Impact of the Different Grid Resolutions of the WRF Model for the Forecasting of the Flood Event of 15 July 2020 in Palermo (Italy)

One of the most important challenges in atmospheric science and, in particular, in numerical weather predictions (NWP), is to forecast extreme weather events. These events affect very localized areas in space, recording high pluviometric accumulations in short time intervals. In this context, with the present study, we aim to analyze the extreme meteorological event that occurred in the northwestern and eastern parts of Sicily on 15 July 2020, by using the weather research and forecasting (WRF) model. In particular, during the afternoon, several storms affected those areas, causing intense precipitation, with maximum rainfall concentrated on the city of Palermo and in the Etna area. The rainfall at the end of the event reached 134 mm in Palermo and 49 mm in Catania, recorded by the Sicilian network meteorological stations. Because the event at Palermo was strongly localized, the analyses have been carried out by employing different sets of numerical simulations, by means of the WRF model, with horizontal spatial grid resolutions of 9, 3, and 1 km. Furthermore, the output of the performed simulation has been used to assess the thermodynamic profile and atmospheric instability indices. It allowed us to check the adopted parameters against those usually implemented in the flash flood scenario. By using the finest grid resolutions (3 and 1 km), the WRF model was able to provide more accurate predictions of the rainfall accumulation, even if they were strongly localized. Conversely, the implementation of less-refined spatial domain (9 km) did not allow us to obtain predictive estimates of precipitation.