Quantifying the shade provision of street trees in urban landscape: A case study in Boston, USA, using Google Street View

Shade provision by street trees during the hot summer months is a primary factor for the thermal comfort of people in urban areas. In this study we present a novel method to estimate the shade provision of street trees in the downtown area of Boston, Massachusetts using a quantification of the sky view factor (SVF) from street-level imagery. The SVF is an indicator to quantify the level of enclosure of street canyons. It has been widely applied and has become a standard metric employed by urban designers because it relates to the amount of direct solar radiation reaching the ground and, thus, holds direct implications on the thermal comfort of citizens. In a novel methodology, Google Street View panoramas were used to represent the street canyon unit and to compute the SVF. Street-level imagery allowed us to consider obstructions along street canyons without relying on simplifications or simulations of the environment. In turn, a building height model was used to calculate the SVF, considering only the obstruction of solar radiation by building blocks. Thus with these two quantifications of the SVF, the difference between the two SVF estimations were treated as an estimate of the shading effect of street trees. In the case of Boston, the results showed that the street trees decrease the SVF by 18.52% in the downtown areas. This study can provide an important reference for future urban greening projects for urban climate moderation.