Comparison of different methods of estimating the mean radiant temperature in outdoor thermal comfort studies

Correlations between outdoor thermal indices and the calculated or measured mean radiant temperature T_mrt are in general of high importance because of the combined effect on human energy balance in outdoor spaces. The most accurate way to determine T_mrt is by means of integral radiation measurements, i.e. measuring the short- and long-wave radiation from six directions using pyranometers and pyrgeometers, an expensive and not always an easily available procedure. Some studies use globe thermometers combined with air temperature and wind speed sensors. An alternative way to determine T_mrt is based on output from the RayMan model from measured data of incoming global radiation and morphological features of the monitoring site in particular sky view factor (SVF) data. The purpose of this paper is to compare different methods to assess the mean radiant temperature T_mrt in terms of differences to a reference condition (T_mrt calculated from field measurements) and to resulting outdoor comfort levels expressed as PET and UTCI values. The T_mrt obtained from field measurements is a combination of air temperature, wind speed and globe temperature data according to the forced ventilation formula of ISO 7726 for data collected in Glasgow, UK. Four different methods were used in the RayMan model for T_mrt calculations: input data consisting exclusively of data measured at urban sites; urban data excluding solar radiation, estimated SVF data and solar radiation data measured at a rural site; urban data excluding solar radiation with SVF data for each site; urban data excluding solar radiation and including solar radiation at the rural site taking no account of SVF information. Results show that all methods overestimate T_mrt when compared to ISO calculations. Correlations were found to be significant for the first method and lower for the other three. Results in terms of comfort (PET, UTCI) suggest that reasonable estimates could be made based on global radiation data measured at the urban site or as a surrogate of missing SR data or globe temperature data recorded at the urban area on global radiation data measured at a rural location.     

The Effects of Urban Warming on Herbivore Abundance and Street Tree Condition

Trees are essential to urban habitats because they provide services that benefit the environment and improve human health. Unfortunately, urban trees often have more herbivorous insect pests than rural trees but the mechanisms and consequences of these infestations are not well documented. Here, we examine how temperature affects the abundance of a scale insect, Melanaspis tenebricosa (Comstock) (Hemiptera: Diaspididae), on one of the most commonly planted street trees in the eastern U.S. Next, we examine how both pest abundance and temperature are associated with water stress, growth, and condition of 26 urban street trees. Although trees in the warmest urban sites grew the most, they were more water stressed and in worse condition than trees in cooler sites. Our analyses indicate that visible declines in tree condition were best explained by scale-insect infestation rather than temperature. To test the broader relevance of these results, we extend our analysis to a database of more than 2700 Raleigh, US street trees. Plotting these trees on a Landsat thermal image of Raleigh, we found that warmer sites had over 70% more trees in poor condition than those in cooler sites. Our results support previous studies linking warmer urban habitats to greater pest abundance and extend this association to show its effect on street tree condition. Our results suggest that street tree condition and ecosystem services may decline as urban expansion and global warming exacerbate the urban heat island effect. Although our non-probability sampling method limits our scope of inference, our results present a gloomy outlook for urban forests and emphasize the need for management tools. Existing urban tree inventories and thermal maps could be used to identify species that would be most suitable for urban conditions.     

城市街道空气污染物扩散模型综述

城市街道是城市居民的活动场所,其空气质量与居民健康密切相关.空气污染扩散模型是模拟和评估街道空气质量的重要方法,近年来广受关注,但模型应用存在问题,亟待解决.本文介绍了4种常用的空气污染物扩散模型:ENVI-met、FLUENT、MISKAM和OSPM.通过工作原理、运算流程、时空分辨率等的对比分析,明确了各模型的适用范围及其对街道峡谷内空气质量模拟能力的差异,阐述了各模型在时间尺度、物理建模、天气模拟、湍流模拟及光化学污染方面处理能力的局限性,提出了模型优化途径.通过综合分析4种模型的研究案例,总结了模型应用中存在的问题,提出未来研究可以通过激光雷达等新技术提高模型参数的获得精度,并强调综合模拟污染效应与热效应等对评估城市街道空气质量的重要性.     

Quantifying street tree regulating ecosystem services using Google Street View

The urban heat island is a particular challenge for tropical cities, which receive year-round high inputs of solar radiation. Plants can help mitigate elevated urban temperatures by providing shade and increasing evaporative cooling, although the resulting increase in humidity may negatively affect thermal comfort. Street trees offer particular potential for cooling urban microclimates, as well as providing other ecosystem services, because they can be integrated within dense urban street networks. However, we have little quantitative information about the role of street trees in providing regulating ecosystem services in tropical cities. In this study, we analysed hemispherical photographs extracted from Google Street View to quantify the proportion of green canopy coverage at 50 m intervals across more than 80% of Singapore’s road network. Canopy coverage data were then used to estimate the proportion of annual radiation that would be blocked from reaching ground level by the canopy. Across all locations, a median of 13% of the annual diffuse and direct solar radiation was shaded, and over 70% of this shading effect was due to the tree canopy. There was significant variation between different urban landuse types, with trees providing more shade in parks and low-density low-rise areas than in industrial and higher-density residential areas. Mapping the provision of street tree ecosystem services could help to prioritise areas for new planting by identifying streets or street sections with low shading. The approach developed in this article could be readily applied to quantify the proportion of canopy coverage and proportion of solar radiation shaded across other tropical cities. The method may also be applicable in temperate cities if Google Street View photographs were collected during the growing season.     

南京城市街区湿球温度时空变化特征及其影响因子

全球气候变化和局地城市热岛加剧了城市热胁迫问题,但针对城市街区的研究仍不多见。湿球温度指示气温和湿度的综合效应,能更准确地反映人体热舒适度。本研究以南京市江北新区为对象,在不同时段、季节和天空状况下,基于移动观测方法获取气温、相对湿度和地理信息等数据,分析了街区尺度湿球温度的时空分布特征;结合天空状况、地表覆盖和城市形态指标(天穹可见度),探究了城市街区湿球温度的影响机制。结果表明: 1)南京城市街区湿球温度的时空特征与气温较为一致;与水汽压相比,气温对湿球温度的变化起主导作用;该地区湿球温度的极端高值主要是由于气温和水汽压协同增长所致。2)天穹可见度在白天与湿球温度呈显著正相关,夜间为负相关关系。植被覆盖比率的增加能够降低湿球温度,不透水面则呈现相反的作用。阴天条件下,湿球温度明显降低并且空间分布更均匀。3)植被和不透水面对湿球温度的水平尺度效应存在昼夜和季节差异,并且在夜间这一效应对天空状况更敏感;与植被相比,冬季夜间不透水面的影响范围比夏、秋季更大;两者对湿球温度的水平尺度效应与气温一致。研究结果可为改善和优化城市街区热环境、缓解城市热胁迫提供有效的科学支持和理论依据。     

基于城市微气候模拟软件的城市道路绿化带对PM2.5消减作用的研究

随着经济的快速发展及机动车保有量的持续增长，车辆造成的道路污染问题日益严重。广州作为中国重要的经济发展城市，交通源排放问题高度集中，机动车排放是城市PM2.5的主要来源之一，开展减缓城市道路污染危害的研究具有重要意义。本研究为调查绿化带对广州城市道路PM2.5的影响，运用实测与城市微气候模拟软件（ENVI-met）模拟结合的研究方法，实测并分析城市道路空间PM2.5的浓度分布及其影响因素，使用实测数据对模拟软件进行验证分析，模拟研究理想道路模型下不同高宽比、风向等因素及绿化带植配类型对PM2.5的消减作用。研究表明：（1）城市道路空间PM2.5浓度分布受污染源、街道高宽比、风速风向、绿化带等综合影响，自然消减情况下，其主要受风速风向和高宽比双因素影响；（2）通常街道高宽比越大，越有利于道路空间PM2.5的扩散；（3）城市道路空间PM2.5自然沉降最小距离为12 m，0-12 m范围内应保持无障碍物的开敞环境，PM2.5消减的关键范围是12-24 m，此范围内可以利用生态手段沉降颗粒物；（4） PM2.5消减率受绿化带和风向的双控制，应根据主导风向选择绿化带植配方式。在主导风平行面和垂直迎风面绿化带对PM2.5有正消减效应，建议植配类型为"乔-乔+灌+草"；在主导风垂直背风面绿化带对PM2.5呈负消减效应，植配类型为"乔-灌"绿化带消减率接近于自然消减率，而植配类型为"乔-灌+草"和"乔-乔+灌+草"的绿化带加重了颗粒物在该区域的积聚。     

The influence of urban design on outdoor thermal comfort in the hot, humid city of Colombo, Sri Lanka

The outdoor environment is deteriorating in many tropical cities due to rapid urbanization. This leads to a number of problems related to health and well-being of humans and also negatively affects social and commercial outdoor activities. The creation of thermally comfortable microclimates in urban environments is therefore very important. This paper discusses the influence of street-canyon geometry on outdoor thermal comfort in Colombo, Sri Lanka. Five sites with different urban geometry, ground cover, and distance from the sea were studied during the warmest season. The environmental parameters affecting thermal comfort, viz. air temperature, humidity, wind speed, and solar radiation, were measured, and the thermal comfort was estimated by calculating the physiologically equivalent temperature (PET). The thermal comfort is far above the assumed comfort zone due to the combination of intense solar radiation, high temperatures, and low wind speeds, especially on clear days. The worst conditions were found in wide streets with low-rise buildings and no shade trees. The most comfortable conditions were found in narrow streets with tall buildings, especially if shade trees were present, as well as in areas near the coast where the sea breeze had a positive effect. In order to improve the outdoor comfort in Colombo, it is suggested to allow a more compact urban form with deeper street canyons and to provide additional shade through the use of trees, covered walkways, pedestrian arcades, etc. The opening up of the city's coastal strip would allow the sea breeze to penetrate further into the city.     

Thermal bioclimatic conditions and patterns of behaviour in an urban park in Göteborg,Sweden

People in urban areas frequently use parks for recreation and outdoor activities. Owing to the complexity of the outdoor environment, there have only been a few attempts to understand the effect of the thermal environment on people's use of outdoor spaces. This paper therefore seeks to determine the relationship between the thermal environment, park use and behavioural patterns in an urban area of Sweden. The methods used include structured interviews, unobtrusive observations of the naturally occurring behaviour and simultaneous measurements of thermal comfort variables, i.e., air temperature, air humidity, wind speed and global radiation. The thermal environment is investigated through the mean radiant temperature (T_mrt) and the predicted mean vote (PMV) index. The outcome is compared to the subjective behaviour and thermal sensation of the interviewees. It is found that the thermal environment, access and design are important factors in the use of the park. In order to continue to use the park when the thermal conditions become too cold or too hot for comfort, people improve their comfort conditions by modifying their clothing and by choosing the most supportive thermal opportunities available within the place. The study also shows that psychological aspects such as time of exposure, expectations, experience and perceived control may influence the subjective assessment. Comparison between the thermal sensation of the interviewees and the thermal sensation assessed by the PMV index indicates that steady-state models such as the PMV index may not be appropriate for the assessment of short-term outdoor thermal comfort, mainly because they are unable to analyse transient exposure.     

基于CFD的城市绿地空间格局热环境效应分析

运用CFD数值模拟方法,结合RS技术,对城市中五类常见的绿地空间格局在垂直和水平方向上进行温度场和风速场数值模拟,以探讨绿地空间格局对城市热环境的影响程度及方式。在绿地的垂直结构上,灌木层对流场的影响要大于乔木层;而乔木层对绿地内部的降温作用更为明显。在绿地的水平布局形式中,在绿地率相当的情况下,楔状格局具有较好的热环境效应,即该格局在城市中的降温效果最为明显;放射状和条带状的次之,点状格局对周边环境的降温效果要弱些,但各"绿点"(即组成该格局的各块绿地)在小范围内降温效果比较明显,可以作为改善局部小气候的手段;环状格局热环境效应最弱。将CFD技术引入城市热环境研究,利用遥感技术对其进行参数修正,使热环境研究更加准确完整,具有经济高效方便等优点。     

基于夏季小气候效应的杭州街道适应性设计策略研究

随着城市热岛效应日趋严重,小尺度公共空间的气候研究已成为风景园林学科的研究热点之一。选取杭州市文一西路和古墩路作为实测对象,于2017年8月对各测点空间的空气温度、相对空气湿度、太阳辐射强度、风速风向进行测定,分析小气候因子日变化趋势,并运用Rayman 1.2模型评价人体舒适度,针对性提出街道空间小气候适应性设计策略。研究表明,尽可能设定与城市主导风平行或接近的街道朝向,通过人为增建遮阴空间、调控街道界面小气候一致、采用植物或绿色建筑材料、增设道路中央景观界面,且当人行道及机非分隔绿带分别种植落叶、常绿乔木,设五条绿带,选用乔—灌—草复层结构,同时增设垂直绿化时,能够有效缓解夏季极端热感受,从而营建舒适健康的城市街道空间。     

The effects of tree characteristics on rainfall interception in urban areas

Trees in urban areas have significant effects on the urban ecosystem. They can be used to improve the water cycle in urban areas by increasing evaporation and reducing runoff through rainfall interception. Street trees placed in planters on impervious areas reduce runoff by intercepting rainfall and by temporarily storing raindrops on leaves. Therefore, understanding tree canopy geometry and the effect of rainfall interception is important in urban hydrology. In this study, we assessed the effect of tree canopy morphology on rainfall interception using four major street tree species, Sophora japonica L., Ginkgo biloba L., Zelkova serrata (Thunb.) Makino, and Aesculus turbinata Blume, in Seoul, South Korea. We measured throughfall for each tree and also derived three-dimensional data of tree canopy morphology with a terrestrial laser scanner. Tree height, canopy crown width, leaf area index (LAI), leaf area density, mean leaf area, and mean leaf angle were used to determine canopy morphology. The interception rate was mostly affected by the LAI; a higher LAI tended to result in a higher interception rate. Leaf area affected the rainfall interception rate when trees had similar LAIs. These findings on individual tree canopy rainfall interception can help us to understand the importance of rainfall interception in hydrology and for ecological restoration when planning urban green spaces.

     

基于“风感”的紧凑型城市开放空间风环境实测和CFD模拟比对研究

城市开放空间的风场不仅影响微环境的"风感"舒适度还影响宏观尺度的城市气候。从景感生态学的角度出发,首先阐述"风感"的定义,总结了街道峡谷空间风场的基本规律和特点。运用Kestrel NK4500手持气象站对城市开放空间的风环境进行实测,采用CFD(Computational Fluid Dynamics)模拟软件Fluent 14.0对不含绿地的同一空间进行风环境模拟,通过两者的数据比对来研究紧凑型城市开放空间内绿地对行人高度风场的实际干扰程度。结果发现,紧凑型城市开放空间的"风感"受建筑和绿地空间布局的共同影响。当建筑高于绿地时,风场受建筑的控制;当林带高于建筑时,林带对风环境的影响程度受其疏密度影响。疏密度较高的常绿林带对风向和风速影响很大,而疏密度较低的林带会影响风速,对风向影响不大。影响风速的主要因素是空间围合所形成的空气域,相比实体、多孔介质,空气域对风的阻力要小的多。如铺装、草坪上方的通风廊道是影响行人高度层通风、导风的关键因素。紧凑型空间内的绿地在行人高度应保持通畅以保证通风,并通过建立平面和竖向上的通风、导风廊道体系,促进空气循环。     

Mean radiant temperature in idealised urban canyons—examples from Freiburg, Germany

Studies on the thermal comfort of humans in urban areas require meteorological data such as air temperature, air humidity, wind speed, and short- and long-wave fluxes. In such studies radiation fluxes can be expressed by the mean radiant temperature—a parameter with high variability in urban areas due to variability in global radiation. Wind speed in urban areas is influenced by urban obstacles and their orientation. Both mean radiant temperature and wind speed can be modified or changed by different height-to-width ratios or orientation of urban structures. Modifications to these parameters by typical urban structures (represented by the height-to-width ratio) can result in variation of mean radiant temperature over a range of more than 30°C, which can correspond to three levels of thermal stress. The results presented here provide a possible means of comparing different urban configurations in different climate regions.     

Thermal comfort of various building layouts with a proposed discomfort index range for tropical climate

Recent years have seen issues related to thermal comfort gaining more momentum in tropical countries. The thermal adaptation and thermal comfort index play a significant role in evaluating the outdoor thermal comfort. In this study, the aim is to capture the thermal sensation of respondents at outdoor environment through questionnaire survey and to determine the discomfort index (DI) to measure the thermal discomfort level. The results indicated that most respondents had thermally accepted the existing environment conditions although they felt slightly warm and hot. A strong correlation between thermal sensation and measured DI was also identified. As a result, a new discomfort index range had been proposed in association with local climate and thermal sensation of occupants to evaluate thermal comfort. The results had proved that the respondents can adapt to a wider range of thermal conditions.Validation of the questionnaire data at Putrajaya was done to prove that the thermal sensation in both Putrajaya and UTM was almost similar since they are located in the same tropical climate region. Hence, a quantitative field study on building layouts was done to facilitate the outdoor human discomfort level based on newly proposed discomfort index range. The results showed that slightly shaded building layouts of type- A and B exhibited higher temperature and discomfort index. The resultant adaptive thermal comfort theory was incorporated into the field studies as well. Finally, the study also showed that the DI values were highly dependent on ambient temperature and relative humidity but had fewer effects for solar radiation intensity.     

街道峡谷绿化带设置对空气流场及污染分布的影响模拟研究

合理设置道路绿化带能够改变街道空气流场进而改善空气质量。利用风洞试验结合数值模型的方法测试了树冠形状和绿化带位置对街道峡谷的风场影响。在数值模型中,采用针对植物模型不同高度赋予不同叶面积密度(leaf area density,LAD)值的新方法近似模拟不同树冠形状的植物,通过输入污染源数据,得到风场及污染物浓度数据结果;与风洞试验结果进行对比,验证了其有效性;进而,利用数值模型分析了不同绿化带设置下街道峡谷内行人的污染暴露特征,结果表明绿化带位置及树冠形状影响街道峡谷中的涡流结构,形成复杂的细小湍流,从而影响街道峡谷中的风环境和污染物分布。阔叶树冠和位于街道峡谷中央的绿化带位置有利于降低行人污染暴露风险。未来研究中,通过增加风洞试验布点、考虑热力作用及气象因子的影响,或许可以提供更加详细的改善街道峡谷微环境的绿化带布局,为城市大气环境管理和绿地系统建设提供科学依据。     

基于ENVI-met的城市道路绿地植物配置对PM2.5的影响研究

随着城市化的快速发展,大气污染尤其细颗粒物(PM_(2.5))已成为制约城市环境的重要因素,相关研究表明,在众多的PM_(2.5)来源中道路交通是在其中的重要来源之一,而道路绿地植物群落能够消减来自道路的PM_(2.5)。运用场地观测和ENVI-met模拟相结合的方法探讨城市道路绿地植物群落对PM_(2.5)的影响,分析仅有乔木(i)、乔木+树篱(ii)、乔木+树篱+灌木(iii)3种模式下的植物群落配置对PM_(2.5)的影响,揭示绿地植物群落的长度、宽度、高度和LAI对PM_(2.5)的影响。结果表明:(1)场地观测中的道路绿地植物群落的3种配置模式对PM_(2.5)的消减率分别是iii(14.2%)ii(12.9%)i(9.2%)。(2)绿地中植物的种类、绿地宽度、绿地植物的叶面指数等要素对消减作用起正面作用,高度和长度起负面作用。(3)绿地的长度的一定量的减少可以在绿地后方形成一个宽度约为绿地长度80%的、随着与绿地的距离的增加而宽度递减的较绿地长度更长环境PM_(2.5)浓度更低的低谷区,但其他没有绿地的空间的PM_(2.5)浓度会加重。(4)绿地高度的增加会迫使PM_(2.5)向更高的空间运动。     

城市三维空间形态的热环境效应研究进展

城市的三维空间形态,通过影响地表能量平衡过程和空气流动,改变城市内部热环境,并可能加剧城市热岛效应。在三维空间上定量解析格局-过程-效应关系对于城市生态安全和可持续发展具有重要意义,可为城市生态规划与景观设计提供重要科学依据。从城市三维形态的热环境效应研究角度,综述了城市三维形态的定量化研究进展;总结了城市三维形态对热环境以及空气流动、太阳辐射等过程的影响;分析了当前城市三维形态的热环境效应研究领域存在的不足。未来的研究应注重建筑与植被三维特征的综合表征,三维形态指标的选择应综合考虑其对设计规划的指导作用,并加强城市三维形态对热环境影响机理及其尺度效应的研究。     

Thermal sensation prediction by soft computing methodology

Thermal comfort in open urban areas is very factor based on environmental point of view. Therefore it is need to fulfill demands for suitable thermal comfort during urban planning and design. Thermal comfort can be modeled based on climatic parameters and other factors. The factors are variables and they are changed throughout the year and days. Therefore there is need to establish an algorithm for thermal comfort prediction according to the input variables. The prediction results could be used for planning of time of usage of urban areas. Since it is very nonlinear task, in this investigation was applied soft computing methodology in order to predict the thermal comfort. The main goal was to apply extreme leaning machine (ELM) for forecasting of physiological equivalent temperature (PET) values. Temperature, pressure, wind speed and irradiance were used as inputs. The prediction results are compared with some benchmark models. Based on the results ELM can be used effectively in forecasting of PET.     

Variation in ecosystem services of street tree assemblages can guide sustainable urban development

城市行道树集合生态服务功能变化研究及对城市可持续发展管理的启示     

Species of street tree is important for southern hemisphere bird trophic guilds

Abstract Urban environments are highly modified with unique assemblages of bird species. Much of the research on urban bird assemblages comes from the northern hemisphere. Southern hemisphere bird assemblages differ from northern hemisphere assemblages in that they contain a large proportion of nectarivores. In this study we focus on bird use of street trees in Australia. We investigate the relative influence of tree species (plane tree, Platanus x acerifolia; red gums, Eucalyptus camaldulensis; jacaranda, Jacaranda mimosifolia; bottlebrush, Callistemon citrinus), season and the environment surrounding street trees, on the abundance and species richness of birds in Adelaide, South Australia. Our study considers birds in terms of granivore, nectarivore and insectivore trophic guilds. Nectarivores accounted for the greatest proportion of observations, in terms of abundance, in each of the tree species investigated. Species of street tree was a significant influence on bird use of the trees for all birds and each dietary guild. Red gums were used more than the other tree species by nectarivores, while plane trees were used more than the other trees by insectivores. Use of the tree species by granivores varied with the season. The measures of the environment surrounding street trees were largely unimportant with the exception of traffic for nectarivores in some cases. Urban avifauna use street trees and the species of tree will strongly influence its use by birds. However, the pattern of use of street tree species varied at different times of year and differed between different trophic guilds of birds. The dominance of nectarivores in the southern avifauna will likely produce different patterns of urban environment use to northern hemisphere avifaunas.