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Deluge in Italy sets European record: 29 inches in 12 hours

It follows a summer of climate-change-fueled extreme precipitation events in the Northern Hemisphere

Heavy rain drenched Italy from the Piedmont region to Sicily Oct. 4 and 5, with rising waters catching some people by surprise. (Video: The Washington Post)
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An intense complex of thunderstorms stalled over northwestern Italy on Monday, unleashing a 12-hour torrent unrivaled in the history of European weather observations.

It’s the latest extreme rain event supercharged by climate change that follows a summer of historic deluges in the Northern Hemisphere.

In just 12 hours, 29.2 inches of rain fell in Rossiglione in Italy’s Genoa province, roughly 65 miles south-southwest of Milan and 10 miles north of the Mediterranean coastline. It marked the greatest 12-hour rainfall on record in Europe, according to Maximiliano Herrera, a climatologist who specializes in world weather extremes.

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The amount of rain that came down in 12 hours is more than half the typical amount of rain that falls in the region over an entire year, which is just over 50 inches. It’s several times the average October rainfall of 6 to 7 inches.

In six hours, 19.5 inches of rain poured down in Cairo Montenotte, about 22 miles to the west of Rossiglione. Herrera tweeted that amount set a new six-hour rainfall record in Italy. It also established a six-hour rainfall for all of Europe, tweeted Etienne Kapikian, a forecaster for France’s meteorological agency.

A whopping 7.1 inches fell in just one hour in Vicomorasso, about 16 miles east of Rossiglione, according to FloodList, a website that aggregates information about flood events around the world. For comparison, that’s more than double the 3.15 inches that fell during the record-setting one-hour cloudburst that overwhelmed New York City on Sept. 1 as the remnants of Hurricane Ida passed.

The large complex of storms bombarded much of Liguria, which is the northwestern region of Italy bordering France, resulting in flooding and mudslides. The storm complex was also a prolific lightning producer, generating more than a half-million strikes.

The Associated Press and FloodList wrote that the Mediterranean port city of Savona, just south of Cairo Montenotte, was hit hardest by the flooding and that the Letimbro River running through it overflowed.

In Genoa, the largest city in Liguria, schools, parks and cemeteries closed Monday, the AP reported.

No casualties were reported, but FloodList tweeted that dozens of people were rescued or evacuated in the region.

The exceptional rainfall came from a stormy zone of low pressure that approached from the southwest off the Mediterranean Sea. The counterclockwise circulation around the slow-moving low drew moisture-rich air into northwestern Italy. Computer models showed exceptional moisture levels, up to 250 percent of normal.

Temperatures were about 10 degrees above average ahead of the storm.

Scientists have found that human-caused climate change and the resulting rising temperatures are intensifying heavy downpours. Numerous exceptional precipitation events occurred this summer, including historic flooding in China, Central Europe and the northeastern United States during Ida.

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In its review of the science published this summer, the Intergovernmental Panel on Climate Change reported that heavy precipitation events have increased since the 1950s over most land areas.

With more warming, the panel projects, heavy precipitation events will intensify further, increasing by 7 percent for every 1.8 degrees Fahrenheit (1 Celsius) of warming.

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