Spatiotemporal Dynamics And Thermal Environment Effects Of Urban Impervious Surfaces In Xuzhou

As an effective indicator of urbanization,impervious surfaces play a significant role in urban planning and ecological protection.It is,therefore,of great importance to examine the spatiotemporal dynamics of impervious surfaces for urban development and thermal environment analysis.As the central city of the Huaihai Economic Zone,Xuzhou has been strengthening the construction of ecological city after rapid urbanization,which in return makes its urbanization process attract growing attention.Using Landsat images of 1995,2003,2010,and 2018,this thesis explores the spatiotemporal dynamics of urban impervious surfaces and their relationship with land surface temperatures in Xuzhou.Linear spectral mixture analysis(LSMA)and classification were performed to extract multi-temporal impervious surfaces at both pixel and sub-pixel levels.At the pixel level,the overall expansions of impervious surfaces were analyzed by differencing.The expansion directions of impervious surfaces were detected by means of median center and standard deviation ellipse.Gravity model,Lorentz curve,and Gini coefficient were adopted to reflect spatial agglomeration of impervious surfaces.Expansion speed index and spatial autocorrelation model were combined to analyze the expansion rates of impervious surfaces.At the sub-pixel level,the overall and local growth changes of impervious surface fractions were measured through change trajectories and profile lines.Transition matrices and dynamic degrees were calculated to reveal the change characteristics of impervious surface fractions of different levels.Landscape patterns of impervious surfaces were described using landscape indices.Based on the results of multi-temporal land surface temperature inversion,the spatiotemporal variations of urban thermal environments were characterized by landscape indices and differencing statistics.Then the correlations between impervious surfaces and land surface temperatures were analyzed in multiple grid sizes.Deviation and contribution ratio were adopted to quantify the impacts of impervious surface changes on land surface temperature changes.The main results and conclusions are as follows:(1)Impervious surface areas at the pixel level and impervious surface fractions at the sub-pixel level were extracted.Validation results show that the root mean square(RMS)of the LSMA in 1995,2003,2010,and 2018 were 0.017,0.019,0.020,and 0.018,respectively,which were all acceptable.The linear fitting goodness(R~2)of impervious surface fraction in 2018 was 0.86,and the overall accuracy and Kappa coefficient of impervious surface area in 2018 were 0.85 and 0.70,respectively,indicating that the extraction accuracy was high.The dense buildings in the downtown area resulted in a high impervious surface fraction,while the scenic area in the southeast of the study area had high vegetation coverage with relatively low impervious surface fractions.Impervious surfaces were mainly distributed in the downtown area and expanded to the surrounding areas continuously.Impervious surfaces in the districts of Jiawang and Tongshan were relatively small and scattered.(2)At the pixel level,the spatiotemporal dynamics of the impervious surface expansions were revealed.The impervious surface area of study area was constantly expanding,showing two forms of expansion,namely from the downtown area outward and along the traffic road.The expansion directions of the impervious surfaces of the entire study area were not obvious,while the expansion directions of impervious surfaces of each district were clear and different.Impervious surfaces of the central urban area expanded towards the east and southeast in general.Differences existed in the spatial agglomeration of impervious surfaces,but it decreased on the whole,showing a gradually coordinated development.Expansion rates of impervious surfaces showed a significant spatial agglomeration.The districts within central urban area had earlier urbanization construction,and their impervious surface areas accounted for the high proportions.The development of the downtown area tended to be saturated,leading to the relatively slow expansion rates of impervious surfaces.Meanwhile,the Jiawang and Tongshan districts,which were relatively backward in the past,have accelerated their development in recent years,and the expansion rates of impervious surfaces rose significantly.(3)At the sub-pixel level,spatiotemporal dynamics of the increases in impervious surface fractions were measured.Generally,impervious surface fractions showed an increasing trend.Impervious surface fractions in central urban area were always relatively high and had a large increase,but ecological protection made it decrease slightly in recent years.In general,impervious surface fraction levels showed that low-density impervious surfaces decreased and other levels increased,showing the agglomeration effect of urban impervious surfaces.The change between impervious surface fraction levels was the most dramatic from 2003 to 2010 due to the rapid urban development.Landscape pattern of impervious surfaces became complicated,the low-density impervious surfaces tended to be fragmented while the high-density ones were opposite.The coordination of urban construction and ecological environment protection made urban landscape relatively balanced,increasing its diversity and heterogeneity.(4)Based on the results of land surface temperature inversion,the thermal environment effects of impervious surfaces were explored.By the Mono-window algorithm,multi-temporal land surface temperatures were retrieved.Land surface temperatures were relatively high in the central urban area,industrial and mining areas and bare areas,which were more likely to result in urban heat islands.Generally,urban thermal landscape patches tended to be uniform and increased in diversity.Urban thermal environments improved after deterioration.There is a positive correlation between impervious surfaces and land surface temperatures.Dense impervious surfaces were more likely to cause urban heat islands,but it was worth noting that the increase in impervious surfaces was not the only reason for rising land surface temperatures due to the complexity of urban thermal environments.Impervious surface expansion areas showed relatively drastic changes of land surface temperatures,and their areas accounted for a large proportion,leading to a greater impact on the overall changes of land surface temperatures,and played an important role in urban thermal environments.There are 25 figures,30 tables,and 188 references in this thesis.