A New 3D Urban Building Community Model for Earth System Modeling: Model Formulation and Evaluation

A new three-dimensional (3D) urban canopy model is presented. Unlike the two-dimensional (2D) canyon assumption used in most urban canopy models, this model proposes a 3D building community conceptualization. A key parameter, the ratio of building height to side length (H/L), is introduced to replace the ratio of building height to street width (H/W) used in canyon models. Based on this 3D framework, new 3D radiation transfer and turbulence exchange models are developed, both of which explicitly account for vegetation. A comprehensive representation of human activities is also incorporated. This paper introduces the new 3D urban building community model (UBCM), including the model structure and parameterizations of radiation, turbulence, thermal processes, hydrology, and human activities, with a focus on differences from existing urban parameterizations. Furthermore, the model is evaluated using both idealized Monte Carlo experiments and simulations at a representative urban site. The results demonstrate that the 3D urban building community model accurately captures urban radiative and turbulent fluxes. This model is designed to better represent real-world urban structures and to make optimal use of 3D morphology data. As an urban component of land surface models, it is suitable for weather and Earth system modeling and can be applied from mesoscale to large scales at high resolution. The corresponding urban datasets and comprehensive model evaluation are presented in the companion paper.