More than 70% of flood events in Europe involved other hazards such as drought, heatwaves or windstorms, and these combined events were linked to far higher economic losses.
Floods are often treated as standalone events in risk models, insurance frameworks and early warning systems, but the study found most European floods were “compound events”, with at least one additional hazard occurring before or alongside flooding, according to a new study led by scientists at the European Commission’s Joint Research Centre released on Wednesday.
Average losses from floods combined with other hazards were 2.8 times higher than losses from floods occurring alone over the study period, the study reported.
Every flood in the top 1% for economic losses was a compound event.
Compound flood events involving two or more additional hazards became more common over time, rising by 186% between the 1980s and the 2010s, compared with a 16% rise for floods that occurred alone.
Study examined 1,349 flood events
Researchers built what they described as the first systematic pan-European picture of compound flood risk by combining a database of historical flood impacts with meteorological and hydrological records, covering 1,349 flood events between 1981 and 2020.
They analysed five types of combined flood events: floods preceded by wet conditions; drought-to-flood transitions; heatwave–flood sequences; cold spell–flood events; and windstorm–flood events.
The authors used machine learning — a method that finds patterns in large datasets — alongside “explainable AI”, which is designed to show how a model reaches its conclusions, and a causal inference approach.
Regions where floods occur alongside other hazards suffered higher average losses even after accounting for flood size and local vulnerability, the study found. The effect was stronger in areas described as already fragile.
The study was led by the Joint Research Centre in collaboration with the Potsdam Institute for Climate Impact Research, Vrije Universiteit Amsterdam and the University of Louvain.
