*4.3. Climatic Analysis*

The microclimatic features of the study area were analyzed considering the historical thermo–pluviometric series available at the Pietracamela gauge (1043 m a.s.l.), covering a 50-year time period (1951–2004); nevertheless, the selected gauge is located approximately 400 m below the Prati di Tivo area and at least 1000 m downstream of the main avalanches and landslides detachment areas (Table 2). Nonetheless, for the study area, it was impossible to define spatial and altitudinal meteoric features since snowfall and rainfall events are often coupled with strong winds that can induce relevant rates of underestimations, especially at the highest elevations.

**Table 2.** Main values of the temperature and rainfall, resulting from the climatic analysis at the Pietracamela gauge (1043 m a.s.l.).


The average annual temperature is ~10.7 ◦C, with an average daily thermal excursion of ~7 ◦C; the maximum temperatures can eventually exceed 35 ◦C, while the minimum ones almost reach −15 ◦C. Frost days (Tmin < 0 ◦C) are ~65 per year, while ice days ( Tmax < 0 ◦C) are no more than 10 per year.

The total rainfall is moderately abundant with respect to the Gran Sasso Massif geographic location, exposed to "Tramontana" and "Bora" dry and cold winds, as well as to "Scirocco" and "Libeccio" wetter ones, which often release the moisture taken in charge. During the summer, the ascent of convective cells from the near L'Aquila Basin and the middle Vomano River valley is common. The total annual rainfall is approximately 1100 mm, distributed along with an average of 106 rainy days; the hourly and daily maximum values, respectively, correspond to 58 mm and 267 mm. The meteoric regime shows peculiar features pertaining to the Apennine–Adriatic type [81,100], with a bimodal rainfall distribution characterized by a global maximum value in November with a secondary peak in April and a global minimum in July/August—months not in a drought, given the frequent occurrence of convective phenomena—with a secondary peak in February. It should also be stressed that the monthly rainfalls never drop below 50 mm.

Snowfalls are frequent during every winter season, with high amounts with respect to the geographic position of the study area, as previously reported in the thematic literature [100,119]. Considering the possible influence of disturbing fluxes coming from the south and associated with negative temperatures, the study area can present cumulative values among the highest of the Central Apennine area, as happened in February 2017 [119].

The performed climatic analysis confirms, even in this area, an increase of the temperature values of about 1.1 ◦C during the last 50 years; unfortunately, the weather station located at Pietracamela ceased its activity in 2004, thus making a more recent trend analysis impossible. The rainfall regimes, on the other side, do not show significant variations (−1.5 mm/year), but it is possible to observe a decrease of about 10% in the number of days with precipitation rates > 1 mm from 110 to 101; consequently, the average daily rainfall

intensities have slightly increased. Considering the recorded datasets, homogeneous and complete data relating to short and intense precipitation events is unavailable. It was not possible to perform a comprehensive analysis for this specific climatic aspect.

The detailed climatic analysis shows that average annual temperatures for the year 2020, as observed for the Teramo gauge (blue line in Figure 7a), was approximately 1 ◦C higher than the conventional 30-year time period (1971–2000), known as CliNo (Climate Normal). Consequently, the elevations of the 0 and −1 ◦C isotherms correspond to 3099 and 3296 m a.s.l., far above those calculated by Dramis et al. [120], corresponding, respectively, to 2615 and 3028 m a.s.l. Considering that the average annual temperature recorded at the Pietracamela (1043 m a.s.l.) and Rifugio Franchetti (2433 m a.s.l.; green line in Figure 7a) gauges are, respectively, 10.7 and 2.6 ◦C, given a difference in elevation of about 1500 m, a vertical thermal gradient of approximately 6.1 ◦C/km can be estimated. Thus, an average annual temperature of 7.6 ◦C and 4.2 ◦C can be derived at, respectively, Prati di Tivo (orange line in Figure 7a) and the avalanche detachment areas located at ~2200 m a.s.l.

**Figure 7.** Monthly average temperature (**a**) and monthly average rainfall (**b**) trends for the year 2020.

The monthly average rainfalls (Figure 7b) show a noticeable growth with a direct relationship as the altitude increases due to an orographic effect, in accordance with previous estimates made for this sector of the Central Apennine Chain (30 mm/100 m) [100,119]. Nevertheless, a drastic decrease of these values occurs at higher elevations, which is typical of an arid boreal habitat. This substantial underestimation, up to 70%, occurs in areas exposed to powerful winds during rainfall and/or snowfall events [121].

The anemometric signal is significant in the whole area from 260 up to 2400 m a.s.l., thus promoting the accumulation of frames and lenses above all on the ridges of Gran Sasso Massif and in correspondence of steep channels and depressed morphologies downwind of the main flow during and after snowfalls (Figure 8a). In particular, at high elevations, the number of days with a maximum wind speed greater than 30 km/h, sufficient for inducing a reworking of the snow cover, is around 40. Main winds come from the second and the third quadrants during the winter, reaching speeds greater than 200 km/h (Figure 8b).

**Figure 8.** (**a**) Monthly average wind speed for the year 2020 and (**b**) monthly wind speed recorded at Rifugio Franchetti (2433 m a.s.l.). Black arrows indicate the monthly average direction of winds.
