Bad weather emergency yesterday a Bardonecchiain Piedmont on the border with France, where the strong rains have transformed the Rio Frejus In a flow of water and mud that destroyed arguments and bulkheads and flooded the municipality of the Alta Val di Susa causing the death of the 70 -year -old Franco Chiaffinodragged by the current. All this happened almost two years after the flood that hit the tourist resort between 13 and 14 August 2023. As reported by Arpa Piemonte, yesterday in Bardonecchia rained about 25 millimeters of rain throughout the day, with a peak of 15mm in an hour. These are values that would not have caused great damage to a more open and flat territory, but the torrential character of the Frejus, the particular orographic conformation of the territory and its hydrogeological fragility have caused the serious situation of yesterday.
Yesterday, however, Bardonecchia was not the only victim of bad weather: rainfall caused a landslide to San Vito di Cadorein Veneto, with mud flows that led to the closure of a stretch of the state road between Cortina d’Ampezzo and Belluno, while in Valtellina The intense rainfall caused landslides and flooding. In short, bad weather hit the Italian alpine side in the hours when so -called “Pluto anticyclone” (a term actually improper to indicate the North African promontory) was reaching its maximum extension, overlooking Italy and most of the central Europe bringing a strong heat with temperatures well above the norm throughout the country. The question is recurring in these cases: How is it possible that torrid heat can live with strong bad weather? It is not a paradox or a contradiction, but two sides of the same medal. To understand it we can take a small journey into the physical atmosphere.
What happened to Bardonecchia: the role of the “Pluto anticyclone”
We can imagine an anticyclone, like the African promontory that stationed on Italy these days, like one high pressure air mass at high altitude which compresses the air below, warming it and preventing the formation of clouds and therefore bad weather. In the case in question in these days, the African promontory has brought an intense heat wave with soil temperatures in Italy in Italy. 40 ° Ccertainly anomalous for the end of June, with one zero thermal (i.e. the share to which the air temperature reaches 0 ° C) well beyond 5000 meters throughout the country.
Now, an important feature of hot air is that it is more “good” than cold air to retain water vapor without this liquid condensation. In other words, the hot air can be significantly more humid than the same air at a lower temperature. A spannometric rule derives from the so -called Clausius-Clapeyron equation – among the best known in the meteorological field – and states that at the typical temperatures on the ground The maximum humidity rises by 7% for each temperature increase of 1 ° C.
And the North African promontory in these days is literally load of humidity. We are talking about Saharian hot air currents who have to cross the Mediterranean to get to us. Mediterranean who in recent days had temperatures even 5 ° C above average of the period, which would also be high at the end of the summer. A warmer sea means a sea that evaporates more, that is, that it enters large quantities of water vapor in a very hot air and therefore very inclined to welcome that steam.
How extreme heat can cause strong bad weather
Until the anti -cluster promontory is robust, it does a good job in keeping the low pressure cold air that is generally associated with rainfall and bad weather. For this reason, with the anticyclone you generally have a peaceful time. But in recent days the North African promontory was confined to two flashes of cold air, one to the east that brought Arctic cold air in the Danubian area, and one west of Icelandic origin who had reached the United Kingdom, pushing against the French front of the promontory. Just from here came some Atlantic cold air infiltrations which, associated with a general weakening of the anticyclonic front, have created some strong thermal contrasts precisely in correspondence with the Italian Alpine arc.
Remember? The hot air is better at retaining water vapor: it means that part of this will tend to condense if the air temperature should drop. The infiltrations of cold air of which I was talking about above do this: lower the air temperature in the margin of the promontory. The large amount of water vapor contained there quickly, forming clouds ready to download excess humidity. At this point the system is ready for get rid of the enormous accumulated thermal energy. And the way it does is what we call “bad weather”: rains, thunderstorms, strong winds, storms. It is the way the atmosphere returns to balance after having accumulated too much thermal energy and too much humidity. What hit Bardonecchia and other areas of northern Italy was the atmosphere atmosphere to return to a condition of balance, in a context in which climate change tend to create rapid and strong imbalances.
The effects of global warming
In short, the correlation is clear: warmer leads to more humidity that leads to multiple violent weather phenomena. This means that the anticyclones are not a guarantee of Beltempo but, more and more often, they have the effect of widen the gap between deep droughts on the one hand and intense floods and floods on the other. And there is no doubt that all this is worsening – and it will continue to worsen in the future – in terms of frequency so much of intensity because of the global warmingwhich increases the parameter knob which is at the origin of all this: the temperature.
