Influence Of Urban Expansion On Air Temperature

With the rapid development of urbanization, more attentions were paid on the influence of urbanization on the local climate and environment. This study takes Nanjing City as an example, and the satellite remote sensing images were classified using supervised classification algorithm to get the information of land use cover in Nanjing City. Climatic data acquired from Nanjing meteorological station from 1960 to 2011. Annual average air temperature, average maximum air temperature and average minimum air temperature were analyzed to get the climatic features of Nanjing City. The Linear Regression model was utilized to construct the relationship model between air temperature and time, and a new model was obtained to depict the trend of air temperature of Nanjing city. Multiple indexes that were employed to express the level of urbanization were transformed using principal component analysis (PCA) to get the first and the second principal components. In addition, the urbanization index was further constructed using the principal components to analyze the trend of urbanization index along with the time. Linear regression analysis was utilized to get the relationship model between urbanization index and urban air temperature. Combined with the development level of Nanjing city, impacts of climate change were analyzed, and some suggestions were given according to the analysis of driving force of land use. Main results of this study indicated that:(1) From 2001 to 2007, the land use of Nanjing city had obvious change, especially the increasing of residential area and the decreasing of arable land, water, grassland area.(2) A strong linear correlation relationship was found between the population of Nanjing city and the average annual air temperature. Impacts of population growth on the annual temperature and the annual minimum temperature was significant.(3) The built-up area has significant influence on the average annual air temperature. Increasing in the built-up area per 1 square kilometers, there were 0.0026,0.0022 and 0.0013 degrees Celsius increasing of the average annual air temperature, average maximum temperature and average minimum temperature.(4) There was a slow growth stage of the urbanization index before 2000, and the average annual air temperature was slowly increasing. After 2000, urbanization index increased rapidly, and there was an obvious upward trend of the amplitude of air temperature.(5) Influence of urbanization index on the annual air temperature was obvious. Urbanization index increased every 0.1; there were 0.883,0.407 and 0.698 degrees Celsius increase of the average annual air temperature, the average annual maximum temperature and the average annual minimum temperature, respectively.Several innovative points of this study were:(1) information of land use land cover of Nanjing City were obtained using multi-temporal remote sensing images and supervised classification method, which will help us to analyze objectively the statue of land use of Nanjing City during its rapid urban expansion process.(2) A model was constructed using linear regression analysis to express the relationship between air temperature and time. The model could be employed to predict the change pattern of air temperature.(3) By constructing the urbanization index, a new relationship model about urbanization index and air temperature was discovered, and the model verified in theory the impact of urbanization on air temperature, which will give us a deep understanding about the influence of urbanization on climate change.