Urban microclimate modeling of a 2D street canyon for pedestrian thermal comfort: a case study in Toulouse, France

As climate change intensifies and urban areas expand, city dwellers become more exposed to heat stress. The built environment plays a significant role in shaping local microclimates through complex interactions between radiation, airflow and materials. Understanding these interactions is essential to developing effective mitigation strategies.

This study presents a two-dimensional urban microclimate model developed using COMSOL Multiphysics to simulate the thermal and radiative dynamics within a street canyon. The street is represented by two façades and one ground. The model couples a radiative model that accounts for multiple reflections, a thermal model solving the heat equation within building façades and ground, and an aeraulic model which solve the flow inside the street while considering buoyancy effects. In addition, a thermal comfort model allows to calculate the radiative flux absorbed by a human by means of Mean Radiant Temperature (Tmrt). Thermal comfort indicator such as the Universal Thermal Climate Index (UTCI) is calculated through Tmrt, temperature and velocity of the air at the pedestrian level. This model establishes heat balances with detailed resolution, making it possible to quantitatively attribute the impact of each physical phenomenon on the urban microclimate and thermal comfort.

The developed model is applied to a case study in Toulouse, France, where multiple streets with varying geometries, orientations and materials are analyzed. The choice of streets varies from a narrow canyon in the city center to more open streets in the outskirts. Meteorological conditions representative of summer heat waves are used to conduct microclimate simulations. Toulouse has a temperate climate and its buildings are mainly made of brick. The results highlight the impact of urban morphology, material properties or meteorological conditions on thermal comfort.