Building shading affects the ecosystem service of urban green spaces: Carbon capture in street canyons
Graphical abstract
Introduction
Along with the global urbanization process, the contradiction between the persistent population migration into cities and the shortage of land sources has driven architectural designers and municipal administrators to explore urban space at the vertical dimension (Watts et al., 2010). Consequently, the urban building environment has dramatically transited from the original style of low-rise and low-density buildings into a modern style with tall, large, and high floor area ratio features (Joshi and Kono, 2009). Especially in rapidly developing economies and regions, the average building volumes and heights in different scales of cities are constantly increasing (Pan and Wei, 2015).
Compared to low-rise buildings, high-rise buildings occupy far fewer land sources at the same usable floor area. Besides, skyscrapers can reduce the construction of pipeline network and other public utilities, cut down investment per unit area, and provide substantial socioeconomic benefits (Watts et al., 2010). In recent years, however, the increase in high-rise buildings within the boundaries of urban systems has presented the intensive characteristics of continuous clusters, and the structures tend to be more complicated, which largely reshapes urban skylines, and leads to microclimate variation at the city's underlying surface, thereby causing a series of eco-environmental effects (Niu, 2004). The urban building system and its environmental effects have become a multi-disciplinary research hotspot involving architecture, urban ecology, landscape planning, and management (Cheema and Abdur, 2015).
Generally, the existing studies involving building environmental effects are mainly focused on different aspects of the residual environment (light, wind, thermos, pollutants, etc.).
The screen effect is one of the most important research directions in studies of the urban building environment. With the number of vehicles rising sharply, a large number of studies have focused on the variation in the wind field in “street canyons”, thereby influencing the dispersion of pollutants and particulate matters from vehicle exhaust (Baik et al., 2007; Habilomatis and Chaloulakou, 2015; Zhong et al., 2015). On-site multipoint continuous observations, scaling model control experiments (wind tunnel, flume experiments, etc.), and numerical simulations based on Computational Fluid Dynamics (CFD) were conducted to explore the effects of building geometrical shape, roof wind, and heat on the dynamic pollutant dispersion characteristics in the complex flow field environment (Baik et al., 2007; Huang et al., 2009; Pavageau and Schatzmann, 1999).
With the process of rapid urbanization, buildings, roads, squares, and other artificial impervious surfaces have replaced vast natural surfaces, which thereby change the hydrothermal exchange of the underlying surfaces (Xu et al., 2018). For the urban thermal effect induced by the building environment, researchers have mainly conducted field measurements, thermal infrared remote sensing inversion, and thermodynamics analysis to study the spatiotemporal temperature fluctuation and time lag characteristics (Chen et al., 2006; Creutzig et al., 2017; Oke, 2017; Peng et al., 2012). Moreover, some scholars have investigated the relationship between the thermal effect of modern building materials and urban heat islands, as well as energy conservation and somatosensory comfort of buildings, from the meteorological perspective (Mirrahimi et al., 2015; Pasupathy et al., 2008; Perini and Magliocco, 2014).
High-rise buildings accommodate a larger population due to their large volumes. However, the excessive configuration of skyscrapers causes immense pressures on traffic control, energy supply, and public safety (Deng et al., 2016). In addition, from the view of urban planning, blind construction and irrational distribution would impair the harmony of urban landscapes and destroy the original cultural scenes (Whitehand and Gu, 2010).
For the urban daylight environment, the gathering of large buildings around streets blocks overhead solar radiation, forming dim street canyons. With variations in the solar elevation angle, a massive contiguous shadow projects onto the surroundings, severely impacting the internal residual environment and the eco-environmental condition of nearby streets (Yu et al., 2009). To date, studies of the effects of the urban building environment on daytime solar radiation have focused primarily on (a) indoor comfort analysis (Marino et al., 2015), (b) guidance of rooftop solar panel distribution based on local solar radiation analysis (Erdélyi et al., 2014; Hofierka and Kaňuk, 2009; Yadav and Chandel, 2013), and (c) solar radiation effect on pollutant dispersion in street canyons (Xie et al., 2005) but have rarely linked the environmental factor to the typical ecological process caused by the variation in the building environment (Pugh et al., 2012).
As mentioned above, the spatiotemporal heterogeneity of incoming solar radiation drives many of the earth's physical and biological processes (e.g., air and soil temperature regimes, evapotranspiration, snowmelt patterns, soil moisture, and light available for photosynthesis) (Budyko, 1969). In the urban daytime light environment, the artificial structures directly change the spatial distribution of ground-received solar radiation, shorten the sunshine duration, weaken the radiation intensity and alter the spectral composition, consequently forming a typical artificial overshadow environment (Bertamini et al., 2006; Valladares et al., 2012). As relevant research indicated, building shade leads to a severe attenuation of near-ground shortwave radiation in cities, which declines to 21%−95% of solar radiation on open ground (Kjelgren and Clark, 1992). Hamerlynck found that the sunlight intensity under the typical building shading environment in New Jersey declined to 10–15 μmol m−2 s−1, which was smaller than 1.5% of total solar radiation intensity (Hamerlynck, 2001). Navrátil and Bell et al. compared the shading spectra between buildings and vegetation canopy and found that the proportion of blue rays in shortwave radiation under the building shade circumstances was higher than that of canopy shade, indicating that building shading filtered fewer blue rays (Bell et al., 2000; Navrátil et al., 2007).
Further, the light environment is closely related to photosynthesis. Street canyons enclosed by buildings are a significant zone for urban greening, and their unique daytime light environment directly causes variation in photosynthesis and carbon storage rates of plants and indirectly affects plant growth and physiological development, such as blossoming and fruiting (Getter et al., 2009; Szeicz, 1974). Such changes and effects severely challenge the exertion of ecological service function and the management of urban greening. Thus, conducting a 3D-based systematic analysis to reveal how urban buildings, featuring different shapes and uneven spatial distributions, change the ground solar radiation and further impact the carbon sequestration process of surrounding greening plants dynamically, can provide methodological and technical support for the study of efficient utilization of sunlight resources in street canyons, sound planning for urban green space, and eco-friendly building designs that support ecosystem services promotion.
However, since such interdisciplinary research involves the coupling of multiple physical and ecological processes (e.g., 3D modeling, light transmission, and vegetation photosynthesis) between the urban building subsystem and the urban green space subsystem, quantitative studies are rare. Most of the studies concerning the effects of shading on photosynthesis mainly implemented potted plant experiments at different shading levels using light incubators (Cruz, 1997; Pierson et al., 1990). Those studies were unable to reflect the complex light environmental characteristics in real urban street canyons. Besides, the green spaces in cities are highly biodiverse, owing to the pursuit of landscape beautification (Hope et al., 2003). Reportedly, the built-up area of Beijing possesses 255, 101, and 122 species of herbaceous plants, shrubs, and trees, respectively (Zhao et al., 2009). The change of biodiversity under the high-intensive human disturbances also increases the difficulty of assessing carbon capture capacity at the block or urban scales.
In this study, a new approach combining radiation simulation and in situ observations was proposed. The dynamic changes of buildings on the spatial distribution of solar radiation, as well as the effects on the photosynthetic carbon capture of the surrounding green space, were investigated on July 10, 2017, aiming to assess potentially impairs the ecological service of the urban green space and provide support towards sustainable urban spatial planning and management.
Section snippets
Study area
The Beijing Central Business District (CBD) is located between the East 2nd and 4th ring roads (116°26′32″−116°28′24″ E, 39°54′10″−39°55′18″ N) and has an area of 3.9 km2 (Fig. 1). The CBD houses many Chinese headquarters of Fortune Global 500 enterprises, including finance, insurance, real estate, and IT industries; the district also possesses plenty of magnificent super-high buildings (Guo and Shan, 2017). Some landmark buildings include the CCTV buildings and the Chinese headquarters of
Object interpretation and DSM building
The ground objects in the CBD were interpreted from the Worldview 3 image (Aug 2017, 0.5 m). Via in situ investigation, the revised shapefiles were used for updating the land use information (Fig. 3). The floor area of various buildings was 0.92 km2 and the area of green space was 0.82 km2, which accounts for 23.6% and 21.0% of the total area in the CBD, respectively. More specifically, the areas of trees, shrub, and grassland communities were 0.57, 0.16 and 0.09 km2, respectively, which
Scenario analysis of building height-increasing impact on the carbon capture of urban vegetation
In Fig. 10, the results indicated that the overall increment of building height pro rata was significantly negatively correlated with the daytime carbon capture of the surrounding green space (p < 0.01). When the building height increased by 10%, the average carbon capture decreased by 0.24±0.06 tCO2•d−1; namely, 0.29 tCO2•km−2 d−1 in the CBD. In Scenario 5, when the building height increased by one floor, the carbon capture of the green space declined by 0.40 tCO2•km−2 d−1. The above findings
Conclusions
Urban ecosystems play an increasingly important role in global climate change (Pataki et al., 2010). Currently, the urban building environment is undergoing considerable changes following old town renewal and new district construction projects in those emerging countries. From the perspective of the urban artificial – natural coupling ecosystem, this study targeted the variation in the daylight environment in street canyons caused by urban buildings and the variation in sun elevation angle, as
Credit author statement
We certify that this manuscript has not been published previously and will not be submitted elsewhere for publication. All authors of this paper have directly participated in the study and have read and approved the final submitted version.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research was supported by the National Foundation of Natural Sciences of China (41501595), and the China-Thailand MSP Collaborative Study Project (B19029).
References (47)
- et al.
Modeling reactive pollutant dispersion in an urban street canyon
Atmos. Environ.
(2007) - et al.
Analyzing building-height restrictions: predicted impacts and welfare costs
Reg. Sci. Urban Econ.
(2005) - et al.
Remote sensing image-based analysis of the relationship between urban heat island and land use/cover changes
Remote Sens. Environ.
(2006) - et al.
The study of the effects of building arrangement on microclimate and energy demand of CBD in Nanjing
China. Procedia Eng
(2016) - et al.
Three-dimensional SOlar RAdiation Model (SORAM) and its application to 3-D urban planning
Sol. Energy
(2014) - et al.
A geometric solar radiation model with applications in agriculture and forestry
Comput. Electron. Agric.
(2002) - et al.
Solar radiation intensity influences extensive green roof plant communities
Urban For. Urban Gree.
(2009) - et al.
A CFD modeling study in an urban street canyon for ultrafine particles and population exposure: the intake fraction approach
Sci. Total Environ.
(2015) - et al.
Assessment of photovoltaic potential in urban areas using open-source solar radiation tools
Renew Energy
(2009) - et al.
Impact of wedge-shaped roofs on airflow and pollutant dispersion inside urban street canyons
Build. Environ.
(2009)
Optimization of floor area ratio regulation in a growing city
Reg. Sci. Urban Econ.
Mapping of the indoor comfort conditions considering the effect of solar radiation
Sol. Energy
Some significant environmental issues in high-rise residential building design in urban areas
Energy Build
Phase change material-based building architecture for thermal management in residential and commercial establishments
Renewable Sustainable Energy Rev
Wind tunnel measurements of concentration fluctuations in an urban street canyon
Atmos. Environ.
Effects of vegetation, urban density, building height, and atmospheric conditions on local temperatures and thermal comfort
Urban For. Urban Gree.
Conserving urban landscape heritage: a geographical approach
Procedia Soc. Behav. Sci.
The impact of solar radiation and street layout on pollutant dispersion in street canyon
Build. Environ.
Measuring spatio-temporal dynamics of impervious surface in Guangzhou, China, from 1988 to 2015, using time-series Landsat imagery
Sci. Total Environ
Tilt angle optimization to maximize incident solar radiation: a review
Renewable Sustainable Energy Rev
Modelling the dispersion and transport of reactive pollutants in a deep urban street canyon: using large-eddy simulation
Environ. Pollut.
Beijing Meteorological Service
Spectral irradiance available for turfgrass growth in sun and shade
Crop Sci
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