| Against the background of the rapid development of global urbanization,the population and construction areas of some large and medium-sized cities will still be dominated by growth,but affected by the decrease in population,some cities will begin to shrink.As representatives of typical structural crisis-type shrinking cities,Hegang City and Dongguan City have attracted the attention of the government.This article does not study shrinking cities in terms of population change and economic development,but focuses on the characteristics of urban thermal environment changes caused by land use and ecosystem changes,the change of urban thermal environment at two different stages after the contraction of Hegang City and the expansion of Dongguan City was studied.This paper uses Hegang administrative district and Dongguan as research areas,and combines GIS and RS to study the spatial and temporal evolution characteristics of the heat island effect in 2009 and 2019.The spatial distribution of the intensity of urban heat islands is explored as a whole,and the transfer and source of heat island intensity are analyzed,the correlation between ground surface temperature and underlying surface parameters was pointed out.At the same time,the thermal landscape pattern index was introduced to explain the overall spatial configuration characteristics.The main conclusions were:(1)The range of urban heat islands in Hegang City is scattered from scattered to clusters,moving from the south to the north from the Xing’an District to the Gongnong District and Xiangyang District,and it is also the central urban area.The urban thermal environment as a whole has not shown a strong heat island phenomenon accompanied by mitigation,which is related to the control of construction land,the increase of green area,the focus on the development of ecological cities,and the slow industrial transformation in recent years.The distribution characteristics of heat islands in Dongguan are scattered.The intensity of heat islands in urban districts,mainly Wancheng Street,Dongcheng Street,and Nancheng Street,has slowed down.The water town new city area,mainly in Mayong Town and Hongmei Town,and Humen Town,Changan Town The intensity of heat islands in coastal areas has increased.Dongguan’s urban thermal environment as a whole did not show a strong heat island phenomenon.Due to the financial crisis in the previous period,a large number of foreign populations were lost,factories were vacant,economic development was down,and the intensity of heat islands was reduced;In the later period,the city quickly transformed,and the development of high-tech industries eased the labor force to a certain extent.At the same time,the government also focused on the development of ecological cities.The shrinkage and expansion of the city showed a perforated distribution.Therefore,the development of the city did not cause a strong heat island phenomenon.Changan Town,another typical outward-oriented economic feature in Dongguan,was selected to study the thermal environment characteristics of its expansion after contraction.When the town contracted,the intensity of the heat island decreased,but the original impervious surface will not disappear in the short term.Certain influence.When the city expands,the strong heat island effect tends to increase.The low-temperature areas of the two cities are mainly distributed in green areas and water bodies.Therefore,shrinking cities with population and economy as the main research dimensions,combined with the characteristics of urban development,have corresponding thermal environment changes.(2)From 2009 to 2019,Hegang City is mainly based on the strong green island area and the heat island area,with the smallest proportion of the strong heat island area.The green island area and the middle area are in the middle,and there is no strong urban heat island phenomenon.Low heat environment is the main factor,and the urban heat island effect is gradually decreasing.The strong green island area and heat island area of Dongguan City maintained a high proportion.The total area of the strong green island area and the green island area maintained nearly half of the proportion,and the total proportion increased,indicating that the overall thermal environment of Dongguan city did not show a strong heat island phenomenon.,Slow down first and then stabilize.From 2009 to 2019,the process of mitigation of urban heat islands in the two cities is mainly: strong heat island → heat island → middle → green island → strong green island.(3)Based on the fitting of surface temperature and building land index(RRI),soil-adjusted vegetation index(SAVI)and improved normalized difference water body index(MNDWI),it can be concluded that both cities in 2009-2019 were not The permeable surface has a positive correlation with ground temperature,and vegetation and water bodies have a negative correlation with ground temperature.In Hegang City,the cooling effect of vegetation and water body is higher than that of buildings,and the heating effect of buildings in Dongguan city is higher than that of vegetation and water bodies.It shows that the increase of vegetation and water bodies in small and medium-sized cities or a small area can restrain the heat island effect of the city to a certain extent.In large and medium-sized cities,the building temperature effect plays a leading role.Therefore,a reasonable layout of the area of vegetation and water can alleviate or eliminate the urban heat island effect to a certain extent.(4)Through the thermal landscape pattern index patch density(PD),average patch area(AREA_MN),area_perimeter sub-dimension(PAFRAC),spread(CONTAG),Shannon diversity index(SHDI)and Shannon uniform Analysis of degree index(SHEI),the two cities are relatively speaking,the thermal landscape of Hegang City is not fragmented to a high degree,and its openness is not strong.It is not easy to exchange material energy with the surrounding patches.After the degree of interference is strengthened,it weakens.A certain type of advantage in the landscape has formed a good connectivity and rich in types.Low degree,with dominant types and uneven distribution of each type,high dominance.Dongguan City’s thermal landscape has become more fragmented and more open,and it is easy to carry out material energy circulation with surrounding patches,which indicates that the greater the degree of interference,the richer the types,the more dominant types are,and the types are evenly distributed,the lower the degree of superiority.The characteristics of the landscape pattern index also reflect the difference in the development level of the two cities,indicating that Dongguan has a higher urbanization and is more affected by human interference. |
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