After days of intense heat over the whole peninsula, bad weather hit, bringing its load of disasters. The most striking case is that of Bardonecchia, in the upper Val di Susa, submerged for the second time in a few years by a river of mud and rocks due to the flood of the Frejus stream, which unfortunately also caused a death on this occasion. Similar situations, however, also repeated themselves in San Vito di Cadore, in the province of Belluno, in the Adamello park, in Trentino, and in various other Alpine locations. They are phenomena known in technical language such as debrical flows, or landslides in which rocks, stones and mud mix with large quantities of water, and flow towards the valley with potentially devastating effects, especially when they have innoating themselves in the river and streams, hitting the inhabited centers by surprise. Unfortunately, we have to get used to hearing them to name more and more often, because they are increasingly being made on our mountains due to climate change.
Deritical flows are a phenomenon that exists practically in every part of the world. Because they take place, three ingredients are needed: the presence of rocky material accumulated on the ground and ready to be mobilized; A sufficient slope so that the landslide takes place; And water in large quantities that are brought to you quickly, bringing the rocks, mud and strictly taken into the deposit in the deposit basin.
In itself, therefore, they are phenomena that have always occurred, and that would continue to take place even if the climate was the same as two centuries ago. The fact, however, is that climate change make the presence of two of the three prerequisites for the trigger of a debris flow, and consequently more and more often more often, and will increasingly take place in the next decades.
The first, and more obvious, are the thunderstorms: in fact, the global warming increases the frequency of extreme weather events, and therefore of intense and localized rainfall, perfect to kick off a lecturer. Without rocks and stones ready to be dragged downstream, summer water bombs are not enough. But climate change also think of this. With the withdrawal of Alpine glaciers, more and more accentuated in recent years, the ice leave behind enormous blackberries and recently formated debris deposits. That in the right conditions, they can also be saturated with water from retreating glaciers, and therefore ready to be destabilized at the first rain of a certain entity.
The dissolution of the permafrost, the perennially frozen soil that is normally found above a certain altitude, is another factor that feeds the debris flows: without the ice, the materials deposited on the ground have nothing more that keeps them tied, and are therefore prone to landslides and Slavine. Even the rocky walls of the mountains become less resistant with the increase in temperatures, because the ice that contributed to their stability is lacking. And therefore they are more exposed to the degradation caused by atmospheric agents, which determines the accumulation of debris to their slopes, and to the large landslides which – in turn – can act as a trigger for debrical flows. Finally, the forest fires also create a perfect material tank for a casting, because they eliminate the vegetable cover that contributes to stabilizing the soil. And also in this case, the increase in temperatures is making them more and more frequent.
Unstable mountains, glaciers that collapse and the risk map that is not there: the areas most at risk
The climate change, which have particularly intense effects on the Alps, therefore create the “perfect storm” for the increase in frequency of debrical flows. There are still no certain data, but the perception of many experts is that they are actually increasing. And not being able to count only on the mitigation of climate change (which, among other things, for now it seems to be intended for bankruptcy), you just have to be ready, with adaptation projects that allow communities that live in areas at risk of living with increasingly frequent and destructive debris flows. Between saying and doing, of course, there is an abyss, because money, time and political will is needed to secure a complex territory such as the alpine one, and more generally that of the whole peninsula. In Bardonecchia, for example, the risks were known: the debris flow of the past few days was the reply of that of two years ago. Yet it was not possible to avoid a new disaster.