Numerical simulations of boundary-layer phenomena and urban-scale processes in the Alpine city of Trento

Simulations are performed with the Weather Research and Forecasting (WRF) model, coupled with an urban parameterisation scheme, to evaluate the alterations induced by the urban area of Trento on boundary-layer processes in the Alpine Adige Valley. Simulations, with 500-m grid spacing, focus on a typical summer sunny day, when both valley winds and the urban heat island are well developed. Specific gridded datasets of urban morphology parameters and anthropogenic heat flux releases were created to provide high resolution input information to the urban scheme. Validation of numerical results against measurements from surface weather stations shows that the model is able to simulate with reasonable accuracy valley winds, as well as the urban heat island, characterised by strong intensities at night and low values in the central hours of the day. It is found that the city inhibits the development of the groundbased thermal inversion at night, especially in the city centre, displaying a denser urban morphology and higher buildings. Furthermore comparisons with an idealised simulation, where all the urban land use grid points are replaced by cropland, suggest that the city also affects the development of valley winds, modifying both the typical down-valley wind in the early morning, and the interaction between the up-valley wind in the Adige Valley and a lake breeze flowing from a tributary valley.