A microscale three-dimensional model of urban outdoor thermal exposure (TUF-Pedestrian)

Urban street design choices relating to tree planting, building height and spacing, ground cover, and building façade properties impact outdoor thermal exposure. However, existing tools to simulate heat exposure have limitations with regard to optimization of street design for pedestrian cooling. A microscale three-dimensional (3D) urban radiation and energy balance model, Temperatures of Urban Facets for Pedestrians (TUF-Pedestrian), was developed to simulate pedestrian radiation exposure and study heat-reducing interventions such as urban tree planting and modifications to building and paving materials. TUF-Pedestrian simulates the spatial distribution of radiation and surface temperature impacts of trees and buildings on their surroundings at the sub-facet scale. In addition, radiation absorption by a three-dimensional pedestrian is considered, permitting calculation of a summary metric of human radiation exposure: the mean radiant temperature (T_MRT). TUF-Pedestrian is evaluated against a unique 24-h observational dataset acquired using a mobile human-biometeorological station, MaRTy, in an urban canyon with trees on the Arizona State University Tempe campus (USA). Model evaluation demonstrates that TUF-Pedestrian accurately simulates both incoming directional radiative fluxes and T_MRT in an urban environment with and without tree cover. Model sensitivity simulations demonstrate how modelled T_MRT and directional radiative fluxes respond to increased building height (ΔT_MRT reaching -32 °C when pedestrian becomes shaded), added tree cover (ΔT_MRT approaching -20 °C for 8 m trees with leaf area density of 0.5 m² m^-3), and increased street albedo (ΔT_MRT reaching + 6 °C for a 0.21 increase in pavement albedo). Sensitivity results agree with findings from previous studies and demonstrate the potential utility of TUF-Pedestrian as a tool to optimize street design for pedestrian heat exposure reduction.