WRF simulations for a heavy rainfall event in southern Italy: Verification and sensitivity tests

In this paper we study the sensitivity of the quantitative precipitation forecast (QPF) to different physical parameterization schemes and configuration settings of WRF (Weather Research and Forecasting) model for a catastrophic event occurred in Calabria, Southern Italy. The event lasted four days, from 30 October 2015 to 2 November 2015, and affected mostly the eastern side of the peninsula. Several raingauges measured >500 mm for the whole event, with the maximum recorded in Chiaravalle (739 mm for the whole event, which is about half of the yearly rainfall). Damages to railway, roads and properties were extensive. To show the sensitivity of the QPF to the model settings and physical parameterization schemes, twelve configurations of WRF are considered, in addition to the control run (CC), which is the configuration used for the operational forecast at ISAC-CNR in Lamezia Terme. In particular, we tested the sensitivity of the QPF to four different microphysical schemes, three Planetary Boundary Layer (PBL) schemes (non-local and local), two cumulus parameterization schemes, two different horizontal resolutions (1 km vs 3 km), and different initial and boundary conditions. The QPF is verified both by quantitative measures and qualitative scores, using the observations of 156 raingauges quite uniformly distributed over Calabria. The analysis refers to 12 h and 24 h rainfall, but some details are given also for shorter time scales. Results show that most of the WRF configurations are able to predict most of the features of the precipitation field. However, there are differences at the local scale (few tens of kilometers) that are important for several purposes, including civil protection. In particular, using a non-local PBL closure scheme was fundamental to correctly simulate the heavy precipitation close to the sea for this case, while other configurations predicted the rainfall more anchored to mountain peaks. The good performance of non-local PBL scheme confirms the findings of a previous study over Calabria. The results of this paper show the sensitivity of the QPF at the local scale for different WRF configurations and an ensemble approach is envisaged to improve the prediction of such catastrophic events.