The director of the Climatological Association of the Middle Garonne (ACMG) returns for “Sud Ouest” to the destructive floods of October 29, which left 230 dead, in Spain. This extreme meteorological episode, and its possible variation on our territory, calls for the need to accept and adapt to the reality of global warming
Could we expect, in the short or medium term, here, the same climatic phenomenon that occurred in Valencia on October 29?
Meteorologically, cold air stagnating at the same time as warm and humid air in the lower layers is possible. It has already happened and it happens regularly, especially in September, from August 15 until the beginning of December. The difference with Valencia is that we don’t have a warm sea so close, with the certainty of the presence of humidity. We, in Agen, are at the confluence of air arriving from the Atlantic Ocean and the Mediterranean Sea. However, we must remember that in September 2021, 3 million cubic meters of water fell on the city in two hours, so we experienced it. But so far in the region, we have never recorded more than 220 mm in a few hours. Valencia, it was between 400 and 600 mm.
So, the Valencian disaster scenario is not for tomorrow?
We have never experienced so much rain falling in such a short period of time. On the other hand, having a significant flow of water which can no longer enter the soil and which flows downwards, with a wave of water which pours out, we have experienced it: Roquefort and Pont-du-Casse are examples of this. We have to think that this is possible and that everyone asks themselves: do I live in a place where the wave will pass? You have to prepare for it, and also translate it into an advantage. Having 200 mm of water, when you plan to run out of it, potentially means having enough for the next 18 months. In this respect, Pont-du-Casse is an example: they made two dams, two lakes, which mitigate the risk of flooding downstream, which are not full all the time and which empty to recover part of this blade of water.
Is this type of high intensity weather event, which occurred two months ago, linked to climate change?
Yes and no. No because it has always existed, and yes because the intensity and frequency of these phenomena are now greater. We can experience it several times in a lifetime, in a given region, not always in the same place: Pont-du-Casse, Roquefort, Bruch, Marmande, Sainte-Livrade… But it will continue to happen. It is hotter in summer, up to 3-4 degrees warmer. This energy produces natural convection, through clouds which transport this energy to high altitudes.
The Valencians denounced the faulty management of the weather alert. What do you think, and what is the situation with us?
European and global weather services had predicted the phenomenon. For me, the problem comes more from the chain of transformation of this information, and from these risks. In 2019, I worked with the deputy head of 112 of Murcia, who with the same data, had convened, 24 to 48 hours before meetings with those in charge, the mayors of the province to ensure that schools were closed , that people stay at home. And then, you should know that it is not in Valence where these significant quantities of water fell, but a few kilometers upstream, and this could be the case in Agen. For me, forecasting services now have the means to warn us. Afterwards, people must accept that, sometimes, they can be wrong. And we shouldn’t say, when something ultimately didn’t happen, that we shouldn’t listen to them next time. We must accept that there is a certain flaw and be humble in the face of such serious phenomena.
