“If global warming continues at its current rate, many areas in the Mediterranean will be uninhabitable.”

TThe deadly floods that hit Spain have just been added to the long list of devastating events that have ravaged Europe and France for more than three decades. This latest disaster comes as the UN has published a new report on the inadequacy of climate policies, which will drag the planet towards +3.1°C of warming by the end of this century, and the third National Climate Change Adaptation Plan has just been unveiled . For anyone who has worked on disasters for the past twenty years, the one astonishing fact is that we still find a way to be amazed.

There is nothing unusual about these types of storms. They occur every year in autumn and are typical of the Mediterranean climate. They are responsible for a sudden increase in the flow of rivers, which overflow their banks and flood coastal plains. Their violence is even more difficult to imagine, since most Mediterranean streams have low flow velocities. Yet the sheer width of the downstream valleys is enough to convince you of the volumes of water that can flow in a matter of hours, making any possibility of resistance or even evacuation illusory.

The phenomenon of heavy flooding was well known to the ancients. They were even given names locally: “aiguats” in Languedoc, “vidourlades” in Sommières (in the Gard in southern France). Over the centuries, Mediterranean societies have adapted. Houses were built on higher ground and bridge arches and piers were calibrated to prevent them from being washed away or causing destructive jams.

Artificial environment

During the 20^e century, advances in science and technology led to better weather forecasts, improved warning systems and strengthened dikes. Yet disasters still happen every year. Damage costs are rising steadily, while the number of victims remains high.

There are two reasons for this paradox. First, the number of people exposed to these risks has increased sharply. Many communities have been dependent on tourism and the residential economy, with the constant arrival of new residents, young households or retirees, permanent or temporary residents (second homes). Demographic growth has been driven by urban expansion in river valleys and coastal plains. Agricultural lands in particular are divided into one-story houses, which do not provide refuge from a sudden rise in water levels.

On the other hand, the environment has been extensively engineered, with the effect of altering infiltration potential and surface runoff conditions. Roads, slabs and roofs have made the soil impenetrable. Natural drains (called “vallons” or “cadereaux” depending on the region) are crossed or covered with concrete. In the huertas (areas with intensive irrigated agriculture), orchards have been replaced by greenhouses. During heavy storms, the deposited water can no longer infiltrate: it flows into the rivers, increasing the flow. Watercourses have also been dammed, excavated, ‘rectified’ or diverted. Some are covered and channels are blocked.

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