Research Of Numerical Simulation For Urban Microclimate On Block-scale

Microclimate is significance of urban environment. It is a fact that rationally structure layout pattern can be improving the urban microclimate environment. With the rapid development of urban construction and the ever increasing urban population, caused that the urban population increased, the massive structure, asphalt and other artificial structures complicate the urban form. The high density, high rate of volume of built-up area changed the city underlying surface properties, coupled with a volume of anthropogenic heat emissions, resulted in the obvious" heat island effect ". Because of the high density and tall buildings, the air flow is blocked, a large number of gases and particulate matter discharged into the air are difficult to diffuse and settlement, resulting in serious air pollution problems such as PM pollutants.With the gradually increasing urban issues, urban ecological research is more important. From the long term,urban environmental issues is greatly resulted from the unreasonable spatial layout of urban material and energy which is caused by the unreasonable industrial layout. By choosing the types of underlying surface, optimizing the structure of form layout, rationally allocating the relationship and influence between greening species and the urban ecological environment, we can provide the reference for the urban planning, infrastructure facilities, urban renewal and management.This study targeted at the urban micro-climate, summarizing the latest research and trend in the field of the urban microclimate, introduce numerical simulation methods of ENVI-met. First of all, 3D building databases of digital surface models were built to provide the basic data for the study of urban ecological problems. The research choose Beijing CBD region as the research object using a combination of methods with interpret satellite images and geometric correction. According to the information of the area and geographic coordinates of the building, The height of all the buildings in CBD area are measured by telescopic rangefinders. After all the 457 height data of the buildings are input into ArcGIS and calculated the area, the digital surface model database is complete. Then, the region was divided into different spatial area based on pattern of buildings in study area.From the perspective of ecology, the spatial distribution characteristics of microclimate environment for three-dimensional model was established based on satellite images by ENVI-met, combining with the specific initial time, temperature, and other control parameters in study area. At the same time, we compared with the measured data with simulation result and evaluated the precision of the model using the root mean square error and mean absolute percentage error, and the determinate coefficient and adjusted R square were used to evaluated the quality. On the one hand, Beijing typical residential area was simulated, According to three-dimensional modeling results of actual situation and simulation scenario (roof greening), the spatial distribution characteristics of microclimate environment were obtained, compared the measured data with simulation of both scenarios. Meanwhile, focusing on the urban microclimate environment of clarify definition different spatial pattern of buildings, Beijing CBD region was divided into different spatial structure patterns, based on comparative analysis of the different spatial structure patterns, such as temperature, relative humidity, wind speed and direction by ENVI-met three-dimensional model.The study showed that:(1)The results of ENVI-met model simulation are similar to the measured results, and the model could reflect the micro-scale climate distribution characteristics after multiple parameter calibration. (2)The cooling and humidification effects of roof greening improved the city’s microclimate condition and the urban living comfort largely.(3)Semi-enclosed morphology and building high density areas, show high temperatures and low relative humidity and wind speed; scattered determinant form regions, poor air flow resulting in lower wind speed. Difference spatial pattern of buildings has different microclimate environment in the urban neighborhood scale; at scattered of determinant pattern would slow wind speed and the air flow. The high vegetation coverage for open pattern usually show higher relative to humidity than determinant pattern of structures.Our research showed that ENVI-met could be used in the microclimate simulation through effective three-dimensional model. Setting up more simulation scenarios are combining with the specific plant greening, which provide scientific information for local microclimate design and urban planning.