Compounding hazards increase flood economic losses across Europe.

Area of Science:

• Environmental Science
• Climate Science
• Disaster Risk Reduction

Background:

• Compound events, multiple hazards occurring simultaneously or sequentially, can amplify disaster impacts.
• The economic losses from compound flood events remain poorly quantified, hindering effective risk assessment.
• Understanding the interplay of various hazards is crucial for comprehensive disaster management.

Purpose of the Study:

• To quantify the economic losses associated with compound flood events in Europe.
• To investigate the trend and prevalence of compounding hazards in flood events.
• To develop and apply a novel metric for compound hazard complexity in risk modeling.

Main Methods:

• Utilized a pan-European multi-hazard dataset (1981-2020) at sub-national resolution.
• Introduced a compound hazard complexity metric and integrated regional exposure and vulnerability data.
• Employed ensemble machine learning with explainable AI and Double Machine Learning Causal Forest for analysis.

Main Results:

• Over 70% of recorded flood events involve compounding hazards (e.g., heatwaves, windstorms, river discharge anomalies).
• A clear increasing trend in compounding hazards over time was observed.
• The top 1% of loss-generating events were all compound, with economic losses exceeding single-hazard floods by over 167 billion euros.
• Higher compound hazard complexity correlated with greater economic losses, independent of flood magnitude and vulnerability.

Conclusions:

• Compound events significantly exacerbate flood-related economic losses in Europe.
• The prevalence of compound hazards in floods is increasing, necessitating updated risk assessment strategies.
• Incorporating compound hazard complexity into risk models is essential for accurate disaster impact evaluation and mitigation planning.