Developing an Urban Canopy Model for Neighborhood Scale Thermal Exposure Assessment

Mesoscale modeling is a powerful tool for assessing urban climate and has been widely used to evaluate various mitigation strategies for addressing urban overheating, and consequently thermal comfort, at the neighborhood and city scale. However, to date, mesoscale modeling has mainly focused on the analysis of urban air temperature, neglecting the variability in mean radiant temperature and wind speed at the pedestrian level that highly affect thermal comfort in cities. This is mainly due to limitations of mesoscale models in assessing the spatial distribution of environmental parameters at the microscale. Urban canopy models (UCMs) have been developed to approximate the net impact at the grid scale of the flow and thermal exchanges from the 'subgrid' scale phenomena and to couple with mesoscale models. The recent developments on the multi-layer urban canopy model, BEP-Tree (Krayenhoff et al., 2019), represents such UCMs that model urban energy exchange and flow at the neighborhood scale considering the interaction between buildings and trees. To assess thermal comfort more comprehensively, this study aims to a) extend the BEP-Tree model to estimate the spatial variability of mean radiant temperature in the street canopy and b) using previous microscale simulations of urban flow, parameterize the extent of wind speed variability with urban density. Together with the mesoscale assessment of urban temperature, these parameterizations provide a comprehensive set of environmental parameters for thermal comfort and therefore, the variability in thermal comfort indices can be estimated at the neighborhood scale. Lastly, to incorporate the temporal variability of thermal comfort, we plan to incorporate metrics such as Outdoor Thermal Comfort Autonomy (Nazarian et al 2019) at the mesoscale such that the performance of urban neighborhoods with regards to thermal comfort and heat stress is comprehensively assessed.