Pappaccogli et al. (2025) MLUCM BEP + BEM: an offline one-dimensional multi-layer urban canopy model based on the BEP + BEM scheme

Identification

• Journal: Geoscientific model development
• Year: 2025
• Date: 2025-10-10
• Authors: Gianluca Pappaccogli, Andrea Zonato, Alberto Martilli, Riccardo Buccolieri, Piero Lionello
• DOI: 10.5194/gmd-18-7129-2025

Research Groups

• Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy
• Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands
• Atmospheric Modelling Unit, Environmental Department, CIEMAT, Madrid, Spain

Short Summary

This study develops and validates MLUCM BEP + BEM, an offline one-dimensional multi-layer urban canopy model, demonstrating its reliable reproduction of urban surface-atmosphere fluxes with significantly reduced computational demands compared to coupled mesoscale models.

Objective

• To develop and validate MLUCM BEP + BEM, an offline one-dimensional multi-layer urban canopy model, designed to reduce computational demands for urban microclimate simulations and assess its performance in reproducing surface-atmosphere fluxes.

Study Configuration

• Spatial Scale: A suburban site in Preston, Melbourne, Australia (Local Climate Zone 6). The model operates as a one-dimensional column with a vertical resolution of 1 meter up to 40 meters above ground level.
• Temporal Scale: Validation period of 16 months (12 August 2003 to 28 November 2004), with a 10-year spin-up period. The model integration time step is 60 seconds.

Methodology and Data

• Models used:
  • MLUCM BEP + BEM (Multi-Layer Urban Canopy Model based on Building Effect Parameterization and Building Energy Model).
  • Building Effect Parameterization (BEP; Martilli et al., 2002).
  • Building Energy Model (BEM; Salamanca et al., 2010).
  • One-dimensional vertical turbulent diffusion model (Santiago and Martilli, 2010) with updates to turbulent length scales and eddy coefficients inspired by Bougeault and Lacarrere (1989).
  • Modules for green areas (Zonato et al., 2021) and street trees (Stone et al., 2021).
  • For comparison: CM-BEM, TEB-SPARTCS, VTUF-3D, BEPCOL, REG1, REG3.
• Data sources:
  • Urban-PLUMBER project "in situ" eddy covariance observational data from Preston, Melbourne, Australia, for validation.
  • ERA5 global reanalysis data for gap-filling forcing data.
  • UT-GLOBUS database (Kamath et al., 2024) for detailed building distribution in the "Complex" experiment.

Main Results

• The MLUCM BEP + BEM model reliably reproduces upward shortwave radiation (SWup), upward longwave radiation (LWup), latent heat flux (Qle), sensible heat flux (Qh), and momentum flux (Qtau).
• Its overall performance is comparable to, and in several cases surpasses, other established urban models, with notable improvements in momentum flux (Qtau) simulation.
• The "detailed" experiment showed the best agreement for SWup (bias = 1.51 W m⁻², normalized mean error (NME) = 0.07, correlation (COR) = 1.00).
• All model configurations demonstrated strong capability in capturing LWup (NME 0.02–0.03, COR = 0.99).
• Latent heat flux (Qle) was slightly underestimated across all configurations, with the "complex" experiment showing improved correlation (0.64) and NME (0.88).
• Sensible heat flux (Qh) was slightly overestimated, with the "complex" experiment achieving the lowest bias (17.86 W m⁻²) and a slope of 1.03.
• Momentum flux (Qtau) was consistently and robustly represented across all experiments (bias 0.02–0.07 N m⁻², NME = 0.36, COR = 0.88), outperforming most other models.
• The model exhibits significantly low computational demands, running a one-year simulation in approximately 30–40 minutes on a workstation, compared to over a day for a 24-hour simulation with a coupled mesoscale model on a single core.
• Some refinements are still needed, particularly in modeling tree-soil moisture dynamics to reduce surface energy budget imbalances.

Contributions

• Development of MLUCM BEP + BEM, an offline one-dimensional multi-layer urban canopy model, which significantly reduces computational demands for urban microclimate simulations.
• Integration of advanced physics, including updated turbulent length scales, eddy diffusivity coefficients accounting for atmospheric stability, and explicit representation of urban vegetation (street trees and green spaces).
• Demonstrated competitive or superior performance in simulating key urban surface-atmosphere fluxes, particularly momentum flux, compared to existing urban models, even with standardized input data.
• Provides a flexible and efficient tool suitable for long-term climate simulations, assessing urban overheating, building energy demand, and evaluating urban mitigation strategies under various future climate scenarios.

Funding

• ICSC – Centro Nazionale di Ricerca in High Performance Computing, Big Data and Quantum Computing, funded by the European Union – NextGenerationEU (CUP F83C22000740001).

Citation

@article{Pappaccogli2025MLUCM,
  author = {Pappaccogli, Gianluca and Zonato, Andrea and Martilli, Alberto and Buccolieri, Riccardo and Lionello, Piero},
  title = {MLUCM BEP + BEM: an offline one-dimensional multi-layer urban canopy model based on the BEP + BEM scheme},
  journal = {Geoscientific model development},
  year = {2025},
  doi = {10.5194/gmd-18-7129-2025},
  url = {https://doi.org/10.5194/gmd-18-7129-2025}
}