| As an important part of urban ecological space,the urban green spaces are one of significance factors to alleviate urban heat island effect.In this study,we take Liwan Park as an example to study the cooling effect of green space inside the urban core area.The spatial and temporal variation of the air temperature and human thermal comfort in the interior and surrounding area of the green space was analyzed,and the cooling effect intensity(CEI)and the scale of cooling effect(SCE)under different season and different urban environment were quantitatively calculated.The UAV remote sensing is used to extract the internal and external 2D and 3D environmental factors of urban green space,and the main factors influencing the cooling effect of urban green space are revealed from 2D and 3D perspectives.On this basis,the influence factors of urban air temperature within the scale of cooling effect of urban green space are analyzed,and the prediction model of air temperature within the scale of cooling effect of the external heat release of the park is constructed.The main experimental results are as follows:(1)The underlying surface of woodland,shrub,grassland,water body and hard surface in Liwan Park have significant thermal environment characteristics.In the summer and winter,the diurnal variations of the temperature of the five underlying surface types all exhibit an inverted "U" shape.During summer daytime,the temperature of the grasslands and impervious surfaces is higher than the temperature of reference point and becomes the heat source of the park.At night,the temperature of the grasslands and shrubs falls most rapidly and becomes a “cold island” inside the park.During the daytime in winter,the temperature of the five underlying surfaces in the park is lower than that of the reference point;while in the winter night,the air temperature of the woodland,grassland and water body is higher than that of the reference point,showing the "warm island effect" of the urban park green space.The vegetation,such as woodland,shrubs,and water bodies in the park,can effectively improve the human body’s thermal comfort,but the degree of improvement in human comfort during the high temperature period(12:00~14:00)is relatively limited.For high-temperature and humid summers in Guangzhou,increasing the surface area of woodland,shrubs,and water bodies can effectively alleviate the discomfort caused by high temperatures.(2)The cooling effect of urban green space has obvious seasonal variation.During the summer and winter daytime,the average temperature inside the Liwan Park was lower than the outside temperature of the park.The temperature gradually increases with the distance from the park boundary.This further proves that the urban green space has the cooling effect on the surrounding urban thermal environment.However,in winter nighttime,the average temperature inside the park is higher than that of the external urban environment,indicating that the urban parkland in winter has no cooling effect at night and presents the “warm island effect” of the urban green space.From summer to winter,the average cooling effect intensity(CEI)decreased from 3.62 centigrade to 2.01 centigrade,and the average scale of cooling effect(SCE)decreased from 245 m to 171 m.(3)The two-dimensional/three-dimensional landscape configuration around the park has a certain influence on the cooling effect of the green space,and the proportion of build-up area(PB)and the three-dimensional green volume(3d-GQ)have a greater impact.The cooling effect intensity(CEI)of the Liwan Park is mainly negatively correlated with the three dimensional Green Quantity(3d-GQ),and has a significant positive correlation with the proportion of buildup area,the building density and the building height.The scale of cooling effect(SCE)has a significant positive correlation with the three dimensional Green Quantity,which has a significant negative correlation with the proportion of build-up area,the building density and the building height,and the correlation coefficient r in summer is generally greater than that in winter.The higher the proportion of build-up area(PB),a certain degree of increase in the surface temperature of the external environment of the park,which leads to an increase in the cooling effect intensity.However,with the increase of the proportion of build-up area,it will weaken the scale of cooling effect.In addition,with the increase of the building density or the building height around the park,the more obstacles to the cooling effect of urban green space,it is difficult to form an effective urban ventilation corridor,which weaken the cooling effect of the park.Thus,with the increase of 3d-GQ,the local circulation of the park and its surrounding environment will be effectively promoted,and the scale of cooling effect will be increased.Therefore,in order to the maximum the cooling effect of urban green space,the landscape configuration of the urban environment around the park should be taken into consideration on the basis of the landscape characteristics of the park itself.(4)The air temperature and human comfort in the area of scale of cooling effect(SCE)of Liwan Park has obvious spatial distribution characteristics.The distribution pattern of air temperature and human comfort in the park shows that the temperature is increasing with the distance from the park boundary,and the comfort of the human body is gradually reduced.In summer and winter,the places with higher external temperature in the park are located in the areas with dense buildings,high impermeable surface and more anthropogenic heat discharge(main road),while the regions with lower temperature are mainly located in the community of the Xiguan house in the southeast of Liwan Lake.(5)The air temperature within the scale of cooling effect(SCE)of Liwan Park is mainly influenced by the vegetation coverage(VC),the construction land ratio(PB),the building density(BD),the building height(BH),the sky view factor(SVF)and the distance from the park boundary distance(DIST).In summer and winter,the temperature is mainly affected by urban environmental factors within a 50 m spatial scale.When the spatial scale exceeds 50 m,the relationship between the two is significantly reduced.With the change of the season,there is obvious seasonal variation in the scale effect.In summer,the air temperature is affected by the environmental factors with 20 m spatial scales and is generally smaller than the spatial scales of winter(50m).In addition,the regression model shows that vegetation coverage,construction land ratio,building density,and building height are the most significant variables in each regression model.Therefore,in the planning of urban green space,the urban environmental factors around green space should be fully considered.In order to further reduce the air temperature around the green space and improve the thermal comfort,the vegetation area should be added around the urban green space as much as possible.The building density and the height of the buildings should not be too high.It is beneficial to promote the air movement and energy exchange between the park green space and the surrounding environment,and further exert the sustained release of the urban green space to the surrounding thermal environment. |
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