Stratospheric Drivers of Extreme Weather: Implications for European Storm Damage and Flood Risk

The downward coupling between the stratosphere and the troposphere, as occurs during sudden stratospheric warmings (SSWs) or strong polar vortex events, can have a detectable impact on surface weather in winter, especially over Europe and the North Atlantic. These changes include shifts in the pathways of extratropical cyclones and the associated change in the location of the risk of extreme winds, flooding, or heavy snowfall. 

As changes in the stratospheric circulation contribute to predictability at the surface, understanding the stratospheric drivers to surface weather - from precursors to hazards and impacts - is essential for enhancing societal preparedness and building effective early warning systems for these events. However, there has been no systematic effort to quantify the impacts with respect to stratospheric forcing. 

This work establishes the connection between stratospheric extremes and midlatitude storm damage and flooding events in the Euro-Atlantic region using a combination of ERA5 reanalysis and multiple impact datasets for the period 1998-2023. We show that stratospheric extremes contribute up to 34% of the total counts of storm-related disasters and up to 12% of flood-related disasters in Europe during winter. The geographic distribution of storm-related disasters is influenced by stratospheric forcing, with more frequent storm impacts found over Scandinavia, northern and central Europe and the UK following strong vortex events as compared to the period after SSW events.

Furthermore, using multi-model ensemble of climate models (CMIP6) under future socio-economic scenarios, we examine the variability of extreme storms over the Euro-Atlantic region and investigate their connection to stratospheric drivers and biases in present-day climate and under climate change. Quantifying the connections between stratospheric drivers and surface extremes across various timescales can enable earlier warnings and risk mitigation in both present-day climate and under climate change conditions.