A triple-whammy of cyclones caused Italy’s deadly floods, but climate-driven drought made them worse, according to the first attribution study.
Climate change did not have a “significant” influence on the likelihood or intensity of Italy’s recent devastating floods, new analysis shows.
A rare, triple-whammy of cyclones caused the exceptionally heavy rainfall which claimed 17 lives and displaced 50,000 people in northern Italy last month.
But scientists at the World Weather Attribution (WWA) group - which analyses the links between extreme weather events and global warming - say climate change is not necessarily to blame.
“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 added.
“Remember there was a drought before” the first storm pummelled the Emilia-Romagna region on 2 May, and “this [drought] was due to climate change.”
The study estimated there was a 1-in-200 probability that three cyclones would strike within a three-week period. Precisely because having three exceptionally heavy downpours in such a short timeframe is so rare, the climate experts cautioned that more time for study is needed.
How do the experts know what role climate change played in the floods?
Using computer simulations and past observations, the researchers looked for but found no evidence of human-caused warming behind the drenching.
WWA compared what happened to a computer simulated world of no human-caused warming and didn't see the fingerprints of fossil-fuel-induced climate change, unlike in many past studies.
While the flood-prone region has a history of severe flooding, "the heavy rainfall over the first 21 days of May 2023 is the wettest event of this type in the record,'' the study concluded.
But “of the 19 models used, none of them show a significant likelihood or intensity of such an event to occur,'' the study said. "This suggests, that in contrast to most parts of the world, there is indeed no detectable increase in heavy rainfall in the Emilia-Romagna region in spring."
The study's findings corroborated earlier research that found that “with human-induced climate change, the number of low-pressure systems in the Mediterranean has decreased. This leads to a reduction in heavy rainfall, offsetting the expected increase in heavy rain from global warming.”
But climate-driven drought exacerbated the damage
As Faranda points out, two years of scant or no rainfall left the land so parched it couldn't absorb the first rainfall. Drought derived in large part to lack of Alpine snowfall, which usually replenishes the Po River and other, smaller waterways in Italy's north.
Emilia-Romagna is one of Italy's most productive regions for both agriculture and manufacturing. Like elsewhere in the north, during the nation's post-war economic boom, much of region was rapidly urbanised, depriving the area of terrain needed for drainage and increasing the risk of flooding.
All that "has exacerbated the impacts 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.
Although episodes of heavy spring rainfall are not increasing in Emilia-Romagna, the researchers warned that extreme rainfall is on the up in other parts of Italy.
Almost 94 per cent of Italian municipalities are at risk of landslides, floods and coastal erosion, according to the Italian Institute for Environmental Protection and Research (ISPRA).
Emilia-Romagna is particularly at risk, with a history of flooding and landslides, but nothing even comparable to May's disaster has occurred since 1939, the study found.