How climate change shapes weather patterns: Storm Boris analysis

How climate change shapes weather patterns: Storm Boris analysis
by Robert Schreiber
Berlin, Germany (SPX) Nov 11, 2024
The storm "Boris" recently caused significant flooding across Central and Eastern Europe, leaving at least 27 people dead and many displaced. A study by the Alfred Wegener Institute (AWI) has found that without current global warming levels, Boris would have delivered approximately nine percent less rainfall. This finding was made possible through a new modelling approach called 'storylines', detailed in 'Communications Earth and Environment'.

The storm, which struck in mid-September, brought unprecedented precipitation to parts of Poland, the Czech Republic, Austria, and Romania. While communities work on recovery, attention shifts to ongoing extreme weather events. Public discourse often questions if climate change is behind these phenomena. According to Dr. Marylou Athanase, a physicist at AWI, "As early as one or two weeks after an event, probabilistic attribution studies can indicate how much more likely the event was due to climate change."

However, such probabilistic data can be difficult for non-experts to grasp. Dr. Antonio Sanchez-Benitez, co-lead author of the study, explains that this challenge inspired the development of the 'storyline' method. "We apply the 'what if' principle, comparing actual weather events to scenarios without climate change. This helps clearly identify climate change's role in both severe and everyday weather."

The research on storm Boris revealed that the storm intensified as it traveled from the eastern Mediterranean and Black Sea toward Central Europe due to water temperatures around two degrees Celsius higher than preindustrial levels. This contributed to more moisture in the atmosphere, fueling heavier rainfall. While nine percent may seem small, it can be crucial for flood impacts, influencing how well infrastructure like rivers and dams can handle excess water.

The AWI team used their CMIP6 climate model, aligned with the IPCC's Sixth Assessment Report, and integrated ERA5 reanalysis wind data from the ECMWF. Dr. Helge Gossling, leader of the storyline research team, notes that they applied a technique called 'nudging' to synchronize the model with observed wind conditions. This allowed accurate replication of real-world weather, which was then compared to a pre-climate change scenario by adjusting greenhouse gas levels.

Automated analyses now run daily on a supercomputer at the German Climate Computing Center, and results are available via AWI's public online tool here. This platform provides interactive insights into temperature and precipitation impacts from January 2024 onward, aiming to improve public understanding of climate-related changes in weather and support media coverage.

Research Report:How climate change intensified storm Boris' extreme rainfall, revealed by near-real-time storylines