On the role of an AR-like moisture plume in the October 2024 Valencia extreme rainfall event

On 29 October 2024, a cut-off low triggered an extreme rainfall event over eastern Spain, with daily accumulations exceeding annual precipitation in several areas. The impacts were particularly severe in the province of Valencia, where widespread totals above 300 mm were recorded and local maxima reached up to 771 mm, resulting in more than 200 fatalities. Given the magnitude of the disaster, the dynamical and thermodynamical drivers of the event, as well as the potential role of climate change, have already prompted extensive investigation. Several media reports and recent studies (Campos et al., 2025) have pointed to the presence of an upper-level tropospheric moisture plume resembling an atmospheric river (hereafter AR-like structure) connecting the Mediterranean region with the tropical Atlantic via North Africa, suggesting that it may have contributed to the event’s intensification. However, the quantitative contribution of this structure to the observed precipitation remains unclear.

Here we address this issue using the WRF model coupled with Water Vapor Tracers (WRF-WVTs), which allows tracking moisture from prescribed source regions to precipitation while fully resolving the event dynamics. Our results show that the Mediterranean Sea was the dominant direct moisture source, while moisture associated with the AR-like structure contributed approximately 20-30% of the total precipitation. To further assess the role of this remote moisture transport, we introduce a methodology to quantify its indirect impact through enhanced latent heat release and the resulting increase in atmospheric instability. We find that this indirect mechanism is substantially more important than the direct moisture contribution, highlighting the key role of the AR-like structure in intensifying the event.

Campos, D. A., Grayson, K., Saurral, R. I., Beyer, S., John, A., Olmo, M., and Doblas-Reyes, F.: The October 2024 Extreme Precipitation Event over Valencia: Storyline Attribution of the Synoptic-Scale Thermodynamic Drivers, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-5929, 2025.