## 5 Results and Discussion
### The Simulated Precipitation  
WRF simulated precipitation fields were computed during the two meteorological events (12 August 2019 and 13-16 October 2000) that triggered the investigated mass wasting events. The performance of the predictive system is evaluated by comparison with observations at the weather stations in the investigated area (Table 1). The October 2000 and August 2019 meteorological events, as examined above (Section 3.2), were very different: the first one was characterised by a long-lasting, continuous and diffuse precipitation, while the second one was related to a short-timed, intense and extremely localised precipitation. The difficulties in predicting the second event could be much higher due to the short duration and the small spatial localisation that request high-spatial resolution and a well-tuned convection scheme. The 12 th August 2019 event was simulated by WRF (Figures 8 and 9). In particular, the precipitation patterns (Figure 8) reflect the cold front shape and localises the position of the maximum of precipitation on a small area, including the investigated slope. The precipitation fields showed that the principal rain event occurred at the station sites in one hour and half, from 0600 UTC to 0730 UTC. The rain gauges network (Table 1) confirms the duration of the principal event. Moreover, in a further inspection of observations versus simulated rain rate at the station locations (not shown), it is clear that WRF caught the time of each peak, with some very small time-shift. In particular, the most intense rain rate (13.6 mm in 10 min) was registered at 0610 UTC (12 August 2019) at San Domenico village, while WRF predicted 10 mm, 15 min later at the same site. Considering the progressive cumulated rain during the event at the five stations (Figure 9 panels A-E), WRF was able to identify the timing of the episode occurred at all station sites and it simulated correctly also the timing of the two moderate precipitation events that occurred on 10 and 11 August. The precipitation quantity was underestimated of about 20 to 50 mm at all stations with the exception of Alpe Veglia (Figure 9B) where the simulated precipitation was overestimated of 10 mm. In this specific event the high spatial variability of precipitation related to the mountainous terrain was evident. In fact, the precipitation at Alpe Veglia station, that suffered of orographic shadowing by peaks on North-North-West side, was overestimated by WRF due to imprecise and smoothed model topography; meanwhile, the precipitation amounts at all the other stations were underestimated due to some imprecision in the determination of lee-slope convection. Between 0500 UTC and 0700 UTC at San Domenico, the precipitation was 61.4 mm, with a mean hourly rain rate of 30.5 mm. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Rio Croso Morphometric Data** & \multicolumn{4}{c}{**Alluvial Fan Measure at the 12 August 2019 Event**} \\ \hline _Crown altitude Qc (m)_ & 1925 & _Area (m2)_ & 1800 & _Length (m)_ & 6445 \\ _Toe altitude Qt (m)_ & 1366 & _Section_ & _Area (m2)_ & _Distance (m)_ & _Volume (m3)_ \\ _Horizontal length HL (m)_ & 1890 & Bridge & 162 & 1009 & 29321 \\ _Altitude difference H (m)_ & 620 & Lower & 376 & 39 & 8438 \\ _Slope S (\({}^{\circ}\))_ & 18.2 & Check dam & 60 & 83 & 10249 \\ _Total area A (m2)_ & 116899 & Upper & 187 & 72 & 6710 \\ _Width Wi (m)_ & 40 & & _Total volume (m2)_ & 37759 \\ \hline \hline \multicolumn{5}{c}{**Interferometric Data**} \\ \hline \hline \multicolumn{5}{c}{_Moving velocity along the Line_} \\ \multicolumn{5}{c}{_DatasET_} & \multicolumn{2}{c}{_of Sight (LOS) (mm/year)_} \\ \multicolumn{5}{c}{_Min_} & \multicolumn{2}{c}{_Max_} \\ \hline RADARSAT\_asce\_nord & \(-0.69\) & \(0.31\) & \(-0.23\) & \(4\) & \(1\) & \(0\) & \(0\) \\ ERS\_summ\_desce & \(-1.1\) & \(-1.1\) & \(-1.1\) & \(0\) & \(1\) & \(0\) & \(0\) \\ pst\_ENVISAT\_desce & 0.52 & 0.52 & 0.52 & 0 & \(1\) & \(0\) & \(0\) \\ \hline \hline \end{tabular}
\end{table}