Study On The Urban Microenvironment Numerical Simulation Based On ENVI-met

In the process of rapid urbanization,the number of artificial structures such as buildings and tarmac and cement pavements in the city has increased.The nature of urban underlying surfaces are changed,which are causing the changes in urban microclimates,especially the urban thermal environment issues have attracted the attention of scholars.With the development of the remote sensing technology,the thermal infrared remote sensing provides a new platform for the study of urban thermal environment.The study on the urban thermal environment has a large number of achievements in all aspects.However,limited to the low spatial resolution of remote sensing images,and it is impossible to obtain the thermal environment characteristics of the urban surface objects.It is difficult to comprehensively reveal the thermal environment of the complex structures within the city,and can not meet the research on the street-scale thermal environment.In view of this,the UAV oblique photography was used to obtain the information of the underlying surface of the study area in this study.Based on this,the ENVI-met model of the study area was constructed.Numerical simulation was used to simulate the microclimate thermal environment in different study areas.The distribution of temperature,relative humidity,mean radiant temperature and thermal comfort evaluation index PMV in different study areas were compared and analyzed,and base on this the factors that affect the temporal and spatial distribution of the thermal environment were summarized.On this basis,we set the comparison scheme by changing the vegetation greening,building surface reflectivity and sky view factor of the study area,and make sure the initial meteorological conditions and parameter settings are same so that to quantitatively analyze the effect on the temporal and spatial distribution of the thermal environment.Therefore,it provides the decision-making reference for the improvement of the urban microclimate thermal environment and the urban planning.The conclusions of this study are as follows:(1)The height of the building can be accurately extracted by the UAV data and the orthophoto can clearly identify the spatial distribution of the underlying surface information,which can meet the requirements of the ENVI-met model.(2)The coefficient R~2 of the simulated data and he measured data is above 0.85,so the simulated data has a high correlation with the measured data.The RMSE between the measured data and the simulated data is between 0.62?and 1.35?,and the error is within the allowable range.It shows that the ENVI-met can better predict the thermal environment distribution of urban microclimate.(3)Through the analysis of the simulation results of different research areas,we found that the main factors that affecting the distribution of thermal environment are the underlying surface,solar radiation and wind field flow.(4)The vegetation and greening have obvious cooling and humidifying effects.Increasing the building surface reflectance would increase the temperature and MRT of pedestrian height.The effective distance of the vegetation and reflectivity changes to the vertical temperature can be extended to 15 m and 50 m,respectively.(5)The increase in the SVF will cause the near-surface temperature inside the building to increase,however,as the SVF increases to a certain extent,it reduced the rate of temperature increase.