Numerical modeling of urban microclimate in a real compact area in the Mediterranean region: impact of urban morphology

The combination of urbanization and climate change provides several challenges to the built environment, such as the mitigation of heat waves and the Urban Heat Island (UHI) effect. Summer heat waves and the UHI effect are likely to cause thermal discomfort and increased heat-related morbidity and mortality in urban areas. This can be more problematic for the Mediterranean area, since recent studies have identified it as a hot spot of future climate change. Knowledge of the microclimate in real urban areas is therefore essential for evaluating and implementing mitigation strategies to reduce heat stress and improve comfort in cities. In the last decades, Computational Fluid Dynamics (CFD) has proven to be a useful tool to investigate the urban microclimate. Although, CFD has been used to investigate wind flow, pollutant dispersion, outdoor and indoor thermal environment in both idealized and real urban areas, the impact of different street widths, building heights, and urban arrangements has been studied mainly for idealized urban configurations. Therefore, a detailed evaluation of the impact of urban morphology on microclimate for real complex areas with the Mediterranean climate has not yet been carried out. In this study, CFD simulations are performed to investigate the microclimate in the Tuscolano-Don Bosco district as a compact urban area in the city of Rome, Italy. The outdoor thermal comfort conditions in different urban morphologies are assessed using the universal thermal comfort index (UTCI). The Tuscolano-Don Bosco district, located in the South-East of Rome, is about 7.5 km2 large. It is composed of different urban morphologies and several narrow streets. The average height of buildings is about 22 m with the highest building of 40 m. The vegetation level inside the area is low. The dimensions of the computational domain are 5000x5000x240 m3 (length x width x height). The computational grid consists of about 103 million hexahedral cells. The 3D unsteady Reynolds-averaged Navier-Stokes (URANS) equations with the realizable k-ε turbulence model are performed in combination with the energy equation. The P-1 model is employed to calculate the solar radiation and buoyancy is modeled with the Boussinesq approximation. The inlet boundary conditions are determined based on meteorological data obtained from the Ciampino airport, approximately 5 km far from the Tuscolano-Don Bosco district. The simulations are carried out for four days between 13th and 16th July, 2009. The resulting surface temperature is validated using experimental data from high-resolution thermal infrared satellite imagery that are available for 16th July.