In the aftermath of the Sant Llorenç tragedy, a question arises after half of the casualties so far are foreigners. Do tourists and foreign residents know the flood risk they face?

The answer is no and it was exemplified last week during the flood. Even locals are not aware of the dangers they can face when a sudden outburst of water appears from nowhere and hit urban areas but at least they have the opportunity to know the local history, even if they do not listen anymore.

The risk is a combination of two factors, one climatological, another hydrogeological.
On the one hand, the Mediterranean Sea and, especially, the Western Mediterranean basin, are well known for the extreme precipitation that happens during the fall season. A combination of high sea temperature and the arrival of cold fronts from the Atlantic Ocean often results in daily rainfall averages exceeding 100 mm or even more (a record of 817 mm was recorded in Oliva (Valencia) in November 1987).

On the other hand, the rain falls in a dry environment, where the water runs, streams called torrents in the Islands or rieres in Catalonia or barrancs in Valencia, which are dry a large part of the year. Its circulation is sporadic and related to the precipitation so, when a large amount of rain falls, there is a sudden increase of water and, if stream beds cannot hold that amount of it, it results in a spill-off, with the flooding of the closest areas of the stream.

So far, nothing to be worried about. It is a natural cycle, well documented through history. The problem arises when man, knowingly or unknowingly, sets his feet in these flood-prone areas, or worse, inside the stream bed. Through Mallorca's history, there were towns that had been hit by floods since as early as 1403, when Palma was destroyed, but man knew where to build and which places must be avoided. Fast forward to the 20th century, when more and more land was needed to be built. The pressure was so high that history was forgotten and flood-prone areas, first in coastal zones, then all around the island, were constructed to host tourists and new residents. Then new roads were needed to support the communication network and the arrival of millions of visitors, roads that usually crossed streams or were too close to them.

The results were seen last week in Sant Llorenç but the problem is not only in urban areas. How many hikers or bikers visit Mallorca yearly? How many know the danger they can face while walking around in mountains where a sudden flash flood can hit them? How many bikers know that a large part of the paths they follow cycling are located close to beds in flood-prone areas?

You can guess the answer but what we should do is hope we never need to answer that question. Solutions should be provided, and the sooner the better. My proposal is education, locals and foreign residents must learn what to do and what not to do. And for tourists, maybe a simple leaflet at the airport could be life saving.

Only one thing is sure, someday, somewhere, it will rain again and a flood will start. That is nature after all.

Joan Rossello, Geography PhD. Grup de Climatologia, Hidrologia, Riscs Naturals i Paisatge. Universitat de les Illes Balears.

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