Study On The Scale Effect Of Microclimate In Urban Green Space

With the increasing shortage of land resources,urban green space is more precious.The scientific evaluation of the microclimate effect and its impact scale of green space are particularly important for urban and landscape planning and design.In order to explore the scale effect of urban green space microclimate,this paper took a centralized green space with an area of about 1 hm2 on the campus of Henan Agricultural University and the decentralized green space with some areas of less than 1 hm2 in six typical residential areas in Zhengzhou as the research objects.The microclimate and thermal comfort observation experiments in spring,summer,autumn and winter were carried out respectively.Then,using multivariate statistical method to analyze quantitatively the impact scales of two types of urban green space with different scale,land use and site background on thermal comfort in different seasons.The results showed that:(1)The scale ranges of the impact of concentrated green space with an area of about 1 hm2 on the thermal comfort of the whole day in spring,summer,autumn and winter were 16.1 ~ 25.59 m,14.8 ~ 36.6 m,20.84 ~ 27.78 m and 12.97 ~ 22.91 m.The maximum influence scales of thermal comfort throughout the day were summer >autumn > spring > winter,and the minimum influence scales were autumn > spring >summer > winter.Among them,the maximum influence scale of 36.6 m appeared at7:00 in summer,while the minimum value appeared at 19:00 in winter,which was12.97 m.(2)The influence scale ranges of decentralized green space with some areas of less than 1 hm2 in six typical residential areas in Zhengzhou on daytime thermal comfort in spring,summer,autumn and winter were 35 ~ 50 m,15 ~ 35 m,10 ~ 50 m and 5 ~ 45 m respectively.The maximum influence scales of daytime thermal comfort were spring = autumn > winter > summer,and the minimum influence scales were spring > summer > autumn > winter;the influence scale range of three-dimensional green quantity on daytime thermal comfort in autumn was 10 ~ 50 m,but there was no significant effect in spring,summer and winter;among all green space shape indicators,only the perimeter area ratio of green space had a significant impact on the daytime thermal comfort in spring,summer,autumn and winter,the impact scale range was 20 ~ 50 m;The fractal dimension of green space had a significant impact on thermal comfort only in winter,and the impact scale was 15 m;The impact scale ranges of green space shape index,green space related circumscribed circle index and green space adjacency index on daytime thermal comfort in different seasons were 15~ 35 m,10 ~ 35 m and 5 ~ 45 m respectively.(3)The time period from 8:00 to 18:00 was selected to compare and analyze the impact of two types of green space on thermal comfort in white days.The impact scales of green space in residential areas on thermal comfort were higher than that on campus as a whole.Among them,the maximum impact scales were 32.42 m,11.74 m,22.22 m and 22.09 m higher in spring,summer,autumn and winter respectively.The minimum impact scales were higher than that of campus only in spring and summer,and the opposite law was shown in autumn and winter.Compared with the centralized green space,the decentralized green space in residential areas had a certain superposition effect on the thermal environment,which could affect the thermal comfort in a further horizontal range,and this effect was the most significant in spring and summer.(4)In order to give full play to the climate regulation benefits of green space,it is suggested that the area is about 1 hm2,the distance threshold between green space and pedestrian space should be kept at 12.97 m,and the distance threshold between green space and pedestrian space in residential areas should be set at 5 m;the planning and design of decentralized green space in residential areas should consider the influence of controllable landscape elements such as three-dimensional green quantity in 10 m circular buffer zone,perimeter area ratio of green space in 20 m circular buffer zone,shape index and fractal dimension of green space in 15 m circular buffer zone,relevant circumscribed circle index of green space in 10 m circular buffer zone,adjacency index of green space in 5 m circular buffer zone and sky view factor on human thermal comfort.