Arboriculture & Urban Forestry 48(2): March 2022 Arboriculture & Urban Forestry 2022. 48(2):95–112 https://doi.org/10.48044/jauf.2022.008 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & Modeling the Shading Effect of Vancouver’s Urban Tree Canopy in Relation to Neighborhood Variations By Yuhao Lu, Justin McCarty, Jeri Sezto, Zhaohua Cheng, Nicholas Martino, Cynthia Girling, Adam Rysanek, Sara Barron, and Giona Matasci Abstract. Background: Cities consume a disproportionate amount of energy for internal temperature regulation. Being able to reduce cities’ cooling load on hot summer days can decrease energy consumption while improving occupants’ thermal comfort. The urban canopy is an effec- tive shading agent, adding cooling benefits to existing buildings and streets while providing other ecological and physiological values. Yet the building and street shading dynamic is a highly complex system that involves micro-level building components and macro-level variables. Introducing urban canopy to such a complex system creates another challenge, as urban canopy variables can also interact with buildings at both micro- and macro-levels. In order to accurately represent the urban canopy shading effect, it is necessary to account for the interactions among buildings, streets, and urban canopies. Methods: This study simulates the shading effect of urban canopy measured by aerial laser scan- ning (ALS) in the City of Vancouver, Canada, through the integration of a Radiance daylight simulation engine and geographic information system (GIS) data. All trees detected by ALS were included in the analysis. Results: The results indicate that street surfaces receive more solar irradiance reduction than building roofs and façades (i.e., exterior walls). Neighborhoods with less density and lower buildings were shaded noticeably better than areas with higher density and taller buildings. Among Vancouver’s 22 neighborhoods, 2 neighborhoods, Kitsilano and the West End, demonstrated a promising sign where both building density/height and urban canopies are maintained. There was evidence of high canopy shading and high-density urban morphologies. Conclusion: Overall, this work provided an authentic canopy assessment from sin- gle building to city scale, creating opportunities to investigate intracity urban canopy variations, equality, and the balance between urban green- ing and urban densification. Keywords. 3D Tree Canopy Mode; Aerial Laser Scanning; Canopy Shading; Radiance Model; Street Trees; Urban Forestry. 95 INTRODUCTION Covering approximately 3% of the terrestrial surface, cities consume a disproportionate amount of energy and are therefore a major emitter of greenhouse gas- ses (GHGs). In Canada, cities are responsible for over 42% of the GHG emission (Torrie 2015). As a result, local municipalities have included various measures to reduce GHG emissions through either improving operational efficiency (i.e., higher building perfor- mance standards), reducing energy demand (i.e., dis- courage private vehicle usage), or both. Cities tend to have higher air and land surface temperatures than surrounding landscapes (known as the urban heat island, or UHI, effect), with a difference ranging from 1 to 3 °C (Rosenfeld et al. 1995), but sometimes can exceed 10 °C (Stone et al. 2010; Stone et al. 2012). Climate change, along with fast urbanization, has caused cities more intense and frequent heat waves, which are periods with exceptionally high tempera- tures (Li and Bou-Zeid 2013). Currently, over 60% of the urban population is experiencing above-average temperatures in cities compared to nonurbanized areas (Estrada et al. 2017). City dwellers face increased heat-related health and safety risks due to the synergetic relationship between UHI and heat wave effects (Li and Bou-Zeid 2013), adversely impacting not only local and regional cli- mates but also ecosystem function and human health (Grimm et al. 2008). For example, in the United States, extreme heat events have caused the highest number of climate-related fatalities (Stone et al. 2010). Climate change is only expected to exacerbate heat risk in the urban environment, which will lead to the use of space cooling technologies and consequently ©2022 International Society of Arboriculture
March 2022
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