invert the surface temperature of each year,and the accuracy was verified.(2)Study the spatiotemporal characteristics of impervious surfaces,vegetation and water bodies from multiple levels and perspectives.In addition,the thermal environment is analyzed from the perspective of thermal level in terms of its spatial and temporal changes.(3)Explore the relationship between surface factors and thermal environment from the perspective of coverage and landscape pattern.In terms of coverage,correlation and regression analysis were performed on single factor and multi-factor and thermal environment,respectively.In terms of landscape pattern,the spatial distribution of the surface pattern index of each surface element was calculated,and the correlation analysis and regression modeling were performed with the surface temperature to obtain the relationship between each landscape pattern index and thermal environment.The conclusions reached are as follows:(1)Compared with the two methods of LSMA and NDISI,random forest classification has a higher accuracy in extracting impervious surfaces in Nanchang,especially in the northern part of the study area,which is close to the Poyang Lake area.The single-window algorithm is used to invert the surface temperature,and the MODIS surface temperature product data is used to verify the accuracy of the surface temperature inversion results,which shows that the error of the temperature inversion results in this paper is small.(2)In general,the impervious surface of Nanchang shows a continuous expansion trend,but the dynamic degree gradually decreases.In the gradient direction,the proportion of impervious surfaces(area proportion)decreases with increasing distance from the city center,but the proportion of impervious surfaces in each gradient zone increases with time.In the azimuth direction,the impervious surface expands around,but the main direction of expansion in different stages is different.From the perspective of landscape pattern,the overall fragmentation of the impervious surface patches is reduced,and the degree of aggregation is enhanced.The change trend is transformed from outward diffusion to a combination of infill and extension.Vegetation and water areas are generally decreasing.For the landscape pattern of the two,the medium and high coverage vegetation is more fragmented and the shape is more complex,and the extremely high coverage vegetation patches are larger.The fragmentation of the water in general has increased,the largest plaque has become smaller,and the shape of the plaque has become more complicated.In terms of the spatiotemporal changes of the thermal environment,the study area is dominated by"medium temperature zone",and"high temperature zone"is mainly distributed in the densely populated areas of the city and expands with the expansion of the urban area.(3)From the perspective of coverage,the coverage of impervious surfaces is positively correlated with surface temperature,and the correlation is gradually increasing,with R2being as high as 0.762;both the vegetation and water coverage are negatively correlated with surface temperature,and the correlation is lower than that of impervious surfaces.The regression analysis results show that at 600 meters,the three factors have a higher degree of fitting than the single factor and two factor regression models,and the ability of the impervious surface,vegetation,and water coverage to jointly describe the surface temperature is stronger;The impervious surface plays a warming role,vegetation and water bodies play a cooling role,and the cooling effect of water is stronger than that of vegetation.From the perspective of landscape pattern,CA,LPI,ED on the impervious surface,vegetation ED,LSI,water CA,LPI,etc.have a significant correlation with surface temperature.In addition,the fitting degree of each landscape pattern index on the impervious surface and the surface temperature regression model is higher than that of the vegetation and water,and the highest of R~2 is 0.615.According to the above conclusions,in order to alleviate the urban heat island effect and rationally regulate the composition of surface elements in various regions,the proportion of vegetation and water bodies can be appropriately increased,and the proportion of impervious surfaces can be reduced.From the perspective of landscape pattern,scientifically designing the shape,size,edges,etc.of urban construction land,landscaping,urban waters,etc.can effectively improve urban thermal environment problems.