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

Abstract

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.

Early Detection and Analysis of an Unpredicted Convective Storm over the Negev Desert

“…This means that observed weather features too small for the model to resolve correctly are left out of the analysis [42]. Moreover, extreme or rapidly changing situations, such as Paran's event, may not be handled well in the analysis [43]. Since these are precisely the situations in remote, unpopulated, arid areas, in which the model's initial conditions are likely to be poor and the forecast unreliable, the forecaster's challenge is to recognize potentially extreme or rapidly evolving weather events and place more emphasis on satellite analysis and other observations in developing a forecast, rather than leaning on NWP models alone.…”

Impact of Domain Nesting on High-Resolution Forecasts of Solar Conditions in Central and Eastern Europe

“…Higher resolution downscaling enabled better simulation results, as well as a more complete understanding of the impact of environmental elements on specific meteorological elements [62,63]. The most commonly chosen domain configuration for analysis or prediction of meteorological elements, as well as extreme phenomena, is triple nested with a grid parent ratio of 3 (usually with the following spatial resolution of the individual grids: 9 km, 3 km, and 1 km [34,[39][40][41][42]). For the WRF model, two values of grid parent ratio were recommended: 3 and 5 [60,61].…”

“…The size of the area for which future atmospheric conditions are simulated is important in terms of the quality of forecasts, as well as for technical reasons-the selection of the right size and spatial resolution of domains affects the duration of the simulation and optimization of the process of its acquisition (appropriate use of computing power, including by selecting the appropriate number of grid nodes in the domains, reducing the duration of the simulation, etc.) [32][33][34]. We decided to study the effect of the grid parent ratio used on the results of WRF model forecasts for a specific area located in the CEE region that covers the southern part of eastern Germany.…”

“…In many studies related to the modeling of atmospheric conditions, including meteorological elements directly related to cloud cover (convective phenomena, precipitation, thunderstorms, tornadoes, lightning, etc.) have been used, with sequence of domains 9 km, 3 km, 1 km [34,35,[39][40][41][42][43][44], which we also implemented. This method is one of the most widely used domain nesting schemes.…”

Performance of the WRF Model for the Forecasting of the V-Shaped Storm Recorded on 11–12 November 2019 in the Eastern Sicily

“…Table 1 shows the parameterizations adopted. Their choice was based on the results obtained previously [54][55][56][57]. Explicit [64,65] With the aim to study the severe weather event occurred in Sicily on 11 and 12 November 2019, a simulation with the WRF model was performed.…”