| With the rapid development of China's economy,the speed of urbanization in Guiyang City is accelerating constantly.The changes in the regional ecological environment caused by rapid urbanization,especially the changes in the thermal environment,have had a significant impact on the regional ecological environment.Due to the unique geological features of the karst region,the ecological environment in the region is very fragile and difficult to repair;therefore,studying the impact of urbanization on the regional thermal environment is very important to regional sustainable development.In this paper,we chose Guiyang City and its surrounding areas as the research area.Based on the land use/cover change(LUCC)maps extracted of form the Landsat,combined with the land surface temperature(LST)data retrieved form the MOD11A2 data,and taking the unique karst geological and landform characteristics of the research area into consideration,the correlations among the LUCC factors,the geological factor and LST are analyzed in order to explore the driving factors of the yearly,seasonal and diurnal variation of LST in the study area.Moreover,variation of regional thermal environment caused by rapid urbanization is discussed by extracting and calculating the influence intensity of the heat island,combined with the meteorological temperature data of the study area.The results of this study are shown as follows:(1)Land use/cover changes and urban thermal environment chnages: 1).The dominate land use/cover type of the study areas was green spaces that with low vegetation coverage from 2002 to 2018.the proportion of green spaces occuping more than 63% of the totoal area.Forests that with high vegetation caverage is the second dominate land use/cover types,accounting for about 30% of the total area of the study area;the proportions of water bodies,construction land and unused land are very low,all of them occupied less than 5% of the total area of the study area.2).From 2002 to 2017,the total area of green spaces decreased significantly,and the totoal area of water body area decreased slightly.In the other hand,forests,construction land and unused land increased rapidly during these years.The totoal area of construction land increased by nearly 4 times and the total area of unused land increased by more than 10 times from 2002 to 2017.3).The thermal environment in the study area was deteriorated by rapid ubanization,and will be worth if not being protected.In the metropolitan area of Guiyang,patterns of changes in the totoal area of high temperature zone and sub-high temperature zone were as follows.Generally,the total area of high temperature zones and sub-high temperature zones during the daytime is larger than the total area of high-temperature area and sub-high temperature area during the nighttime.Moreover,the total area of high-temperature area in summer was the largest and the area of high-temperature area in winter is the smallest.Besides,with the expansion of urban areas,the total area of high-temperature zones and sub-high temperature zones increased obviously.(2)Variation of driving factors of thermal environment in the study area: the regional thermal environment was affected by rapid urbanization,topographic condition and lithological charicteristics,and the impact of the same factor on regional thermal environment presented seasonal,diurnal and inter-annual differences.On the one hand,land use / coverage factors play a leading role in the regional thermal environment.At both scales,forests and water body were negatively correlated(p<0.01)with daytime land surface temperature,while construction lands,green spaces and unused lands were positively correlated with daytime land surface temperature.However,water bodies and construction land were significantly positively correlated with night surface temperature,and forests is significantly negatively correlated with night surface temperature.It is worthy noting that the correlations between green spaces and nighttime land surface temperature were significantly negative at the metropolitan scale while were not significant(p>0.05)at the large scale;and the correlations between unused land and nighttime land surface temperature were not significant at both scale expected those in 2002 at the metropolitan scale(p<0.05).Moreover,the correlation coefficients of water bodies,construction lands,forests and unused lands with land surface temperature in spring and winter were less than those in summer and autumn,while correlation coefficients of green spaces with land surface temperature in summer and autumn seasonswere less than those in spring and winter.With the expansion of uban areas and the implementation of the policy of returning farmland to forests,the impact of green spaces and water bodies on land surface temperature weakened due to the reduction in total area,while the influences of construction lands,forests and unused lands increased due to the increase in total area.On the other hand,topographic condititions and lithological charicteristics also had strong influences on regional thermal environment of the study area.Elevation was significantly negatively correlated with the daytime and nighttime land surface temperature at both scales,and its correlation coefficient with land surface temperature increased graudually from 2002 to 2017.Slope was significantly negatively correlated with the daytime land surface temperature at both scales and significantly negatively correlated with the nighttime surface temperature at the metropolitan scale.However,at the large sclae,slope showed a significant positive correlation with nighttime land surface temperature.The lithological characteristics has a strong influence on the surface temperature of the low-vegetation-covered lands(green land and unsed land).The correlation between the low-vegetation-covered surface with different lithological backgrounds and the daytime surface temperature of all low-vegetation-covered lands were different.Cells of low-vegetationcovered lands with greater proportion of the karst area tended to have higher LST values,and cells of low-vegetation-covered lands with smaller proportion of the karst area tended to have lower LST values,and three different lithologies The difference in LST values of lowvegetation-covered cells with different lithological characteristics were smaller in summer and autumn than those in spring and winter.(3)Changes in the leading factors of regional thermal environment: within these four periods,the influences of urban heat islands on regional thermal environment during the nighttime were greater than those during the daytime,and were greater in summer and autumn than those in spring and winter.With the development of cities,the influences of urban heat islands increased gradually.However,the influences of abnormal heat islands on regional thermal environment cannot be ignored for four periods.Even in 2017,when the proportion of urban area is the largest,its impacts were still greater than those of urban heat island,indicating it was still an important leading factor in the regional thermal environment.(4)Vatiation of regional atmospheric thermal environment: due to the impacts of abnormal heat islands,the annual average temperature of the suburban stations was commonly higher than the annual average temperature of urban stations,while the exurban stations,which was less affected by the abnormal heat islands,had an obvious lower annual average temperature than those of suburban stations and urban stations.With expansion of urbanization,annual temperature of the suburban and urban stations increased obviously,while the annual average temperature of the exurban sites increased slightly during these 16 years.Moreover,differences of annual average temperature between the suburbs and exurban stations and differences of annual average temperature between the urban and exurban stations hadincreased significantly because of urbanizing,and t difference between annual average temperature betwen suburbs and urban stations decreased slightly.The above results show that under the background of regional rapid urbanization,the deterioration trend of thermal environment in Guiyang become obvious.Since the urbanization trend in Guiyang city is inevitable,it is necessary to manage urban layout and regional ecological environment governance work scientifically,which can improve the living comfort of the regional residents,and promote the harmonious development of regional ecology and social economy. |
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