Study On Influencing Factors Of Urban Thermal Environment In Chongqing In Summer Based On ENVI-met

The current situation and needs of China’s rapid urban process at the present stage urgently need to face the serious problems that will be brought about by climate change.Focusing on the urban environment,urban planning and design strategies can positively affect the occurrence of these extreme situations and help cities adapt to climate change.The formation of urban microclimate is closely related to the factors such as street canyons,buildings,greening and human activities in the city,and the change of urban microclimate will,in turn,affect human activities and the further planning of buildings and roads.With the development of urban climatology,scholars have found that different urban patterns produce different urban micro-environments.At the urban scale,urban spatial morphology is mainly affected by various spatial parameters,such as the enclosure mode of the built environment,the geometric appearance of buildings and the form of the regional road network.In the research on a smaller scale,the key points to be discussed include the influence of spatial factors such as building height,openness and aspect ratio on the air temperature and humidity,average radiation temperature and human thermal comfort inside the regional street canyon.In this paper,the thermal environment in the mountainous city of Chongqing was studied firstly.After field investigation,the Jiefangbei Pedestrian Street and the North Square of Chongqing Bei Station were selected as the typical areas of compact high-rise and open low-rise urban form.ENVI-met software was used to simulate urban climate.The meteorological station data（hourly air temperature,air humidity,wind speed,solar radiation intensity,etc.）were used as the input boundary condition for the summer city microclimate simulation of the study area.Then the measured parameters were utilized to test the accuracy of the results obtained by simulation.Next the variation trend and distribution of thermal environment-related parameters were analyzed from the two dimensions of time and space,and the optimization measures of the thermal environment were put forward.Finally,the optimized thermal environment parameters were compared with the original ones to discuss and analyze the most suitable thermal environment optimization measures for the two study areas with different urban spatial forms.The results show that:for the thermal environment,the urban spatial pattern has a great influence on that.The open low-level area has a large SVF value,and its temperature rises rapidly due to the influence of solar radiation intensity.Also,its highest air temperature,T_mrt and PMV throughout the day are also higher than those of the other pattern in this paper.During the night,more energy is radiated outward,so the temperature drops faster.In compact high-rise areas,the SVF value is small,so the temperature rises more slowly during daytime,and in the evening its drop is slower as well.Also,its highest air temperature,T_mrt and PMV throughout the day are also lower.The optimization measures,such as strengthening building self-shelter,adding shading facilities and improving vegetation coverage rate all have positive effects on the improvement of outdoor thermal environment and thermal comfort of citizens.For the open low-rise areas,adding shading facilities can ensure that the overall thermal environment of the whole day can be improved.However,this measure has a small spatial impact,so it is a better choice to increase the vegetation coverage rate when the requirements for the thermal environment at night are not high.For the compact high-rise area,the improvement effect of building self-sheltering on the thermal environment is significant,and the influence range is relatively wide in space,so it is an ideal thermal environment optimization measure.However,improving vegetation coverage is only applicable to small scale and precise optimization.The regulation mechanism of outdoor thermal environment in mountainous urban hot and humid areas is obviously different.Based on software simulation and observation,this paper puts forward and demonstrates the method suitable for the regulation of thermal environment in Chongqing.The results of this paper have certain guiding significance for urban planning and urban humid and hot environment regulation.