Study On Urban Expansion And Spatio-temporal Variations Of Land Surface Temperature In Hotan City

In this paper,the Landsat series remote sensing images of 1990,2000,2010 and2018 in Hotan City are used as basic research data.Combined with field investigation,the random forest classification method is used to extract land use/cover information in four periods.On this basis,the characteristics of land use/cover type change in Hotan City from 1990 to 2018 are explored by means of the land use transfer matrix and dynamic index.The spatial analysis methods,such as expansion speed index(ESI),expansion intensity index(EII),expansion degree index(EDI),center of gravity transfer track,spatial orientation analysis and buffer zone analysis,are selected to study the spatial and temporal characteristics of construction land in Hotan City.Combined with the results of LST inversion,the temporal and spatial distribution pattern of LST in Hotan City is studied,and the relationship between different land use/cover types and LST is analyzed.The main conclusions are as follows:(1)From 1990 to 2018,the construction land area continued to grow,with a total increase of 38.84km~2,mainly from cropland?other land and green land.From 1990 to2000,the EDI of construction land is the smallest,from 2000 to 2010,the EDI of construction land is the largest,and from 2010 to 2018,the EDI of construction land is between the two.In the past 28 years,the center of gravity of construction land in Hotan City has shifted from northeast to northwest to southwest.Based on the analysis of spatial orientation,it can be seen that the construction land in four periods is mainly concentrated in the north and northeast.According to the analysis of buffer zone,the construction land in Hotan City is mainly characterized by agglomerative development.With 10km buffer zone as the dividing line,the construction land areas in four periods within 10km increase year by year,which are 22.94km~2,24.18km~2,36.05km~2and50.6km~2respectively.Beyond 10km,the area of construction land increased before2010 and decreased after 2010.(2)Hotan City,as a typical desert oasis city,shows obvious"cold island effect".That is to say,low temperature in oasis area and high temperature in Gobi(desert)area.Oasis area is mainly distributed in the middle of Hotan City,and Gobi(desert)area is distributed in the southwest and northeast of Hotan City.With the expansion of construction land,the LST disturbance of oasis area is obvious,"heat island"increases,distributed in patches around the main urban area of Hotan City,and spreads to the direction of railway station.From 1990 to 2018,the average LST of Hotan City increased by 2.63?,and the spatial distribution pattern of LST has also changed greatly,it can be found that Mesothermal zone and sub high temperature zone increased significantly,while the area of low temperature and very low temperature increased slightly,while the area of sub low temperature and high temperature decreased,while the area of extra high temperature remained unchanged basically.The growth direction of Mesothermal zone and sub high temperature zone were basically the same as the expansion direction of construction land.The spatial pattern of LST in Hotan City also shows obvious characteristics of aggregation.That is to say,the regions with similar LST gather obviously in spatial distribution.(3)Different land use/cover types have obvious differences in LST.The average value of LST in different land use/cover types is:other land>construction land>green land>cropland>water body.During the 28 years,the average LST of construction land,cropland and green land increased by 7.37?,5.07?and 2.74?respectively,and the average LST of water body and other land basically remained unchanged.It can be seen from the LST profile that the spatial pattern of LST changes with the type of underlying surface cover.Other land and construction land are positively correlated with the LST,among which the construction land has the most obvious disturbance to the LST,and the closer to the main urban area,the more intense the change of the LST is;the cropland,water body and green land are negatively correlated with the LST,which is very effective to alleviate the regional high temperature and easy to produce cold island.To sum up,the expansion of construction land in Hotan City not only changed the local land use/cover type,but also affected the spatial pattern of LST.The research results can provide a reference for future research on the relationship between Hotan City's land use/cover and LST.They can also provide scientific basis to maintain the stability of Hotan City's ecosystem,improve the surface thermal environment and promote the healthy development of the city and the land reasonable planning.