The Influence Of Urban Spatial Morphology On Thermal Environment In Zhengzhou

With the development of social economy,China's urbanization process has been accelerating.Large-scale urban construction activities have caused dramatic changes in the spatial form of urban areas,which in turn has a greater impact on the urban thermal environment.As a central hub city in the Central Plains region,Zhengzhou has developed rapidly in recent years,and the level of urbanization has been continuously improved,which has caused the deterioration of the thermal environment in Zhengzhou.Taking Zhengzhou and typical urban districts as the research object,this paper studied the influence of urban spatial form on urban thermal environment from two aspects of urban scale and block scale,and tried to find the relationship between urban spatial form and thermal environment,which provided scientific basis for the future development of the city.On the urban scale,based on Landsat8 remote sensing data,combined with OSM data,the regional climate zone(LCZ)of Zhengzhou was divided,and then the influence of Zhengzhou spatial form on urban surface thermal environment was analyzed.The study on the block scale was carried out on the basis of the LCZ partition.The Wenhua road block in Zhengzhou was selected as the research object.The difference of air temperature in different LCZs in the block was observed,and the spatial form indicators(Building density,vegetation coverage,hardening rate,building height,sky openness)were extracted.Using these two sets of data to construct a regression equation between the spatial shape in the urban block and air temperature.The main results are as follows:(1)Zhengzhou has divided 13 types of LCZs,of which 7 are built environment types: compact high-rise(LCZ-1),compact middle layer(LCZ-2),compact low-rise(LCZ-3),open high-rise(LCZ-4),open middle layer(LCZ-5),open lower layer(LCZ-6)and large low-rise industrial area(LCZ-10);The other are 6 types of land cover areas: dense forest area(LCZ-A),sparse forest area(LCZ-B),low vegetation area(LCZ-D),bare rock or road area(LCZ-E),bare soil or Sand area(LCZ-F)and water body(LCZ-G).The Zhengzhou built-up area is mostly compact andmedium-rise buildings,and the open building area is small,indicating that Zhengzhou has a dense building density,less urban vegetation,and most of the buildings are mainly middle-level residential areas or commercial areas.(2)Based on the results of LCZ partitioning,the urban heat island intensity(UHII)of Zhengzhou in the four seasons was calculated.It was found that UHII summer(6.03 °C)>UHII spring(3.09 °C)>UHII autumn(1.40 °C)>UHII winter(-1.32 °C).In summer,urban heat islands have the strongest intensity,while winter urban areas show a cold island effect.(3)Superimpose the LCZ partition map and the land surface temperature(LST)to analyze the LST difference in different LCZ.The overall temperature difference in spring,summer and autumn is not large.The built environment LST is higher than the surface cover type,and the LST of the compact building area is generally higher than the open building area.It can be seen that the vegetation shows the cooling effect in these three seasons.The winter temperature distribution shows the opposite characteristics.The built environment LST is lower than the surface cover type,and the compact building area LST is lower than the open building area,so the winter vegetation shows a certain warming effect.(4)At the block scale,there are significant differences in air temperatures in summer,autumn and winter in different LCZ areas.In general,the air temperature in the block(LCZ-F)differs greatly from the air temperature of the other three types of LCZ,and its volatility is large;the average temperature is LCZ-6>LCZ-F>LCZ-5>LCZ-A in summer;LCZ-F>LCZ-6>LCZ-5>LCZ-A in autumn;LCZ-5>LCZ-6>LCZ-F>LCZ-A in winter?(5)Analysis of the relationship between block air temperature and spatial form indicators shows that air temperature is negatively correlated with vegetation coverage in summer,autumn and winter,vegetation can effectively reduce ambient temperature,and nighttime cooling effect is more obvious;The hardening rate is positively correlated with the air temperature in the summer,autumn and winter,and the hardening can significantly increase the air temperature,and the nighttime warming effect is more obvious;Sky Vision Factor(SVF)has a greater impact on air temperature during the daytime,but has no correlation with air temperature at night.The higher the SVF in summer and autumn,the higher the air temperature during the day,and the higher the SVF in winter,the lower the air temperature during the day.(6)The influence of spatial shape index on air temperature shows obvious diurnal variation.Vegetation coverage and hardening area mainly affect night air temperature,SVF mainly affects daytime air temperature;Different indicators have different influences on air temperature.In summer and autumn,the best influence range of vegetation coverage on air temperature is 20 m and in winter is 10 m.In summer and autumn,the best influence range of hardened area on air temperature is 10 m,70m in autumn and 30 m in winter.