| With the rapid increase of urban population and the continuous expansion of urban scale,urban heat island(UHI)plays a key parameter in the physics of urban thermal environment change and has become an important factor affecting urban environmental quality.As the fastest urbanization country,China has a great significance to improve residents' quality of life and scientifically guiding urban planning by researching on spatial-temporal evolvement of thermal environment and establishing the protection and improvement plan for high temperature condition in the cities.Anhui province is adjoining the Yangtze River Delta economic zone(which includes Shanghai),with diversified terrain,physiognomy and climate conditions.In Hefei city,the urban built-up area has expanded nearly 3 times from 2000 to 2015.Hefei is a typical international emerging characterized by high level urbanization and high population density.Therefore,it is very important to make a quantitative analysis of the long term spatial-temporal changes of the heat island effect in Hefei city and its surrounding areas,which will provide technical supports for improving the living environment,building the Great Lake city and the national regional central city.The thermal infrared band data of Landsat TM/ETM+,Landsat 8 OLI/TIRS images acquired in 2000 to 2015 are used to invert the land surface temperature of Hefei.The Landsat TM/ETM+ satellite data are modeled by the single-window algorithm,and Landsat 8 OLI/TIRS data are modeled by the atmospheric correction method.The MODIS temperature product data(MOD11A1)and the Landsat temperature data were used to obtain the missing data of 2006 and 2008.However,presently existing MOD11A1 data can suffer from cloud cover,cloud contamination and atmospheric disturbance,resulting in missing data.To solve this problem,an approach for reconstructing missing MOD11A1 data based on space clustering method.The weights of space are determined using the spectral multi-manifold clustering algorithm(SMMC).Then the Gradient plus Inverse Distance Squared(GIDS)is used for reconstructions of missing data.Long term spatial-temporal changes of the heat island effect in Hefei city is analysis,with the differences of eco-environmental index(such as urban impervious surface area,urban vegetation coverage and other urban land use types and urbanization development index),the main conclusions are as follows:(1)Long-term Landsat surface temperature data set obtained.Using the existing mature land surface temperature inversion method to obtain accurate summer Landsat land surface temperature data in 2000-2016(2006,2008 data are missing)of Hefei city.MODIS land surface temperature data in 2005 and 2006 and Landsat land surface temperature data in 2005 are used to obtain Landsat land surface temperature data in 2006;MODIS land surface temperature data(2007 and 2008)and Landsat land surface temperature data(2007)are used to obtained Landsat land surface temperature data in 2008.In the process of MODIS land surface temperature missing data restoration,the S-GIDS method of clustering algorithm is used to estimate missing MOD11A1 data,and has better results than GIDS method.The accuracy of ground surface reconstruction is obviously higher than that of mixed surface type,and the stability is higher.The results of GIDS and S-GIDS show that the estimation of cultivated land and forest land is better than urban construction land and bare soil.(2)Spatiotemporal variation characteristics of urban heat islands in Hefei City.From the time point of view,urban heat island distribution is more concentrated in 2000-2006,urban heat island effect to the old city center area into oval shape distribution,urban heat island center is similar in 2006 and 2008,but the urban heat island area in 2008 is more visible than the expansion in 2006.In 2010,due to the urban population density increased year by year,construction land increased cultivated land and vegetation area decreased year by year,heat island distribution from the city center to the surrounding expansion.The distribution of heat island effect in Hefei is similar.Although the area of the built area is expanding and the human activities is intensified,the heat in the air caused by industry and transportation,transportation and so on increased,which made the tendency of urban heat island effect more serious.However,due to increased greening construction significantly reduced the city's heat island strength.Therefore,this period of Hefei heat island strength overall change is not great.From the spatial distribution,the distribution characteristics of Hefei hot island are consistent with the layout of urban built-up area from 2000 to 2016.The spatial distribution of heat island effect is higher in northeast-southwest and lower in southeast-northwest.With the expansion of new industrial zone and the green building in old city area,the areas with strong heat island effect were mainly concentrated in the old city in early time,and extend to the eastern and southern new industrial areas(3)Causes of urban heat islands in Hefei City.The exponential model can well represent the quantitative relationship between surface temperature and impervious surface,and the distribution trend of surface temperature is almost the same as that of impervious surface.The increase in temperature in areas with high impermeability coverage is greater than that in areas with low impermeability coverage.The coverage of vegetation and water body is low,mainly in the form of sensible heat,and the transpiration and evaporation are less,which lead to the rapid increase of surface temperature.The exponential model can better reflect the quantitative relationship between surface temperature and vegetation coverage.With the increasing of vegetation coverage,whereas,the surface temperature is decreasing.The temperature decrease in the low vegetation coverage area was greater than that in the high vegetation coverage area.The relationship between urban heat island and land use of urban city has different land surface temperature,but the average temperature of construction land is higher than other surface types,and the average temperature of water body is the lowest,the average temperature of forest land and farmland is close.The temperature standard of construction land is the largest among all land use types,the change of agricultural land is bigger than that of forest land,and the standard deviation of water body is the smallest.The economic development has contributed to the construction area and the rapid expansion of urban scale,and the expansion of urban heat island effect.In addition,due to urban greening efforts are increasing,the landscape area of green space showed a significant acceleration trend,changing the underlying surface structure of the city,the rate of growth and urban built-up area of the rate of increase,which makes this period urban heat island effect does not appear dramatic expansion,the garden green space reflects the effective inhibition of urban heat island development.(4)The solution of urban heat islands in Hefei City.The heat island effect is not only a serious obstacle to the city's socio-economic and ecological environment,sustained,stable and healthy development,and poses a serious threat to the health of residents.Therefore,in the creation of eco-city,we should firmly grasp the virtuous circle of ecological environment as the basis,to alleviate the urban heat island effect as an important indicator to improve the water drainage system performance,improve urban green coverage,control city size and urban Population,rational planning,layout of urban construction,retention of wetlands and urban waters.Take effective measures to protect the natural ecological environment,urban planning and construction should pay attention to the principle of environmental priority,and then promote climate change and social and economic development into a virtuous circle. |
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