In May 2023, torrential rains battered Italy's Emilia-Romagna region, leaving seventeen people dead, displacing thousands, and causing more than €8.5 billion in damage. It was one of the worst flooding disasters in the country's recent history — and not the last.

Published in Scientific Reports, the new research examines the atmospheric and geographical conditions that made the floods so severe, highlighting how a combination of factors can amplify such events.

When the skies don't clear

Floods typically occur when intense rainfall overwhelms land and river systems. As global temperatures rise, heavy rainfall events are becoming more common, intensifying flood risks across Europe.

The Mediterranean is particularly exposed. Its complex geography — with mountain ranges, narrow valleys, and warm sea surfaces — often traps moisture-laden air, creating a perfect setup for extreme precipitation.

The study found that the Emilia-Romagna floods weren't triggered by a single burst of rain, but by several days of persistent downpours. The region's terrain prevented water from draining efficiently, worsening the impact.

The "cul-de-sac" effect

Researchers identified what they call a "cul-de-sac" effect, in which mountain barriers trapped humid air from the Adriatic Sea. The moisture couldn't escape, and a stationary cyclone kept feeding the storm system. The result: days of relentless rainfall and widespread inundation.

This pattern, scientists say, reappeared during subsequent floods in 2024 — and could threaten other Mediterranean regions with similar topographies.

"The kind of persistent cyclone that caused the Emilia-Romagna floods is not unique to this area," explained Dr. Enrico Scoccimarro, lead author of the study and senior scientist at the Euro-Mediterranean Centre on Climate Change. "Other parts of the Mediterranean could face the same risks."

Predicting the next disaster

With climate change expected to intensify such weather systems, early warning and preparedness are becoming increasingly urgent. The researchers propose a new forecasting metric — "cyclone density persistence" — to better identify storm systems likely to trigger extreme floods.

"This is just the first step toward developing seasonal flood early-warning systems," Scoccimarro said. "Our aim is to improve forecasting precision and help communities better prepare for the events we know are coming."