Introduction: Urban residential complexes in Seoul have faced severe flooding during recent extreme rainstorms, highlighting an urgent need for improved flood resilience in site planning. Traditional drainage design often overlooks landscape elements such as paving, outdoor furniture, and planting, yet these features significantly influence stormwater behavior. Building Information Modeling (BIM) offers a promising modeling-based approach to address this gap by virtually simulating drainage performance before construction. This study focuses on Landscape BIM – the application of BIM to landscape architecture – to model and evaluate stormwater drainage in large residential complexes. By using a detailed BIM model of the site, I aim to identify potential flood issues under extreme rainfall conditions and inform landscape design decisions to prevent real-world flooding events like those recently experienced in Seoul. Methodology: The research adopts a simulation-driven methodology. A representative residential complex in Seoul serves as the case study. Using Autodesk Revit, I developed a comprehensive 3D BIM model of the site’s landscape and infrastructure, incorporating topography, pavement materials (pervious and impervious surfaces), green spaces, and outdoor installations (benches, planters, etc.). This model is imported into Autodesk InfraWorks to perform stormwater drainage simulations. A design storm (e.g. a 100-year return-period cloudburst) is applied to the model to generate runoff and flow patterns. The simulation accounts for infiltration rates of different pavement types and the presence of vegetation. Key performance metrics such as runoff volume, peak discharge, and water ponding depth/extent are measured. No real sensor data are used; instead, the approach relies on scenario modeling based on historical extreme rainfall statistics. The drainage performance is evaluated for the existing design configuration, and then the model is iteratively used to test design interventions (for instance, adding bio-swales, enlarging drain inlets, or altering surface materials) to improve flood mitigation. Preliminary Results: Initial simulation results reveal several drainage hotspots in the base-case design, such as low-lying courtyard areas and main entranceways where water accumulates. In the current configuration, the virtual storm produced surface runoff exceeding the capacity of existing drainage points, leading to simulated ponding of over 20 cm in the worst locations. These findings prompted targeted design modifications in the BIM model – for example, replacing certain asphalt pathways with permeable paving and regrading around building entrances for better runoff diversion. Preliminary comparisons indicate significant improvements: peak runoff from the site is reduced and no major ponding occurs in the redesigned scenario under the same extreme rainfall input. The addition of green infrastructure elements (rain gardens and infiltration trenches within the landscape) further attenuated runoff, suggesting that an integrated landscape-based approach can substantially enhance flood resilience. While full results are forthcoming, the early outcomes demonstrate the effectiveness of a Landscape BIM workflow in predicting drainage issues and guiding data-informed design refinements. This modeling-centric approach can help urban planners and landscape architects proactively optimize open space layouts, surface materials, and planting schemes to mitigate flooding before a shovel ever breaks ground.