**5. Discussions**

Snow avalanche hazards are computed to be increasing worldwide due to climate changes [128,129]. Among all the climatic contributors, climate extremization is identified as one of the factors influencing the behavior, irregularity, and frequency of snow avalanches [130,131]. In some areas, it causes the thinning and shortening of the duration of snow cover, contributing to an increased irregularity that raises the hazard. As a result, a correct climatic analysis involving investigations of changes in the snow cover and snow avalanche hazard assessment is vital for administering many crucial societal issues concerning territorial planning, risk mitigation, and resilience activities [25,132,133].

Exposure to this hazard may be voluntary, as is the case with skiing, or involuntary, such as on public transportation corridors and settlements. According to the literature and technical reports [31–33], the techniques used to evaluate avalanche hazards and risks are different depending on the circumstances.

Here, we attempted to understand the main interrelationships between climate extremization and environmental risk in a mass movement-prone area, such as the Prati di Tivo area. We discussed the stepwise approach to be followed for a correct snow avalanche assessment by combining the spatial distribution of the snow avalanches and the main climatic features of the study area. It was also essential to compare the findings with the detailed geomorphological features of the Vallone della Giumenta to outline the role of climate extremization in the triggering of the avalanches.

The combination of preliminary results and thematic maps allowed us to better characterize the study area from a morphometric, geomorphological, climatic, and nivological standpoint. In such a complex and mass movement-prone area, it was necessary to activate a risk mitigation protocol to develop land use policies and activities to define a significant snow avalanche assessment. According to the PIDAV project [99], the safety services for ski resorts and facilities at Prati di Tivo were updated by installing 12 Obellx® gas exploders [109,134] to manage short-term avalanche risks better. The installation was realized in correspondence with the main detachment areas at elevations ranging between 2100 and 2250 m a.s.l.

Moreover, as part of the increasingly more frequent processes of climate extremization, on 24–26 March 2020, a heavy snowfall event affected the study area. It was acknowledged as a prevalently stormy snowfall, which brought 90 cm of fresh snow (with a density of 140 kg/m3) over the ski facilities located at Prati di Tivo at elevations of about 1400 m a.s.l. Given the high snow accumulation rates, explosive pitches were performed on 24 March immediately after the beginning of the snowfall event and on March 26 during the main event, inducing moderate detachments of fresh, humid, and low-cohesion snow. Even if the preventive activity of Obellx® gas exploders reasonably mitigated the snow dynamics, on the night of 27 March, around 4:20 a.m., two natural snow avalanche events occurred following new abundant snowfalls and affected the northern escarpment of the Corno Piccolo ridge (Figure 16). A detailed field survey and a specific site investigation were also performed in the early morning of 28 March, thanks to a clear weather improvement. Considering the information gathered from this survey, it was possible to make several essential deductions:


**Figure 16.** Photo documentation of the snow avalanches of March 2020. (**a**) Evidence of the summit detachment area at the base of Corno Piccolo with a clear surface slab and (**b**) a simplified snow avalanche path (in red) affecting the Vallone della Giumenta and involving the main ski facilities.

The presence of interdigitated snow mass accumulations belonging to the March 2020 avalanches, both partially converged into the Vallone della Giumenta, testified the dynamic avalanche framework of the study area. Unfortunately, this peculiar nivological setting makes it impossible to define the temporal evolution of the two different events. For these reasons, preliminary one- and two-dimensional avalanche simulation models (e.g., AVAL-1D and RAMMS [39,112]) were applied to better describe the possible evolution of the documented avalanche events at a particular site (such as the Vallone della Giumenta), as well as to calculate the consequences of possible hazard scenarios. The avalanche modeling was carried out by employing RAMMS software and implemented with GIS techniques. In detail, it was performed both by considering a scenario characterized by a limited thickness of the snow cover mitigated by the Obellx® devices' activity and a scenario in which the downstream slopes were totally covered by a thick snow cover (i.e., not secured by the preventive action of the Obellx® devices). The resulting data defined different stopping distances and paths of the selected avalanche under scenarios driven by other transmitted pressures, as graphically shown in Figure 16. It showed how, in the absence of the preventive action of the Obellx® devices (red stars in Figure 16), an avalanche event can predominantly occur along the Vallone della Giumenta. Moreover, transmitted pressures, which vary from 30 to 150 kPa, and different heights of snow cover (Hc = 0.5, 1.0, and 1.5 m) were accounted for. Under these scenarios, the avalanche path can widely reach the Prati di Tivo area, involving the residence (reported as the hotel in Figure 14) and the four-seat chairlift line (Figures 16b and 17).

Snow avalanches can generally act as geomorphic agents [135]. Snow avalanches can exert considerable erosive forces playing a significant role in landscape development. Evaluating the morphological features of the mass movement-prone area and the main avalanche features is essential to quantify the material entrained by the avalanche and transported to the deposition zone [136].

A semi-quantitative analysis was applied to the modeled avalanche path at Vallone della Giumenta (Figures 13 and 17) to better describe the geomorphic role of snow avalanches at the Prati di Tivo area. This specific site investigation presents peculiar morphometric features and snow avalanche pressures accounted as representative of the main avalanche events in the study area. The analysis focused on evaluating the pre- and post-avalanche setting, highlighting the variations in the contributing area caused by the snow avalanche along the Vallone della Giumenta. This evaluation showed a variation that increased by about two-fold (>50%), as the contribution of each avalanche track and rock gully was significant in the geomorphic action of the avalanche. It is graphically shown in Figure 18 and summarized in Table 4.

**Figure 17.** Results of the avalanche dynamics simulation under different transmitted pressures and heights of snow cover: (**a**) Hc = 0.5 m, (**b**) Hc = 1.0 m, and (**c**) Hc = 1.5 m.

In conclusion, the resulting data allowed us to properly define the main steps of the developed risk mitigation protocol. It was activated following some recent damaging snow avalanches affecting the Prati di Tivo area to better develop mitigation activities and land use policies needed for the managemen<sup>t</sup> of permanent settlements, recreation infrastructures, and ski facilities. The relevance and the impact of the work are represented by: (1) the provision of new data on the physiography–geomorphology of the study area and the mass movement-prone areas, (2) the outline of a multidisciplinary methodological approach for the definition of snow avalanche critical areas and the configuration of hazard protocols not ye<sup>t</sup> developed for the Central Apennines, and (3) a technical scientific basis to develop the civil protection plans required to increase the knowledge of citizens and interested stakeholders about proper land managemen<sup>t</sup> considering multi-hazard scenarios (i.e., snow avalanches and landslides).

**Figure 18.** Pre- and post-avalanche landslide contributing area.

**Table 4.** Dimensions of the possible landslide area, modified by snow avalanche dynamics.

