Arboriculture & Urban Forestry 48(2): March 2022 advancement of ALS, understanding thermal dynam- ics between urban built environment and urban can- opy still requires additional modeling capability to decode the interwoven relationships among build- ings, streets surfaces, canopies, and local solar and climate conditions. Solely relying on ALS and other remote sensing data therefore cannot create an authen- tic model to simulate canopy shading effect accurately. There is a need for a model capable of reconciling buildings, streets, and urban canopies when simulating canopy shading effect. This study uses ALS remote sensing to create a comprehensive 3D model of the urban canopy in Vancouver, British Columbia, Canada. Using a Radiance-based simulation engine (Ward 1994; Roudsari and Pak 2013), the shading impact of the modeled canopy is studied on various horizontal and vertical urban surfaces under local climate condi- tions. This work consolidates urban canopy modeling through the integration of building energy modeling, remote sensing, and urban design, offering practical planning and research opportunities in understanding urban canopy shading dynamics. The complete data coverage (citywide with over 245,000 trees modeled) and spatial resolution (< 1 m) also provide a solid foundation for researchers interested in urban green- ness inequity, gentrification, and species adaptation (Gould and Lewis 2016; Nesbitt et al. 2019). MATERIALS AND METHODS The following sections introduce the study site, the pro- cessing of ALS, and solar irradiance simulation. Study Area: Vancouver, BC Located in the lower mainland of British Columbia (BC), Canada, the City of Vancouver (Vancouver here- after) has a population of 675,000 and a size of 115 km2 . The city has 2,645 ha of tree cover, giving its resi- dents appropriately 23% canopy cover citywide. This canopy is distributed unevenly across the city, with a general east-west divide of low/high canopy cover (Vancouver Board of Parks and Recreation 2020). Vancouver experiences a mix of an oceanic cli- mate (Köppen climate classification Cfb) and a warm- summer Mediterranean climate (Csb). Its summer is typically dry with an average of 8 hours of sunlight, 18 °C in day temperature, and 9.3 °C at night in August (Environment and Climate Change Canada 2021). As summers become increasingly warmer, the use of air conditioning (AC) in BC has tripled to 34% 97 since 2001, costing British Columbians around $300 in annual electricity bills per household (BC Hydro 2018). Shading from urban canopy can potentially eliminate the use of AC or at least allow a moderate AC usage (Akbari and Taha 1992). For every degree lower that an AC unit is set, the approximate cooling cost can increase by up to 3% (BC Hydro 2018). With its unique climate profile, variations of intracity can- opy cover, and increasing energy demand for cooling, Vancouver is an ideal case study. There are 22 neighborhood planning areas defined by the City of Vancouver. They vary in size from 217 to 907 ha. Building density and height are highest in and near Downtown areas, with the lowest-density neighborhoods being along the south and west edge of the city. Building heights range from 2 to 190 m, with the majority of buildings over 30 m located in the Downtown area. Data Acquisition and Processing In order to accurately simulate individual canopy shading effects on buildings and streets, 3 primary data layers were generated to represent buildings as a 3D model (including their location, heights, and ori- entation), streets as a 2D polygon (including their widths, lengths, and location), and lastly urban trees as a 3D model (including their height, crown sizes, densities, and shapes). A 3D building layer was derived by extruding the existing building footprints by their heights using Microsoft’s open building data (GitHub 2021) and BC Assessment Data (BC Assessment 2021). A 2D street raster surface was generated using Van- couver’s latest land cover and land use classification at 2-m spatial resolution (Metro Vancouver 2014). The advantage of using a raster-based street layer over a conventional vector-based (i.e., polylines) layer was to offer accurate measurement on the right- of-way (ROW), as a wider street will have more exposed surface than a narrow one. In addition, by including both a 3D building layer with building height information and a street ROW layer, the model can also take into account the aspect ratio (AR) defined by building height divided by the street width (H/W). Being able to accurately account for various ROWs was therefore critical to this model. A 3D tree canopy model was generated using a set of aerial laser scanning (ALS) point clouds (City of Vancouver Open Data Portal 2013). In 2013, Vancouver acquired a citywide ALS for the extent of its legal juris- diction with a minimal point density of 12 points/m2 ©2022 International Society of Arboriculture
March 2022
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