Enhancing BEP-BEM for Urban Climate Modeling: Coupling with a 3D-TKE Scale-Adaptive PBL Scheme, Refining Urban Morphology, and Incorporating Urban Gardens

This study presents significant updates to the BEP-BEM (Building Effect Parameterization - Building Energy Model) urban canopy parameterization, aiming to improve the representation of atmospheric flows in urban areas. The enhancements include the coupling of BEP-BEM with a hybrid LES-RANS planetary boundary layer (PBL) scheme and the incorporation of a novel urban gardens model. Furthermore, the urban vegetation fraction is computed in greater detail using the Corine Land Cover, improving the representation of vegetation-atmosphere interactions within urban environments. These advancements collectively aim to enhance the accuracy of urban climate modeling under extreme weather conditions such as heat waves.

Traditional RANS-based PBL schemes struggle to capture horizontal turbulence and urban canopy-layer interactions effectively. To overcome these limitations, this study introduces a novel 3D TKE Scale-Adaptive PBL scheme. This scheme blends local and non-local components to enable the concurrent application of 3D TKE, RANS, LES, and BEP-BEM. This approach ensures a more physically consistent representation of turbulence within the boundary layer.

To validate these updates, a detailed case study is conducted for the Ruhr area, Germany, during the July 2019 heatwave (July 19–28). The model evaluation leverages ~1700 quality-controlled crowd weather stations from the Netatmo network, providing a unique opportunity to assess the performance of urban parameterizations at high spatial density. Three urban morphology datasets are compared, including one refined using WUDAPT_INTERP, which applies W2W-based interpolation techniques to improve LCZ mapping precision.

Findings indicate that the newly developed 3D TKE LES-RANS closure with BEP-BEM, combined with the refined urban morphology dataset, significantly enhances temperature predictions, particularly for minimum temperatures. This improvement suggests a better representation of horizontal advection processes and stable boundary layer structures. Moreover, the integration of urban gardens as a distinct urban canopy element introduces additional surface heterogeneity, demonstrating localized cooling effects and a potential improvement in thermal comfort.