Flooded Futures: Understanding the Rising Threats and How We Prepare | Stefan Rahmstorf

Flooding has shaped human settlement for millennia—but the scale, speed and complexity of flood risk in the 21st century are unprecedented. In this opening keynote at the Holcim Foundation Forum 2025, climate scientist Stefan Rahmstorf sets the scientific foundation for the Forum, outlining why flood risk is accelerating globally and why urgent, coordinated action is now unavoidable. Rahmstorf presents the full spectrum of flooding—from coastal, riverine and pluvial flooding to groundwater and compound flood events—showing how multiple hazards increasingly coincide to create extreme impacts. Drawing on the latest climate science, he explains how rising sea levels, intensifying storms and shifting precipitation patterns are being amplified by urbanisation, land-use change and ageing infrastructure designed for past conditions. A central focus of the talk is time. Rahmstorf challenges the audience to consider what we are planning for—and over what horizons—by examining projections for 2050 and 2100, the limits and strengths of flood models, and the growing role of real-time data, AI-driven analysis and historical records in improving preparedness. The keynote also addresses the wider societal consequences of flooding, including cascading infrastructure failures, economic exposure, climate migration and the question of who ultimately pays for precautionary measures. Closing the talk, Rahmstorf frames the critical questions that will guide the Forum discussions, positioning the Retreat – Resist – Respond framework as essential for navigating an era of accelerating climate risk. Recorded at the Holcim Foundation Forum 2025.