Impact of Shading on Urban Surface Energy Balance and Microclimate

Understanding how urban surfaces exchange energy with the atmosphere is crucial for predicting microclimate variability and improving urban resilience. This study investigates the role of shading distribution on the surface energy balance (SEB) in urban environments at both micro- and neighborhood scales. Using the building-resolving large-eddy simulation (LES) code uDALES, we model a realistic vegetated urban setting under convective conditions. Two solar zenith angles (0° and 45°) are considered while maintaining constant incoming shortwave radiation to isolate shading effects.

Our results show that shading significantly influences local SEB fluxes, particularly net shortwave radiation and sensible heat flux, which differ by approximately 424 Wm⁻² and 277 Wm⁻², respectively, between shaded and sunlit surfaces. Despite these variations, domain-averaged SEB fluxes remain largely unchanged, except for latent heat flux, which is 22% higher when the sun is directly overhead. Additionally, while the mean radiant temperature (MRT) varies only slightly between cases (ΔMRT = 0.19 K), localized effects are substantial: unshaded areas at 45° zenith experience MRT values up to 10 K higher due to increased radiative contributions from walls.

These findings highlight the critical influence of shading distribution on urban microclimates, emphasizing the need for high-resolution modeling in climate-sensitive urban planning. By explicitly resolving shading effects, this work advances our understanding of urban thermal dynamics and provides valuable insights for improving thermal comfort and reducing heat stress in cities.