Parameterizing urban canopy radiation transfer using three-dimensional urban morphological parameters

Abstract

The radiative schemes in urban canopy models are typically based on the two-dimensional street canyon model, which cannot fully capture the three-dimensional geometries in East Asia cities. This study addresses this limitation by parameterizing radiative flux by three-dimensional urban morphology parameters: frontal area density (λ_f) and plan area density (λ_p). The parameterization is supported by simulation results from the newly developed building-resolving radiative model (PyUray), which utilizes the Monte Carlo ray tracing method to achieve high accuracy and leverages GPU processing to accelerate simulation. The PyUray model is fully validated by comparing the urban canyon albedo with field measurements from the SOMUCH project. To support the parameterization, the solar gain and longwave radiative heat loss at ground surfaces and urban canyon surfaces are evaluated at various λ_f (0.16 ≤ λ_f ≤ 2.49) and λ_f (0.16 ≤ λ_p ≤ 0.83) using PyUray. With regression models, this study formulates functions to estimate the radiative flux of urban surfaces using three-dimensional morphological parameters λ_f and λ_p, along with the three-dimensional solar direction. The simulation indicates that λ_f and λ_p have different impacts on the net radiative absorption of the urban canopy layer, with ground and street canyon surfaces exhibiting different responses to these morphological parameters.