Actually, not that much. The rivers in the area that has been suffering from the most casualties had been restored over the past years. When you get 150-200l/m² of rainfall in an area of hills and valleys, there's just little you can do to prevent such a catastrophe.
Apparently, there were flood warnings by an EU institution already on July 10th.
So at least, there would have been enough time to evacuate people. But it seems these alarms were ignored by national and state authorities.
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