The Impact of Green Spaces on Thermal Comfort in Urban Street Canyons during Hot Summer Days and Nights

The Impact of Green Spaces on Thermal Comfort in Urban Street Canyons during Hot Summer Days and Nights | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The Impact of Green Spaces on Thermal Comfort in Urban Street Canyons during Hot Summer Days and Nights Junyou Liu, Bohong Zheng, Haifang Tang, Jia Fan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4113689/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Road greening plays an important role in improving the thermal comfort of street canyons. Optimizing the landscape pattern of road green spaces is undoubtedly beneficial for better utilizing the effect of green spaces in improving thermal comfort in limite street greening area. Given that road greening can have completely different impacts on the thermal comfort of street canyons during the day and at night, this study attempts to explore how to optimize the landscape pattern of road greening to maximize its overall improvement in thermal comfort throughout the summer. This study takes a section of Guihua Road in Changsha, a city in central and southern China as an example, built a model based on the actural situation of the road, and based on this, constructs five optimization models to explore the effectiveness on improving thermal comfort. Research has found that optimizing the landscape pattern of road green spaces has a more significant effect on the daytime thermal comfort of street canyons, with the maximum difference in UTCI between models being 0.76 ℃. However, the maximum difference in UTCI between nighttime models is only 0.06 ℃. Therefore, fully utilizing the effect of plants can be effective to improve daytime thermal comfort of the street canyon. However, for the improvement of the nighttime thermal comfort of the street canyon, peolple should focus more on other measures like improving the ventilation and change the underlying surface materials. Building shadows outdoor thermal environment hot summer and cold winter areas residential area planning Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction 3.6 billion people live in areas highly susceptible to climate change. Climate change presents a critical threat to human health. Heatwave is one of the main extreme weather events caused by climate change (World Health Organization, 2023 ). Heatwaves can increase heat-related deaths. More than 166000 people died because of heatwaves between 1998 and 2017. The number of people exposed to heatwaves grows by approximately 125 million from 2000 to 2016 (World Health Organization, 2024 ). Urban areas can suffer more from the heat wave due to the urban heat island effect. Urban pavements are an important contributor to the urban heat island effect (Anand and Sailor, 2021). Urban street canyon areas can become one of the main high-temperature areas during hot summer days in a city since urban pavement can accumulate a lot of heat. Urban street greening can play quite active role in mitigating the negative impact of urban heat waves and the heat island effect. People stay in streets with higher tree cover can have lower pulse rate, systolic blood pressure, diastolic blood pressure (Ren et al., 2022 ). Thus, it can contribute to a healthier street canyon environment. The attached green spaces within urban roads and transportation facilities areas are an important part of urban green spaces (Ministry of Housing and Urban Development of the People's Republic of China, 2017). The main feature of this type of green space is its strip like distribution along urban roads. Some researchers have researched the impact of road green spaces on the thermal comfort of street canyons. For example, Ren et al., ( 2022 ) explored the impact of the different degrees of street tree cover on the thermal comfort in street canyon, they found street canyon with higher tree cover has lower frequency of strong heat stress. Liu et al., ( 2023 ) focused on the impact of street greening on the thermal comfort of street canyon during hot days and cold days. In general, they find street trees can improve thermal comfort of street canyon during hot days and deteriorate thermal comfort of street canyon during cold days. Narimani et al., ( 2022 ) explored the impact of street orientation and street tree on thermal comfort of the street canyon, they found tree cover have more prominent effect on thermal comfort than orientation’s effect. Some researchers also consider the impacts of green space on thermal comfort at night. For example, Zhang et al.,(2023) explored the impact of green spaces on the climate comfort, they pointed out that exposed to green space can adjust thermal comfort by transpiration, water storage and heat absorption. This can reduce the range of temperature different betweeen day and night.; Zölch et al.,(2018) explored the impacts of different public squares designing on thermal comfort during hot summer daytime and nightime condiitions. They found a model with many trees located in sunlit area can provide relatively good thermal comfort during daytime and a model without trees but with a meadow area have good thermal comfort. They propose that a climate adapted design should include trees to maximize shade area, the wind channel is kept free from trees, also planted with grass to minimize the heat storage. Morakinyo et al., (2017) explored the impact of trees on in-canyon and neighbourhood’s thermal comfort during daytime and nighttime. They found leaf area index, tree height and trunk height are influential factors for improving thermal comfort. In addition, they found that the effectiveness of trees in increasing daytime thermal comfort decreased with increasing urban density during the day, while vice-versa at night. In general, few researchers comprehensively studied the impacts of street greening on thermal comfort during daytime and nighttime simultaneously. 2. Material and methods 2.1 Overview of the study area Changsha is located between 27 ° 51 ′ -28 ° 40 ′ N and 111 ° 53 ′ -114 ° 15 ′ E, and is an important central city in the middle reaches of the Yangtze River in China and the capital of Hunan Province. Changsha City is located in the subtropical monsoon climate zone, with significant temperature changes in spring, sustained high temperatures in summer and autumn, and cold winters(Beck et al., 2018 ; Xiang and Liu, 2016 ). Changsha City governs 6 districts, 1 county, and 2 county-level cities. In 2022, the permanent population was 10.426 million (Changsha Municipal Government, 2023), and the urbanization rate was 83.27%. Among them, the population of the central urban area of Changsha is about 5.546 million people (Changsha Bureau of Commerce, 2022 ). This study selected a section of Guihua Road in the central urban area of Changsha for research. 2.2 Model construction and simulation analysis This study constructs different models based on a section of guihua road in the central urban area of Changsha, and uses ENVI-met 5.6.1 for thermal comfort simulation analysis. The simulation period is from 11:00 to 23:00 on July 8, 2022. The initial simulation data is from the National Meteorological Information Center, and the station information is [57687] Changsha. The meteorological data can be seen in Table 1 below. Model 1 is a model constructed based on the actual situation of the road section. The planation in the model are 15-meter-high Camphora officinarum trees and 10-meter high Osmanthus Fragr trees and 1 meter Ligustrum lucidum trees. In model 2, road trees are 10-meter-high Camphora officinarum trees and 5-meter high Osmanthus Fragr trees and 1 meter Ligustrum lucidum hedges. The location, and number of roadside trees are consistent with model 1. Model 3 are still 15-meter-high Camphora officinarum trees and 10-meter high Osmanthus Fragr trees and 1 meter Ligustrum lucidum hedges, with the same total number and position as Model 1, model 3 has a central bed divider consisting of a 5-meter tree in the middle of the two-way lane. Model 4 has the same 10 m Camphora officinarum trees and 5 m Osmanthus Fragr trees characteristics as model 2 but a larger number of 1 meter Ligustrum lucid um hedges than model 2. The situation of the roadside trees in Model 5 is the same as in Model 1. Model 5 has green roof on the buildings and model 1 does not have. Since 15-meter camphor trees with LAI of 3.0 is generally dense. Except model 6, We uniformly set the LAI of 10 m as 3.3; 15 meter camphor tree as 3.0; 5 meter camphor tree as 3.6; 10 meter Osmanthus fragrans as 3.3. This confirms with Liu et al., ( 2023 ), which has used hemiview (Delta T, UK) to measure the LAIs of trees in Changsha. Through further analyze the LAI of Camphora officinarum trees in Changsha, we found some sparse Camphora officinarum trees only have LAIs of around 2.2. Model 6 has the same condition as model 1 except the LAI of the 15 m Camphora officinarum trees is 2, LAI of the 10 m Osmanthus fragrans trees. The crown width of 15 meter, 10 meter and 5 meter trees are uniformly set as 9m, 7m and 3m respectively. Figure 1 shows the sketchesf the six models. Universal thermal climate index (UTCI), proposed by EU COST Action 730, is an indicator for thermal comfort based on the multi-node Fiala mode. (Wang et al., 2020 ; ENVI-met,2024). It is the air temperature of the reference environment which produces the same strain index value in comparison with the reference individual's response to the real environment. It is calculated by meteorological data like mean radiant temperature, relative humidity, wind speed and non-meteorological data like clothing thermal resistance and metabolic rate (Maqueda et al., 2018). UTCI is the main indicator used to evaluate thermal comfort in this study. Table 1 measured data from meteorological station Date Time Average wind direction during the 13 hours (°) Average wind speed during the 13 hours (m/s) Temperature (℃) Relative Humidity (%RH) 8th July 2022 11:00 183 2.6 30.1 74 12:00 31.3 68 13:00 31.7 69 14:00 32.4 67 15:00 32.8 64 16:00 32.8 63 17:00 32.8 66 18:00 32.3 67 19:00 31.4 71 20:00 30.5 75 21:00 30.1 77 22:00 30.1 72 23:00 29.3 77 Based on the defition of day (the time between sunrise and sunset) and night (the time from sunset to sunrise) (Waite, 2007 ), we calculated the sunrise and sunset time of Changsha on 8th July 2022 and classified the time period into daytime and nightime. We mainly refer NOAA Solar Calculator (Global Monitoring Laboratory, 2024 ) to calculate the sunrise and sunset time of Changsha during this day and classified the time period from 11:00 to 19:00 in to days and between 20:00 and 23:00 in to night. 2.3 Error Analysis We also did validation analysis for the simulated microclimate characteristics. We conducted validation analysis for air temperature and relative humidity. We use the measured data from meteorological station to represent the real temperature and relative humidity in the study area and the average simulated temperature and relative humidity of the study area to represent the simulated temperature and humidity in the study area. We conducted error analysis using 12-hour measured values and simulated values within the study area (12:00–23:00). Because the simulation result of the first hour 11 o clock is not stable, we did not use this hour for analysis. Error analysis mainly relies on Pearson correlation coefficient (r), determination coefficient (R 2 ), mean absolute deviation (MAE), root mean square error (RMSE), and consistency index (d). For temperature analysis, we got r, R 2 , MAE, RMSE, d is 0.97, 0.94, 1.02, 1.21, 0.87 respectively. For relative humidity analysis, we got r, R 2 , MAE, RMSE, d is 0.96, 0.92, 9.94, 10.34, 0.53 respectively. 3. Results and discussion 3.1 A comparison of the thermal comfort of the street canyon during day and night Figure 2 shows the UTCI values of the street canyon at 14:00 and 16:00 during the day and 21:00 and 23:00 during the night. It can be seen from the graph that the street tree and building shadow area form a relatively low UTCI value area during the day. However, the area near buildings and trees do not show obviously better thermal comfort than other areas relatively far from trees and buildings in the street canyon during night. Trees can improve the thermal comfort of the street canyon through shading the sunlight and evaporation to reduce air temperature so that improve thermal comfort during hot summer day (Liu et al., 2023 ). At night, trees do not play the role of shading sunlight. Thus, tree shading area is not one of the most comfort area in the street canyon during the night. It can be seen from the figure that the areas between two buildings at one side of the Guihua road is one of the most comfortable areas during night. This can attribute to the wind direction is 183° in the simulation process. It can below through the areas between two buildings at one side of the Guihua road easily without the blockage of the buildings. This shows wind plays a quite active role in improving the thermal comfort of the street canyon during hot summer night. During the day, the sunlight is sufficient, the transpiration of plants is strong; At night, without light, the stomata of plants close or shrink, and the transpiration is weak (Malek, 1992; Wang et al., 2021 ). This is another reason why street trees play more active role in reducing air temperature during the day than the night. These indicate relevant practitioners like urban planners that make full use of tree and bulding shadow can create many good thermal comfort areas in the street canyon during the day. At night, wind can play a quite positive role in creating areas with low UTCI value and maintain good ventilation condition for the street canyon is good for the thermal comfort of the street canyon. 3.2 A comparison of the thermal comfort of the six models based on average UTCI values. It can be seen from the Fig. 3 that the differences in UTCI value at the same time among different models are more obvious during the daytime than during the night. According to Table 2 and Fig. 3 , considering the difference in UTCI values among the six models between 12:00 and 19:00, it can be inferred that the maximum difference in UTCI values occurred between Model 2 and Model 3 among the six models at 17:00. The difference in UTCI is 0.76 ℃. From 20:00 to 23:00, there is only a small difference in UTCI values among the models. The maximum difference in UTCI among the six models during this period occurred between model 3 and model 6 at 23:00. The UTCI value of model 3 was 0.06 ℃ higher than that of model 6 at this time. This indicates that different plant characteristics in the street canyon can have a relatively large impact on the thermal comfort of the street canyon between 12:00 and 19:00, while the impact difference between 20:00 and 23:00 is very small. One of the main reasons may be that plantation plays a quite positive role in blocking the sunlight and creating cool areas beneath vegetation during the daytime. Different street canyon vegetation characteristics have different effects in blocking sunlight and intercepting solar radiation and this can have different influences on land surface temperature and air temperature in the street canyon during the daytime (Bowler rt al., 2010; Oke, 1989 ). The soil in the area where the vegetation is located also has a different effect on absorbing and reflecting solar radiation compared to impermeable underlying surfaces such as asphalt and concrete. Soil can retain water for evaporation and this is beneficial for reducing air temperature. Impervious surfaces can quickly absorb and retain heat when exposed to solar radiation (Oke, 1989 ). Transpiration transports water from the roots of plants to the top, and then evaporates, taking away a large amount of heat. At night, transpiration is the main way for the plantation to reduce land surface temperature and air temperature in the street canyon. Even if the transpiration effects of different vegetation characteristics are different. The difference in average air temperature at 1.4-meter height in the street canyon area of different models is very small. At night, due to the lack of sunlight, plant stomata are closed and plant transpiration is weak (Caird et al. 2007 ; Dawson et al. 2007 ). This is also one of the main reasons why there is a small difference in the average UTCI values among the model street canyon areas at 19:00 and 23:00. According to Table 3 , Model 3 has the lowest average UTCI value during these 12 hours. The other features of Model 3 are the same as Model 1, but Model 3 has a median road divider with many 5 m trees and Model 1 does not. The 12-hour average UTCI value of Model 3 is 0.11 ℃ lower than Model 1. This indicates that the plants in the central divider of the road have played a significant role in improving the thermal comfort of the street canyon. In general, the more vegetations distribute in the street canyon, the better the thermal comfort of the street canyon during the hot day (Dawson et al., 2007 ), especially tall trees with large canopies can play a significant role in improving thermal comfort. The average UTCI of Model 2 is the highest among the six models. The difference between Model 2 and Model 1 is the size of the plant canopy and the height of the tree. Tree size and tree canopy characteristics can significantly influence the penetration of solar radiation (Dawson et al., 2007 ). In Model 1, the 15-meter camphor tree and 10-meter Osmanthus Fragr can block more sunlight and form more shadow areas than the 10-meter camphor tree and 5-meter Osmanthus Fragr in Model 2. Having more leaves in a larger canopy can also better utilize the transpiration of plants to lower temperatures. Model 2 has an average UTCI value 0.2 ℃ higher than Model 1 during these 12 hours. Hedges can also affect solar radiation, wind speed and wind direction (de Quadros and Mizgier, 2023 ). The average UTCI value of Model 4 is only 0.05 ℃ lower than that of Model 2. This indicates that adding a larger area of 1 meter of hedge ( Ligustrum lucidum ) based on Model 2 has a weak effect on improving the thermal comfort of the street canyon. Vegetation applied to the building envelope can also influence radiant and convective energy exchange. This can also influence human comfort in the built environment (de Quadros and Mizgier, 2023 ). The average UTCI value of Model 5 is only 0.03 ℃ lower than Model 1. This indicates that adding ivy to the roof of the building has a weak effect on improving the overall thermal comfort of the street canyon. The average UTCI value in the street canyon area of Model 6 is 0.08 ℃ higher than Model 1. This indicates that when the LAI of the plant canopy is two-thirds of its original value, the sparse canopy has a significantly weaker improvement effect on street canyon thermal comfort compared to the dense canopy. This mainly due to tree canopy can reduce the penetration of shortwave solar radiation and intercepts long-wave radiation from the ground surface to atmosphere and desnse canopy can have stronger effect. According to Table 3 , if the 12 hours from 12:00 to 23:00 are divided into two periods: 12:00 to 19:00 and 20:00 to 23:00, and the UTCI means of the 6 models are compared in these two periods, it can be seen that the UTCI means of each model between 12:00 and 19:00, from highest to lowest, are Model 2 > Model 4 > Model 6 > Model 1 > Model 5 > Model 3; The average UTCI of each model between 20:00 and 23:00, in descending order, is Model 3 > Model 2 > Model 1 > Model 5 > Model 4 = Model 6. This shows that although the model 3, which has tall street trees, large canopies and a large number of trees, has a good cooling effect from 12:00 to 19:00, the UTCI value of the whole model is the lowest and the comfort level is the best, but this model has the highest average UTCI value and the worst comfort level at 20:00 to 23:00 at night. Tree canopies have been demonstrated as being able to retain heat at night (de Quadros and Mizgier, 2023 ). According to Wang et al., ( 2021 ) tree cover can reduce heat dissipation at night and aggravate the urban heat island in certain situations.Thus, planting more trees may not be reasonable measure to reduce urban heat island at night. Model 2 showed relatively poor thermal comfort in both periods, which further indicates that short trees with small crowns have poor effects on improving thermal comfort in street canyons during both day and night. Although the improvement effect Model 4 and 6 on street canyon thermal comfort is poor from 12:00 to 19:00. Model 6, which has sparse canopies, and Model 4, which has shorter crown diameter but a larger area of hedges, have the best improvement effect on street canyon thermal comfort from 20:00 to 23:00. One plausible explanation for this result is that, at model 6, tree leaves play a important role in preventing heat transfer and slowing down heat loss at night (Akbari, 2002 ). When the canopy is sparse, the effect become weak; At model 4, the hedges are 1-meter tall, the height which we analyze the UTCI vallue is 1.4 meter. The area we analyze is located above the hedges. Hedges may worse the thermal comfort of the area under the leaves of hedges because leaves can attenuate solar radiation and prevent the night’s heat flow from the surface to the sky at night (Wang et al., 2015 ). The areas where shrubs and soil are located have better thermal comfort compared to impermeable underlying surfaces (Oke, 1989 ). Model 4 has a larger area of underlying soil and shrubs compared to Model 2. This provides an explanation for Model 4 having lower PET values than Model 2 during both day and night. In addition, at night, hedges may also be able to have weak transpiration effect (Dawson et al., 2007 ). The weak transpiration effect of hedges also be able to improve thermal comfort of the area above or near the hedges weakly. This accords with Meili et al., ( 2021 ) that tree coving is more efficient in decreasing UTCI during daytime and vegetated ground fraction provides more cooling during night. Model 1 (constructed based on the actual situation of the street canyon) has a median UTCI value in both periods, indicating that there are still many ways to further improve the thermal comfort of the street canyon based on the actual situation. The significant differences in the improvement of street canyon thermal comfort by different models during the two different time periods mentioned above also indicate the importance of studying the different effects of plants on improving street canyon thermal comfort during the day and at night. Although Model 5, which increases roof greening, has a weak effect on improving the thermal comfort of the street canyon, this method slightly reduces the mean UTCI of the street canyon in both periods mentioned above. Therefore, when considering both the daytime and nighttime thermal comfort of the street canyon, increasing roof greening can slightly improve both the daytime and nighttime thermal comfort of the street canyon. However, the effect of this method on improving the thermal comfort of the street canyon is relatively weak, with an average decrease of only around 0.04 ℃ in UTCI value in the street canyon UTCI values from 12:00 to 19:00, and only approximately 0.01 ℃ decrease in UTCI value in street canyon UTCI values from 20:00 to 23:00. However, we choose ivy as the roof vegetation, if we chose trees or hedges as building wall and roof vegetation, the improvement effect may be more obvious. We only consider the impact of street greening on the thermal comfort of the street canyon at 1.4 m height outdoor. Green walls and roofs can have more obvious influences on the indoor thermal comfort of roadside buildings (Hao et al., 2020 ) and deserve to be considered as a measure to improve summer thermal comfort. Overall, there is a relatively large difference in UTCI values among the models between 12:00 and 19:00, and a relatively small difference in UTCI values between 20:00 and 23:00. From 12:00 to 19:00, Model 2 with the highest UTCI mean was 0.48 ℃ higher than Model 3 with the lowest UTCI mean, while from 20:00 to 23:00, Model 3 with the highest UTCI mean was only 0.05 ℃ higher than Model 4 and Model 6 with the lowest UTCI mean. Therefore, optimizing the landscape pattern of the green space of the street canyon can have a noticeable effect on improving the daytime thermal comfort of the street canyon, but the effect is not obvious at night. Given this situation, we believe that considering both the daytime and nighttime thermal comfort of the street canyon. Street canyons with a large number of tall trees, large crown width, high leaf area index, wide shrub coverage area, and vertical greening, may bring greater benefits overall after weighing the pros and cons of their influence on the thermal comfort of the street canyon during a hot summer day and night. In addition, the planting of street trees needs to comply with the minimum distance between street trees, meet the convenience of daily traffic and pedestrian walking, and maintain the overall aesthetics of the street canyon. Therefore, when optimizing the landscape pattern of the green space of a street canyon, it is not feasible to blindly add too much greening to have a significant negative impact on the street canyon from many other aspects. Table 2 The UTCI values of different models during day and night. Time Model 1 (℃) Model 2 (℃) Model 3 (℃) Model 4 (℃) Model 5 (℃) Model 6 (℃) 12:00 39.72 40.04 39.64 40.00 39.66 39.86 13:00 41.47 41.70 41.40 41.63 41.44 41.59 14:00 42.94 43.20 42.85 43.13 42.90 43.08 15:00 43.45 43.81 43.27 43.75 43.41 43.61 16:00 42.64 43.04 42.36 42.98 42.59 42.82 17:00 40.34 40.73 39.97 40.66 40.30 40.53 18:00 36.49 36.81 36.07 36.75 36.42 36.58 19:00 32.40 32.45 32.38 32.41 32.38 32.41 20:00 30.53 30.55 30.55 30.51 30.52 30.52 21:00 29.87 29.88 29.90 29.85 29.86 29.85 22:00 29.24 29.24 29.27 29.22 29.23 29.22 23:00 28.80 28.80 28.84 28.79 28.80 28.78 Table 3 The average UTCI values of the six models. Model 1 (℃) Model 2 (℃) Model 3 (℃) Model 4 (℃) Model 5 (℃) Model 6 (℃) Average UTCI value from 12:00 to 23:00 36.49 36.69 36.38 36.64 36.46 36.57 Average UTCI value between 12:00 and 19:00 39.93 40.22 39.74 40.16 39.89 40.06 Average UTCI value between 20:00 and 23:00 29.61 29.62 29.64 29.59 29.60 29.59 3.3 A comparison of the thermal comfort of the six models based on the UTCI values at 13:00 and 20:00. Figure 4 compares the UTCI values of six models at 13:00. From the comparison between Model 1 and Model 2, it can be seen that during the daytime, the UTCI value of the area where the street trees are located in Model 1 is relatively low, indicating that tall trees with larger crown width form a larger shaded area that blocks sunlight. In theory, roadside trees with different heights and crown widths have varying degrees of impact on the wind environment, which in turn affects the thermal comfort of local spaces (Hsieh et al., 2016 ). However, due to the low wind speed during this period and the dense construction in the area, the difference in UTCI values measured by Model 1 and Model 2 in this study is relatively small. From Model 1 and Model 3, it can be seen that under the same conditions, the increase of the median divider with trees in the middle of the road will reduce the UTCI value through the influence of sunlight obstruction and transpiration. Trees can reduce wind speed and this can have negative impact on thermal comfort (Hsieh et al., 2016 ). By comparing the UTCI values around the central reservation of the Model 3 and the corresponding part in Model 1, it can be seen that the trees in the central reservation of the road has very limited impact on the thermal comfort of the surrounding area through wind blockage and transpiration. Except for the significant difference in UTCI values between the shaded area of trees in the central reservation of the road in Model 3 and the corresponding part in Model 1, there is no significant difference in UTCI values between the other areas where the vehicle lane is located in the two models. Although the underlying surface absorb and re-emit the sun’s heat more than natural landscape (United States Environmental Protection Agency, 2023 ), Model 4 has a larger soil coverage area and a smaller area of impermeable underlying surfaces such as asphalt and concrete compared to Model 2. This is beneficial for reducing the air temperature rise caused by absorbing and emitting sun’s heat from the ground (United States Environmental Protection Agency, 2023 ). Compared Model 2 with Model 4, the difference in the effect of adding soil covered area and hedges on the illustrated results is relatively small, and the difference in UTCI values between the two models in the same spatial area is not obvious. Increasing roadside trees can produce a more significant cooling effect than hedges during daytime. In the street canyon area, after meeting the needs of both traffic and pedestrian flow, the remaining road greening area is very limited and needs to be fully utilized. Improving the coverage of trees is more beneficial for improving thermal comfort at 1.4 meters than increasing the coverage of hedges during the daytime. From the simulation results of Model 1 and Model 5, it can be seen that increasing roof greening has very limited effect on the UTCI value of local space. Greenery on the roof can help reduce the mean radiation temperature and improve the thermal comfort of the surrounding area due to it emit less short-wave radiance than hard surface (D'SOUZA, 2013 ). The analysis area is located 1.4 meters above the ground in the street canyon. It is far from the roof of buildings. The changing the underlying surface did not cause noticeable differences in thermal comfort in different areas of the street canyon. Comparing Model 1 and Model 6, it can be found that Model 1 with higher leaf area density has a relatively lower UTCI value at the tree shadow area, which is mainly due to more leaves blocking sunlight and transpiration. Even if the layout of street trees is thought as having significant impact on the thermal comfort of the surrounding environment (Zhao et al., 2018), it is hard to change the spatial layout of street trees in street canyon because the area designated for road green space is very limited, and plants such as roadside trees need to meet the requirements of the minimum distance between roadside trees in the city, maintain good permeability, and improve the aesthetic level of the street (Hunan municipal government, 2020 ). Under the premise of difficulty in improving the layout of roadside trees, selecting appropriate tree species and providing favorable conditions for the growth of roadside tree branches and leaves to increase the leaf area density and leaf area index of roadside trees will be a good method to improve the daytime thermal comfort during summer in the street canyons. Figure 5 shows the UTCI values of six models at 20:00. Figures 4 and 5 can be used to compare the impacts of plants on thermal comfort during both daytime and nighttime, respectively. It can be seen that compared to the impacts of plants on thermal comfort during daytime, the impacts of plants on the nighttime thermal comfort of the respective areas are very small. At night, urban temperature can often be much higher than those in rural areas (United States Environmental Protection Agency, 2023 ). The variance of air temperature between urban and rural area can be higher during nighttime than daytime in some cases (Peng et al., 2012 ; Xu et al., 2022). Thus, it is also important to reduce nighttime heat island effect for the street canyon area. It can be observed from Fig. 5 that the six models exhibit minimal differences in street canyon thermal comfort due to varying characteristics of roadside trees. The corresponding UTCI values for the same area in all six models show no significant variation. Optimizing the road greening characteristics such as street tree height, crown width, road green divider, roof greening, and leaf area density have very limited impact on nighttime thermal comfort. The areas with better thermal comfort during the day and night are also different. During the day, they are more influenced by green space and distributed in areas with highly concentrated plantations. At night, areas with better thermal comfort are mainly concentrated in well-ventilated areas or areas far away from buildings. Thus, improving the ventilation condition is a good way to improve thermal comfort of the street canyon. Road pavement has the capacity to absorb a large amount of heat during the day. They release heat slowly in to the atmosphere at night (Katzschner, 2009 ; Ibrahim et al., 2018 ). Good ventilation environment plays a quite active role in reducing the heat release by the road pavement. During the daytime, shaded areas created by buildings typically offer good thermal comfort by blocking sunlight, thereby creating a cooler environment. However, at night, due to buildings slowly release heat absorbed during the day (Ahmed et al., 2014 ) and the building's ability to provide wind protection, areas with poor thermal comfort are formed around the building. Although the simulation results of the six models at 20:00 are not significantly different, road greening and soil underlying surfaces undoubtedly do not absorb large amounts of heat during the day and gradually release it at night, like impervious underlying surfaces such as asphalt and cement. From this perspective, this can still have a positive impact on nighttime thermal comfort. Meili et al., ( 2021 ) found that ground vegetation plays an active role in decreasing UTCI at night. This shows that soil and low-growing plants can be more beneficial to street canyon nighttime thermal comfort than impervious underlying surfaces during hot summer days. 4. Conclusion Although many studies have focused on the impact of green spaces on the thermal comfort of street canyons, most have not simultaneously considered the different effects of road greening on the thermal comfort of street canyons during the day and at night. This study attempts to explore how optimizing road green spaces can maximize the improvement of street canyon thermal comfort, taking into account both the impact of green spaces during the day and night. This study takes a road section in the central urban area of Changsha, a city in central south part of China, as an example. This study comprehensively considers the relevant road green space regulations, the need for road green space to meet various needs, and the actual situation of the street canyon, such as the minimum spacing between roadside trees, maintaining the beauty and permeability of the street canyon, and avoiding excessive increase in road green space areas that may cause traffic congestion in the street canyon. One model based on the real situation of the street canyon and five models based on commonly used road greening opimization strategies were created such as the central green space divider, roof greening, and different tree height and crown characteristics. Research has found that during the day, the more vegetations especially the trees, the larger the crown width, and the higher the leaf area density, the better the cooling effect of vegetations. In addition, roof greening can also slightly improve the thermal comfort of street canyons. This is mainly due to the shading area formed by plants blocking sunlight, the transpiration effect of plants, and the weaker heating effect of soils and vegetated areas than impervious underlying surfaces such as concrete and asphalt on street canyons through reflected shortwave radiation. The impact of different road green space landscape patterns on the thermal comfort of street canyons during the day varies significantly. In this study, six models were simulated during the daytime period, and the maximum PET value difference between the models in the street canyon area occurred between Model 2 and Model 3 at 17:00, with a difference of 0.76 ℃ in UTCI values between the two models. However, in nighttime periods, the maximum PET value difference between the models in the street canyon area occurred between Model 3 and Model 6 at 23:00, with a difference of only 0.06 ℃ in UTCI values between the two models. Therefore, we believe that in this situation, even if street trees may have negative impacts on the nighttime thermal comfort of the street canyon, we can still plant more street trees because the negative impact is very small. On the contrary, this can have a significant positive impact during the day. In addition, we can compensate for the slight negative impact of street trees on the thermal comfort of the street canyon at night by increasing roof greening, low shrubs in road greening areas, and improving the ventilation environment of the street canyon. Declarations Author contributions Junyou Liu: Investigation, Methodology, Software, Data Analysis, Visualization, writing– original draft, review and editing. Bohong Zheng: Supervision, writing– review and editing. Haifang Tang: Data Analysis. Jia Fan: writing– original draft. All authors have read and agreed to the published version of the article. Funding No funding was received for this work Data availability Not applicable. Ethics approval Not applicable. Competing interests The authors declare no competing interests. References Ahmed, AS.F., Khan, KM.M.K., Maung Than Oo, AA. et al. Selection of suitable passive cooling strategy for a subtropical climate. Int J Mech Mater Eng 9, 14 (2014). https://doi.org/10.1186/s40712-014-0014-7 Akbari, H. 2002. Shade trees reduce building energy use and CO2 emissions from power plants. Advances in Terrestrial Ecosystem: Carbon Inventory, Measurements, and Monitoring Conference, 116, S119-S126. Anand, J.; Sailor, D.J. Role of pavement radiative and thermal properties in reducing excess heat in cities. Sol. Energy 2022 , 242 , 413–423. Beck, H.E.; Zimmermann, N.E.; McVicar, T.R.; Vergopolan, N.; Berg, A.; Wood, E.F. Present and future Köppen-Geiger climate classification maps at 1-km resolution. Sci. Data 5, 180214 (2018）. Blazejczyk K (1994) New climatological- and -physiological model of the human heat balance outdoor (MENEX) and its applications in bioclimatological studies in different scales. Zeszyty IgiPZ PAN 28: 27–58. Caird MA, Richards JH. Donovan LA. Nighttime stomatal conductance and transpiration in C3 and C4 plants. Plant Physiol. 2007;143:4–10. Changsha Bureau of Commerce. （2022）. Changsha, a mega city http://swt.changsha.gov.cn/zfxxgk/zxzx_35631/WXZX/202210/t20221020_10848406.html. (accessed on 30 December 2023) Changsha Municipal Government. Overview of Changsha CityAvailable online: http://www.changsha.gov.cn/xfzs/zjmlzs/zsgl/200907/t20090727_5686409.html?ivk_sa=1024320u (accessed on 20 July 2022). Dawson, T. E., Burgess, S. S. O., Tu, K. P., Oliveira, R. S., Santiago, L. S., Fisher, J. B., et al. (2007). Night-time transpiration in woody plants from contrasting ecosystems. Tree Physiol. 27, 561–575. doi: 10.1093/treephys/27.4.56 De Quadros, B.M.; Mizgier, M.G.O. Urban Green Infrastructures to Improve Pedestrian Thermal Comfort: A Systematic Review. Urban For. Urban Green. 2023, 88, 128091. Diana E. Bowler, Lisette Buyung-Ali, Teri M. Knight, Andrew S. Pullin.Urban greening to cool towns and cities: A systematic review of the empirical evidence.Landscape and Urban Planning,2010,Vol.97(3): 147-155 D'SOUZA, U. 2013. The thermal performance of green roofs in a hot, humid microclimate. SUSTAINABLE DEVELOPMENT AND PLANNING. volume 173 ENVI-met. (2024). UTCI. https://envi-met.info/doku.php?id=apps:biomet_utci. Accessed 28th January 2024. Görgen, F., and M. Rossi-Schwarzenbeck. 2021. “Evaporative cooling strategies in urban areas: The potential of vertical greening systems to reduce nocturnal heat stress.” J. Phys. Conf. Ser. 2042 (1): 012056. https://doi.org/10.1088/1742-6596/2042/1/012056. Global Monitoring Laboratory. 2024. NOAA Solar Calculator. Available at: https://gml.noaa.gov/grad/solcalc/. Accessed 29th Feburary 2024. Hao, X.; Xing, Q.; Long, P.; Lin, Y.; Hu, J.; Tan, H. Influence of vertical greenery systems and green roofs on the indoor operative temperature of air-conditioned rooms. J. Build. Eng. 2020, 31, 101373. Hsieh, CM;Jan, FC;Zhang, L.A simplified assessment of how tree allocation, wind environment, and shading affect human comfort. URBAN FORESTRY AND URBAN GREENING,2016,Vol.18(1): 126-137 Hunan municipal government. 2020. Regulations on Urban Greening Management in Changsha City (Revised). https://www.hunan.gov.cn/hnszf/xxgk/wjk/zcfgk/202007/t20200730_729e1610-3249-4e8d-ab9a-0d374857bdb6.html. Accessed 13 March 2024. Ibrahim, S.H., Ibrahim, N.I.A., Wahid, J., Goh, N.A., Koesmeri, D.R.A., Nawi, M.N.M., 2018. The Impact of Road Pavement on Urban Heat Island (UHI) Phenomenon. International Journal of Technology. Volume 9(8), pp. 1597-1608 Katzschner, L., 2009. Urban Climate in Dense Cities. In: Designing High-density Cities for Social and Environmental Sustainability, Ng, E., (ed.), Earthscan, London, UK, pp. 71–78 Liu, J.; Zheng, B.; Yang, F. A Simulation Study of the Impact of Urban Street Greening on the Thermal Comfort in Street Canyons on Hot and Cold Days. Forests 2023, 14 , 2256. https://doi.org/10.3390/f14112256 Malek, E. Night-time evapotranspiration vs. daytime and 24h evapotranspiration.Journal of Hydrology,1992,Vol.138(1): 119-129 Maqueda, A.I.;del-Blanco, C.R.;Jaureguizar, F.;Garcia, N..Comparing Universal Thermal Climate Index (UTCI) with selected thermal indices/environmental parameters during 12 months of the year.Weather and Climate Extremes,2018,Vol.19(8): 49-57 Ministry of Housing and Urban-Rural Development. (2012). Urban green space classification standards CJJ/T85-2017. Meili, N.; Acero, J.A.; Peleg, N.; Manoli, G.; Burlando, P.; Fatichi, S. Vegetation cover and plant-trait effects on outdoor thermal comfort in a tropical city. Build. Environ. 2021, 195, 107733 Narimani, N.; Karimi, A.; Brown, R.D. Effects of street orientation and tree species thermal comfort within urban canyons in a hot, dry climate. Ecol. Inform. 2022, 69, 101671. Oke, T.R., 1989. The micrometerology of the urban forest. Phil. Trans. R. Soc. Lond. B. 324, 335–349. Peng, S.; Piao, S.; Ciais, P.; Friedlingstein, P.; Ottle, C.; Bréon, F.-M.; Nan, H.; Zhou, L.; Myneni, R.B. Response to Comment on “Surface Urban Heat Island Across 419 Global Big Cities”. Environ. Sci. Technol. 2012, 46, 6889–6890. Ren, Z.; Zhao, H.; Fu, Y.; Xiao, L.; Dong, Y. Effects of urban street trees on human thermal comfort and physiological indices: A case study in Changchun city, China. J. For. Res. 2022, 33, 911–922. Ruiz, M.A.; Sosa, M.B.; Correa, E.N.; Cantón, M.A. Design tool to improve daytime thermal comfort and nighttime cooling of urban canyons. Landsc. Urban Plan. 2017, 167, 249–256. United States Environmental Protection Agency. 2023. Learn About Heat Islands. Available at: https://www.epa.gov/heatislands/learn-about-heat-islands. Accessed 12th March 2024. United States Environmental Protection Agency. 2023. Learn About Heat Islands. https://www.epa.gov/heatislands/learn-about-heat-islands. Accessed 14th March 2024. Waite, M. 2007. Oxford Dictionary & Thesaurus. Oxford. Oxford University Press. Wang, Y，Pan, C，Huang, Z. Comparison of Applicability of PET and UTCI in Different Seasons in Shanghai . Building Science,2020, 36(10): 55-61 Wang, Y., Bakker, F., de Groot, R. et al. Effects of urban trees on local outdoor microclimate: synthesizing field measurements by numerical modelling. Urban Ecosyst 18, 1305–1331 (2015). https://doi.org/10.1007/s11252-015-0447-7 Wang, Y., Ni, Z., Hu, M., Chen, S., Xia, B., 2021. A practical approach of urban green infrastructure planning to mitigate urban overheating: a case study of Guangzhou. J. Clean. Prod. 287 https://doi.org/10.1016/j.jclepro.2020.124995. World Health Organization. (2023). Climate change. Available at: https://www.who.int/news-room/fact-sheets/detail/climate-change-and-health. Accessed January 22th 2024. World Health Organization. (2024). Heatwaves. Available at: https://www.who.int/health-topics/heatwaves#tab=tab_1. Accessed January 22th 2024. Xiang, J.; Liu, H. Study on Optimal Design of Exterior Sunshade for Residential Buildings in Hot Summer and Cold Winter Zone. Build. Sci. 2016, 32, 80–84+126. Xu, Y.; Zhang, C.; Hou, W. Modeling of Daytime and Nighttime Surface Urban Heat Island Distribution Combined with LCZ in Beijing, China. Land 2022, 11, 2050. https://doi.org/10.3390/land11112050 Wang, Y.; Anderegg, W.R.L.; Venturas, M.D.; Trugman, A.T.; Yu, K.; Frankenberg, C. Optimization theory explains nighttime stomatal responses. New Phytol. 2021, 230, 1550–1561. Zhang D, Xie X, Zhou C. 2023. Spatial influence of exposure to green spaces on the climate comfort of urban habitats in China. Urban Clim. 51:101657. doi: 10.1016/j.uclim.2023. 101657. Zhao, Qunshan;Sailor, David J.;Wentz, Elizabeth A..Impact of tree locations and arrangements on outdoor microclimates and human thermal comfort in an urban residential environment.URBAN FORESTRY AND URBAN GREENING,2018,Vol.32(1): 81-91 Zölch, T., Rahman, M, A. Pfleiderer, E., Wagner, G., Pauleit, S. Designing public squares with green infrastructure to optimize human thermal comfort.Building & Environment,2019,Vol.149(1): 640-654 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4113689","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":288604225,"identity":"65cc1682-0310-4555-a932-164af9350cc1","order_by":0,"name":"Junyou Liu","email":"","orcid":"","institution":"Central South University","correspondingAuthor":false,"prefix":"","firstName":"Junyou","middleName":"","lastName":"Liu","suffix":""},{"id":288604226,"identity":"5fdb2fb6-a6db-4f40-9809-bb17b8c5ef58","order_by":1,"name":"Bohong Zheng","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8klEQVRIiWNgGAWjYDACCSBmbGBIAFEPIEIJxGthNiBZC5sEUVrkZzcfe/h1h00ev3T7tYoffw4z8LPnGDD83IFbC+OcY+nGsmfSiiXnnCm72dt2mEGy540BY+8Z3FqYJXLMpCXbDiduuJGTdpux4TCDwY0cA2bGNtxa2CTyv8G1FDMAHWZPSAuPRA6b5EewlvRjzAxsQFskCGiRkEgzk2Y8k5Y4c0YOs2RvWzqPxJlnBQd78WiRn5H8TPLnDpvEfon0hx9+/LGW429P3vjgJx4t4CDggbgRHJNg9gH8GoAB/QNMsT8gpHAUjIJRMApGKAAAVRlTEn85zmQAAAAASUVORK5CYII=","orcid":"","institution":"Central South University","correspondingAuthor":true,"prefix":"","firstName":"Bohong","middleName":"","lastName":"Zheng","suffix":""},{"id":288604227,"identity":"9aaf2900-a3a6-4537-a9ca-a1c7f4a4af9a","order_by":2,"name":"Haifang Tang","email":"","orcid":"","institution":"China Machinery International Engineering Design and Research Institute Co., Ltd","correspondingAuthor":false,"prefix":"","firstName":"Haifang","middleName":"","lastName":"Tang","suffix":""},{"id":288604228,"identity":"b728e8a8-bcf9-456a-9c98-90d3553dff88","order_by":3,"name":"Jia Fan","email":"","orcid":"","institution":"Central South University","correspondingAuthor":false,"prefix":"","firstName":"Jia","middleName":"","lastName":"Fan","suffix":""}],"badges":[],"createdAt":"2024-03-16 14:59:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4113689/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4113689/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54483608,"identity":"8ff11161-25ae-476e-a875-094fb44d105c","added_by":"auto","created_at":"2024-04-11 08:45:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2076339,"visible":true,"origin":"","legend":"\u003cp\u003eA figure to show the six models\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4113689/v1/3f8880747afcc6eb991a5f01.png"},{"id":54483602,"identity":"106288fa-c48c-4573-97ca-d6c29a67b0bd","added_by":"auto","created_at":"2024-04-11 08:45:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":610368,"visible":true,"origin":"","legend":"\u003cp\u003eA comparision of the UTCI values of model 1 at 14:00, 16:00, 21:00 and 23:00\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4113689/v1/1193c6c7ac099f21d7b631fe.png"},{"id":54483609,"identity":"5c9d6198-d1f2-44a9-9ef8-499d21b3b7db","added_by":"auto","created_at":"2024-04-11 08:45:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":326091,"visible":true,"origin":"","legend":"\u003cp\u003eA comparison of the UTCI values of the six models.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4113689/v1/18ffa2979d6428b7a38b225a.png"},{"id":54483613,"identity":"438ce67a-afae-4f22-afd6-0145501aed09","added_by":"auto","created_at":"2024-04-11 08:45:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1535994,"visible":true,"origin":"","legend":"\u003cp\u003ecomparison of the UTCI values of the six models at 13:00\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4113689/v1/0ecf2b911c571e53bef858c4.png"},{"id":54483606,"identity":"b93ad6aa-400c-4774-8bc9-93486eec4cf1","added_by":"auto","created_at":"2024-04-11 08:45:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1464051,"visible":true,"origin":"","legend":"\u003cp\u003ecomparison of the UTCI values of the six models at 20:00\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4113689/v1/6464257d939ec837cd3d86be.png"},{"id":54485336,"identity":"cc28633f-777d-444e-91ca-83b0852b16b0","added_by":"auto","created_at":"2024-04-11 09:09:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5141966,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4113689/v1/680a0567-a1c0-4d4d-96a7-871f98e49165.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The Impact of Green Spaces on Thermal Comfort in Urban Street Canyons during Hot Summer Days and Nights","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e3.6\u0026nbsp;billion people live in areas highly susceptible to climate change. Climate change presents a critical threat to human health. Heatwave is one of the main extreme weather events caused by climate change (World Health Organization, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Heatwaves can increase heat-related deaths. More than 166000 people died because of heatwaves between 1998 and 2017. The number of people exposed to heatwaves grows by approximately 125\u0026nbsp;million from 2000 to 2016 (World Health Organization, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Urban areas can suffer more from the heat wave due to the urban heat island effect. Urban pavements are an important contributor to the urban heat island effect (Anand and Sailor, 2021). Urban street canyon areas can become one of the main high-temperature areas during hot summer days in a city since urban pavement can accumulate a lot of heat. Urban street greening can play quite active role in mitigating the negative impact of urban heat waves and the heat island effect. People stay in streets with higher tree cover can have lower pulse rate, systolic blood pressure, diastolic blood pressure (Ren et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Thus, it can contribute to a healthier street canyon environment.\u003c/p\u003e \u003cp\u003eThe attached green spaces within urban roads and transportation facilities areas are an important part of urban green spaces (Ministry of Housing and Urban Development of the People's Republic of China, 2017). The main feature of this type of green space is its strip like distribution along urban roads. Some researchers have researched the impact of road green spaces on the thermal comfort of street canyons. For example, Ren et al., (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) explored the impact of the different degrees of street tree cover on the thermal comfort in street canyon, they found street canyon with higher tree cover has lower frequency of strong heat stress. Liu et al., (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) focused on the impact of street greening on the thermal comfort of street canyon during hot days and cold days. In general, they find street trees can improve thermal comfort of street canyon during hot days and deteriorate thermal comfort of street canyon during cold days. Narimani et al., (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) explored the impact of street orientation and street tree on thermal comfort of the street canyon, they found tree cover have more prominent effect on thermal comfort than orientation\u0026rsquo;s effect.\u003c/p\u003e \u003cp\u003eSome researchers also consider the impacts of green space on thermal comfort at night. For example, Zhang et al.,(2023) explored the impact of green spaces on the climate comfort, they pointed out that exposed to green space can adjust thermal comfort by transpiration, water storage and heat absorption. This can reduce the range of temperature different betweeen day and night.; Z\u0026ouml;lch et al.,(2018) explored the impacts of different public squares designing on thermal comfort during hot summer daytime and nightime condiitions. They found a model with many trees located in sunlit area can provide relatively good thermal comfort during daytime and a model without trees but with a meadow area have good thermal comfort. They propose that a climate adapted design should include trees to maximize shade area, the wind channel is kept free from trees, also planted with grass to minimize the heat storage. Morakinyo et al., (2017) explored the impact of trees on in-canyon and neighbourhood\u0026rsquo;s thermal comfort during daytime and nighttime. They found leaf area index, tree height and trunk height are influential factors for improving thermal comfort. In addition, they found that the effectiveness of trees in increasing daytime thermal comfort decreased with increasing urban density during the day, while vice-versa at night. In general, few researchers comprehensively studied the impacts of street greening on thermal comfort during daytime and nighttime simultaneously.\u003c/p\u003e"},{"header":"2. Material and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Overview of the study area\u003c/h2\u003e \u003cp\u003eChangsha is located between 27 \u0026deg; 51 \u0026prime; -28 \u0026deg; 40 \u0026prime; N and 111 \u0026deg; 53 \u0026prime; -114 \u0026deg; 15 \u0026prime; E, and is an important central city in the middle reaches of the Yangtze River in China and the capital of Hunan Province. Changsha City is located in the subtropical monsoon climate zone, with significant temperature changes in spring, sustained high temperatures in summer and autumn, and cold winters(Beck et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Xiang and Liu, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Changsha City governs 6 districts, 1 county, and 2 county-level cities. In 2022, the permanent population was 10.426\u0026nbsp;million (Changsha Municipal Government, 2023), and the urbanization rate was 83.27%. Among them, the population of the central urban area of Changsha is about 5.546\u0026nbsp;million people (Changsha Bureau of Commerce, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This study selected a section of Guihua Road in the central urban area of Changsha for research.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Model construction and simulation analysis\u003c/h2\u003e \u003cp\u003eThis study constructs different models based on a section of guihua road in the central urban area of Changsha, and uses ENVI-met 5.6.1 for thermal comfort simulation analysis. The simulation period is from 11:00 to 23:00 on July 8, 2022. The initial simulation data is from the National Meteorological Information Center, and the station information is [57687] Changsha. The meteorological data can be seen in Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e below. Model 1 is a model constructed based on the actual situation of the road section. The planation in the model are 15-meter-high \u003cem\u003eCamphora officinarum\u003c/em\u003e trees and 10-meter high \u003cem\u003eOsmanthus Fragr\u003c/em\u003e trees and 1 meter \u003cem\u003eLigustrum lucidum\u003c/em\u003e trees. In model 2, road trees are 10-meter-high \u003cem\u003eCamphora officinarum\u003c/em\u003e trees and 5-meter high \u003cem\u003eOsmanthus Fragr\u003c/em\u003e trees and 1 meter \u003cem\u003eLigustrum lucidum\u003c/em\u003e hedges. The location, and number of roadside trees are consistent with model 1. Model 3 are still 15-meter-high \u003cem\u003eCamphora officinarum\u003c/em\u003e trees and 10-meter high \u003cem\u003eOsmanthus Fragr\u003c/em\u003e trees and 1 meter \u003cem\u003eLigustrum lucidum\u003c/em\u003e hedges, with the same total number and position as Model 1, model 3 has a central bed divider consisting of a 5-meter tree in the middle of the two-way lane. Model 4 has the same 10 m \u003cem\u003eCamphora officinarum\u003c/em\u003e trees and 5 m \u003cem\u003eOsmanthus Fragr\u003c/em\u003e trees characteristics as model 2 but a larger number of 1 meter \u003cem\u003eLigustrum lucid\u003c/em\u003eum hedges than model 2. The situation of the roadside trees in Model 5 is the same as in Model 1. Model 5 has green roof on the buildings and model 1 does not have. Since 15-meter camphor trees with LAI of 3.0 is generally dense. Except model 6, We uniformly set the LAI of 10 m as 3.3; 15 meter camphor tree as 3.0; 5 meter camphor tree as 3.6; 10 meter \u003cem\u003eOsmanthus fragrans\u003c/em\u003e as 3.3. This confirms with Liu et al., (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), which has used hemiview (Delta T, UK) to measure the LAIs of trees in Changsha. Through further analyze the LAI of \u003cem\u003eCamphora officinarum\u003c/em\u003e trees in Changsha, we found some sparse \u003cem\u003eCamphora officinarum\u003c/em\u003e trees only have LAIs of around 2.2. Model 6 has the same condition as model 1 except the LAI of the 15 m \u003cem\u003eCamphora officinarum\u003c/em\u003e trees is 2, LAI of the 10 m \u003cem\u003eOsmanthus fragrans\u003c/em\u003e trees. The crown width of 15 meter, 10 meter and 5 meter trees are uniformly set as 9m, 7m and 3m respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the sketchesf the six models.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUniversal thermal climate index (UTCI), proposed by EU COST Action 730, is an indicator for thermal comfort based on the multi-node Fiala mode. (Wang et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; ENVI-met,2024). It is the air temperature of the reference environment which produces the same strain index value in comparison with the reference individual's response to the real environment. It is calculated by meteorological data like mean radiant temperature, relative humidity, wind speed and non-meteorological data like clothing thermal resistance and metabolic rate (Maqueda et al., 2018). UTCI is the main indicator used to evaluate thermal comfort in this study.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003emeasured data from meteorological station\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTime\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAverage wind direction during the 13 hours (\u0026deg;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAverage wind speed during the 13 hours (m/s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTemperature\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRelative Humidity\u003c/p\u003e \u003cp\u003e(%RH)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"12\" rowspan=\"13\"\u003e \u003cp\u003e8th July 2022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"12\" rowspan=\"13\"\u003e \u003cp\u003e183\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"12\" rowspan=\"13\"\u003e \u003cp\u003e2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e31.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e31.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e32.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e32.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e32.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e32.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e32.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e31.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e77\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e22:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e29.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e77\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eBased on the defition of day (the time between sunrise and sunset) and night (the time from sunset to sunrise) (Waite, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), we calculated the sunrise and sunset time of Changsha on 8th July 2022 and classified the time period into daytime and nightime. We mainly refer NOAA Solar Calculator (Global Monitoring Laboratory, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) to calculate the sunrise and sunset time of Changsha during this day and classified the time period from 11:00 to 19:00 in to days and between 20:00 and 23:00 in to night.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Error Analysis\u003c/h2\u003e \u003cp\u003eWe also did validation analysis for the simulated microclimate characteristics. We conducted validation analysis for air temperature and relative humidity. We use the measured data from meteorological station to represent the real temperature and relative humidity in the study area and the average simulated temperature and relative humidity of the study area to represent the simulated temperature and humidity in the study area. We conducted error analysis using 12-hour measured values and simulated values within the study area (12:00\u0026ndash;23:00). Because the simulation result of the first hour 11 o clock is not stable, we did not use this hour for analysis. Error analysis mainly relies on Pearson correlation coefficient (r), determination coefficient (R\u003csup\u003e2\u003c/sup\u003e), mean absolute deviation (MAE), root mean square error (RMSE), and consistency index (d). For temperature analysis, we got r, R\u003csup\u003e2\u003c/sup\u003e, MAE, RMSE, d is 0.97, 0.94, 1.02, 1.21, 0.87 respectively. For relative humidity analysis, we got r, R\u003csup\u003e2\u003c/sup\u003e, MAE, RMSE, d is 0.96, 0.92, 9.94, 10.34, 0.53 respectively.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 A comparison of the thermal comfort of the street canyon during day and night\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the UTCI values of the street canyon at 14:00 and 16:00 during the day and 21:00 and 23:00 during the night. It can be seen from the graph that the street tree and building shadow area form a relatively low UTCI value area during the day. However, the area near buildings and trees do not show obviously better thermal comfort than other areas relatively far from trees and buildings in the street canyon during night. Trees can improve the thermal comfort of the street canyon through shading the sunlight and evaporation to reduce air temperature so that improve thermal comfort during hot summer day (Liu et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). At night, trees do not play the role of shading sunlight. Thus, tree shading area is not one of the most comfort area in the street canyon during the night. It can be seen from the figure that the areas between two buildings at one side of the Guihua road is one of the most comfortable areas during night. This can attribute to the wind direction is 183\u0026deg; in the simulation process. It can below through the areas between two buildings at one side of the Guihua road easily without the blockage of the buildings. This shows wind plays a quite active role in improving the thermal comfort of the street canyon during hot summer night. During the day, the sunlight is sufficient, the transpiration of plants is strong; At night, without light, the stomata of plants close or shrink, and the transpiration is weak (Malek, 1992; Wang et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This is another reason why street trees play more active role in reducing air temperature during the day than the night. These indicate relevant practitioners like urban planners that make full use of tree and bulding shadow can create many good thermal comfort areas in the street canyon during the day. At night, wind can play a quite positive role in creating areas with low UTCI value and maintain good ventilation condition for the street canyon is good for the thermal comfort of the street canyon.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 A comparison of the thermal comfort of the six models based on average UTCI values.\u003c/h2\u003e \u003cp\u003eIt can be seen from the Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e that the differences in UTCI value at the same time among different models are more obvious during the daytime than during the night. According to Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, considering the difference in UTCI values among the six models between 12:00 and 19:00, it can be inferred that the maximum difference in UTCI values occurred between Model 2 and Model 3 among the six models at 17:00. The difference in UTCI is 0.76 ℃. From 20:00 to 23:00, there is only a small difference in UTCI values among the models. The maximum difference in UTCI among the six models during this period occurred between model 3 and model 6 at 23:00. The UTCI value of model 3 was 0.06 ℃ higher than that of model 6 at this time. This indicates that different plant characteristics in the street canyon can have a relatively large impact on the thermal comfort of the street canyon between 12:00 and 19:00, while the impact difference between 20:00 and 23:00 is very small. One of the main reasons may be that plantation plays a quite positive role in blocking the sunlight and creating cool areas beneath vegetation during the daytime. Different street canyon vegetation characteristics have different effects in blocking sunlight and intercepting solar radiation and this can have different influences on land surface temperature and air temperature in the street canyon during the daytime (Bowler rt al., 2010; Oke, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). The soil in the area where the vegetation is located also has a different effect on absorbing and reflecting solar radiation compared to impermeable underlying surfaces such as asphalt and concrete. Soil can retain water for evaporation and this is beneficial for reducing air temperature. Impervious surfaces can quickly absorb and retain heat when exposed to solar radiation (Oke, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). Transpiration transports water from the roots of plants to the top, and then evaporates, taking away a large amount of heat. At night, transpiration is the main way for the plantation to reduce land surface temperature and air temperature in the street canyon. Even if the transpiration effects of different vegetation characteristics are different. The difference in average air temperature at 1.4-meter height in the street canyon area of different models is very small. At night, due to the lack of sunlight, plant stomata are closed and plant transpiration is weak (Caird et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Dawson et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). This is also one of the main reasons why there is a small difference in the average UTCI values among the model street canyon areas at 19:00 and 23:00.\u003c/p\u003e \u003cp\u003eAccording to Table \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Model 3 has the lowest average UTCI value during these 12 hours. The other features of Model 3 are the same as Model 1, but Model 3 has a median road divider with many 5 m trees and Model 1 does not. The 12-hour average UTCI value of Model 3 is 0.11 ℃ lower than Model 1. This indicates that the plants in the central divider of the road have played a significant role in improving the thermal comfort of the street canyon. In general, the more vegetations distribute in the street canyon, the better the thermal comfort of the street canyon during the hot day (Dawson et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), especially tall trees with large canopies can play a significant role in improving thermal comfort. The average UTCI of Model 2 is the highest among the six models. The difference between Model 2 and Model 1 is the size of the plant canopy and the height of the tree.\u003c/p\u003e \u003cp\u003eTree size and tree canopy characteristics can significantly influence the penetration of solar radiation (Dawson et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). In Model 1, the 15-meter camphor tree and 10-meter \u003cem\u003eOsmanthus Fragr\u003c/em\u003e can block more sunlight and form more shadow areas than the 10-meter camphor tree and 5-meter \u003cem\u003eOsmanthus Fragr\u003c/em\u003e in Model 2. Having more leaves in a larger canopy can also better utilize the transpiration of plants to lower temperatures. Model 2 has an average UTCI value 0.2 ℃ higher than Model 1 during these 12 hours. Hedges can also affect solar radiation, wind speed and wind direction (de Quadros and Mizgier, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The average UTCI value of Model 4 is only 0.05 ℃ lower than that of Model 2. This indicates that adding a larger area of 1 meter of hedge (\u003cem\u003eLigustrum lucidum\u003c/em\u003e) based on Model 2 has a weak effect on improving the thermal comfort of the street canyon. Vegetation applied to the building envelope can also influence radiant and convective energy exchange. This can also influence human comfort in the built environment (de Quadros and Mizgier, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The average UTCI value of Model 5 is only 0.03 ℃ lower than Model 1. This indicates that adding ivy to the roof of the building has a weak effect on improving the overall thermal comfort of the street canyon. The average UTCI value in the street canyon area of Model 6 is 0.08 ℃ higher than Model 1. This indicates that when the LAI of the plant canopy is two-thirds of its original value, the sparse canopy has a significantly weaker improvement effect on street canyon thermal comfort compared to the dense canopy. This mainly due to tree canopy can reduce the penetration of shortwave solar radiation and intercepts long-wave radiation from the ground surface to atmosphere and desnse canopy can have stronger effect.\u003c/p\u003e \u003cp\u003eAccording to Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, if the 12 hours from 12:00 to 23:00 are divided into two periods: 12:00 to 19:00 and 20:00 to 23:00, and the UTCI means of the 6 models are compared in these two periods, it can be seen that the UTCI means of each model between 12:00 and 19:00, from highest to lowest, are Model 2\u0026thinsp;\u0026gt;\u0026thinsp;Model 4\u0026thinsp;\u0026gt;\u0026thinsp;Model 6\u0026thinsp;\u0026gt;\u0026thinsp;Model 1\u0026thinsp;\u0026gt;\u0026thinsp;Model 5\u0026thinsp;\u0026gt;\u0026thinsp;Model 3; The average UTCI of each model between 20:00 and 23:00, in descending order, is Model 3\u0026thinsp;\u0026gt;\u0026thinsp;Model 2\u0026thinsp;\u0026gt;\u0026thinsp;Model 1\u0026thinsp;\u0026gt;\u0026thinsp;Model 5\u0026thinsp;\u0026gt;\u0026thinsp;Model 4\u0026thinsp;=\u0026thinsp;Model 6. This shows that although the model 3, which has tall street trees, large canopies and a large number of trees, has a good cooling effect from 12:00 to 19:00, the UTCI value of the whole model is the lowest and the comfort level is the best, but this model has the highest average UTCI value and the worst comfort level at 20:00 to 23:00 at night. Tree canopies have been demonstrated as being able to retain heat at night (de Quadros and Mizgier, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). According to Wang et al., (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) tree cover can reduce heat dissipation at night and aggravate the urban heat island in certain situations.Thus, planting more trees may not be reasonable measure to reduce urban heat island at night. Model 2 showed relatively poor thermal comfort in both periods, which further indicates that short trees with small crowns have poor effects on improving thermal comfort in street canyons during both day and night. Although the improvement effect Model 4 and 6 on street canyon thermal comfort is poor from 12:00 to 19:00. Model 6, which has sparse canopies, and Model 4, which has shorter crown diameter but a larger area of hedges, have the best improvement effect on street canyon thermal comfort from 20:00 to 23:00. One plausible explanation for this result is that, at model 6, tree leaves play a important role in preventing heat transfer and slowing down heat loss at night (Akbari, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). When the canopy is sparse, the effect become weak; At model 4, the hedges are 1-meter tall, the height which we analyze the UTCI vallue is 1.4 meter. The area we analyze is located above the hedges. Hedges may worse the thermal comfort of the area under the leaves of hedges because leaves can attenuate solar radiation and prevent the night\u0026rsquo;s heat flow from the surface to the sky at night (Wang et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The areas where shrubs and soil are located have better thermal comfort compared to impermeable underlying surfaces (Oke, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). Model 4 has a larger area of underlying soil and shrubs compared to Model 2. This provides an explanation for Model 4 having lower PET values than Model 2 during both day and night. In addition, at night, hedges may also be able to have weak transpiration effect (Dawson et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The weak transpiration effect of hedges also be able to improve thermal comfort of the area above or near the hedges weakly. This accords with Meili et al., (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) that tree coving is more efficient in decreasing UTCI during daytime and vegetated ground fraction provides more cooling during night. Model 1 (constructed based on the actual situation of the street canyon) has a median UTCI value in both periods, indicating that there are still many ways to further improve the thermal comfort of the street canyon based on the actual situation. The significant differences in the improvement of street canyon thermal comfort by different models during the two different time periods mentioned above also indicate the importance of studying the different effects of plants on improving street canyon thermal comfort during the day and at night. Although Model 5, which increases roof greening, has a weak effect on improving the thermal comfort of the street canyon, this method slightly reduces the mean UTCI of the street canyon in both periods mentioned above. Therefore, when considering both the daytime and nighttime thermal comfort of the street canyon, increasing roof greening can slightly improve both the daytime and nighttime thermal comfort of the street canyon. However, the effect of this method on improving the thermal comfort of the street canyon is relatively weak, with an average decrease of only around 0.04 ℃ in UTCI value in the street canyon UTCI values from 12:00 to 19:00, and only approximately 0.01 ℃ decrease in UTCI value in street canyon UTCI values from 20:00 to 23:00. However, we choose ivy as the roof vegetation, if we chose trees or hedges as building wall and roof vegetation, the improvement effect may be more obvious. We only consider the impact of street greening on the thermal comfort of the street canyon at 1.4 m height outdoor. Green walls and roofs can have more obvious influences on the indoor thermal comfort of roadside buildings (Hao et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and deserve to be considered as a measure to improve summer thermal comfort.\u003c/p\u003e \u003cp\u003eOverall, there is a relatively large difference in UTCI values among the models between 12:00 and 19:00, and a relatively small difference in UTCI values between 20:00 and 23:00. From 12:00 to 19:00, Model 2 with the highest UTCI mean was 0.48 ℃ higher than Model 3 with the lowest UTCI mean, while from 20:00 to 23:00, Model 3 with the highest UTCI mean was only 0.05 ℃ higher than Model 4 and Model 6 with the lowest UTCI mean. Therefore, optimizing the landscape pattern of the green space of the street canyon can have a noticeable effect on improving the daytime thermal comfort of the street canyon, but the effect is not obvious at night. Given this situation, we believe that considering both the daytime and nighttime thermal comfort of the street canyon. Street canyons with a large number of tall trees, large crown width, high leaf area index, wide shrub coverage area, and vertical greening, may bring greater benefits overall after weighing the pros and cons of their influence on the thermal comfort of the street canyon during a hot summer day and night. In addition, the planting of street trees needs to comply with the minimum distance between street trees, meet the convenience of daily traffic and pedestrian walking, and maintain the overall aesthetics of the street canyon. Therefore, when optimizing the landscape pattern of the green space of a street canyon, it is not feasible to blindly add too much greening to have a significant negative impact on the street canyon from many other aspects.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe UTCI values of different models during day and night.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTime\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eModel 1 (℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eModel 2\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eModel 3\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eModel 4\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eModel 5\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eModel 6\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e39.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e40.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e39.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e40.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e39.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e39.86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e41.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e41.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e41.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e41.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e41.59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e43.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e42.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e43.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e42.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e43.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e43.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e43.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e43.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e43.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e43.61\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e42.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e43.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e42.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e42.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e42.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e42.82\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e17:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e40.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e40.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e39.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e40.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e40.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e40.53\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e18:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e36.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e36.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e36.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e36.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e36.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e36.58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e19:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e32.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e32.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e32.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e32.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e32.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e32.41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e20:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e30.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e30.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e30.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e30.52\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e21:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e29.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e29.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e29.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e29.85\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e22:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e29.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e29.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e29.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e29.22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e23:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e28.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e28.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e28.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e28.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e28.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e28.78\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe average UTCI values of the six models.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eModel 1\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eModel 2\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eModel 3\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eModel 4\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eModel 5\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eModel 6\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage UTCI value from 12:00 to 23:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e36.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e36.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e36.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e36.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e36.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e36.57\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage UTCI value between 12:00 and 19:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e39.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e40.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e39.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e40.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e39.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e40.06\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAverage UTCI value between 20:00 and 23:00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e29.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e29.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e29.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e29.59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e3.3 A comparison of the thermal comfort of the six models based on the UTCI values at 13:00 and 20:00.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e compares the UTCI values of six models at 13:00. From the comparison between Model 1 and Model 2, it can be seen that during the daytime, the UTCI value of the area where the street trees are located in Model 1 is relatively low, indicating that tall trees with larger crown width form a larger shaded area that blocks sunlight. In theory, roadside trees with different heights and crown widths have varying degrees of impact on the wind environment, which in turn affects the thermal comfort of local spaces (Hsieh et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). However, due to the low wind speed during this period and the dense construction in the area, the difference in UTCI values measured by Model 1 and Model 2 in this study is relatively small. From Model 1 and Model 3, it can be seen that under the same conditions, the increase of the median divider with trees in the middle of the road will reduce the UTCI value through the influence of sunlight obstruction and transpiration. Trees can reduce wind speed and this can have negative impact on thermal comfort (Hsieh et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). By comparing the UTCI values around the central reservation of the Model 3 and the corresponding part in Model 1, it can be seen that the trees in the central reservation of the road has very limited impact on the thermal comfort of the surrounding area through wind blockage and transpiration. Except for the significant difference in UTCI values between the shaded area of trees in the central reservation of the road in Model 3 and the corresponding part in Model 1, there is no significant difference in UTCI values between the other areas where the vehicle lane is located in the two models. Although the underlying surface absorb and re-emit the sun\u0026rsquo;s heat more than natural landscape (United States Environmental Protection Agency, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), Model 4 has a larger soil coverage area and a smaller area of impermeable underlying surfaces such as asphalt and concrete compared to Model 2. This is beneficial for reducing the air temperature rise caused by absorbing and emitting sun\u0026rsquo;s heat from the ground (United States Environmental Protection Agency, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Compared Model 2 with Model 4, the difference in the effect of adding soil covered area and hedges on the illustrated results is relatively small, and the difference in UTCI values between the two models in the same spatial area is not obvious. Increasing roadside trees can produce a more significant cooling effect than hedges during daytime. In the street canyon area, after meeting the needs of both traffic and pedestrian flow, the remaining road greening area is very limited and needs to be fully utilized. Improving the coverage of trees is more beneficial for improving thermal comfort at 1.4 meters than increasing the coverage of hedges during the daytime. From the simulation results of Model 1 and Model 5, it can be seen that increasing roof greening has very limited effect on the UTCI value of local space. Greenery on the roof can help reduce the mean radiation temperature and improve the thermal comfort of the surrounding area due to it emit less short-wave radiance than hard surface (D'SOUZA, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The analysis area is located 1.4 meters above the ground in the street canyon. It is far from the roof of buildings. The changing the underlying surface did not cause noticeable differences in thermal comfort in different areas of the street canyon. Comparing Model 1 and Model 6, it can be found that Model 1 with higher leaf area density has a relatively lower UTCI value at the tree shadow area, which is mainly due to more leaves blocking sunlight and transpiration. Even if the layout of street trees is thought as having significant impact on the thermal comfort of the surrounding environment (Zhao et al., 2018), it is hard to change the spatial layout of street trees in street canyon because the area designated for road green space is very limited, and plants such as roadside trees need to meet the requirements of the minimum distance between roadside trees in the city, maintain good permeability, and improve the aesthetic level of the street (Hunan municipal government, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Under the premise of difficulty in improving the layout of roadside trees, selecting appropriate tree species and providing favorable conditions for the growth of roadside tree branches and leaves to increase the leaf area density and leaf area index of roadside trees will be a good method to improve the daytime thermal comfort during summer in the street canyons.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the UTCI values of six models at 20:00. Figures\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e can be used to compare the impacts of plants on thermal comfort during both daytime and nighttime, respectively. It can be seen that compared to the impacts of plants on thermal comfort during daytime, the impacts of plants on the nighttime thermal comfort of the respective areas are very small. At night, urban temperature can often be much higher than those in rural areas (United States Environmental Protection Agency, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The variance of air temperature between urban and rural area can be higher during nighttime than daytime in some cases (Peng et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Xu et al., 2022). Thus, it is also important to reduce nighttime heat island effect for the street canyon area. It can be observed from Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e that the six models exhibit minimal differences in street canyon thermal comfort due to varying characteristics of roadside trees. The corresponding UTCI values for the same area in all six models show no significant variation. Optimizing the road greening characteristics such as street tree height, crown width, road green divider, roof greening, and leaf area density have very limited impact on nighttime thermal comfort. The areas with better thermal comfort during the day and night are also different. During the day, they are more influenced by green space and distributed in areas with highly concentrated plantations. At night, areas with better thermal comfort are mainly concentrated in well-ventilated areas or areas far away from buildings. Thus, improving the ventilation condition is a good way to improve thermal comfort of the street canyon. Road pavement has the capacity to absorb a large amount of heat during the day. They release heat slowly in to the atmosphere at night (Katzschner, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Ibrahim et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Good ventilation environment plays a quite active role in reducing the heat release by the road pavement. During the daytime, shaded areas created by buildings typically offer good thermal comfort by blocking sunlight, thereby creating a cooler environment. However, at night, due to buildings slowly release heat absorbed during the day (Ahmed et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) and the building's ability to provide wind protection, areas with poor thermal comfort are formed around the building. Although the simulation results of the six models at 20:00 are not significantly different, road greening and soil underlying surfaces undoubtedly do not absorb large amounts of heat during the day and gradually release it at night, like impervious underlying surfaces such as asphalt and cement. From this perspective, this can still have a positive impact on nighttime thermal comfort. Meili et al., (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) found that ground vegetation plays an active role in decreasing UTCI at night. This shows that soil and low-growing plants can be more beneficial to street canyon nighttime thermal comfort than impervious underlying surfaces during hot summer days.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eAlthough many studies have focused on the impact of green spaces on the thermal comfort of street canyons, most have not simultaneously considered the different effects of road greening on the thermal comfort of street canyons during the day and at night. This study attempts to explore how optimizing road green spaces can maximize the improvement of street canyon thermal comfort, taking into account both the impact of green spaces during the day and night. This study takes a road section in the central urban area of Changsha, a city in central south part of China, as an example. This study comprehensively considers the relevant road green space regulations, the need for road green space to meet various needs, and the actual situation of the street canyon, such as the minimum spacing between roadside trees, maintaining the beauty and permeability of the street canyon, and avoiding excessive increase in road green space areas that may cause traffic congestion in the street canyon. One model based on the real situation of the street canyon and five models based on commonly used road greening opimization strategies were created such as the central green space divider, roof greening, and different tree height and crown characteristics. Research has found that during the day, the more vegetations especially the trees, the larger the crown width, and the higher the leaf area density, the better the cooling effect of vegetations. In addition, roof greening can also slightly improve the thermal comfort of street canyons. This is mainly due to the shading area formed by plants blocking sunlight, the transpiration effect of plants, and the weaker heating effect of soils and vegetated areas than impervious underlying surfaces such as concrete and asphalt on street canyons through reflected shortwave radiation. The impact of different road green space landscape patterns on the thermal comfort of street canyons during the day varies significantly. In this study, six models were simulated during the daytime period, and the maximum PET value difference between the models in the street canyon area occurred between Model 2 and Model 3 at 17:00, with a difference of 0.76 ℃ in UTCI values between the two models. However, in nighttime periods, the maximum PET value difference between the models in the street canyon area occurred between Model 3 and Model 6 at 23:00, with a difference of only 0.06 ℃ in UTCI values between the two models. Therefore, we believe that in this situation, even if street trees may have negative impacts on the nighttime thermal comfort of the street canyon, we can still plant more street trees because the negative impact is very small. On the contrary, this can have a significant positive impact during the day. In addition, we can compensate for the slight negative impact of street trees on the thermal comfort of the street canyon at night by increasing roof greening, low shrubs in road greening areas, and improving the ventilation environment of the street canyon.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJunyou Liu: Investigation, Methodology, Software, Data Analysis, Visualization, writing\u0026ndash; original draft, review and editing.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBohong Zheng: Supervision, writing\u0026ndash; review and editing.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHaifang Tang: Data Analysis.\u003c/p\u003e\n\u003cp\u003eJia Fan: writing\u0026ndash; original draft. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll authors have read and agreed to the published version of the article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u0026nbsp; \u0026nbsp;No funding was received for this work\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e The authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAhmed, AS.F., Khan, KM.M.K., Maung Than Oo, AA. et al. Selection of suitable passive cooling strategy for a subtropical climate. Int J Mech Mater Eng 9, 14 (2014). https://doi.org/10.1186/s40712-014-0014-7 \u003c/li\u003e\n\u003cli\u003eAkbari, H. 2002. Shade trees reduce building energy use and CO2 emissions from power plants. Advances in Terrestrial Ecosystem: Carbon Inventory, Measurements, and Monitoring Conference, 116, S119-S126.\u003c/li\u003e\n\u003cli\u003eAnand, J.; Sailor, D.J. Role of pavement radiative and thermal properties in reducing excess heat in cities. \u003cem\u003eSol. Energy\u003c/em\u003e \u003cstrong\u003e2022\u003c/strong\u003e, \u003cem\u003e242\u003c/em\u003e, 413\u0026ndash;423. \u003c/li\u003e\n\u003cli\u003eBeck, H.E.; Zimmermann, N.E.; McVicar, T.R.; Vergopolan, N.; Berg, A.; Wood, E.F. Present and future K\u0026ouml;ppen-Geiger climate classification maps at 1-km resolution. Sci. Data 5, 180214 (2018）. \u003c/li\u003e\n\u003cli\u003eBlazejczyk K (1994) New climatological- and -physiological model of the human heat balance outdoor (MENEX) and its applications in bioclimatological studies in different scales. Zeszyty IgiPZ PAN 28: 27\u0026ndash;58. \u003c/li\u003e\n\u003cli\u003eCaird MA, Richards JH. Donovan LA. Nighttime stomatal conductance and transpiration in C3 and C4 plants. Plant Physiol. 2007;143:4\u0026ndash;10.\u003c/li\u003e\n\u003cli\u003eChangsha Bureau of Commerce. （2022）. Changsha, a mega city http://swt.changsha.gov.cn/zfxxgk/zxzx_35631/WXZX/202210/t20221020_10848406.html. (accessed on 30 December 2023)\u003c/li\u003e\n\u003cli\u003eChangsha Municipal Government. Overview of Changsha CityAvailable online: http://www.changsha.gov.cn/xfzs/zjmlzs/zsgl/200907/t20090727_5686409.html?ivk_sa=1024320u (accessed on 20 July 2022).\u003c/li\u003e\n\u003cli\u003eDawson, T. E., Burgess, S. S. O., Tu, K. P., Oliveira, R. S., Santiago, L. S., Fisher, J. B., et al. (2007). Night-time transpiration in woody plants from contrasting ecosystems. Tree Physiol. 27, 561\u0026ndash;575. doi: 10.1093/treephys/27.4.56\u003c/li\u003e\n\u003cli\u003eDe Quadros, B.M.; Mizgier, M.G.O. Urban Green Infrastructures to Improve Pedestrian Thermal Comfort: A Systematic Review. Urban For. Urban Green. 2023, 88, 128091.\u003c/li\u003e\n\u003cli\u003eDiana E. Bowler, Lisette Buyung-Ali, Teri M. Knight, Andrew S. Pullin.Urban greening to cool towns and cities: A systematic review of the empirical evidence.Landscape and Urban Planning,2010,Vol.97(3): 147-155\u003c/li\u003e\n\u003cli\u003eD\u0026apos;SOUZA, U. 2013. The thermal performance of green roofs in a hot, humid microclimate. SUSTAINABLE DEVELOPMENT AND PLANNING. volume 173\u003c/li\u003e\n\u003cli\u003eENVI-met. (2024). UTCI. https://envi-met.info/doku.php?id=apps:biomet_utci. Accessed 28th January 2024. \u003c/li\u003e\n\u003cli\u003eG\u0026ouml;rgen, F., and M. Rossi-Schwarzenbeck. 2021. \u0026ldquo;Evaporative cooling strategies in urban areas: The potential of vertical greening systems to reduce nocturnal heat stress.\u0026rdquo; J. Phys. Conf. Ser. 2042 (1): 012056. https://doi.org/10.1088/1742-6596/2042/1/012056.\u003c/li\u003e\n\u003cli\u003eGlobal Monitoring Laboratory. 2024. NOAA Solar Calculator. Available at: https://gml.noaa.gov/grad/solcalc/. Accessed 29th Feburary 2024.\u003c/li\u003e\n\u003cli\u003eHao, X.; Xing, Q.; Long, P.; Lin, Y.; Hu, J.; Tan, H. Influence of vertical greenery systems and green roofs on the indoor operative temperature of air-conditioned rooms. J. Build. Eng. 2020, 31, 101373.\u003c/li\u003e\n\u003cli\u003eHsieh, CM;Jan, FC;Zhang, L.A simplified assessment of how tree allocation, wind environment, and shading affect human comfort. URBAN FORESTRY AND URBAN GREENING,2016,Vol.18(1): 126-137\u003c/li\u003e\n\u003cli\u003eHunan municipal government. 2020. Regulations on Urban Greening Management in Changsha City (Revised). https://www.hunan.gov.cn/hnszf/xxgk/wjk/zcfgk/202007/t20200730_729e1610-3249-4e8d-ab9a-0d374857bdb6.html. Accessed 13 March 2024.\u003c/li\u003e\n\u003cli\u003eIbrahim, S.H., Ibrahim, N.I.A., Wahid, J., Goh, N.A., Koesmeri, D.R.A., Nawi, M.N.M., 2018. The Impact of Road Pavement on Urban Heat Island (UHI) Phenomenon. International Journal of Technology. Volume 9(8), pp. 1597-1608\u003c/li\u003e\n\u003cli\u003eKatzschner, L., 2009. Urban Climate in Dense Cities. In: Designing High-density Cities for Social and Environmental Sustainability, Ng, E., (ed.), Earthscan, London, UK, pp. 71\u0026ndash;78\u003c/li\u003e\n\u003cli\u003eLiu, J.; Zheng, B.; Yang, F. A Simulation Study of the Impact of Urban Street Greening on the Thermal Comfort in Street Canyons on Hot and Cold Days. \u003cem\u003eForests\u003c/em\u003e 2023, \u003cem\u003e14\u003c/em\u003e, 2256. https://doi.org/10.3390/f14112256\u003c/li\u003e\n\u003cli\u003eMalek, E. Night-time evapotranspiration vs. daytime and 24h evapotranspiration.Journal of Hydrology,1992,Vol.138(1): 119-129\u003c/li\u003e\n\u003cli\u003eMaqueda, A.I.;del-Blanco, C.R.;Jaureguizar, F.;Garcia, N..Comparing Universal Thermal Climate Index (UTCI) with selected thermal indices/environmental parameters during 12 months of the year.Weather and Climate Extremes,2018,Vol.19(8): 49-57\u003c/li\u003e\n\u003cli\u003eMinistry of Housing and Urban-Rural Development. (2012). Urban green space classification standards CJJ/T85-2017.\u003c/li\u003e\n\u003cli\u003eMeili, N.; Acero, J.A.; Peleg, N.; Manoli, G.; Burlando, P.; Fatichi, S. Vegetation cover and plant-trait effects on outdoor thermal comfort in a tropical city. Build. Environ. 2021, 195, 107733 \u003c/li\u003e\n\u003cli\u003eNarimani, N.; Karimi, A.; Brown, R.D. Effects of street orientation and tree species thermal comfort within urban canyons in a hot, dry climate. Ecol. Inform. 2022, 69, 101671. \u003c/li\u003e\n\u003cli\u003eOke, T.R., 1989. The micrometerology of the urban forest. Phil. Trans. R. Soc. Lond. B. 324, 335\u0026ndash;349.\u003c/li\u003e\n\u003cli\u003ePeng, S.; Piao, S.; Ciais, P.; Friedlingstein, P.; Ottle, C.; Br\u0026eacute;on, F.-M.; Nan, H.; Zhou, L.; Myneni, R.B. Response to Comment on \u0026ldquo;Surface Urban Heat Island Across 419 Global Big Cities\u0026rdquo;. Environ. Sci. Technol. 2012, 46, 6889\u0026ndash;6890.\u003c/li\u003e\n\u003cli\u003eRen, Z.; Zhao, H.; Fu, Y.; Xiao, L.; Dong, Y. Effects of urban street trees on human thermal comfort and physiological indices: A case study in Changchun city, China. J. For. Res. 2022, 33, 911\u0026ndash;922. \u003c/li\u003e\n\u003cli\u003eRuiz, M.A.; Sosa, M.B.; Correa, E.N.; Cant\u0026oacute;n, M.A. Design tool to improve daytime thermal comfort and nighttime cooling of urban canyons. Landsc. Urban Plan. 2017, 167, 249\u0026ndash;256.\u003c/li\u003e\n\u003cli\u003eUnited States Environmental Protection Agency. 2023. Learn About Heat Islands. Available at: https://www.epa.gov/heatislands/learn-about-heat-islands. Accessed 12th March 2024.\u003c/li\u003e\n\u003cli\u003eUnited States Environmental Protection Agency. 2023. Learn About Heat Islands. https://www.epa.gov/heatislands/learn-about-heat-islands. Accessed 14th March 2024.\u003c/li\u003e\n\u003cli\u003eWaite, M. 2007. Oxford Dictionary \u0026amp; Thesaurus. Oxford. Oxford University Press.\u003c/li\u003e\n\u003cli\u003eWang, Y，Pan, C，Huang, Z. Comparison of Applicability of PET and UTCI in Different Seasons in Shanghai . Building Science,2020, 36(10): 55-61\u003c/li\u003e\n\u003cli\u003eWang, Y., Bakker, F., de Groot, R. et al. Effects of urban trees on local outdoor microclimate: synthesizing field measurements by numerical modelling. Urban Ecosyst 18, 1305\u0026ndash;1331 (2015). https://doi.org/10.1007/s11252-015-0447-7\u003c/li\u003e\n\u003cli\u003eWang, Y., Ni, Z., Hu, M., Chen, S., Xia, B., 2021. A practical approach of urban green infrastructure planning to mitigate urban overheating: a case study of Guangzhou. J. Clean. Prod. 287 https://doi.org/10.1016/j.jclepro.2020.124995.\u003c/li\u003e\n\u003cli\u003eWorld Health Organization. (2023). Climate change. Available at: https://www.who.int/news-room/fact-sheets/detail/climate-change-and-health. Accessed January 22th 2024.\u003c/li\u003e\n\u003cli\u003eWorld Health Organization. (2024). Heatwaves. Available at: https://www.who.int/health-topics/heatwaves#tab=tab_1. Accessed January 22th 2024.\u003c/li\u003e\n\u003cli\u003eXiang, J.; Liu, H. Study on Optimal Design of Exterior Sunshade for Residential Buildings in Hot Summer and Cold Winter Zone. Build. Sci. 2016, 32, 80\u0026ndash;84+126. \u003c/li\u003e\n\u003cli\u003eXu, Y.; Zhang, C.; Hou, W. Modeling of Daytime and Nighttime Surface Urban Heat Island Distribution Combined with LCZ in Beijing, China. Land 2022, 11, 2050. https://doi.org/10.3390/land11112050\u003c/li\u003e\n\u003cli\u003eWang, Y.; Anderegg, W.R.L.; Venturas, M.D.; Trugman, A.T.; Yu, K.; Frankenberg, C. Optimization theory explains nighttime stomatal responses. New Phytol. 2021, 230, 1550\u0026ndash;1561.\u003c/li\u003e\n\u003cli\u003eZhang D, Xie X, Zhou C. 2023. Spatial influence of exposure to green spaces on the climate comfort of urban habitats in China. Urban Clim. 51:101657. doi: 10.1016/j.uclim.2023. 101657.\u003c/li\u003e\n\u003cli\u003eZhao, Qunshan;Sailor, David J.;Wentz, Elizabeth A..Impact of tree locations and arrangements on outdoor microclimates and human thermal comfort in an urban residential environment.URBAN FORESTRY AND URBAN GREENING,2018,Vol.32(1): 81-91\u003c/li\u003e\n\u003cli\u003eZ\u0026ouml;lch, T., Rahman, M, A. Pfleiderer, E., Wagner, G., Pauleit, S. Designing public squares with green infrastructure to optimize human thermal comfort.Building \u0026amp; Environment,2019,Vol.149(1): 640-654\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Building shadows, outdoor thermal environment, hot summer and cold winter areas, residential area planning","lastPublishedDoi":"10.21203/rs.3.rs-4113689/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4113689/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRoad greening plays an important role in improving the thermal comfort of street canyons. Optimizing the landscape pattern of road green spaces is undoubtedly beneficial for better utilizing the effect of green spaces in improving thermal comfort in limite street greening area. Given that road greening can have completely different impacts on the thermal comfort of street canyons during the day and at night, this study attempts to explore how to optimize the landscape pattern of road greening to maximize its overall improvement in thermal comfort throughout the summer. This study takes a section of Guihua Road in Changsha, a city in central and southern China as an example, built a model based on the actural situation of the road, and based on this, constructs five optimization models to explore the effectiveness on improving thermal comfort. Research has found that optimizing the landscape pattern of road green spaces has a more significant effect on the daytime thermal comfort of street canyons, with the maximum difference in UTCI between models being 0.76 ℃. However, the maximum difference in UTCI between nighttime models is only 0.06 ℃. Therefore, fully utilizing the effect of plants can be effective to improve daytime thermal comfort of the street canyon. However, for the improvement of the nighttime thermal comfort of the street canyon, peolple should focus more on other measures like improving the ventilation and change the underlying surface materials.\u003c/p\u003e","manuscriptTitle":"The Impact of Green Spaces on Thermal Comfort in Urban Street Canyons during Hot Summer Days and Nights","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-11 08:45:15","doi":"10.21203/rs.3.rs-4113689/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"be602786-ce77-42a8-bfb4-b4ad2b89cdee","owner":[],"postedDate":"April 11th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-04-11T08:45:17+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-11 08:45:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4113689","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4113689","identity":"rs-4113689","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}