Evidence from 2024 Storm Boris indicates anthropogenic climate change amplifies floods more than extreme...

Anthropogenic climate change intensifies extreme precipitation, but how it affects flood hazards remains uncertain. In September 2024, Storm Boris triggered catastrophic flooding across central Europe, underscoring the need to quantify the contribution of human-caused climate change to flood intensity for effective risk management. Using a storyline approach, we show that precipitation associated with Storm Boris would have been 6 to 9% lower in the absence of anthropogenic climate change, whereas flood peaks would, on average, have been reduced by 14 to 22%. Our estimates are based on nudged simulations from two climate models coupled with two hydrological models across hundreds of affected catchments. The results imply that anthropogenic forcing amplified flood peaks by a factor of 2.1 to 2.9 relative to the increase in event precipitation. Overall, we demonstrate that attributing precipitation alone would substantially underestimate flood hazard amplification from climate change-an effect that should inform future risk assessments and loss estimates.