Thermal vulnerability of compact urban tissues: CFD simulation and validation

Summer heat waves and the urban heat island effect are likely to increase energy demand and consumption in urban areas, but also to cause increased thermal discomfort and heat-related morbidity and mortality. This can be more problematic for the Mediterranean urban areas where a continuous increase in the mean air temperature can be already observed. Investigations of the urban microclimate are therefore imperative for evaluating and implementing mitigation strategies to reduce heat stress and improve comfort in cities. Computational Fluid Dynamics (CFD) has been used on different occasions in the past to investigate the urban microclimate. However, to the best of our knowledge, a detailed investigation of the microclimate for actual compact urban areas with a Mediterranean climate has not yet been performed. Therefore, CFD simulations are performed to investigate the microclimate in a compact area in the city of Rome, Italy. In addition, the vulnerability of different urban tissues in this area is evaluated in terms of thermal discomfort. The focus is on Tuscolano-Don Bosco, a district located in the South-East of the city. The area is about 7.5 km2 large and it has been chosen for its typo-morphological characteristics. The 3D unsteady Reynolds-averaged Navier-Stokes equations are solved in combination with the energy equation and the realizable k-ε model. Conduction, convection and radiation are fully coupled with the wind flow. The assessment of outdoor comfort is based on the universal thermal comfort index (UTCI). The results confirm that CFD is a very useful tool for predicting urban microclimate in real compact areas. In addition, the knowledge of thermal vulnerability of urban tissues is essential for evaluating and implementing mitigation strategies in urban areas.