| The health and life of the people of the city were seriously affected by urban heat island effect,the study of urban heat island effect plays an important role in alleviating this phenomenon.However,the characteristics and regulars of the heat island effect of each city will be different because of the different in the geographical location,size,population density,the nature of the underlying surface and the level of industrial development of the city.Therefore,it is very important to study the urban heat island from various angles for the urban ecological construction and sustainable development in the future.Nanning as the cultural,political and economic development center of Guangxi,is in the stage of rapid development of city,the increase of urbanization will change the urban underlying surface.Therefore,this paper studies the seasonal and annual variation characteristics of heat island effect in Nanning city and its relationship with the urban underlying surface,to explore the spatial distribution of green space and water and urban construction land in Nanning city under the background of rapid urbanization,hope to provide valuable reference for future city planning and construction of science.In this paper,Landsat5,Landsat7 and Landsat8 images are used to retrieve the land surface temperature and normalized difference vegetation index(NDVI),modified normalized difference water index(MNDWI),normalized difference built-up index(NDBI)was derived.The study area is divided into 126 statistical areas according to the 3km×3km specification,the seasonal and annual characteristics of heat island in Nanning were studied from the two scales of the pixel and the small area.The relationship between the surface temperature and the underlying surface is quantitatively analyzed in order to investigate the influence of different land cover types on the surface temperature.The results showed that:(1)The accuracy of Landsat8 inversion land surface temperature is verified by the method of the measured surface temperature,it is concluded that the single window algorithm has a high accuracy in retrieving the surface temperature of landsat8 images.(2)The results of the correlation analysis show that the LST had nonlinear relationships with NDVI and MNDWI,but significant linear relationships with positive NDVI.The LST had significant linear relationships with NDBI and BSI,that is,Green land and water body have the function of cooling,and the construction land and bare land have warming effect.According to the analysis of small areas,area proportion of green land and water have negative correlation to the average surface temperature in small areas,area proportion of construction land and bare land showed significantly positive correlation to average surface temperature in small areas.the surface temperature decreases with the increase of the proportion of green land and water in the same area,however,the surface temperature increases with the increase of the proportion of construction land and bare land,This shows that green land and water have the effect of cooling and the construction land and bare land have warming effect.(3)The results of the analysis of seasonal heat island show that Nanning has similar seasonal heat island in 2000a and 2015a.There was no significant change in the area of each land cover type for four datas.spring,summer,autumn and winter in Nanning have heat island effect of different degrees,The heat island effect is more obvious in summer,followed by autumn and spring,the heat island is not very obvious in the winter of 2000a,but the heat island is very obvious in the winter of 2015a.The average surface temperature of the same land cover type in different seasons has order:summer>autumn>spring>winter.In the same season,the average surface temperature of different land cover types order was construction land>bare land>green land>water.On the whole,the spatial pattern of urban heat island effect has not changed greatly for four datas of 2015a,high temperature area and sub-high-temperature area are mainly distributed in the fast ring,low temperature area and sub-low temperature area are mainly distributed in the forest,park,Yongjiang River.The total surface temperature is mainly in the middle level.(4)The analysis of annual heat island show that Surface cover types of Nanning have changed greatly from 2000 to 2015a,during the period of 2000a～2015a,green area decreased 6784.65hm2,water area reduced 188.82hm2,construction land area increased by 10894.86hm2,while the larger changes in the type of surface is concentrated in Anji overpass,Nanning east railway station and Nanning sports center from a small regional scale.The average surface temperature of the land cover types order was construction land>bare land>green land>water,the average surface temperature of the green land and water body is lower than the average surface temperature of the study area,and the average surface temperature of the building land and bare land is higher than the average surface temperature of the study area in 2000a,2009a and 2015a.In 2000～2009a,the high temperature zone and sub high temperature region of Nanning were expanded from the region of the fast ring to the periphery of the fast ring,langdong and the Kunlun Avenue.the area of high temperature and sub high temperature area increased by 3255.21hm2.During the period of 2009～2015a,the high temperature zone and the sub high temperature area were extended from the surrounding area of the fast ring to the Nanning Dong Railway Station and the Wuxiang area.The area of high temperature and sub high temperature area increased by 569.6 1hm2.The expansion of high temperature zone and sub high temperature area is consistent with the expansion of urban construction land. |
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