Research On Evolution Of Thermal Environment And Ventilation Corridor Planning In Zhengzhou City

Faced with global warming,the development of high-density cities has aggravated the severity of urban microclimate.And rapidly urbanization is an important factor leading to the rise in surface temperature.How to effectively reduce the land surface temperature(LST)has become a significant proposition of city planning.As the core city of the Central Plains Economic Zone,and also the national central city determined by the “National Urban System Planning(2016-2030)”,the construction of Zhengzhou is of great significance to central China and even the whole country.However,in recent years,with the rapidly development of urbanization and industrialization in Zhengzhou,extensive economic development mode and unreasonable development and utilization of human beings have caused serious ecological problems,especially the environmental heat pollution represented by urban heat island(UHI)effect.So,how to provide strategic support for building an ecologically livable and sustainable city is a common challenge faced by planners.Some studies have shown that,urban ventilation corridors are effective in improving urban air quality and alleviating heat island problems.The adequate urban ventilation system can introduce clean and cool air into urban high-temperature areas,so as to alleviate the UHI effect and improve the thermal comfort of residents,which has been widely used in cities all over the world.In order to understand the evolution characteristics of LST and UHI in Zhengzhou City and build a ventilation corridor for it to alleviate the rising trend of LST,this study used MODIS surface temperature data to quantify the change of LST in Zhengzhou City from 2005 to 2020,and determined the time mutation point by Nonparametric Mann-Kendall trend test(M-K test).Moreover,the mean-variance method was used to divided the LST into seven grades,among which the high temperature area,relatively high temperature area and extremely high temperature area were identified as the heat island area of this study,and the spatial and temporal evolution pattern of urban heat island in Zhengzhou from 2005 to 2020 was determined by quantitatively detected the changes of LST grades.Correlation analysis,trend analysis and grey correlation analysis were used to discuss the main driving factors of LST change and their internal relations.Furthermore,based on the main driving factors of surface temperature and factors affecting urban ventilation,the influencing factors of underlying surface were reconstructed,and the comprehensive evaluation value of ventilation potential in each region was calculated.And the action and compensation space of ventilation corridor were determined based on the comprehensive value of ventilation potential of underlying surface and the spatial distribution of thermal environment in Zhengzhou.Finally,Combined with the dominant wind direction of each meteorological station,the ventilation corridor of Zhengzhou was planned to ensure that the fresh air flow in the compensation space can flow to the action space with the help of air guide channel and dominant wind direction.The results of this study show that:(1)From 2005 to 2020,the annual change of LST in Zhengzhou City was small,and a mutation occurred in 2013.In addition,compared with 2005,the mean value of LST in 2020 increased by 0.92℃,while the percentage of LST-enhanced areas was 22.77,and the heat island area increased by 2.08%.Furthermore,the spatial pattern of UHI was irregularly distributed,gradually spreading from west to east from 2005 to 2020.And it showed a large block distribution in the main city and southeast industrial agglomeration area in 2020,while,in the areas where woodlands were concentrated and in the Yellow River Basin,there was an obvious “cold island” effect.In addition,trend analysis and gray correlation analysis revealed that human factors were positively correlated with LST,which intensified the formation of the UHI effect,and the influence of Albedo on LST showed obvious spatial heterogeneity.While natural factors were negatively correlated with LST.Among them,the intensity of urban construction has the highest contribution to the formation of heat island effect,and the cooling effect of vegetation water was better than that of topography.(2)In the main urban city,although there was a large area of water distribution,due to the high building density and low vegetation coverage,the increase of the proportion of impervious water surface increased the absorption of solar radiation,and with a large number of social and economic activities,it was difficult for the heat generated by natural and human activities to spread rapidly,so the ventilation potential value was low.However,in the west of Zhengzhou,the terrain was high and there were a lot of woodland and vegetation distribution,which has high ventilation potential.According to the spatial distribution of the heat island area,the action space numbered A1-A22 was determined,in which A12,A14 and A22 have the highest temperature,and were distributed in the main urban area and the southeast industrial agglomeration area.Besides,according to the spatial distribution of the location of low temperature area,vegetation,water body and comprehensive value of ventilation potential,the Yellow River,Yanming Lake,Longhu Park,Wanshan Forest Park in Zhengzhou,Suohe Country Park in Zhengzhou,Fenghuang Island,Yingtaogou Scenic Area,Shuangfeng Mountain,Yinji Animal Kingdom,Fuxi Mountain Tourist Area,Baisha Reservoir,Songshan National Scenic Area and Nan ’eling were selected as compensation spaces.(3)The "most wind directions" of meteorological stations in Zhengzhou were mainly "SE,SW,NW" in summer and "SW,W,NW,N,S" in winter.In the city,the wind flow was usually influenced by many factors,such as building layout,underlying surface characteristics,people flow and so on,which leads to the changeable wind direction of Zhengzhou main city and Xinzheng.However,the purpose of building urban ventilation corridor was to introduce fresh air and cold air from the periphery of the city into the interior of the city smoothly,so the source direction of cold air flow was considered more.Due to the influence of topography and urban land use,cold air in Zhengzhou mainly comes from mountains,woodlands and waters,so the main wind direction of cold air sources should be considered when constructing ventilation corridors.To sum up,the wind direction in Zhengzhou was mainly northwest,southwest and southeast in summer,and north,southwest and northwest in winter.Finally,based on the influence of urban underlying surface and dominant wind direction,the "three horizontal and two vertical" primary ventilation corridor and the "one horizontal and two vertical" secondary auxiliary ventilation corridor were planned.