September 22, 2023

A triple whammy of cyclones, a once-in-200-year event, caused Italy’s deadly floods, scientists say

ROME (AP) — A rare, triple-blow from cyclones triggered the deadly floods that devastated much of northern Italy this month, but scientists said Wednesday that climate change does not appear to be to blame for the intense rainfall.

Using computer simulations and past observations, a team of researchers looked for but found no evidence of human-induced warming behind the drenching. World Weather Attribution compared what happened to a computer-simulated world with no human-induced warming and did not see the fingerprints of fossil fuel-induced climate change, unlike many previous studies.

Still, precisely because having three exceptionally heavy downpours in such a short time is so rare — the study estimated there was a 1 in 200 chance that three cyclones would strike in a three-week period — the climate experts warned that more time for study is needed.

“This is not the end of the story,” said study co-author Davide Faranda, a researcher in climate physics at the Pierre-Simon Laplace Institute in France. “This event is too rare,” he said during a panel to present the findings.

“Remember there was a drought before” the first storm hit the Emilia-Romagna region on May 2, and “this (drought) was due to climate change,” Faranda said. He was referring to two years of little or no rainfall that left the land so dry that it could not absorb the first rainfall. Drought largely caused by lack of snowfall in the Alps, which mostly replenishes the Po River and other smaller waterways in northern Italy.

This study was conducted “to answer the question of whether and to what extent climate change” was having an impact on flooding in Emilia-Romagna, said Friederike Otto of Imperial College London, and a founding member of the scientific group.

With hundreds of streets, homes, farms and other businesses still deeply submerged, the survey was conducted just a week ago and has not been peer-reviewed.

While the flood-prone region has a history of severe flooding, “heavy rainfall during the first 21 days of May 2023 is the wettest event of this type on record,” the study concluded.

But “of the 19 models used, none of them show a significant probability or intensity of such an event,” the study said. “This suggests that, unlike most parts of the world, there is indeed no discernible increase in heavy rainfall in the Emilia-Romagna region in the spring.”

Looking at the May floods, that phenomenon is “one where we clearly don’t see a trend,” Otto said.

The last of three floods in May was the most devastating, claiming 15 lives. The extremely heavy and concentrated rainfall caused some 300 landslides and caused nearly two dozen rivers to overflow. The water was so high that fire and Coast Guard helicopters were needed to rescue some residents who climbed onto the roofs of three-story buildings to avoid drowning.

The study’s findings confirmed previous research showing that “with human-induced climate change, the number of low-pressure systems in the Mediterranean has declined. This leads to a reduction in heavy rainfall, offsetting the expected increase in heavy rainfall due to global warming.”

Emilia-Romagna is one of Italy’s most productive regions for both agriculture and manufacturing. As elsewhere in the north, during the country’s post-war economic boom, much of the region quickly became urbanized, depriving it of area needed for drainage and increasing the risk of flooding.

All of that “exacerbated the effects of the heavy rainfall. However, this was an extremely rare event, and most infrastructure cannot reasonably be built to withstand such low-frequency events,” the scientists said in their findings.

“Disasters just don’t happen from rain falling from the sky,” said study co-author Roop Singh of the Red Cross Red Crescent Climate Center, based in the Netherlands.


Borenstein contributed from Washington.


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