A fieldwork study on the diurnal changes of urban microclimate in four types of ground cover and urban heat island of Nanjing,China

Records of the past years showed that the climate of built-up regions differs significantly from rural regions and one of the most obvious and important modifying effects of urbanization on local climate is the urban heat island (UHI). In this paper, four types of land cover, namely urban bare concrete cover, urban woods or the shade of trees, urban water areas and urban lawn, were selected to study their microclimate, and the UHI was also analyzed using air temperature data measured at four fixed observation spots in Nanjing, China, during hot weather from July to September, 2005. Dry and wet bulb temperature data were obtained by whirling psychrometers, and wind speed data by cup anemometers. Our observed data focused on the detailed statistical analysis of the microclimate variation in the four types of land cover during the whole day. The results showed that: (1) the microclimate of these four types of land cover had significant differences among different observation sites. In general, the air temperature of these four types of land cover complied with the order during daytime: bare concrete cover>lawn>water areas>woods or the shade of trees, with reversed order during nighttime when the air temperature of the lawn became the lowest. Compared with the bare concrete cover, the other three types of land cover showed the effect of dropping air temperature ranging between 0.2 and 2.9 °C. There were some instant dynamic characteristics in detailed temporal series among these four types of cover in the different observation sites. (2) The UHI effect could be detected obviously by the air temperature difference between the urban center area and the rural area. The average UHI intensity during the monitoring period was between 0.5 and 3.5 °C; however, there were also significant day-to-day variations. A strong UHI effect usually occurred around midnight; while about 2–3 h after sunrise the UHI began to decrease till midday time; and during 13:00–15:00, the UHI effect had a sudden increase and then decreased again; after sunset, a peak UHI effect was frequently observed during 18:00–21:00. (3) Finally, by means of the standard deviation (SD), this paper provides a concise and comprehensive understanding for the temporal and spatial microclimatic dynamics of these four kinds of urban cover in the four observation sites. Air temperature at the height of 1.5 m in Nanjing showed that the nocturnally horizontal temperature gradient was somewhat different from that reported in other large cities, and a marked heterogeneity in a smaller ground cover scale could be detected from the microclimatic spatial pattern. There is no doubt that the analysis of these four types of land cover presents the insight into possible countermeasures to decrease the high air temperature in hot summers, and is relevant to the urban planning redevelopment.     

Urban design to lower summertime outdoor temperatures: An empirical study on high-rise housing in Shanghai

This research investigates the effect of urban design factors on summertime urban heat island (UHI) intensity. Ten high-rise residential quarters in the inner city of Shanghai were empirically investigated during mid July to mid August in 2008. On-site design variables were developed to quantify the thermal impacts from density, building layout and greenery. The design variables that were measured on site were correlated with the variation in UHI intensity during the day and night. The results show that variations in UHI are in part due to site planning, building design, and greenery. The overall daytime and nighttime UHI models explain up to 77 and 90 percent of UHI variation, respectively. On-site shading from either buildings or vegetation canopy is the most important factor influencing daytime UHI. The shading factor can distort and dilute behavior of other variables, e.g., green ratio and surface albedo. Nighttime UHI is more complicated due to the influence from anthropogenic heat, and is significantly related to greenery density and coverage. Based on the findings, potential design strategies are proposed in an effort to mitigate UHI, including manipulating building layout and mass to improve shading during the day while facilitating site ventilation at night and increasing site vegetation cover through strategic tree planting. Further recommendations for urban planning approaches to mitigate UHI on the urban scale are proposed.     

Lowering the outdoor temperature in high-rise high-density residential developments of coastal Hong Kong: The vegetation influence

This paper investigates the impact of on-site variables on the influence of vegetation in lowering outdoor temperature. The study uses six critical on-site variables such as surface albedo, sky view factor, altitude, shrub cover, tree cover and average height to floor area ratio to carry out analysis in five data sets. The climatic parameters and physical characteristics were measured and surveyed, respectively in 216 stations in high-rise high-density residential developments of coastal Hong Kong. The data set is mainly categorised into peak summer clear sky days (PSCS-days), peak summer partially cloudy days (PSPC-days) and late summer days to address the issues related to cloudy sky conditions in Hong Kong. The trend analysis shows that at a lower sky view factor, ranging from 0.1 to 0.25, shrub cover as low as 10–15% in a 1000 m² open area is more effective in reducing outdoor temperature than the same level of tree cover in a location with a higher sky view factor (0.4 or above). The regression models used in this study were able to explain the influence of on-site variables on vegetation in lowering the outdoor temperature within the respective urban settings. In high-rise high-density environments, on-site variables such as sky view factor and altitude have a substantial impact on the influence of vegetation in lowering outdoor temperature. However, off-site variables such as high urban density and anthropogenic heat could negate the behaviour of sky view factor and altitude. The study suggests that increasing the tree cover from 25% to 40% in the pocket parks in coastal area residential developments of Hong Kong could reduce daytime urban heat island intensity (UHI) by further 0.5 °C.     

A master plan for low carbon and resilient housing: The 35 ha area in Hashtgerd New Town, Iran

With 60% of the population younger than 26 years, a need of about 1.5 million residential units per year for the next 5 years and the necessity of mitigating its rapidly growing GHG emissions together with adapting cities to the expected drastic effects of climate change, Iran’s urban agglomerations are facing tremendous challenges now and in the future. The paper presents interim findings of the German–Iranian research initiative “Young Cities” (2005–2013) that investigates approaches for these immense challenges. The project aims at developing energy-efficient and resilient housing in a real-life pilot project, the 35 ha area in Hashtgerd New Town in the Tehran province. The article explores the framing conditions and the master plan of this pilot and identifies four key planning strategies. Besides applying climate-sensitive urban form, the project stresses the need to develop culturally adapted building typologies for reduced heating and cooling, an efficient public transport in a mixed and dense urban structure and integrated water and energy systems on the neighborhood level. Simulations of these planning approaches have proven a significant reduction of energy- and resource consumption and the capacity of the design to adapt to (a potentially changing) environment. These promising strategies for energy-efficiency and resilience were transferred into a legally binding comprehensive plan commissioned in October 2010, though the major challenge in the second phase of the project (2011–2013) will be making these innovations a built reality.     

The cooling effect of green spaces as a contribution to the mitigation of urban heat: A case study in Lisbon

Green areas in the urban environment can contribute to the mitigation of the Urban Heat Island. In a context of climate change, with the expected increase in temperature, dryness and intensity of heat waves, green areas assume even higher importance as they can create a cooling effect that extends to the surrounding areas. This study analyses the thermal performance of a small green space (0.24 ha) and its influence in the surrounding atmospheric environment of a densely urbanised area in Lisbon. Measurements of weather parameters (temperature, relative humidity, wind speed, solar and infrared radiation) were carried out along a selected path, starting from inside the green area to surrounding streets with different orientations and solar exposure. It was found that the garden was cooler than the surrounding areas, either in the sun or in the shade. These differences were higher in hotter days and particularly related to the mean radiant temperature (Tmrt). The highest difference found was of 6.9 °C in relation to air temperature and 39.2 °C in relation to Tmrt; in both cases this difference occurred between the shaded site inside the garden and the sunny site in an E–W oriented street in the southern part of the studied area. Besides the local weather conditions, particularly the low wind speed, the sun exposure and the urban geometry are the potential factors that explain these differences. The cooling effect of green areas on the surrounding environment can be enhanced by additional measures related to the urban features of each city.     

The dimensions of global urban expansion: Estimates and projections for all countries, 2000–2050

Our study of the expansion of a representative sample of 30 cities showed that 28 of them expanded more than 16-fold during the twentieth century. More generally, cities are now expanding at twice their population growth rates, on average, and now cover almost 0.5% of the planet's land area. We created a new dataset comprising the universe of all 3646 named metropolitan agglomerations and cities that had populations in excess of 100,000 in the year 2000, their populations in that year, and their built-up area identified in the Mod500 map, currently the best of eight satellite-based global maps of urban land cover. Using this dataset, we estimated urban land cover in smaller cities and towns in all countries and calculated total urban land cover in every country in the year 2000. We then employed multiple regression models that could explain more than 90% of the variations in our urban land cover estimates amongst countries. Then, using U.N. urban population projections in combination with three realistic density change scenarios based on our previous global and historical study of densities, we projected urban land cover in every country and world region from 2000 to 2050. According to our medium projection, urban land cover in developing countries will increase from 300,000 km² in 2000 to 770,000 km² in 2030 and to 1,200,000 km² in 2050. Containing this expansion is likely to fail. Minimal preparations for accommodating it – realistic projection of urban land needs, the extension of metropolitan boundaries, acquiring the rights-of-way for an arterial road grid that can carry infrastructure and public transport, and the selective protection of open space from incursion by formal and informal land development – are now in order.     

Green plot ratio: an ecological measure for architecture and urban planning

Current research on sustainability of cities has favoured the implementation and conservation of greenery in the urban context. The benefits of plants are not just environmental but recreational, aesthetic and emotional. The full benefits of plants and the role they play in the ecology of cities remain to be mapped out but the general significance of plants appears to be uncontested. This paper proposes a new architectural and planning metric for greenery in cities and buildings. This new metric, the green plot ratio (GPR), is based on a common biological parameter called the leaf area index (LAI), which is defined as the single-side leaf area per unit ground area. The green plot ratio is simply the average LAI of the greenery on site and is presented as a ratio that is similar to the building plot ratio (BPR) currently in use in many cities to control maximum allowable built-up floor area in a building development. GPR allows more precise regulation of greenery on site without excluding a corresponding portion of the site from building development. It provides flexibility to the designer while simultaneously protecting the green quota in the design. This concept has been applied in a number of design competitions in which the author has collaborated with colleagues and various architectural practices. It has also been adopted as a planning requirement by the client authority for one of the competitions for which the author has entered. While seen as a fundamental and important metric, GPR is not in itself an indicator for all the ecological relationships between plants and cities. A larger set of related metrics need to be developed.     

Birds are also sensitive to landscape composition and configuration within the city centre

Maintaining biodiversity in urbanised landscapes has become a conservation issue. Although numerous studies have shown that avifauna decreases according to urbanisation level, little is known about the influence of urban characteristics on avifauna in densely urbanised areas. This study took place in the centre of a highly urbanised area, Paris, France, where we defined a grid of 94 cells of 1 km² each. Using Bayesian model averaging, we examined the variation of diversity and abundance of breeding birds (41 species) through their feeding and nesting behaviours. We then analysed the responses of these guilds to composition (proportion of different types of buildings and green spaces) and configuration (heterogeneity, spatial arrangement of green spaces). The abundance of omnivorous and tree nester species was influenced by urban characteristics such as building heterogeneity. The positive influence of shrub cover on insectivorous species abundance was greater in areas with a high density of medium-height buildings. Omnivorous species abundance increased with the juxtaposition of vegetation when the bare soil cover was low, and decreased otherwise. Globally, the abundance of omnivorous, ground and tree nester species was sensitive to building characteristics, whereas insectivorous and granivorous species as well as roof nesters may benefit from green space management. We concluded that urban planning can also promote avifauna abundance in the city centre by varying the heights of buildings in urban renewal projects rather than clustering buildings of similar height, or by focusing on the spatial configuration of green spaces (especially their proximity) rather than their area.     

Seasonal heat flux properties of an extensive green roof in a Midwestern U.S. climate

Green roofs, or vegetated roofs, can reduce heat flux magnitude through a building envelope as a result of insulation provided by the growing medium, shading from the plant canopy, and transpirational cooling provided by the plants. This study quantifies the thermal properties of an inverted 325 m² retro-fitted extensive green roof versus a traditional gravel ballasted inverted roof in a Midwestern U.S. climate characterized by hot, humid summers and cold, snowy winters. In autumn, green roof temperatures were consistently 5 °C lower than corresponding gravel roof temperatures. Even during chilly and moist conditions, the heat flux leaving the building was lower for the green roof than the gravel roof. Temperatures at the top of the insulation layer were more variable for both green roof and gravel roof on winter days with no snow cover than on days with snow cover. Variation in temperatures between roof types in spring was similar to those in autumn. Peak temperature differences between gravel and green roof were larger in summer than other seasons (sometimes by as much as 20 °C). Over the course of a year (September 2005-August 2006), maximum and minimum average monthly temperatures and heat fluxes were consistently more extreme for the gravel roof than the green roof.     

地表温度与城市空间分布结构的关系及其 预测模型

就城市尺度级别下的热环境进行评价,为了能够落 实影响绿地规划的具体空间区域,并提供可以指导绿地布局的 方法,以西安为例,量化植被、建设用地空间分布与地表温度 的关系,确定绿地降温的具体区域;通过卷积计算,以温度变 化为0作为界限,细化冷区和热区,提取城市微更新下绿地布 局待调整的位置;基于机器学习的回归算法,由绿地、建设用 地和水体分布预测作为热环境指示因子的地表温度,从而为规 划的合理性提供参考。通过对研究结果的评价,以及与已有方 法的比较,利用地表温度和地表覆盖变化,量化城市空间分布 结构,为绿地规划提供可以落实的具体空间区域。     

小尺度公园对于城市热岛效应的缓解作用——基于南京市中心城区社区公园的实证研究

Cities have suffered from urban heat island (UHI) effect due to rapid urbanization, which can be effectively adjusted by urban green space. Taking the community parks in central area of Nanjing, Jiangsu Province as an example, this paper explored the size and shape of smallscale parks to mitigate the UHI effect. Land surface temperature was retrieved from Landsat 8-OLI remote-sensing image of 2019. The 52 studied community parks were identified with ArcGIS 10.4, and classified by kernel building density. The threshold-size and optimal shape of community parks to mitigate UHI effect were then discussed. The results showed that 1) with the increase of buffer ring distance around the community parks, the cooling intensity decreased and the cooling extent were mostly less than 180 m; 2) the area, shape, and the NDVI of the parks were important factors affecting the cooling intensity; 3) the cooling intensity of community parks under a high kernel building density was better, with a higher threshold-size (0.848 hm2) than that of the low ones (0.384 hm2); and 4) the optimal cooling intensity would occur when the park in a shape of circle or square. In conclusion, it is suggested that small green space should be planned in the areas under a high building density. Through renewal design and refined management measures in the urban green space system planning, giving full play to the ecological benefits of urban green spaces in mitigating the local UHI effect can also be expected.     

城市高温灾害的规划应对研究进展

随着全球气候不断升温,城市高温 灾害越来越严重,严重影响城市人居环境。 通过CNKI和Web of Science检索城市高温 灾害相关文献,采用Met a-a na lysis方法和 CiteSpace工具,分析近年来城市规划应对高 温灾害的研究进展。结果发现,城市高温灾 害的规划应对研究起源于城市热岛方面,在 气候变化方面得到发展,最后形成城市高温 灾害的研究。在减缓性策略与适应性策略两 大主题下,主要应对途径是土地利用、空间 结构、道路交通、绿化景观以及建筑等,每种 途径又分为多种具体策略。目前在规划体系、 针对性规划以及效益评估等方面存在明显不 足。在理论上应加强构建规划体系,以及效 益评估系统的研究;在实践中制定应对高温 灾害的规划编制标准,探索气候友好型城市 规划设计方法,为韧性城市建设提供参考。     

Blue-green architecture: A case study analysis considering the synergetic effects of water and vegetation

Blue–green infrastructure is a network of natural and near-natural areas that has a positive effect on the quality of urban environment. This multifunctional planning approach addresses different issues and objectives depending on whether the focus is on the blue (water) or the green (vegetation) elements. Green-motivated projects aim to densify urban vegetation and include the growing sector of building greening. A good climatic effect of vegetation can be achieved by sufficient irrigation. In many cases, this approach results in additional water requirements. Blue-motivated projects consider water accumulation in cities (e.g., by heavy rainfall) as a waste product and look for solutions for local drainage and evaporation. These planning approaches offer only one-sided solutions and create no sufficient interfaces between water availability and water demand. Based on four case studies, this work examines the extent to which blue–green projects take advantage of the possibilities for the synergetic use of resources. The projects are analyzed graphically by applying the daily tools of architects as a scientific method. A graphic presentation of the blue and green components makes existing solutions and missing links visible. Analytical results show that buildings can be considered to be an interface for blue–green systems. Moreover, the possible synergies are often overlooked during the planning process. This fact highlights the need for a new planning approach that interlinks blue and green aspects that are already in the early planning stages.     

Decision making, planning and design for the conservation of indigenous vegetation within urban development

Utilization of indigenous vegetation as parts of the urban landscape is still a problematic matter in decision making and planning. On one hand, there are many activities in cities and towns aimed at providing more green areas. On the other hand, there is an increasing destruction of indigenous vegetation, not only for building purposes, but also partly by extreme maintenance of urban open spaces and an increasing number of recreation activities. Despite there is a considerable amount of scientific knowledge on indigenous plants in urban and sub-urban areas, the use of this knowledge is still low. The socio-economic knowledge about such vegetation (acceptance, utilization, economic value, etc.) is mostly non-existent in many regions.The indigenous vegetation has to become an important aspect of urban biodiversity as well as part of the living space of the urban dwellers. This links two important subjects: the specific nature of the original biomes in which the urban region is situated, and the cultural aspect of acceptance of various kinds of nature. The nature preservation strategies, especially of Central European cities, show a lack of willingness to preserve indigenous vegetation sites. But there are instruments of planning and methods which allow better preservation of these areas.Furthermore, it must be determined whether it is possible to reduce the human impact on open spaces by reintroducing indigenous vegetation, and under what circumstances this works. The cost reduction of maintenance of urban green areas is seen as one major factor linking to this target. Human acceptance is still an uncertam factor which has to be investigated and will, in the long term, be improved by education and evaluated under different cultural and social aspects.The management of the classical conflict between pure species or habitat preservation in open urban spaces of untouched nature and the high pressure of recreation on the same sites, is explained by example. An important question follows: will it be possible to establish “new” indigenous nature in the urban and sub-urban spaces?     

Measurement indicators and an evaluation approach for assessing urban sustainable development: A case study for China's Jining City

Cities are complex ecosystems affected by social, economic, environmental, and cultural factors. The problem of attaining urban sustainable development is thus an important challenge. The development of evaluation indicators and a method for assessing the status of urban sustainable development will be required to support urban ecological planning, construction, and management. By using Jining City in China's Shandong Province as a case study, the authors developed a system of 52 indicators of urban sustainable development that address economic growth and efficiency, ecological and infrastructural construction, environmental protection, social and welfare progress. The authors developed a Full Permutation Polygon Synthetic Indicator method to evaluate the capacity for urban sustainable development at different times during the next two decades. The results of our research indicate that the value of a synthetic indicator for sustainable development of Jining City was 0.24 in 2004, which indicates a low level of sustainable development. According to the ecological planning of Jining City (2004–2020), the indicator will improve to 0.45 in 2007 and 0.62 in 2010, indicating significant improvements in sustainable development, and will reach 0.90 in 2020, indicating excellent potential for sustainable development. The Full Permutation Polygon Synthetic Indicator method provides a comprehensive, intuitive approach that reflects the system integration principle that the whole can be more than the sum of its parts. The approach thus provides a promising basis for decision-making to support urban sustainable development and monitoring of the effectiveness of these decisions.     

基于气候适应性的城市屋顶绿化系统规划研究以成都为例

城市屋顶绿地应是以本地地域气候特征为基本出发点和落脚点。以适应气候为评价标准的屋顶绿地系统规划则应在规划布局上疏导城市通风;并利用热岛环流造风;利用屋顶绿化分散污染高浓度区域。以成都为例,从改善城市风环境的角度,探讨城市尺度的屋顶绿化系统的气候适应性规划问题。     

Urban microclimate and energy consumption: A multi-objective parametric urban design approach for dense subtropical cities

Climate change within the urban contexts is a crisis that cities are confronting globally. This issue poses numerous negative consequences such as thermal discomfort and increased energy usage within the building sector. This is especially the case in Western Sydney, Australia, where the average maximum temperature has risen by 7–8 °C within the past 30 years. This increase in temperature is highly concerning, since this region is witnessing rapid urban and infrastructural development and is proposed as the third-largest economy of Australia. Temperature changes in this region will also result in considerably increasing the electricity used for cooling purposes. This paper presents a parametric approach driven multi-objective optimization methodology to discover optimum design solution based on the urban microclimate and cooling energy demand of multi-functional buildings within this urban context. Mitigation measures including a range of design factors at both building (typology and window to wall ratio) and urban scales (aspect ratio and urban grid rotation) are further suggested for developing context sensitive optimum urban layouts. The resultant solutions indicate an improvement in urban thermal comfort, cooling and heating energy use by up to 25.85%, 72.76%, and 93.67%, respectively.     

On the development of an urban passive thermal comfort system in Cairo,Egypt

This paper investigates how urban form can be designed to act as a passive thermal comfort system in Cairo. The system utilizes two main elements, the urban fabric form, with its green structure, and thermal comfort adaptation by introducing urban green scene stimulation with the time of exposure to the urban environment. The courtyard form on a large scale is used to study comfort levels, the effect of compactness on solar access and the local radiant heat island potential in a theoretical neighborhood design using a medium population housing concept as required by Egyptian urban planning laws. Urban canyons in a grid network, with three mid latitude orientations 15°, 45° and 75° from the E–W axis, were examined, with one canyon having virtually no shade. Other canyons had a green structure containing two types of native Egyptian trees. Numerical simulations using ENVI-met were performed for hot climate conditions. Although some very hot conditions were recorded, there were evident examples of more acceptable comfort levels and cooling potential for some orientations and degrees of urban compactness due to the clustered form with green cool islands and wind flow through the main canyons. Some design guidance on how to form urban passive cooling systems is presented.     

Outdoor measurements and temperature comparisons of seven monitoring stations: Preliminary studies in Curitiba,Brazil

Urbanization brings several changes to the natural environment. First, vegetation is supressed and natural scenery is modified, in order to accommodate manmade buildings and streets. Consequences bring a direct effect on fauna and flora and, due to a modified environment, with heat fluxes having a different pattern from that of the original site, on climatic features, such as on air temperature and humidity, radiative and convective heat exchanges. Thus, one of the factors that can contribute directly to the creation of urban climate is land use. The present study investigates how land use influences local temperatures in Curitiba, Brazil (25°31′S, 917 m elevation). For that purpose, seven different locations of the city were analyzed during a 1-month period by monitoring air temperature and humidity. Also, land use patterns around each location were quantified, according to five different categories established for that purpose: water area, built area, free area, paved area and green area. The monitoring of climatic data occurred in winter (June/July) of 2002. Comparisons were made regarding averages of the minimum, average and maximum temperatures for each location, qualitatively and quantitatively. As a final step of this study, formulas were developed expressing the local temperatures as a function of air temperatures, solar radiation and the wind speed of the meteorological station, which was used as reference station.     

Shaken,shrinking, hot,impoverished and informal: Emerging research agendas in planning

This is the second of two special issues in Progress in Planning exploring emerging research agendas in planning. It brings together scholars from diverse schools working on new areas of research and application in urban design and planning. Emergent research agendas include both novel areas of research and important shifts in the direction of a research area. The challenge for planning schools is to reflect critically on these changes and develop long-term research agendas that can better position our field in society and academia, and provide a basis from which to assess our academic programmes. The chapters in this issue display the different scales and fields of planning, including planning for: disaster recovery; climate change, especially opportunities for mitigation; shrinking cities in the First World; and rapidly urbanising informal and impoverished cities in the global South. At the same time, the chapters identify research areas that respond to major social and environmental changes. Olshansky and Chang highlight the increasing losses from catastrophic disasters, and address the need for disaster recovery planning. Wheeler, Randolph and London focus on climate change, and, noting the urgency of action now, their research agenda emphasises opportunities for planners to develop research and policies to reduce greenhouse gas emissions. Hollander, Pallagst, Schwarz and Popper look at increasing economic and population trends in many First World cities that result in city ‘shrinkage’. They present new opportunities for improving cities’ green space networks and natural features, and for research. The trebling of urban population in African cities by 2050, in conditions of poverty and informality, is the major trend driving Parnell, Pietriese and Watson's chapter. They present an agenda for new planning theories and for supporting empirical research to address the actual conditions of African cities.