The influence of vegetation structure on urban microclimate: A CFD analysis of urban block and vegetation densities

Urbanization has a considerable impact on the Urban Heat Island (UHI) effect and results in a negative impact on outdoor thermal comfort. In this context, vegetation can be an important lever in alleviating the UHI. Various types of sizes, and densities of vegetation offer different levels of cooling effects in the surrounding areas thereby enhancing thermal comfort.

This paper assesses the impact of urban block layouts and varying vegetation densities on the urban microclimate specifically focusing on the regulation of humidity and air temperature. The objective is to determine how variations in vegetation types, densities, and sizes specifically influence the microclimate. We used Computational Fluid Dynamics (CFD) to analyze airflow patterns, temperature differences, and humidity levels in three different locations on a university campus in Atlanta, Georgia. The vegetation is modeled with different levels of porosity and sizes. The Leaf Area Density (LAD) is a measure that quantifies the leaf surface area in a given volume of vegetation. LAD affects the heat balance of the leaves which affects the surrounding temperature. The density of LAD determines the extent of shading and cooling effects through transpiration and absorption of solar radiation process. The higher the density would generally experience more shading and reduced temperatures, which is essential for regulating urban microclimate. The Universal Thermal Comfort Index (UTCI) is used to show the reduction in the temperature and thermal stress in and around the vegetation regions. The simulation will be investigated in a three-dimensional urban microclimate setting inside the Rhinoceros3d modeling software and carried out using the ‘urbanmicroclimatefoam’ solver in OpenFOAM. Trees are modeled as porous zones where LAD value is set to non-zero.

Through this study we aim to propose guidelines for Sustainable analysts and Urban planners on the influence of vegetation in outdoor temperature and its impacts on local microclimate and neighborhood buildings.