Integrating urban vertical diffusion model into SLUCM: model development and validation

Frequent occurrences of high temperatures and humidity within urban areas adversely affect residents' health and increase building energy consumption. Precise modeling of urban climates to elucidate the vertical distribution characteristics and evolutionary patterns of meteorological elements within urban canopies is of significant value for enhancing the accuracy of thermal comfort assessments and supporting the development of livable and sustainable cities. However, while most previous studies focus on the horizontal variability of urban microclimates, limited research investigates the vertical profiles of meteorological variables and their temporal characteristics. This study develops an Urban Vertical Diffusion Model (UVDM), integrated with the Single-Layer Urban Canopy Model (SLUCM), to simulate temperature, humidity, and wind profiles in complex urban terrains. It elucidates the mechanisms by which urban land processes affect the vertical structure of local meteorological elements, thereby improving simulation accuracy. The technical approach involves introducing a vertical transport sub-model for urban meteorological elements based on a one-dimensional vertical diffusion equation. During development, the k-l turbulence parameterization model is used to determine the vertical distribution of the diffusion coefficient. Given the complexity of heat and moisture source distribution within the urban canopy, this study enhances the reliability and accuracy of calculating these sources by integrating with the self-developed Urban Canopy-Building Energy Model (SLUCM-BEM) based on field observations from various terrains. Upon establishing the vertical profile parameterization scheme, the model is evaluated and validated using field observation data and results from the ENVI-met 3D microclimate simulation software. The findings indicate that the newly developed UVDM can stably simulate long-term local climates, providing reasonable results in the vertical distribution characteristics of meteorological elements and their diurnal variations. After validation, a series of sensitivity tests are performed, and the temporal characteristics of the profiles in different urban neighborhoods are investigated.