The evolution of flood risk in Italy across two centuries: disentangling risk drivers to understand past trends and future issues

Floods are among the most severe natural hazards globally, with around 1.81-2.3 billion people currently exposed to 1-in-100-year events. Understanding the evolution of flood risk is important for targeting investments and policies to address the drivers that dominate in each period, ensuring effective risk reduction. This requires disentangling the relative contribution multiple drivers to understand their behavior and adapt strategies as their relative importance changes. This study focuses on two key factors: population dynamics and climate change.We conduct a national-scale assessment spanning 230 years (1870-2100) using the probabilistic large-scale flood risk model RESCUE-FR to quantify how these drivers have shaped historical trends and will influence future flood exposure in Italy. Our analysis reveals a transition of dominant flood risk drivers. From 1870 to 2000, demographic changes dominated: population growth and migration into flood-prone areas drove an increase in exposure, while climate conditions remained relatively stable. Instead, the future presents a starkly different picture: climate change will be the dominant driver; specifically starting from the second part of this century (year 2060), climate change alone accounts for 57.5% of the projected increase in exposed population, while demographic growth contributes only 12.7%, despite Italy's total population being projected to decline after 2030.Our findings demonstrate that flood risk management in Italy should adapt to this evolving landscape: from managing exposure in known flood zones, and preventing development in areas that will become vulnerable under future climate scenarios.