Science communicator and president of the Società Meteorologica Italiana. Luca Mercalli is one of Italy's foremost experts on climate change. He starts from one premise: it is getting hotter and temperatures will in all likelihood continue to rise; consequently water consumption will increase and waste will have to decrease, beginning with the reinforcement of water networks and infrastructure interventions that help cities adapt to drought waves.

The summer season will last more than 4 months

"In 2003," Mercalli explains, "a temperature above 40 degrees was recorded in the Po Valley for the first time in 250 years. On 4 August 2017, in Forlì, the absolute maximum of 43 degrees was reached. By now all the indicators tell us that we will face increasingly intense and ever more frequent heatwaves. We will have summers with tropical characteristics even in the North, while the South will have to contend with higher temperatures and a summer season lasting beyond the canonical four months. And generally in Western societies, the hotter it gets, the greater the demand for water."

The same cannot be said, however, for intense short-duration rainfall: researchers do not yet have sufficient historical data to identify a statistical trend of increasing intensity. On this particular point, climatologists can only draw on data from the late 1990s, when the automatic stations capable of measuring rainfall amounts for each individual minute were activated. This "does not mean there is no trend in this direction, but the sample we have available is not yet statistically significant enough."

Beyond the climate, the other problem is land consumption

Certainly, the impression is that the frequency of intense cloudburst events is increasing, made all the more damaging in a territory as heavily concreted over as ours. "Indeed, it is not so much the average daily rainfall totals that appear to have increased, but rather intense cloudbursts lasting less than an hour." These do not allow the ground to absorb water and replenish aquifers, and are in fact highly damaging. This is because "for the same amount of rain, that which falls today causes more damage than it did 100 years ago. We have transformed land that was once agricultural into areas laden with infrastructure: this means that water flows more quickly and reaches potentially vulnerable areas faster."

In a few decades we have radically changed our urban fabric. For some, excessive concreting could be linked to the phenomenon of desertification and to that of "reverse drought", which this year sees Sicilian reservoirs full of water while the Po runs dry. Mercalli does not share this view: "The desertification affecting some areas of southern Italy and the islands is closely linked to rising temperatures and the possible extension of the summer dry period." As for the second point, "Sicily has indeed seen more water this year than it has in a long time; but defining a trend requires decades — we could still be looking at a case of normal meteorological variability."

What is certain is that the climate is changing. And to cope with an increasingly complex situation it is necessary to reduce CO2 emissions in line with the Paris Agreement on climate, signed in 2015: the only viable path to avoiding a rise in average temperatures of two degrees by 2100, which would have devastating effects on our ecosystem. But this is a challenge that Italy cannot face without the support of the world's major powers. "Our country," Mercalli stresses, "contributes only 2 per cent of global emissions; we must do our part, but a great deal depends on the choices made by countries such as China or the United States." This is a worrying prospect because, owing to its particular geographical position at the heart of the Mediterranean, Italy is highly exposed to the effects of extreme climate events. In short, "in the not too distant future we may find ourselves dealing with damage caused by others, and there is only one path to take: invest in infrastructure that supports adaptation to the changing climate."