Urban boundary layer modeling with WRF: assessment of different urban parameterizations over the city of Bologna

Urbanization affects all the components of the Earth system, clearly including the atmosphere. It is therefore important the understanding of cities-related processes and their representation in modeling terms. Many different spatial scales pertain urban modeling: processes linked to a single building or to an urban district are well represented with microscale methods, but the city as a whole has influences traceable at the mesoscale, a domain traditionally linked to numerical weather prediction (NWP) models. It is evident the discontinuity of these approaches and the advantage that one would have in connecting them, so that buildings-atmosphere interactions are properly considered in mesoscale atmospheric simulations. Within the Weather Research and Forecasting Model (WRF) community various urban parameterizations, with different degree of sophistication, have been developed. In recent years they have found notable applications, but literature focuses mainly on large cities. The purpose of this work is a comparative evaluation of these parameterizations, applied to a medium-sized city such as Bologna. Their accuracy was evaluated using temperature, wind speed and wind direction data recorded by a set of measurement stations. Finally the spatial structure of 2 m-air temperature and 10 m-wind fields was examined, highlighting the different behavior of urban parameterizations on the city area of Bologna.