Integrating a three-dimensional urban canopy model into WRF for enhanced microclimate representation

This study presents the integration of a novel three-dimensional urban parameterization, the Three-Dimensional Urban Canopy Model (3DUCM), into the Weather Research and Forecasting (WRF) model (WRF/3DUCM). Differently from traditional urban sub-grid scale parameterizations implemented into mesoscale meteorological models that consider a simple two-dimensional canyon geometry, representative of the average urban morphology of the mesoscale model grid cell, 3DUCM is a single-layer urban canopy model taking into account every single building of the urban area for the evaluation of the energy budget. It considers canyon orientation and also includes canyon edge effects, i.e., explicit crossroads modelling. Model output incorporates not only average grid cell variables, but also predicted fields down to the building scale. In this work, WRF/3DUCM is tested in the city of Rome during a summer heat wave. Simulations benefit from detailed information on the geometric characteristics of the city, whereas physical properties of urban materials are assigned based on the local climate zone framework. Simulation results obtained with WRF/3DUCM are compared with those from simulations performed with WRF coupled with the default single-layer and multi-layer urban canopy parameterizations and evaluated against an observational dataset. The results highlight the potential of incorporating single-building details to improve the representation of urban microclimates with mesoscale meteorological models.