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Heat waves are becoming more intense and frequent due, in part, to land cover changes and urbanization that impacts the urban climate. Moreover, city morphology directly influences pollutant dispersion, resulting in major problems on residents’ comfort and well-being. Given cities’ increased vulnerability to urban overheating and air pollution, it is essential to have a high spatial and temporal resolution description of urban physical phenomena (temperature, pollutant concentrations etc.). Therefore, modeling and mapping are valuable tools, particularly for assessing vulnerability, anticipating risks, and supporting decision-making for adaptation policies in urban planning. In this context, the ANR City-FAB project brings together local authorities and researchers from Université Gustave Eiffel to support the transition to more sustainable territories. For the Hauts-de-Seine département, the project assists local authorities in the redeveloping of the RD920 roadway to improve coexistence between pedestrians, cyclists and vehicles, enhance safety, and address climate change challenges. In the City-FAB project, we propose a digital twin to evaluate urban comfort and air quality based on different planning scenarios, while facilitating dialogue with users and suggesting complementary approaches. We employ a multi-physical approach with high-resolution ENVI-met microclimatic and air quality simulations. Starting with a detailed geographic reconstruction of the study area using data from the National Institute of Geographic and Forest Information (IGN) and the Hauts-de-Seine Council (CD92) databases and creating a sufficiently accurate representation using an open-source Geographic Information System (QGIS). From the 3D geometric model, we conduct microclimatic simulations to generate district-scale maps at a 2-meter resolution of key physical phenomena, of pollutant concentrations and of thermal comfort, quantified by the Universal Thermal Climate Index (UTCI). Preliminary numerical results for the day of August 12th, 2022 showed that in exposed mineral areas, air temperatures are above 34 °C and mean radiant temperatures exceed 50 °C, leading to high UTCI values indicative of severe thermal stress for about 8 hours of the day. Importantly, shading provided by street trees on RD920 significantly decreases the heat stress by reducing UTCI values up to 5 °C on sidewalks. Regarding air quality, the simulation results show that several zones are exposed to high NO2 concentrations due to morning traffic, resulting in elevated ozone (secondary pollutant) concentrations by mid-day. A sensitivity analysis tool is then proposed to identify and quantify the parameters that most critically impact thermal comfort. This tool is thus useful to inform local decision-makers about the factors to prioritize in urban planning. In future work, we plan to refine and calibrate the model and validate our simulations using data from in-situ measurement stations. This will enhance its role as a predictive tool and provide valuable guidance for urban redevelopment strategies that adapt to evolving climatic challenges and ensure resident comfort.