How climate change intensified storm Boris’ extreme rainfall, revealed by near-real-time storylines

Understanding the impact of climate change on environmental extremes is of key importance for effective adaptation strategies. In this study, we used an innovative automated system that unveils the thermodynamical climate change signal of the day in near-real-time. To do so, we employed the so-called "event-based storyline approach". This method involves nudging our global CMIP6 coupled climate model (AWI-CM1) towards the observed large-scale free-troposphere winds, including the jet-stream, using various climate background conditions — preindustrial, present and 4ºC warmer climates.

Our analysis focuses on storm Boris, which resulted in record-breaking rainfall across Central and Eastern Europe in September 2024, causing catastrophic flooding. Our findings indicate that human-induced warming led to a 9% increase in rainfall associated with this storm. Furthermore, the area affected by extreme rainfall (exceeding 100 mm) expanded by 18% and would continue expanding in a future warmer climate. However, this future expansion is simulated to be more moderate due to a complex interplay between dynamics and thermodynamics. The case of Storm Boris demonstrates the potential of near-real-time storylines for rapid evidence-based climate change attribution and communication.