PALM-SLUrb v24.04: A single-layer urban canopy model for the PALM model system – Model description and first evaluation

Abstract. Urban areas are recognized as critical zones for climate research due to the high number of people living in these areas and their significant impacts on local and regional climates. However, understanding urban boundary layer processes remains a challenge, as existing mesoscale models cannot resolve their fine-scale features and dynamics, while microscale fluid dynamics simulations remain computationally expensive or unfeasible for the full extent of the urban atmosphere. To address this gap, we present PALM-SLUrb, a single-layer urban canopy model for the PALM model system, offering a computationally efficient and physics-based model to represent urban surfaces on non-building-resolving grids. Together with the model description, we present sensitivity tests and a model comparison against grid-resolved urban canopies to demonstrate the model’s performance. The results demonstrate the model's ability to extend the representation of key urban–atmosphere interactions in PALM into coarser grid resolutions on the order of 10 metres. By bridging the gap between computational efficiency and physical detail, PALM-SLUrb broadens PALM's capabilities in advancing urban climate research.