Research On The Temporal And Spatial Evolution Of Heat Island In Medium-sized Cities And Its Influencing Factors

With the continuous improvement of our country’s economic level,the process of urbanization is accelerating,a large number of rural people have poured into cities,and the pressure on urban population has increased sharply.On the other hand,urban surface types have undergone significant changes,and a large number of green vegetation surfaces have been impervious to cement,asphalt,etc.The surface is replaced,and the water permeability and evaporation performance of the ground are changed,which leads to the intensification of the urban heat island effect,which seriously affects the urban thermal environment and the physical and mental health of urban residents.At present,domestic and foreign scholars have conducted extensive research on the issue of urban heat islands,but the research objects are mainly concentrated in large cities or megacities,and there are few studies on small and medium-sized cities.Based on this,this article takes Mianyang as an example to analyze the spatio-temporal evolution of heat islands in medium-sized cities.Influencing factors are analyzed,and quantitative remote sensing monitoring and landscape analysis methods are used to study the evolution process of urban heat islands,landscape pattern changes and their impact on urban heat islands,and propose corresponding mitigation strategies.The main contents of the research include:(1)The evolution process and distribution characteristics of urban heat island in Mianyang City are studied.The radiative transfer equation algorithm is used to invert the surface temperature,and the mean-standard deviation method is used for further processing.According to the comparative analysis of the evolution of the intensity of the heat island based on the surface temperature images,the results show that from 2004 to 2016,the area of the extremely high temperature area of the surface temperature in Mianyang City gradually increased from 10% in 2004 to 30.81% in 2016,and the intensity of the heat island effect in the entire city continued to increase.Enhancement,the distribution areas of heat islands are mainly concentrated in densely constructed areas such as residential land and commercial land.Analyzing the difference between the distribution of heat islands in medium-sized cities and those in large cities and mega-cities,the results show that medium-sized cities often have only one heat island center of gravity,while large-scale cities have multiple heat island centers at the same time.(2)Research on the changes in land use in Mianyang City and its impact on the urban heat island.The maximum likelihood classification is used to classify surface land use conditions at different times,and all surface types are divided into six categories,and corresponding land use images are made for analysis.A linear regression method was used to study the relationship between NDVI and NDBI values and surface temperature.The results show that from 2004 to 2016,the area of natural vegetation such as woodland,farmland,and arable land in Mianyang City continued to decrease,while the area of urban areas continued to increase.The proportion has increased from 17.9% to 47.6%;there is a significant correlation between NDVI,NDBI and surface temperature.The surface temperature increases by about 2.4℃ for every 0.1 increase in NDBI value;the surface temperature drops by about 1.5℃ for every 0.1 increase in NDVI value.(3)The overall landscape pattern change of Mianyang City and its impact on the urban heat island were studied.Based on four sets of land use images in different years,Fragstats software is used to analyze the changes in the overall urban landscape pattern from two scales of landscape type and landscape level.The results show that the degree of fragmentation of the overall urban landscape continues to increase,and the internal connectivity of the landscape continues to increase decrease,the largest plaque area continues to increase.The correlation analysis between the landscape index and the urban heat island ratio index at the landscape level shows that the patch density,the maximum patch ratio index and the urban heat island ratio index are significantly positively correlated,and the correlation coefficient of the maximum patch ratio index is 0.96;both the rich diversity index and the Xiangnon uniformity index are negatively correlated with the urban heat island ratio index.(4)According to the temporal and spatial evolution and distribution characteristics of urban heat island,Mianyang urban heat island effect mitigation measures are proposed,including rational planning of land functions,overall planning of urban and rural development,promotion of green travel concepts,and vigorous development of new energy technologies and industries.This paper uses remote sensing monitoring and landscape ecology methods to study the spatiotemporal evolution of the heat island effect and its influencing factors in Mianyang City as an example,and proposes strategies to alleviate the heat island effect.The research methods and research conclusions can provide reference for the ecological city construction of medium-sized cities.