| The urban heat island effect is a significant climate change phenomenon caused by changes in the physical properties of the surface ecology,which has an impact on the construction of a civilized society,the economy,and the sustainable development of productivity.Studies have shown that there are many driving factors that cause the urban heat island effect.However,the biochemical reaction of haze aerosol is also one of the important factors affecting the urban heat island effect.Therefore,the selection of influencing factors such as aerosol optical thickness to analyze the mechanism of urban heat island effect is of great significance for understanding and improving urban thermal pollution.This paper takes the Xi'an metropolitan area as the research area,and extracts the surface temperature information of the study area for 17 years using 4 Landsat remote sensing images from2003 to 2019 and long-term series MYD11A2 surface temperature product data.Based on the M-K non-parametric test method,Pearson correlation analysis,R/S analysis method and gradient analysis,this paper analyzes the temporal and spatial variation characteristics of the surface temperature in the Greater Xi'an area with urban expansion,and then explores the temporal and spatial differentiation of urban heat island intensity.The correlation analysis between the intensity of urban heat island and its driving factors is analyzed.Finally,gradient analysis is used to analyze the impact of aerosol radiation effects on the urban heat island in Xi'an area and quantitatively evaluate the contribution to the intensity of the urban heat island.The main conclusions of this research are as follows:(1)Changes in the spatial pattern of urban heat islands.The process of urbanization makes the impervious surface present a pattern of expansion to the surroundings,especially spreading along the Weihe River in the northern part of the city.Xi'an and Xianyang urban areas gradually broke the administrative boundaries and moved closer to the edge of the Weihe River.In 2000-2018,the urban expansion speed and expansion intensity showed the trend characteristics of "rising-falling-rising";based on Tan Zhihao's single-window algorithm inversion,the spatial change pattern of urban heat islands was analyzed.In2000-2018,the urban expansion speed and expansion intensity showed the trend characteristics of "rising-falling-rising";Research on the surface temperature based on inversion analyzes the spatial change pattern of urban heat islands.From 2003 to 2019,the areas of low temperature,sub-low temperature,medium temperature and sub-high temperature areas have gradually increased.The high temperature area shows a trend of increasing first(2003-2014)and then decreasing(2014-2019).(2)City LST time series analysis.The daytime and night surface temperature in the study area fluctuated during the 17 years,but showed an upward trend as a whole.Among them,the daytime surface temperature rose relatively quickly,with an overall increase of about2.53?,while the nighttime average surface temperature increased by 0.737?;Based on the Mann-Kendall non-parametric test method,the Z value of the detection statistic of average ground temperature during the day from 2003 to 2019 was 2.595,while the Z value of the detection statistic of average ground temperature at night was 2.183,both showing an upward trend at a significant level.Combined with the R/S analysis,the Hurst index of the daytime and nighttime average ground temperature time series in the interannual,spring and summer are all greater than 0.5,indicating that the change in the average ground temperature time series in the study area is positively correlated,and the upward trend will continue for a period of time in the future.(3)Temporal and spatial differentiation of urban heat island intensity and its influencing factors.The daytime heat island intensity of United Cities showed an overall trend of rising(2003-2012)and then decreasing(2012-2019)in 17 years,while the night heat island intensity showed an overall increasing trend;Using the M-K mutation test analysis,it is found that the daytime and night heat island footprints both show an upward trend on an inter-annual basis;Correlation analysis shows that the intensity of the interannual daytime heat island has a strong negative correlation with ?AOD,?EVI and evapotranspiration,and the night heat island intensity has a strong positive correlation with ?AOD,?NL,population and construction land,and all have passed the 0.01 significance level.(4)Analysis of the attribution of aerosol radiation effect on Urban Heat Island.Based on the urban-rural gradient analysis and correlation analysis to explore the impact of aerosol radiation effects on urban heat islands,the results show that as the distance from the geometric center is farther,the diurnal LST in 2003 and 2019 shows a gradual downward trend,while AOD shows an upward trend.The analysis shows that daytime LST and nighttime LST respectively have a strong negative correlation with AOD,especially the correlation at night is more significant,indicating that the aerosol radiation effect has a significant cooling effect on the local climate of Xi' an.However,the experimental results show that the difference in aerosol radiation effects between urban and rural areas from2003 to 2019 is a process of heating up the intensity of urban night heat islands as a whole.Using the method of quantitative observation and reanalysis,it is concluded that from 2003 to 2019,the contribution of the difference between urban and rural AOD to the intensity of the urban heat island showed a trend of first increasing and then decreasing. |
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