| China's urbanization and industrialization have developed rapidly,While urbanization is advancing,the area of urban built-up is gradually increasing,and natural landscapes such as water bodies and vegetation are reduced,resulting in urban heat island effect.Shenyang is an important hub city in the northeast,In recent years,the problem of urban heat islands has become more prominent.The water body is the cold source of the city,plays an important role in regulating the ecological environment,can effectively alleviate the urban heat island effect.The application of remote sensing technology to study the mitigation effect of water body on heat island effect and quantify mitigation ability is of great significance to the rational planning and layout of cities.Took the municipal district of Shenyang as the research area,selected the five Landsat images from 2000 to 2017.After pretreatment,used the atmospheric correction method to invert the land surface temperature of the study area,chosen the mean-standard deviation method to divide the heat island level,analyzed the temporal and spatial variation of the heat island effect in Shenyang.Used CART algorithm-based decision tree classification method to obtain classification rules to extract land cover changes,and to explore the correlation between land cover change and urban heat island effect.Picked the typical water body patches to complete the buffer analysis.The cooling range,cooling amplitude and cooling gradient were used as indicators to evaluate the mitigation of water body on heat island effect.The influencing factors of water body mitigation heat island effect were analyzed,and the comprehensive effects of influencing factors on water body mitigation heat island effect were explored.Compared the cooling effect of water body and vegetation,and provided reference for the construction and layout of livable cities.The main conclusions of this paper are as follows:(1)The land surface temperature inversion results show that,low land surface temperature area is gradually decreasing from 2000 to 2017,the land surface temperature is on the rise,about two-thirds of the area in 2016 has shown high temperature distribution.The result of the heat island classification shows that the heat island distribution area is 819.71km~2in Shenyang in 2000,and increase to 1150.12 km~2in 2017,an increase of about 1.4 times.From the perspective of spatial distribution,the central urban area has not changed much,and the heat island distribution area has gradually expanded to the suburbs.The distribution result of the heat island loop in Shenyang shows that the heat island intensity gradually decreases from one ring to four rings,and the proportion of heat island distribution area decreases gradually.(2)The results of land cover division indicates that the water body and vegetation area shows an overall decreasing trend from 2000 to 2017,and the area of the built-up continues to increase.The average land surface temperature of the built-up area is always higher than the research area's,and the average land surface temperature of vegetation and water body is lower than the research area's.There is a linear and significant negative correlation between MNDWI,NDVI and heat island intensity during the study period.There is a significant linear correlation between NDBI and heat island intensity.The water body has a strong mitigation on the heat island effect,and the increase of the built-up area will aggravate the heat island effect.(3)The results of quantitative evaluation of the heat island effect of 14 water patches showed that the temperature difference between the progressive buffers was less than 0.1?,.the average cooling range of the water body is 0.26 km,the average cooling amplitude is0.26?,and the average temperature gradient is 8.25?/km.There is a significant positive correlation between the cooling range of the water body and the water surface area(R~2=0.6934,p<0.01),which is significantly positively correlation with the water body shape index(R~2=0.4982,p<0.05),and is significantly negatively correlation with the proportion of the built-up area around the water body(R~2=0.4757,p<0.05).The cooling amplitude of the water body was significantly positively correlation with the water surface area(R~2=0.72,p<0.01),and is significantly positively correlation with the water body shape index(R~2=0.4316,p<0.05),and is significantly negatively correlation with the proportion of the built-up area around the water body(R~2=0.5658,p<0.01).The cooling gradient of the water body is only negatively correlation with the proportion of the surrounding built-up area(R~2=0.4196,p<0.05).The urban heat island effect can be effectively alleviated by increasing the water surface area,complicating the water body boundary,reducing the type of cover in the built-up area,and increasing the type of other land cover.(4)The determination coefficient R~2of the multivariate regression model of cooling range and cooling amplitude is 0.838 and 0.856,respectively,all through the significance test,the remaining four water patches are used for verification.The average relative error between the actual and the predicted values are 7.36.%and 9.68%,can simulate the cooling range and cooling amplitude of the water body.The multivariate regression model of the cooling gradient fails to pass the significance test.The average relative error of the predicted and actual values of the cooling gradient obtained by dividing the predicted cooling range and cooling amplitude is 5.1%,which can provide a reference for simulating the water body cooling gradient.(5)Among the 17 ring buffers built around the city square in the fourth ring,the land surface temperature of the water in the same level buffer is the lowest,and the cooling effect is strong.The maximum difference between the water body and the built-up area is 8.2?and the minimum is 1.05?.The maximum difference between the vegetation and the built-up area is 3.84?and the minimum is 0.95?.The temperature difference between the water body and the built-up area is always greater than the temperature difference between the vegetation and the built-up area.Under the same external conditions,the water body has a stronger cooling effect than the vegetation. |
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