Attribution of the synoptic-scale meteorological conditions associated with the October 2024 DANA event over Valencia, Spain

In late October 2024, southeastern Spain experienced severe weather, including intense rainfall, hail, and thunderstorms. On October 29th, several AEMET (Spanish Meteorological Agency) stations in the province of Valencia recorded over 300 mm of rainfall in 24 hours. This extreme event triggered flash floods and river overflows, resulting in over 200 fatalities and extensive damage to public and private property. The event was associated with a deep and persistent cut-off low (COL)—known in Spanish as DANA (Isolated Depression at High Levels)—which developed between Spain and Morocco due to the amplification of a mid-tropospheric trough. The quasi-stationary nature of this system promoted high convective instability, leading to intense, localized storms anchored over the Valencia region.

As with other extreme rainfall events worldwide, atmospheric water vapor's horizontal transport and content played a key role in creating the unstable conditions. In this case, satellite and reanalysis data estimate approximately 30 mm of precipitable water over Valencia—equivalent to a 3–4 standard deviation anomaly above climatological values. This anomalously high moisture had two primary sources: low-level easterly flow from the Mediterranean in the days leading up to the event, and an atmospheric-river-like moisture transport from the tropics across North Africa, channeled by the COL’s circulation.

In warmer conditions—whether due to transient sea surface temperature anomalies or long-term anthropogenic trends—atmospheric moisture content increases, raising the likelihood of extreme, short-duration precipitation. This study investigates the influence of anthropogenic warming on the synoptic conditions surrounding the October 2024 event. To this purpose, we analyze high-resolution (∼9 km) physical climate storyline simulations developed under the European Union’s Destination Earth initiative. These simulations were run with the global, coupled IFS-FESOM model nudged with ERA5, and include three climate scenarios: a counterfactual climate (~1950), the actual climate (~2020), and a future climate (~2040).

Results show that anthropogenic warming intensified both the instability and moisture transport associated with the COL. Specifically, about 20% of the Mediterranean moisture influx can be attributed to human-induced warming, and moisture transport from North Africa increased by ~25% in the actual climate compared to the counterfactual scenario. Overall, the Valencia region experienced 15–20% wetter conditions due to this enhanced moisture environment, resulting in approximately 12% more precipitation over Valencia and up to 20% in the surrounding areas during the event. Ongoing analyses aim to confirm these findings and explore the synoptic conditions for the event under future warming scenarios, contributing valuable insights for climate adaptation.