Near Surface Air Temperature Micro-climate Model Simulation And The Major Affecting Variables Analysis In Nanjing City

With the rapid development of urbanization process in China, great changes occurred in human survival urban built environment and micro-climate, and the contact between micro-climate and urban planning has not been taken seriously. Thus, the study of the influence mechanism of urban microclimate to achieve a reasonable urban planning development and construct ecological civilization city is urgent. Temperature is the most common and important indicator to measure climate change, and discussion of temporal temperature variation and their causes is the focus of the present heat island study. In this case, it is important to explore the affecting mechanism of temporal changes in urban temperature and construct reasonable ecological living environment. Thereby changing the underlying surface layout, improve urban micro-climate, energy conservation, cooling humidification is an important step in the construction of ecological urban development. This paper use ENVI-met microclimate micro-climate simulation software to establish a quantitative model to analyze impact factors of urban air temperature and explore the difference of urban surface layout changes on temporal and spatial variation of temperature, so as to provide some reference value for the Nanjing Urban Planning.First, the use of high resolution satellite images and field survey methods to obtain underlying information of the study area, including building structure, building height, water, road direction, vegetation cover, etc. Extracting building height through single remote sensing image building shadow is highly suitable for large gap between adjacent buildings, tall buildings, surrounded by unobstructed situation. The method for building height extraction with Stereo pair is more suitable for building’s dense and height uniform. The method for building height extraction with Stereo pair can control the result error within 2.8 meters, which is more practical to extract a wide range of building heights rapidly. Using vegetation index and visual interpretation gets research underlying surface area distribution information and prepares for the establishment of three-dimensional model of the study area.Secondly, this paper verified ENVI-met micro-climate simulation accuracy and stability through numerical microclimate simulation with four typical areas in Nanjing city. Nanjing meteorological data of the national weather stations in real time as the initial value and observation of automatic stations for each study area as verification value, calculating the correlation of the measured value and the observed value to verify simulation accuracy of ENVI-met. The results show: ENVI-met simulated values and measured values have achieved better fitting effect, which has good suitability in Nanjing city. On this basis, temperature changes affecting mechanisms of different study area have been analyzed, finding that Guanghua Street neighborhood Temperature spatial and temporal distribution is similar with the first secondary school street. In daytime road has high temperature and buildings shaded area and water has low temperatures. In nighttime, road and dense high buildings has high temperature. Because of physical characteristic of water and land in Xuanwu Lake study area, the temperature shows decreasing trend from land center to the periphery. Because of complex topography in Toutuo Ridge study area, the temperature shows decreasing trend from surrounding mountain to the periphery in daytime, and the temperature spatial distribution is consistent in nighttime. When validating the model scale effect on the simulation results, this paper finds that higher the higher simulation spatial resolution, the better fitting results of simulated values and measured values in Low-lying and flat topographical study area. The larger the scope of the study, the better fitting results of simulated values and measured values in the high altitude, undulating terrain of the study area.Finally, factors affecting urban temperature changes can be simulated from city building height changes and urban green coverage changes. Effect of layout and building height changes on temperature from the ground at a height of 1m,15m and 35m is analyzed through features of similar position with the same surface types, different layout and building height in study area of the first secondary school and Guanghua Street. Effect of green cover change on temperature is comparative analyzed by adjusting green area and green form in Guanghua Street. The results show:the shade of tall buildings has cooling effect during the daytime; dense buildings is not conducive to heat diffusion in night; Green area increased helps improve temperature of the study area, especially in daytime; A large area of green belt can effectively regulate daytime temperature distribution within a region and reduce the urban heat island effect in summer daytime.