From October 29-30, 2024, eastern Spain was hit by exceptionally heavy rainfall.
Subsequent floods killed more than 200 people, displaced more than 400 people, and saw hundreds of thousands lose access to water and electricity (GDACS, 2024). The death toll is the highest in a flood event in Europe since 1967 and is expected to rise further in coming days (BBC, 2024).
In the Mediterranean region of eastern Spain, extreme precipitation events such as the one observed, are frequently driven by the presence of an upper-tropospheric cut-off low (COL; known as DANA in Spanish (WMO, 2024), or gota fría, meaning cold drop), which refers to the intrusion of cold air within the COL. At the surface, these systems generate easterly winds that bring warm, moist air inland from the Mediterranean Sea. This air is then forced upward along the complex terrain of eastern Spain, leading to significant rainfall along the coast and often triggering flash floods, locally termed riadas.
The Mediterranean coastline of Spain, particularly the Valencia and Catalonia regions, is highly vulnerable to these floods. Approximately one-third of the most severe floods in this area have been associated with cut-off lows (COLs) (Ferreira 2021). The cut-off low in the higher altitudes, together with very warm air over the Mediterranean, led to large instabilities in the atmosphere which in turn led to strong convection and the very heavy rainfall observed (WMO, 2024).
WWA performed a super rapid analysis, analysing observations only, and therefore this is not a formal attribution study. In addition, we analysed daily precipitation values over a relatively large region rather than the more localised sub-daily precipitation extremes. This means it may underestimate the intensity of heaviest rainfall in particular regions.
In summary, over the past ~75 years, daily rainfall extremes in the September-December season in central and southeastern Spain have increased significantly with global warming, approximately doubling in likelihood and equivalently increasing in intensity by 12%. While a full attribution would require an assessment of trends in climate models as well as observations, the results are in line with other literature on rainfall extremes in the region.