| The nature and spatial structure of urban underlying surface affect the urban heat island(UHI)directly.Among them,the urban topography and land use types are the most important factors for the UHI,besides these,the spatial and temporal variations of which are also the main factors that determine the spatial distribution of the thermal field.In this study,we use Landsat TM/ETM+,Aster GDEM data from1991 to 2015 in Changsha to retrieve the land surface temperature(LST)of built-area of Changsha City built-area,then quantitatively evaluated and analyzed the spatial pattern and intensity of the time varying UHI caused by the urban expansion.In addition,we classified the land use /cover types and extracted the road information of the study area combined with the 2015 Google earth high resolution area,then analyzed the influences of the UHI in Changsha caused by each factor of urban underlying surface.The main conclusions are as follows:(1)Through the comparation of the LST of built-area of Changsha City in different years,we found the spatial distribution and expansion of UHI in Changsha were consistent with the built-up area of the city outline,and expanded and strengthened with the development of the city.The LST of the central city is obviously higher than that of the surrounding suburbs,and the island is formed in the high temperature region.The hightemperature area of the city is mainly concentrated in the industrial and commercial concentration and densely populated urban center,and presents the spatial distribution pattern from high to low of the surface temperature from the city center to the suburbs.(2)The strength of UHI effect is closely related to the underlying surface types.The temperature of different underlying surface types in the study area were compared and analyzed.The results showed that the surface temperature of different underlying surface coverage types was very different,so does the contribution to the UHI intensity.Between different underlying surface coverage types,the surface temperature had obvious difference,and with the development of the city gradually became small differences.The construction land and cultivated land in the study area had a great contribution to the LST,which were closely related to the rapid development of Changsha city and the continuous improvement of economic level.(3)There was a positive correlation between the LST and the road density(RD)in Changsha,and there were some differences in the road temperature with different width,in addition,the contribution to the UHI effect in Changsha was also different.The road raised the surrounding temperature,and with the increase of the distance,the influence decreased.Roads with a width of 15~30m had the highest LST,and the roads with a width of more than 30 m had the largest influence on the LST,which were about 150~200m.Different road level had different thermal effect contribution to different temperature region,the 1st roads had the largest thermal effect contribution to both low and high temperature region,respectively 65.54% and 52.95%,and the next was level-3 road.The secondary road had the largest thermal effect contribution to the middle temperature region with a thermal effect contribution about50.36%,and then was the 1st road.(4)The main urban area of Changsha is rough,with high elevation around the center caused low heat dissipation,which is also an important factor affecting the LST.The elevation of Changsha city has a large span,while the average temperature difference between different elevation gradients is small.The highest LST is located in the second elevation gradient range(30-60m),and decreases with the elevation. |
PDF Full Text Request