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Building shading affects the ecosystem service of urban green spaces: Carbon capture in street canyons
Abstract
The urban building environment has dramatically transited into a high-rise style. Consequently, street canyons have changed the daytime solar radiation distribution and indirectly affected the photosynthesis of the surrounding ecosystems. Because of the interdisciplinary nature of the topic, quantitative studies are rare. In this study, a new approach combining radiation simulation and in situ observations was proposed, aiming to provide support towards sustainable urban spatial planning and management. Taking the Central Business District (CBD) of Beijing as the research area, the range and intensity of the shading effect were assessed based on a Digital Surface Model (DSM) and Solar Radiation Analysis (SRA). The findings reveal the following: 1) The daytime carbon capture of green space was 33.14 ± 12.43 gCO2 m⁻² d⁻¹, which included 85.6%, 11.9%, and 2.5% from trees, shrubs, and grassland, respectively. 2) The Carbon Capture Index (CCI) of the arbor zone was approximately two and five times that of shrubs and grassland, respectively. The sensitivity of carbon capture to the building height increased in the order shrubs < grassland < trees. To enhance current carbon capture, trees and shrubs should play a dominant role in urban greening planning. 3) When constructing enclosed buildings and planting inside, as well as to the north of high buildings in northern hemisphere cities, a setback line is strongly suggested according to the building height. 4) When the building height increased by 10% or by one floor, the carbon capture declined by 0.29 tCO2•km⁻² d⁻¹ or 0.40 tCO2•km⁻² d⁻¹, respectively. These results suggest that the modern urbanization process reduces the utilization efficiency of daytime solar energy and potentially impairs the ecological service of the urban green space.
... A novel approach for estimating floor spaces was presented in [58], a space recognition algorithm for building spaces was used for performance simulations [59], a spatial analysis linked with radiation effects was performed in [60], a decision-making support method was presented using design-space exploration in [61] and information extraction was performed in [62]. Included in the research based on design are the application of BIM and related analyses such as parking space allocation [63], climate daylight simulation [64], building adaptation design using physics-based simulation tools, building design sensitivity analyses [65], graphical visualization assists analyses and flow around buildings and indoor environments including turbulence [66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83]. ...
... The majority of the planning-related papers relate to sustainability, as the papers study the adaptation of natural elements to a particular space. Utilization of green spaces and water bodies within a residential area was analyzed, with the effect of reducing carbon emissions and shade, and a potential index for the amount of green space was proposed [78][79][80][81]. Additional studies relating to the adoption of natural elements were present, where the temperature effect from green spaces [82], applications in various formats [83], a comparison between objective and perceived built environments [84] and an analysis of spatial disparities in urban areas [85] were presented. ...
The development of smart cities has led to transforming modern city operations by applying emerging technologies from the fourth industrial revolution such as the Internet of Things, BIM and machine learning. To prepare for the future development of cities, it is necessary to investigate the current status of city development, research topics and the direction toward future cities. In this study, a systematic literature review was conducted following the combination of literature review guides by Kitchenham and the PRISMA statement. The review identified 141 peer-reviewed academic papers from web-based archives, such as Web of Science and SCOPUS, that were categorized into five topics related to smart cities and urban areas. The technologies applied in the research were analyzed to determine the direction future cities should take based on current smart cities and emerging technologies that will shape individuals’ daily lives. However, it was discovered that research papers on critical areas, such as mobility and management, were lacking compared to those on building design and urban planning. This paper concludes with an example of a future urban area that has been transformed due to adoption of future mobility technology to address the shortcomings of the reviewed literature on building and urban environments.
... Yang et al. also demonstrated that the UGS type has an indirect effect on the carbon pool of regional urban green space [60]. Due to the differences in green coverage rate, hard surface ratio, other indicators of different UGS types, and the regional characteristics in different cities, the proportion of surface soil organic carbon density and vegetation carbon density in different UGS types present strong heterogeneity [61,62]. The carbon pool of different types of urban green space under the influence of multiple factors shows the characteristics of a carbon source or carbon sink. ...
Urban area is a major source of CO2 and other greenhouse gases. Urban green space (UGS) is an essential element to increase carbon sequestration directly and reduce emission indirectly. In this study, the net primary production (NPP) and net ecosystem productivity (NEP) was monitored in order to enhance the carbon sequestration function of UGS and promote urban low-carbon development. Based on the Sentinel-2 L2A satellite images, meteorological data, and vegetation type data in 2019, we used the optimized Carnegie Ames Stanford Approach (CASA) model to estimate the NPP values of UGS types including attached green space, park green space, protective green space, and regional space in Beijing, Guangzhou, Shanghai, Shenyang, and Xi’an. The NEP values were evaluated based on NPP and soil heterotrophic respiration (RH) to quantify the vegetation carbon sink capacity. The accuracy test shows that the estimated NPP values based on the optimized CASA model are effective. The results indicate that the average NPP values (1008.5 gC·m−2·a−1) and vegetation carbon sink capacity (771.49 gC·m−2·a−1) of UGS in Beijing rank first among the cities, which is followed by the values in Guangzhou. The regional green space and park green space in five cities function as carbon sinks with high NPP values and have vegetation carbon sink capacity, whereas the attached green space in Shanghai and Xi’an as well as the protective green space in Guangzhou and Xi’an function as carbon sources. Moreover, the NEP distribution shows obvious spatial aggregation characteristics, that is, the high NEP values of UGS are clustered in mountainous forest areas in the west and north of Beijing, Northeast Guangzhou, and South Xi’an whereas the low NEP values are mostly concentrated in the urban built-up areas under strong influences of human activities. This research provides a new method for NPP and NEP estimation of UGS at the city scale and the scientific basis for the improvement of the vegetation carbon sink capacity of UGS.
... In general, the amount of daylight varies in two ways in urban areas. On the one hand, shading decreases carbon sequestration in street canyons, especially at city centres (Guo et al., 2020). On the other hand, the amount of light available may even increase when the plants are of an even size and grow in strictly specified patterns, as in tree rows, where plants do not cast shade on each other (Van Den Berge et al., 2021). ...
... The quantification of these comfort indicators is usually based on measured data and simulation results (Park et al., 2021). These simulations are required for calculating radiant distribution in urban environments or even air movement, as stated by authors such as Garreau et al. (Garreau et al., 2021) or Guo et al. (Guo et al., 2020). However, at the urban level, different tools appear that either partially solve the required needs, as detailed by Zhu et al. (Zhu et al., 2023) in their comprehensive review, or entirely solve them, as proposed by tools such as ENVI-MET (Bruse, 2018). ...
... 164 It has been reported that the GHG emission reduction potential of sustainable/green buildings can be further enhanced under the influence of specific environmental effects, such as shading produced by vegetation. 168,169 This hypothesis was tested for a non-shaded PCM-enhanced building, and the level of CO 2 was reduced by 10% 77 compared with a similar building with tree shading, which reduced the CO 2 by 16.01%. 165 It has also been revealed that PCM-enhanced personalized conditioning (PC) in buildings could reduce CO 2 emissions by 21.4% per annum, with per capita yearly savings of 37-$ 62 per person. ...
There has been growing interest in applying phase change materials (PCMs) in buildings owing to their energy conservation/latent heat storage properties and potential to improve thermal comfort. Various reviews have extensively discussed the thermophysical properties of PCMs and their energy-saving potential in buildings. However, comprehensive reviews on the indoor thermal/ personal comfort behavior of PCMs under different climates remain limited. Therefore, this study aims to present a comprehensive state-of-the-art review of the impact of PCMs on indoor thermal comfort levels in buildings located in cities within different subclimate zones and their personal cooling effect when integrated with clothing (vest). In addition, greenhouse gas (GHG) mitigation potentials and indoor air pollutant emission properties of PCM-enhanced buildings were also reviewed. Hundreds of published articles of PCMs in PubMed and Scopus databases, including a manual search approach, were utilized. The results from this state-of-the-art study have shown that incorporating PCMs in buildings satisfactorily reduced the indoor air temperature of most buildings located in hot climate (BSh, BWh) zones, but very limited studies have been performed in the cold (Dfc, BSk) environments. In general, there was an improvement in the thermal comfort levels of the PCM-enhanced buildings. However, these were mostly assessed using indices such as predicted mean vote, predicted percentage of dissatisfied, comfort index, and total discomfort change, without any comprehensive survey studies (eg, based on sensation votes) using human subjects. The majority of personal cooling studies of PCM-integrated vests/garments showed good improvement in thermal comfort, especially in terms of skin temperature and thermal sensation. However, very few studies have shown a considerable reduction in the GHG emissions of PCM-enhanced buildings, and the knowledge of the long-term carbon dioxide (CO2) reduction capabilities of PCMs is limited. The profiling of PCMs revealed the presence of volatile organic compounds. However, studies on indoor air pollutant emissions and the potential health effects of PCM-integrated buildings are still lacking. The study is crucial to motivating green building engineers, indoor environmental quality (IEQ) researchers, and epidemiologists to embark on potential future research. Innovative technologies such as machine learning, artificial intelligence, Internet of Things, uncertainty analysis, and optimization can be utilized to predict thermal comfort, IEQ, and GHG emissions in PCM-incorporated buildings.
... Ayrıca kentin morfolojisi, yapıların malzemesi, yapılı çevre ve bina stoku kalitesi, kentsel altyapı, alan kullanımı ve ulaşım ağı gibi unsurlar da fiziksel faktörler arasında sayılmaktadır (EEA, 2012;EC, 2013). Son yapılan çalışmalarda bina kat yüksekliğinin de fiziksel kırılganlığa etki ettiği görülmüştür (Guo et al., 2020). ...
... Moreover, our results on shading levels and changes can be verified from previous research results on the shading effect in local areas in Beijing [49]. For example, the shading changes of the Central Business District (CBD) in our results have the same spatial and diurnal laws as the research on the shading effect and radiation in the CBD based on remote sensing data sources [49,50]. From a macro perspective, the shading coverage distribution in a 1 km grid and administrative areas will help urban planners and managers to make relevant decisions. ...
Urban street shadows can provide essential information for many applications, such as the assessment and protection of ecology and environment, livability evaluation, etc. In this research, we propose an effective and rapid method to quantify the diurnal and spatial changes of urban street shadows, by taking Beijing city as an example. In the method, we explore a novel way of transferring street characteristics to semantically segment street-level panoramic images of Beijing by using DeepLabv3+. Based on the segmentation results, the shading situation is further estimated by projecting the path of the sun in a day onto the semantically segmented fisheye photos and applying our firstly defined shading coverage index formula. Experimental results show that in several randomly selected sampling regions in Beijing, our method can successfully detect more than 83% of the shading changes compared to the ground truth. The results of this method contribute to the study of urban livability and the evaluation of human life comfort. The quantitative evaluation method of the shading coverage index proposed in this research has certain promotion significance and can be applied to shading-related research in other cities.
... The integration of emissions and other transboundary activities that include a lifecycle approach has demonstrated that future carbon reduction efforts can be developed by studying the carbon footprint of large national parks and determining the importance of upstream and downstream carbon emissions (Villalba et al. 2013). The carbon capture index of trees is two-and five-times higher than that of shrubs and grasslands, respectively, and should be the primary focus in urban green space planning (Guo et al. 2020). Information from the analysis of carbon sources and sinks in urban greenspace can be used to understand how carbon uptake and emission from plant communities contributes to the regional carbon cycle. ...
Urban ecosystems are complex systems with anthropogenic features that generate considerable CO2 emissions, which contributes to global climate change. Quantitative estimates of the carbon footprint of urban ecosystems are crucial for developing low-carbon development policies to mitigate climate change. Herein, we reviewed more than 195 urban carbon footprint and carbon footprint related studies, collated the recent progress in carbon footprint calculation methods and research applications of the urban ecosystem carbon footprint, analyzed the research applications of the carbon footprint of different cities, and focused on the need to study the urban ecosystem carbon footprint from a holistic perspective. Specifically, we aimed to: (i) compare the strengths and weaknesses of five existing carbon footprint calculation methods [life cycle assessment, input–output analysis, hybrid life cycle assessment, carbon footprint calculator, and Intergovernmental Panel on Climate Change (IPCC)]; (ii) analyze the status of current research on the carbon footprint of different urban subregions based on different features; and (iii) highlight new methods and areas of research on the carbon footprint of future urban ecosystems. Not all carbon footprint accounting methods are applicable to the carbon footprint determination of urban ecosystems; although the IPCC method is more widely used than the others, the hybrid life cycle assessment method is more accurate. With the emergence of new science and technology, quantitative methods to calculate the carbon footprint of urban ecosystems have evolved, becoming more accurate. Further development of new technologies, such as big data and artificial intelligence, to assess the carbon footprint of urban ecosystems is anticipated to help address the emerging challenges in urban ecosystem research effectively to achieve carbon neutrality and urban sustainability under global change.
... Ayrıca kentin morfolojisi, yapıların malzemesi, yapılı çevre ve bina stoku kalitesi, kentsel altyapı, alan kullanımı ve ulaşım ağı gibi unsurlar da fiziksel faktörler arasında sayılmaktadır (EEA, 2012;EC, 2013). Son yapılan çalışmalarda bina kat yüksekliğinin de fiziksel kırılganlığa etki ettiği görülmüştür (Guo et al., 2020). ...
Urban green infrastructure is recognized for its potential to combat biodiversity loss and enhance carbon sequestration in cities. While residential yards constitute a significant part of urban green infrastructure, their role in providing urban ecosystem services remains largely understated. There is a lack of systematic measures for effectively implementing urban vegetation to enhance ecosystem services. The aim of this study is to investigate how different vegetation types typically found in urban residential yards of apartment blocks can enhance carbon sequestration and biodiversity, and how these benefits can be supported through landscape design. The study encompasses an integrative literature review and qualitative analysis. Drawing from a review of previous research, this study identifies the drivers that indicate either carbon sink potential or biodiversity enhancement potential of urban vegetation types. The drivers are then cross-examined to identify the qualities of urban green that potentially strengthen carbon–biodiversity co-benefits. As the key findings we present versatile measures to enhance the potential co-benefits of carbon sinks and biodiversity within urban yards and summarize them in three main categories: plant diversity, provision of good growing conditions and maintenance. The study stresses that the several potential co-benefits of urban green can only be achieved through the selection and prioritization of solutions during the planning and design process. To exemplify this, we demonstrate how the findings from the literature review can be incorporated into the design and management of urban yards. We conclude that the main actions to be addressed in the future planning and design of urban residential yards are (i) establishing diverse planting areas with a mixture of woody and herbaceous plants to encourage species richness and complexity, (ii) optimizing the use of space and growth conditions, and, (iii) implementing maintenance practices that consider both carbon and biodiversity aspects. The study highlights that through enhancing carbon-biodiversity co-benefits urban yards can significantly contribute to major environmental challenges and provide vital ecosystem services within the built urban environments.
Medan City is a Metropolitan City with a high population growth rate, in line with the growth rate of regional development. These problems spur the occurrence of land use change. The need for land for residential locations, transportation infrastructure facilities and others will impact the reduced availability of green open space as an oxygen producer in the city of Medan. This study aims to examine the distribution of green open space, estimate the need and adequacy of green open space, and develop directions for developing green open space. This research was conducted from January to completion, using the method of interpretation and analysis of spatial data from quick bird images taken from the SAS Planet application, and calculations were carried out using the Gerarchic formula to determine oxygen demand. The results showed that the area of green open space in Medan City was 86.27 km2 (33%), and non-vegetated/non-green open space was 178.83 km2 or equivalent to (67%) of the Medan City area of 265.10 km2. The oxygen plants produce in green open spaces is 4,367,418.75 kg/day. Meanwhile, the oxygen demand in Medan City is 5,150,425.98 kg/day, and when converted into green open space, it is 101.74 km2. Directions for the development of green open spaces can be carried out in several ways, namely managing green spaces, synergizing the natural and artificial environment, implementing a low-cost transportation system, empowering population policy strategies, utilizing water and energy resources, maintaining environmental health based on city planning that favours development principles sustainable.Keywords: Green open space, Oxygen, Quickbird Image, Medan
This study presents a method to estimate the solar energy potential based on 3D data taken from unmanned aerial devices. The solar energy potential on the roof of a building was estimated before the placement of solar panels using photogrammetric data analyzed in a geographic information system, and the predictions were compared with the data recorded after installation. The areas of the roofs were chosen using digital surface models and the hemispherical viewshed algorithm, considering how the solar radiation on the roof surface would be affected by the orientation of the surface with respect to the sun, the shade of trees, surrounding objects, topography, and the atmospheric conditions. The results show that the efficiency percentages of the panels and the data modeled by the proposed method from surface models are very similar to the theoretical efficiency of the panels. Radiation potential can be estimated from photogrammetric data and a 3D model in great detail and at low cost. This method allows the estimation of solar potential as well as the optimization of the location and orientation of solar panels.
This study presents a method to estimate the solar energy potential based on 3D data taken from unmanned aerial devices. The solar energy potential on the roof of a building was estimated before the placement of solar panels using photogrammetric data analyzed in a geographic information system, and the predictions were compared with the data recorded after installation. The areas of the roofs were chosen using digital surface models and the hemispherical viewshed algorithm, considering how the solar radiation on the roof surface would be affected by the orientation of the surface with respect to the sun, the shade of trees, surrounding objects, topography, and the atmospheric conditions. The results show that the efficiency percentages of the panels and the data modeled by the proposed method from surface models are very similar to the theoretical efficiency of the panels. Radiation potential can be estimated from photogrammetric data and a 3D model in great detail and at low cost. This method allows the estimation of solar potential as well as the optimization of the location and orientation of solar panels.
This study aims to investigate the impact of building arrangement on the urban microclimate and energy consumption of buildings in central commercial and business district by using simulation tools, including ENVI-met and HTB2. In order to achieve this goal, a series of numerical calculations and building energy simulations are utilized to evaluate a total of 12 urban scenarios with various building arrangements. The results indicate a quantitative correlation between building arrangement and the microclimate and building energy performance at urban design scale. Furthermore, several recommendations have been provided for urban planners and designers as strategies and methods to mitigate the UHI effect and to reduce the energy consumption.
Containing elevation information, Digital surface model (DSM) data plays an increasingly important role in re mote sensing image processing, especially in the field of building detection. However, due to the lack of spectral and textural information from DSM data, most researchers fused airborne images and DSM data to enhance the detection accuracy. In this paper, a novel building detection technique by only using DSM data has been proposed. The building detection process is performed in three steps. First and foremost, the ground surface is reconstructed by employing the Minimum Description Length (MDL) principle. After that, the non-ground objects including buildings and trees are extracted from the original data. Finally a morphological method is applied to remove trees so that buildings can be recognized. To validate the performance of the proposed method, empirical experiment results have been compared with the interpretation results from the airborne images. Based on the comparison, we prove that our proposed method, which only uses DSM data, has satisfactory detection rate and acceptable detection error with other hybrid detection methods; we prove that DSM data by itself is enough for building detection. Keywords— building detection; ground reconstruction; digital surface model; minimum description length principle I. INTRODUCTION Building detection in DSM is one of the most popular topics in the processing of remote sensing images because DSM data carries the elevation information of terrain surface. Apart from optical images, DSM data can be used as another data source for image interpretation and the interpretation result significantly benefits the post processing application such as 3D building reconstruction, etc.
The aim of this work is to evaluate the potential direct and diffuse solar radiation aggregated at a point location in an urban area. With the three-dimensional (3D) SOlar RAdiation Model (SORAM) presented here, the paper makes three key contributions. Firstly, the model augments the Perez et al. (1990) model by accounting for the aggregated contribution of diffuse radiation using ray-tracing methods. Secondly, the model demonstrates the use of a randomly generated city building distribution and terrain map to simulate the 3D urban solar radiation exposure at any time or over a selected time period. Thirdly, we validate our results using empirical sunlight data measured from a real urban area (Sheffield Solar Farm), and also validate our results against the Perez et al. (1990) model under conditions of no shading.
The heavy concentration of population, economic activities and high-rise buildings have formed a unique and complex urban morphology in the city centre areas of many metropolitan regions. This research exploits high-resolution LIDAR data to quantify three-dimensional urban morphology and its impacts on the spatio-temporal variability of solar radiation in downtown Houston, Texas. Various urban landscape components, including buildings, trees, shrubs and lawns, have been extracted by combining LIDAR data and colour infrared aerial photographs. An efficient solar flux model is re-implemented as an ArcGIS module with extended capabilities. Monthly and seasonal solar radiation fields are computed in terms of radiation intensity and illumination duration. Our analysis suggests that the extensive and dense distribution of tall and large buildings has dramatically changed the spatial pattern of solar radiation and hence imposed significant impacts on other urban landscape components, especially urban vegetation canopy. We have determined three types of vegetation habitats: shade, semi-sunny/partial shade, and sunny habitats. This research represents the first effort to model spatio-temporal variation of solar radiation in an urban built-up environment using high-resolution LIDAR data. The temporal solar radiation maps would benefit the design and selection of appropriate species of trees, shrubs, flowers and lawn grasses for urban vegetation planting and management.
The conservation of cultural heritage in urban physical form has until very recently been almost entirely concerned with individual structures, often notable buildings and monuments, and special areas. Policy-and practice-orientated bodies tend to treat historic features in geographical isolation from the wider landscapes of which they are an integral part. Yet realizing the full potential of the landscape as a cultural, educational, intellectual and economic resource requires appreciation of how individual features are connected historically and geographically: how they fit into the wider historical landscape. Greater recognition of this is belatedly, and sporadically, beginning to become evident. For example, in its World Heritage Cities Programme, UNESCO is broadening its perspective explicitly to consider historic urban landscapes as ensembles, having for long been concerned essentially with individual sites and monuments. And at a national level, English Heritage is undertaking rapid, ‘broad-brush’ characterizations of extensive areas of urban landscape, including those that came into existence as recently as the twentieth century. [1]
The paper demonstrates the relationship existing between the size of a village, town or city (as measured by its population), and the magnitude of the urban heat island it produces. This is accomplished by analyzing data gathered by automobile traverses in 10 settlements on the St. Lawrence Lowland, whose populations range from 1000 to 2 million inhabitants. The locations of these settlements effectively eliminate all non-urban climatic influences. The results are compared with previously published data.The analysis shows the heat island intensity under cloudless skies to be related to the inverse of the regional windspeed, and the logarithm of the population. A simple model is derived which incorporates these controls. In agreement with an extension of Summers' model the heat island appears to be approximately proportional to the fourth root of the population. With calm and clear conditions the relation is shown to hold remarkably well for North American settlements, and in a slightly modified form, for European towns and cities.
Sun-and shade-adapted plants of Ailanthus altissima utilized thermal-dissipative photoprotection (NPQ) across a range of photosynthetic photon flux densities (PPFD), with higher NPQ and lower maximum quantum yield of photosystem 2 photochemistry (Fv/Fm) in sun-adapted individuals, suggesting increased engagement of antennae-based quenching. Photosynthetic quantum requirements (Qreq; number of photons per CO2) were similar in sun and shade plants, but were low and comparable to forest understory species. Diurnal measurements showed that PPFDs in both habitats were consistently above photosynthetic compensation irradiance, and frequently exceeded saturating values. In addition, sun- and shade-adapted individuals possessed stomata that tracked short-term fluctuations in PPFD. Thus A. altissima may be unique in that it couples high, shade-plant like photosynthetic efficiency with high photosynthetic capacity in high-irradiance, while stomatal attributes that optimize water use efficiency are maintained in the shade. These features may contribute to success of A. altissima in establishing in disturbance-prone urban systems, and facilitate its spread into more PPFD-limited and competitive natural ecosystems.
The contents of chlorophyll (Chl) and carotenoids (Car) per fresh mass were lower in shade needles than in sun needles. Ribulose-1,5-bisphosphate
carboxylase (RuBPC) activity and contents of soluble proteins were also significantly lower in shade needles. In isolated
thylakoids, a marked lower rate of whole chain and photosystem (PS) 2 activities were observed in shade needles. Smaller lower
rate of PS1 activity was also observed in shade needles. The artificial exogenous electron donors, diphenyl carbazide (DPC)
and NH2OH, significantly restored the loss of PS2 activity in shade needles. Similar results were obtained when Fv/Fm was evaluated by Chl fluorescence measurements. The marked lower rate of PS2 activity in shade needles was due to the lower
contents of 47, 33, 28–25, 23, and 17 kDa polypeptides. This conclusion was confirmed by immunological studies showing that
the content of the 33 kDa protein of the watersplitting complex was diminished significantly in shade needles.
Street-level concentrations of nitrogen dioxide (NO(2)) and particulate matter (PM) exceed public health standards in many cities, causing increased mortality and morbidity. Concentrations can be reduced by controlling emissions, increasing dispersion, or increasing deposition rates, but little attention has been paid to the latter as a pollution control method. Both NO(2) and PM are deposited onto surfaces at rates that vary according to the nature of the surface; deposition rates to vegetation are much higher than those to hard, built surfaces. Previously, city-scale studies have suggested that deposition to vegetation can make a very modest improvement (<5%) to urban air quality. However, few studies take full account of the interplay between urban form and vegetation, specifically the enhanced residence time of air in street canyons. This study shows that increasing deposition by the planting of vegetation in street canyons can reduce street-level concentrations in those canyons by as much as 40% for NO(2) and 60% for PM. Substantial street-level air quality improvements can be gained through action at the scale of a single street canyon or across city-sized areas of canyons. Moreover, vegetation will continue to offer benefits in the reduction of pollution even if the traffic source is removed from city centers. Thus, judicious use of vegetation can create an efficient urban pollutant filter, yielding rapid and sustained improvements in street-level air quality in dense urban areas.
Global warming has obtained more and more attention because the global mean surface temperature has increased since the late 19th century. As more than 50% of the human population lives in cities, urbanization has become an important contributor for global warming. Pearl River Delta (PRD) in Guangdong Province, southern China, is one of the regions experiencing rapid urbanization that has resulted in remarkable Urban Heat Island (UHI) effect, which will be sure to influence the regional climate, environment, and socio-economic development. In this study, Landsat TM and ETM+ images from 1990 to 2000 in the PRD were selected to retrieve the brightness temperatures and land use/cover types. A new index, Normalized Difference Bareness Index (NDBaI), was proposed to extract bare land from the satellite images. Additionally, Shenzhen, which has experienced the fastest urbanization in Guangdong Province, was taken as an example to analyze the temperature distribution and changes within a large city as its size expanded in the past decade. Results show that the UHI effect has become more prominent in areas of rapid urbanization in the PRD region. The spatial distribution of heat islands has been changed from a mixed pattern, where bare land, semi-bare land and land under development were warmer than other surface types, to extensive UHI. Our analysis showed that higher temperature in the UHI was located with a scattered pattern, which was related to certain land-cover types. In order to analyze the relationship between UHI and land-cover changes, this study attempted to employ a quantitative approach in exploring the relationship between temperature and several indices, including the Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Normalized Difference Bareness Index (NDBaI) and Normalized Difference Build-up Index (NDBI). It was found that correlations between NDVI, NDWI, NDBaI and temperature are negative when NDVI is limited in range, but positive correlation is shown between NDBI and temperature.
Approximately 75-80% of the population of North America currently lives in urban areas as defined by national census bureaus, and urbanization is continuing to increase. Future trajectories of fossil fuel emissions are associated with a high degree of uncertainty; however, if the activities of urban residents and the rate of urban land conversion can be captured in urban systems models, plausible emissions scenarios from major cities may be generated. Integrated land use and transportation models that simulate energy use and traffic-related emissions are already in place in many North American cities. To these can be added a growing dataset of carbon gains and losses in vegetation and soils following urbanization, and a number of methods of validating urban carbon balance modeling, including top down atmospheric monitoring and urban 'metabolic' studies of whole ecosystem mass and energy flow. Here, we review the state of our understanding of urban areas as whole ecosystems with regard to carbon balance, including both drivers of fossil fuel emissions and carbon cycling in urban plants and soils. Interdisciplinary, whole-ecosystem studies of the socioeconomic and biophysical factors that influence urban carbon cycles in a range of cities may greatly contribute to improving scenarios of future carbon balance at both continental and global scales.
Spatial variation in plant diversity has been attributed to heterogeneity in resource availability for many ecosystems. However, urbanization has resulted in entire landscapes that are now occupied by plant communities wholly created by humans, in which diversity may reflect social, economic, and cultural influences in addition to those recognized by traditional ecological theory. Here we use data from a probability-based survey to explore the variation in plant diversity across a large metropolitan area using spatial statistical analyses that incorporate biotic, abiotic, and human variables. Our prediction for the city was that land use, along with distance from urban center, would replace the dominantly geomorphic controls on spatial variation in plant diversity in the surrounding undeveloped Sonoran desert. However, in addition to elevation and current and former land use, family income and housing age best explained the observed variation in plant diversity across the city. We conclude that a functional relationship, which we term the "luxury effect," may link human resource abundance (wealth) and plant diversity in urban ecosystems. This connection may be influenced by education, institutional control, and culture, and merits further study.
This study evaluated the spatio-temporal change characteristics of urban development at different scales with time-series impervious surface fractions. Landsat-5 Thematic Mapper (TM) and Landsat-8 Operational Land Imager (OLI) images were used to extract impervious surface fractions using a modified linear spectral mixture analysis method in Guangzhou from 1988 to 2015. The results indicated that the impervious surface area has substantially increased, from 70.3 km2 in 1988 to 580.5 km2 in 2015. In 2015, the impervious surfaces were distributed almost throughout the whole region of the study area, except in the forest region. Next, impervious surface weighted mean centre (ISWMC) and the standard deviational ellipse (SDE) methods were used to systematically analyse the principle orientation, direction, spatio-temporal expansion trends, and the distribution differences of impervious surfaces at the whole and local region scales from 1988 to 2015. The spatio-temporal dynamics of ISWMC exhibited different expansion directions and intensities of impervious surfaces at the whole and local region scales. On a whole region scale, the principle expansion direction of impervious surfaces was northward. However, the expansion trend of impervious surfaces in the different districts was significantly different from other trends at the local region scale. The parameters of SDE were used to investigate the orientation and the clustering or dispersion degree of impervious surface at different scales. The results from SDE analysis indicated that the impervious surfaces exhibited uncertainty in the expansion direction at the whole region scale; in contrast, they had a distinct preferred orientation and expansion direction at the local region scale. The analysis revealed that urban expansion exhibited different change characteristics in various directions at the local region scale. In summary, the results at the local region scale can better reflect the change trajectory of spatio-temporal dynamics of urban development and its fine spatial structure than at the whole region scale.
This book focuses on China’s urban development. In China, the process of allowing more rural migrants to become registered city residents in urban areas remains stagnant despite its importance to the Chinese government and the existence of a national consensus about it. Cities can compulsorily purchase land from farmers at low or even no costs, and most farmers, whose families have relied on the land to make a living for generations, do not profit from increases in land value. Breaking down the established distributive system of rights and privileges requires legislation and law enforcement. To this end, we need to break through the current pattern of interests and respect the "citizenization-relevant" rights of rural migrant workers.
Cities are becoming increasingly important in combatting climate change, but their overall role in global solution pathways remains unclear. Here we suggest structuring urban climate solutions along the use of existing and newly built infrastructures, providing estimates of the mitigation potential.
It follows from the analysis of observation data that the secular variation of the mean temperature of the Earth can be explained by the variation of short-wave radiation, arriving at the surface of the Earth. In connection with this, the influence of long-term changes of radiation, caused by variations of atmospheric transparency on the thermal regime is being studied. Taking into account the influence of changes of planetary albedo of the Earth under the development of glaciations on the thermal regime, it is found that comparatively small variations of atmospheric transparency could be sufficient for the development of quaternary glaciations. DOI: 10.1111/j.2153-3490.1969.tb00466.x
Based on the daily data of solar radiation and sunshine duration from 1958 to 2000 at Beijing, China, the average annual solar radiation was calculated, and the long-term variation of solar radiation was analyzed in this paper. Subsequently, the relationship between global solar radiation and sunshine duration and the relationship between diffuse and global solar radiation were studied, and the empirical formulas to estimate global and diffuse solar radiation at Beijing was derived. The performance of the empirical formulas was assessed on the basis of statistical error tests, results show that the empirical formulas can be used in engineering practice with adequate accuracy.
This paper is about the research into the effect of building envelopes on energy consumption and thermal performance of high-rise buildings in the Malaysian Tropical climate. A suitable indoor thermal condition in buildings is important because of the building occupants comfort. In addition, it is indicating building energy consumption, staff productivity, less absenteeism, health and well-being effects. Energy consumption can be significantly reduced by adopting energy efficiency strategies in such buildings. Due to environmental concerns and expensive energy costs in recent years, energy efficiency in buildings has garnered renewed interests. A research recently conducted in Malaysia specifies that residential buildings do about 19% of the overall energy consumed in Malaysian sectors. One of the most potential strategies applied on building envelope in hot-humid tropical regions is the passive design method and is done to the building envelope in hot-humid tropical regions. This paper reviews the results of the other studies that establish to the selecting of proper parameters of building envelope to the high-rise residential. The building design criteria has been scrutinized through a set of defined parameters such as climatic conditions, form, width, length and height, external walls, roofs, glazing area, natural ventilation and occupants thermal comfort, as well as external shading devices on energy consumption of high-rise buildings in Malaysia. The thermal comfort zone was investigated by researchers for Malaysian residential buildings, discovering that the comfort ranged between 25 °C and 31 °C. Recommendations are given based on the significant findings as resources to help designers in laying out the design plan for high-rise buildings in hot and humid climate.
Air quality in street canyons is of major importance, since the highest pollution levels are often encountered in these microenvironments. The canyon effect (reduced natural ventilation) makes them "hot spots" for particulate pollution contributing to adverse health effects for the exposed population. In this study we tried to characterize the influence of UFP (ultrafine particle) emissions from traffic on population exposure in an urban street canyon, by applying the intake fraction (iF) approach. One month long measurements of UFP levels have been monitored and used for the need of this study. We applied a three dimensional computational fluid dynamic (CFD) model based on real measurements for the simulation of UFP levels. We used infiltration factors, evaluated on a daily basis for the under study area, to estimate the indoor UFP levels. As a result the intake fraction for the pedestrians, residents and office workers is in the range of (1E-5)-(1E-4). The street canyon is mostly residential justifying partially the higher value of intake fraction for residents (1E-4). The above iF value is on the same order of magnitude with the corresponding one evaluated in a relative street canyon study. The total iF value in this microenvironment is one order of magnitude higher than ours, explained partially by the different use and activities. Two specific applications of iF to assess prioritization among emission sources and environmental justice issues are also examined. We ran a scenario with diesel and gasoline cars and diesel fueled vehicle seems to be a target source to improve overall iF. Our application focus on a small residential area, typical of urban central Athens, in order to evaluate high resolution iF. The significance of source-exposure relationship study in a micro scale is emphasized by recent research.
Copyright © 2015 Elsevier B.V. All rights reserved.
This paper investigates the influence of solar radiation on thermal comfort inside an indoor environment and its effect on the building energy consumptions. Furthermore, it draws up a procedure which allows the rating of the thermal comfort quality of indoor environments in the presence of solar radiation, to be used in correlation with the energy classification of building in order to refer the energy performance to the indoor environmental conditions. Mean Radiant Temperatures (MRT) for a subject exposed to solar radiation in different positions of the environment were calculated, with an hourly time step and for a whole year. These values were utilized to assess the Predicted Percentage of Dissatisfied (PPD) and its variation with time and space, so that long term thermal comfort evaluations were able to be carried out and comparisons among irradiated and not irradiated positions were able to be made.
The tilt angle of a solar energy system is one of the important parameters for capturing maximum solar radiation falling on the solar panels. This angle is site specific as it depends on the daily, monthly and yearly path of the sun. The accurate determination of the optimum tilt angle for the location of interest is essential for maximum energy production by the system. A number of methods have been used for determining the tilt angle at different locations worldwide. Keeping in view the relevance of the optimum tilt angle in energy production and reducing the cost of solar energy systems, the present study has been undertaken. This paper provides the update status of research and applications of various methods for determining solar panel tilt angle using different optimization techniques. The study shows that for maximum energy gain, the optimum tilt angle for solar systems must be determined accurately for each location. The review will be useful for designers and researchers to select suitable methodology for determining optimal tilt angle for solar systems at any site.
Diminished sunlight, characteristic of urban canyons, has been suggested as being potentially limiting to plant growth. This study investigated the response of sweetgum ( Liquidambar styraciflua L.) to variable irradiance in a range of urban locations. Diurnal photosynthesis was measured in situ on mature trees, comparing an open site at an urban park with an urban canyon that received 4 h of midday sun in midsummer. Photosynthesis for trees growing in the canyon was lower both during shaded and sunlit periods compared with trees at the park. Photosynthesis of detached shoots in a growth chamber was greater in canyon than park foliage at low irradiance, indicating possible photosynthetic shade acclimation analogous to tree species growing in the forest understorey. Shoot and trunk growth and morphological characteristics were measured on L. styraciflua growing along boulevards at 15 additional urban sites and related to seasonal interception of solar radiation. Angular elevation and orientation of buildings and trees that defined the horizon topography at each site were used in modeling the potential irradiance of global shortwave radiation. Seasonal irradiance among sites ranged from 21% in the urban core to nearly 95% in outlying residential districts of that potentially received under an unobstructed horizon. Shade acclimation was confirmed by differences in leaf morphology, as foliage became flatter, thinner, and more horizontally oriented at sites with lower irradiance. Photosynthetic and morphological acclimation to shade did not compensate for lower available radiant energy as both shoot and trunk growth decreased at sites of lower irradiance. Unlike the forest understorey, the static light environment of urban canyons may subject shade-intolerant species such as L. styraciflua to chronic, low-radiant-energy stress.
The spectral quality of solar radiance affects plant growth and development. The purpose of this study was to assess the spectral quality of deciduous shade, coniferous shade, building shade, and full sun in a natural environment common to turfgrass growth throughout a day and throughout a growing season. A spectroradiometer was used to acquire solar spectra in these four environments. Acquisitions were made on an hourly basis from 0730 to 1930 h, biweekly, from vernal equinox to autumnal equinox at The Ohio Turfgrass Foundation Research and Educational Center and from 10 April to 1 July 1997 at The Ohio State University campus. Data were tested for variation in spectral quality between morning hours and afternoon hours in full sun and among full sun and deciduous, coniferous, and building shade. Results indicated that changes in spectral quality occurred between morning and afternoon periods in full sun, but total (red + blue) photosynthetically active irradiance was not affected. Measurements indicated that a deciduous tree and a conifer tree filtered significantly more high activity (red + blue) quanta than a building. Blue irradiance relative to total irradiance increased and red irradiance decreased with increasing shade density. Significant differences were detected between full sun, tree shade, and building shade for blue photoreceptor potential (blue photon flux/far-red photon flux) and phytochrome potential (red photon flux/far-red photon flux). Results indicated that relationships among blue, red, and far-red irradiance that influence many plant responses were affected by both shade source and shade density.
Two studies were conducted on a third-story rooftop to quantify the effect of solar radiation (full sun versus full shade) on several US native and non-native species for potential use on extensive green roofs. In the first study, plugs of six native and three non-native species were planted in May 2005 on substrates of two different depths (8.0 and 12.0 cm) both in sun and shade. Absolute cover (AC) was recorded using a point-frame transect during the growing season beginning in June 2005 and every 2 weeks thereafter for a period of 4 years. By week 174 (23 September 2008), most species exhibited different AC within a depth between sun and shade. However, when all species were combined, overall AC did not differ between sun and shade within a depth. This indicated that while species make-up was changing among solar radiation levels, that overall coverage was not significantly different between sun and shade. For all substrate depths and solar levels, the most abundant species were Sedum acre, Allium cernuum, Sedum album ‘Coral Carpet’, and Talinum calycinum. Less abundant species included Talinum parviflorum, Carex flacca, Sedum stenopetalum, and Sedum divergens, which all exhibited 0 or near 0 AC regardless of depth or solar radiation levels. With the exception of T. calycinum, native species were less abundant than non-native species.
Reactive pollutant dispersion in an urban street canyon with a street aspect ratio of one is numerically investigated using a computational fluid dynamics (CFD) model. The CFD model developed is a Reynolds-averaged Navier–Stokes equations (RANS) model with the renormalization group (RNG) k–ε turbulence model and includes transport equations for NO, NO2, and O3 with simple photochemistry. An area emission source of NO and NO2 is considered in the presence of background O3 and street bottom heating (ΔT=5°C) with an ambient wind perpendicular to the along-canyon direction. A primary vortex is formed in the street canyon and the line connecting the centers of cross-sectional vortices meanders over time and in the canyon space. The cross-canyon-averaged temperature and reactive pollutant concentrations oscillate with a period of about 15min. The averaged temperature is found to be in phase with NO and NO2 concentrations but out of phase with O3 concentration. The photostationary state defect is small in the street canyon except for near the roof level and the upper downwind region of the canyon and its local minimum is observed near the center of the primary vortex. The budget analysis of NO (NO2) concentration shows that the magnitude of the advection or turbulent diffusion term is much larger (larger) than that of the chemical reaction term and that the advection term is largely balanced by the turbulent diffusion term. On the other hand, the budget analysis of O3 concentration shows that the magnitude of the chemical reaction term is comparable to that of the advection or turbulent diffusion term. The inhomogeneous temperature distribution itself affects O3 concentration to some extent due to the temperature-dependent photolysis rate and reaction rate constant.
Analyses of theoretical calculations and experimental measurements show that the photosynthetically useful fraction of the solar spectrum, ηT, for the total (= direct + diffuse) radiation is almost independent of atmospheric conditions and is nearly constant at 0.50 ± 0.03. For the direct beam only, in very clean air in the winter ηI varies between 0.35 and 0.45 as solar elevation, β, increases from 10 to 45⚬; in the summer the range is smaller and is from 0.41 to 0.49 for the same range in β. For the diffuse radiation coming from the blue sky ηD is 0.75. The results are taken as evidence that ηT is so nearly constant that climatological measurements of solar radiation can be used confidently in estimating efficiencies of photosynthesis and crop growth in the field.
This paper analyzes the impacts and the welfare costs of building-height restrictions. The theoretical analysis demonstrates that a height restriction causes a city to expand spatially, a consequence of lower densities near the center. The analysis also establishes that the consumer welfare cost generated by the height restriction can be measured by the increase in commuting cost for the household living at the edge of the city. Simulation results for a stylized urban area show that this welfare cost is approximately 2% of household income. Illustrative calculations for Bangalore, India, where a height restriction is in force, suggest a similar welfare cost, which lies in the 1.5–4.5% range.
This study presents a methodology for the assessment of photovoltaic potential in urban areas using open-source solar radiation tools and a 3-D city model implemented in a geographic information system (GIS). The solar radiation tools are represented by the r.sun solar radiation model and PVGIS estimation utility. The applicability of the methodology has been demonstrated on a selected urban area of a small city in eastern Slovakia. The relevant attributes of buildings have been mapped and implemented in a GIS database. The selected urban area consists of various urban zones characterized by different morphology and functionality. The photovoltaic potential of buildings has been assessed using the PVGIS estimation utility. The analysis has shown a high photovoltaic potential that could cover about 2/3 of current electricity consumption in the city. However, this potential exhibits large spatial and temporal variations caused by global and local factors. This study has also shown that national assessments of photovoltaic potential can be improved by extrapolation of local assessments using spatial databases of urban areas.
The objective of this study is to investigate numerically the effect of wedge-shaped roofs on wind flow and pollutant dispersion in a street canyon within an urban environment. A two-dimensional computational fluid dynamics (CFD) model for evaluating airflow and pollutant dispersion within an urban street canyon is firstly developed using the FLUENT code, and then validated against the wind tunnel experiment. It was found that the model performance is satisfactory. Having established this, the wind flow and pollutant dispersion in urban street canyons of sixteen different wedge-shaped roof combinations are simulated. The computed velocity fields and concentration contours indicate that the in-canyon vortex dynamics and pollutant distriburtion are strongly dependent on the wedge-shaped roof configurations: (1) the height of a wedge-shaped roof peak is a crucial parameter determining the in-canyon vortex structure when an upward wedge-shaped roof is placed on the upwind building of a canyon; (2) both the heights of upstream and downstream corners of the upwind building have a significant impact on the in-canyon vortical flow when a downward wedge-shaped roof is placed on the upwind building of a canyon, due to flow separation as wind passes through the roof peak; (3) the height of upstream corner of the downwind building is an important factor deciding the in-canyon flow pattern when a wedge-shaped roof is placed on the downwind building of a canyon; (4) the characteristics of pollutant dispersion vary for different wedge-shaped roof configurations, and pollution levels are much higher in the “step-down” canyons relative to the “even” and “step-up” ones.
The investigation was carried out to reveal the impact of solar radiation on pollutant dispersion in different urban street layouts using computational fluid dynamics (CFD) technique. It is indicated that the street geometry has a strong influence on the wind field and pollution dispersion patterns. For example, when a stepdown configuration is applied, there are two counterrotating vortices in the canyon, a higher concentration appears on the windward side, and the pollution levels within the canyon area increase. Furthermore, it is found that the heating from surfaces leads to a strong buoyancy force close to the surfaces that receive direct solar radiation. This thermally induced flow is combined with mechanically induced flow, and affects the flow field and pollutants dispersion. The upward buoyancy flux divides the flow structure into two counterrotating cells at symmetrical configuration or a small vortex at the lower windward building corner is generated at stepup notch when the windward side is heated. This effect causes the pollutant concentration in the street canyon to increase. In the stepdown notch, when the sun shines on the windward side of the building and the ground level, the intensity of the lower vortex is increased. Pollutant concentrations in the street canyon decrease. If the sun shines on the leeward side of the building, the upper vortex is enlarged downward and pollutant concentrations in street canyon increase. The relative influence of thermal radiation can be estimated by the parameter Gr/Re2.
Light requirements and functional strategies of plants to cope with light heterogeneity in the field have a strong influence on community structure and dynamics. Shade intolerant plants often show a shade avoidance strategy involving a phytochrome-mediated stem elongation in response to changes in red : far red ratio, while shade-tolerant plants typically harvest light very efficiently. We measured plant size, stem diameter, internode and leaf lengths in randomly chosen saplings of 11 woody species differing in their shade tolerance in both a secondary forest and an old-growth temperate evergreen rainforest in southern Chile. We also recorded the irradiance spectrum and the diffuse and direct light availabilities at each sampling point. Significant differences were found for the mean light environment of the saplings of each species, which also differed in basal stem diameter, internode length and leaf length, but not in plant height. Both plant slenderness (plant height/stem diameter) and mean internode length increased with increasing light availability, but no relationship was found between any of these two traits and red : far red ratio. The change in plant slenderness with light availability was of lesser magnitude with increasing shade tolerance of the species, while internode change with light availability increased with increasing shade tolerance of the species. Shade tolerators afford higher costs (thicker stems and plants), which render more biomechanically robust plants, and respond more to the light environment in a trait strongly influencing light interception (internode length) than shade intolerant species. By contrast, less shade-tolerant plants afforded higher risks with a plastic response to escape from the understorey by making thinner plants that were biomechanically weaker and poorer light interceptors. Thus, species differing in their shade tolerances do differ in their plastic responses to light. Our results contribute to explain plant coexistence in heterogeneous light environments by improving our mechanistic understanding of species responses to light.
This paper addresses global economic factors influencing the decisions leading to the development of super-tall towers, including population growth and urbanization, economic cycles and the ‘Skyscraper Index’, regulation and ‘regulatory tax’, and resource availability. The project economics of individual developments are then explored with respect to construction costs. The development, design and construction challenges that impact on cost are also discussed. Furthermore, a breakdown of costs is given in the form of an indicative cost model (for a central London landmark tower) from cost data collected by Davis Langdon in the course of their work as construction consultants. Copyright © 2007 John Wiley & Sons, Ltd.
The spectral composition of photosynthetically active radiation (PAR) during clear and overcast days was studied above the
canopy (U) and at two layers of a dense Norway spruce stand [Picea abies (L.) Karst.] characterized with an average LAI=7.3±0.8 (middle layer: M) and 12.3±0.7 (lower layer: L). Whereas the
spectral composition of PAR incoming on the canopy surface during cloudy days (characterized by diffuse index DI>0.7) was
almost independent of the solar elevation angle, the proportion of the blue-green spectral region of PAR was significantly
reduced at low elevation angles during days with prevailing direct radiation (DI<0.3). The PAR spectrum at both M and L
levels was only slightly enriched in the green spectral region (more pronounced for DI<0.3). The penetration of diffuse
radiation into the canopy resulted in a slight (approx. 5%) reduction of the blue region proportion that remained stable during
the day. On the contrary, under clear sky conditions the penetration of blue and red radiation was dependent on the solar
elevation in an opposite manner in comparison with the spectral composition of PAR incident on canopy, giving almost twofold
proportion of the blue part of the spectrum at a low elevation angle at M layer. We suggest that the blue enhancement of the
spectrum within the Norway spruce canopy during clear days is due to a specific spatial arrangement of the assimilatory apparatus
of a coniferous stand. Further, the possible consequences of the observed dynamics of the PAR spectrum inside the canopy during
clear days on the efficiency of PAR absorption of the needles located within the canopy are discussed.
The effect of full sunlight, 60%, or 90% attenuated light on photosynthetic rate, growth, leaf morphology, dry weight allocation patterns, phenology, and tolerance to clipping was examined in the glasshouse for steppe populations of the introduced grass, Bromus tectorum. The net photosynthetic response to light for plants grown in shade was comparable to responses for plants grown in full sunlight. Plants grown in full sunlight produced more biomass, tillers and leaves, and allocated a larger proportion of their total production to roots than plants grown in shade. The accumulation of root and shoot biomass over the first two months of seedling growth was primarily responsible for the larger size at harvest of plants grown in full sunlight. Plants grown under 60% and 90% shade flowered an average of 2 and 6 weeks later, respectively, than plants grown in full sunlight. Regrowth after clipping was greater for plants grown in full sunlight compared to those grown in shade. Even a one-time clipping delayed flowering and seed maturation; the older the individual when leaf area was removed, the greater the delay in its phenology. Repeated removal of leaf area was more frequently fatal for plants in shade than in full sunlight. For plants originally grown in full sunlight, regrowth in the dark was greater than for shaded plants and was more closely correlated to non-flowering tiller number than to plant size. This correlation suggests that etiolated regrowth is more likely regulated by the number of functional meristems than by differences in the size of carbohydrate pools. Thus, shading reduces the rate of growth, number of tillers, and ability to replace leaf area lost to herbivory for B. tectorum. These responses, in turn, intensify the effect of competition and defoliation for this grass in forests. B. tectorum is largely restricted to forest gaps at least in part because of its inability to acclimate photosynthetically, the influence of shade on resource allocation, and the role of herbivory in exacerbating these effects.
The effect of shading by a shrub legume on the growth and nutrient uptake of a C4 tropical grass was studied during four regrowth cycles. Regrowth periods were characterised by contrasting soil water availability. Dichanthium aristatum (Poir.) C. E. Hubbard swards were grown in full sun and under Gliricidia sepium (Jacq.) Walp. and Leucaena leucocephala (Lam.) de Wit with a light transmission level ranging from 80 to 30% of the incoming photosynthetically active radiation (PAR), depending on shrub regrowth. A treatment with high N and water supply was included in one of the cycles to quantify the effect of shade alone on potential growth.
Aboveground biomass (DM) and leaf area index (LAI) of swards were not depressed by the reduction of incoming PAR. The reduction in transmitted PAR by shrubs was compensated by an increase in the radiation use efficiency (RUE) of shaded swards. Higher RUE of unfertilised, shaded stands may be explained by higher levels of N availability in the soil. This is supported by the analysis of curves relating sward N accumulation to sward DM accumulation. In fact, for similar measured biomass the accummulated N was higher in shaded stands, a consequence of their higher N concentrations. This allowed shaded leaves to improve their CO2 assimilation rates on a leaf area basis. Higher RUE reported on shaded stands may be the consequence of higher leaf CO2 assimilation rates and also possible changes in the shoot:root ratio. As with N, the amount of K taken up by the sward was higher under shade, whereas P data were higher under shade only during the driest cycle. A positive water balance, alone or in combination with high N fertilisation, eliminated the improvement of the N nutrition of shaded stands. Thus, the positive effects of shade may be only observed when N and water are limiting sward growth in the open.
Incoming solar radiation (insolation) is fundamental to most physical and biophysical processes because of its role in energy and water balance. We calculated insolation maps from digital elevation models, using an insolation model that accounts for atmospheric conditions, elevation, surface orientation, and influences of surrounding topography. Herein, we focus on the application of this insolation model for spatial interpolation of soil temperature measurements over complex topography at landscape scales. Existing interpolation techniques generally apply only at continental or broad regional scales and do not capture the high variation of finer scales. In our field study in the vicinity of the Rocky Mountain Biological Laboratory, average soil temperature was correlated with insolation and elevation. Whereas daily minimum temperature was negatively correlated with elevation (r=−0.730, P<0.05), daily temperature change (maximum minus minimum) was positively correlated with daily insolation (r=0.504, P<0.01). We generated daily minimum and maximum soil temperature maps based on regression analyses. Residual variation was explained by factors such as vegetation cover. This application demonstrates the importance of characterizing spatial and temporal variation of insolation for studies of energy and water balance.
A wind tunnel study was performed to examine some turbulent characteristics and statistical properties of the concentration field developing from the steady release of a tracer gas at street level in a canyon amidst urban roughness. The experiment was conducted with the approaching wind direction perpendicular to the street axis and, with a street width to building height aspect ratio equal to one. Concentration time series were recorded at 70 points within the test street cross-section and above. Mean concentrations, variances and related turbulent quantities, as well as other statistical quantities including quantiles were computed. Concentration spectra and autocorrelation functions were also examined. The emphasis is put here on the results concerning mean concentrations and the variance of concentration fluctuations. The main objective of this paper is to put forward potential benefits of the experimental approach taken in this study. Through a simple and already widely studied configuration it is aimed to show how, for modelling purposes, this approach can help improving our understanding of the mechanisms of dipersion of pollution from car exhausts in built-up areas and, with further measurements, how it could assist in drawing specifications for siting monitoring networks.
Almost in all the major cities in Asian countries, residential buildings are characterized with high-rise and high density. Under this circumstance, achieving comfortable and healthy indoor environment with minimized energy consumption becomes a very challenging engineering and societal issue. While the wide use of air-conditioning helped to improve thermal comfort, health problems associated with poor indoor air qualities have appeared more frequently. The increased energy consumption is also a great concern in view of its impact on the energy economics of the region. Drawn from some of the onsite measurements and survey, and also the author’s personal observation, some of the key issues are discussed in this paper.
Efficient and economical technology that can be used to store large amounts of heat or cold in a definite volume is the subject of research for a long time. Thermal storage plays an important role in building energy conservation, which is greatly assisted by the incorporation of latent heat storage (LHS) in building products. LHS in a phase change material (PCM) is very attractive because of its high storage density with small temperature swing. It has been demonstrated that for the development of a latent heat storage system (LHTS) in a building fabric, the choice of the PCM plays an important role in addition to heat transfer mechanism in the PCM. Thermal energy storage in the walls, ceiling and floor of buildings may be enhanced by encapsulating or embedding suitable PCMs within these surfaces. They can either capture solar energy directly or thermal energy through natural convection. Increasing the thermal storage capacity of a building can increase human comfort by decreasing the frequency of internal air temperature swings so that the indoor air temperature is closer to the desired temperature for a longer period of time. This paper aims to gather the information from the earlier works on the developments of PCM's incorporation in building, the problems associated with the selection of PCM and the various methods used to contain them for space heating and cooling applications.
Urban heat island is among the most evident aspects of human impacts on the earth system. Here we assess the diurnal and seasonal variation of surface urban heat island intensity (SUHII) defined as the surface temperature difference between urban area and suburban area measured from the MODIS. Differences in SUHII are analyzed across 419 global big cities, and we assess several potential biophysical and socio-economic driving factors. Across the big cities, we show that the average annual daytime SUHII (1.5 ± 1.2 °C) is higher than the annual nighttime SUHII (1.1 ± 0.5 °C) (P < 0.001). But no correlation is found between daytime and nighttime SUHII across big cities (P = 0.84), suggesting different driving mechanisms between day and night. The distribution of nighttime SUHII correlates positively with the difference in albedo and nighttime light between urban area and suburban area, while the distribution of daytime SUHII correlates negatively across cities with the difference of vegetation cover and activity between urban and suburban areas. Our results emphasize the key role of vegetation feedbacks in attenuating SUHII of big cities during the day, in particular during the growing season, further highlighting that increasing urban vegetation cover could be one effective way to mitigate the urban heat island effect.
Maximum floor area ratio (FAR) regulation is widely imposed in cities to mitigate negative population externalities (e.g. congestion). This paper presents determination of optimal FAR regulation in a two-zone city with a growing population. Results show the following. 1) Maximum FAR regulation alone is generally insufficient. It should be accompanied by minimum FAR regulation in one zone. 2) Optimal regulation at a particular time depends on expected changes in zonal populations over the longest replacement time among newly built buildings at that time. 3) Zonal optimal FAR is expected to vary with time, which might even necessitate replacement of maximum FAR with minimum FAR, and vice versa.
By the method of stratified random sampling, the species composition and spatial structure of the plants in 53 parks in Beijing urban area were investigated, aimed to provide basic information for the protection of plant diversity in the parks and the management of the parks. A total of 492 plant species belong to 96 families and 283 genera were recorded. Based on the data of 21 investigation items about the trees, shrubs, and grasses in the study area and related statistical analyses, the plant structural patterns commonly seen in the green space of the parks of Beijing urban area were introduced. Among the plants in the parks, native species occupied 53.86% of the total. The chorological composition of the genera embraced broad kinds of geographical elements in China, and the predominance of dominant plants was remarkable. In most green patches of the parks, herbaceous species were more abundant and had higher coverage, shrubs had relatively low coverage and were less beneath tree canopy, and trees and shrubs had lower species richness and density. The canopy breadth and the diameter of breast height of trees as well as the breadth of shrubs and the heights of trees and shrubs were basically at the second grade, but the canopy structure of the trees were better, with good conditions of sunlight and growth. The crown missing of the shrubs was relatively low. It was suggested from correlation analyses and document survey of Beijing parks construction history that park landscape design, alien species introduction; and cultivation management were the main factors affecting the species composition and spatial structure of the plants in Beijing urban parks.