South of the coasts of France and Italy, water temperature in the Mediterranean Sea was still in the middle 70’s last week. Just like in North Georgia, tourists enjoyed sunshine and daytime highs around 70 degrees. Unlike Dahlonega, where happy visitors were crowding the Square, things changed suddenly at the Côte d’Azur in France and in a section of Italy east of there. On October 2, temperatures dropped and rain moved in. Then it turned into a deluge.
Between Nice, France and Genoa, Italy, a narrow shore area is framed by steep mountain ranges. Unlike the Georgia Mountains, the “Alpes Maritimes” reach as high as 10,000 feet. So there’s a huge body of water, staying warm long into fall, adjacent to a mountain range that rivals the American Rockies, with freezing temperatures at the tops. Warm, humid air from the Mediterranean is forced to rise on those slopes. When temperature differences are great, a phenomenon known as the “Genoa Low” can form. Heavy rains turn the pleasant streams of Southern France into raging torrents. Village streets suddenly become rivers, ruining local infrastructure as well as tourists’ vacations. I recall seeking refuge in a hotel in Saint-Jean-Du-Gard once during heavy cloudbursts. Several times that night, we heard flood warning sirens.
Last week, a Genoa-Low type of storm named Alex invaded the area northeast of Nice. One of the hardest-hit towns was Saint-Martin-Vésubie. Google Earth instantly shows the source of the trouble. Two rivers, the Vésubie and the Boréon, come together in a narrow, V-shaped valley. Most of Saint-Martin sits in the flat floodplain at 3,100 feet elevation. Le Boréon, the next town upstream, is at 5,000 feet. While Le Boréon has a flood retention basin, Saint-Martin doesn’t. Many buildings are just a dozen feet above the normal water level of the river. Alex produced 24-foot flood waves, taking 8 lives. The water swept a bridge in Saint-Martin away, recorded live on a cellphone.
Genoa Lows have been observed for decades. But a recent article in Nature stated that “the Mediterranean is one of the most prominent and vulnerable climate change hotspots.” Towns in the Alpes Maritimes are popular, picturesque and expanding. But available real estate is limited, and development has shifted into the floodplains. This, and the effects of climate change, will produce more events like the recent floods caused by Alex.
Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.