The effects of urban forms on photosynthetically active radiation and urban greenery in a compact city

Abstract

Urban greenery is increasingly recognized as an important component of urban ecosystems as it provides a range of ecosystem services for environmental and human wellbeing. However, the extent to which the performance of urban greenery is affected by availability of light in high-density urban environment is poorly understood. We examined the effect of shade on the levels of photosynthetically active radiation (PAR) in different urban forms, focusing on urban street canyon, vehicular flyovers, sky terraces, at-grade community gardens and rooftop community gardens surrounded by high-rise residential buildings. Within these urban forms, we examined the effects of PAR levels on the growth of shrubs, trees and palms. PAR was assessed though simulation using the building information modeling tool Ecotect, and direct measurements with quantum sensors. PAR was most reduced in sky terraces, with daily PAR restricted to about 15 % of unshaded conditions in Singapore. Daily PAR in rooftop community garden was about 60 % of unshaded conditions, whereas urban street canyon, planting area around and under vehicular flyovers and at-grade community garden had daily PAR of 41 to 52 % of unshaded conditions. Within these shaded environments, almost half of all shrubs and almost all flowering shrubs showed differences in vegetative and reproductive growth at lower PAR levels, respectively. Slenderness of trees was also significantly higher compared to trees grown in more unshaded conditions. The spatial distribution of PAR levels was highly non-uniform, with PAR differing between two and nine-fold within a site, and differed significantly to that of direct sunshine hours. These findings provide insights on how a better understanding of effects of shade on PAR helps to improve urban green space design and plant selection for better plant performance.

3D city models for urban farming site identification in buildings

“…This movement of the sun suggests a variation in PAR received at a given location. However, this variation during the year may not be significant in the context of this research due to the higher solar elevation given the equatorial position of Singapore (Tan and Ismail, 2015;Tablada and Zhao, 2016).…”

“…This movement of the sun suggests a variation in PAR received at a given location. However, this variation during the year may not be significant in the context of this research due to the higher solar elevation given the equatorial position of Singapore(Tan and Ismail, 2015;Tablada and Zhao, 2016).Figure8shows the role played by shadowing effects on a day-to-day basis. It can be seen from this figure that PAR received on different façades of the buildings was affected by the shadows casted by the building's own façades and surrounding buildings.…”

“…This is primarily because with limited land available for agriculture, these buildings offer underutilized horizontal and vertical spaces that may have farming potential (Figure 1). In addition, improvement of emotional, mental and physical well-being of the occupants (Tan and Ismail, 2015), mitigation of the urban heat island effect (Diehl et al, 2020), creation of job opportunities (Tablada and Zhao, 2016), and reduction in carbon emissions associated with transportation of food (Lim and Kishnani, 2010) are counted among the other benefits of farming in these buildings. In Singapore, urban farming carries special significance as it has been adopted as one of the 'Grow Local' strategies to achieve the '30 by 30' vision of the Singapore Food Agency (SFA) (Zulkifli, 2019).…”

Modeling Photosynthetically Active Radiation using a Spectrally Weighted Raytracing Approach

“…Early attempts to generate contextual PAR simulated maps were incorporated in Ecotect (Tan and Ismail, 2015), a currently defunct software that utilized a simplified calculation directly from solar irradiance. More recent methodologies (Subramaniam, 2020, Benis et al, 2017 leverage the partial overlap between the visible wavelength range and photosynthetically active wavelength range of the solar spectrum to simulate PAR.…”

Predicting sunlight availability for vertical shelves using simulation

“…PAR light depends on diurnal and annual temporal variations based on daytime weather and season. Different PAR light is due to the building's shape, orientation, self-shadowing effects, and shadowing effects of surrounding objects [9]. The results suggested that the structures that experience a minimum of half-day direct insolation will support the growth of plants that mostly fall within moderate to very high DLI categories.…”