the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Dec 2025
The October 2024 Extreme Precipitation Event over Valencia: Storyline Attribution of the Synoptic-Scale Thermodynamic Drivers
Abstract. In late October 2024, the western Mediterranean (WMed) region experienced an extreme precipitation event (EPE) centred over Valencia, southeastern Spain, associated with a quasi-stationary cut-off low (COL), producing record rainfall, flash floods, and severe societal impacts. The COL generated an atmospheric-river-like moisture plume from northwestern Africa, while additional moisture originated from the warm Mediterranean Sea. Interaction with regional orography created a highly unstable environment, favouring deep convection and intense local rainfall. To assess the influence of anthropogenic climate change, we analyse high-resolution (∼9 km) storyline simulations from the European Union’s Destination Earth initiative, using the coupled IFS-FESOM model spectrally nudged with ERA5. Two climate scenarios are compared: Factual (present-day) and Counterfactual (~1950), isolating thermodynamic responses while keeping large-scale circulation fixed. Long-term IFS-FESOM and ERA5 datasets provide a climatological reference for event extremeness. Results show that the synoptic configuration alone was sufficient to produce extreme rainfall, but human-induced warming substantially enhanced its magnitude. Moisture content and transport increased by 18–24 %, convective instability (CAPE) by ~25 %, and precipitation over Valencia increased by ~20 % in the Factual scenario. Sea surface temperatures in the Western Mediterranean were ~2 °C warmer, amplifying evaporation. Peak precipitation rates exhibited nonlinear amplification, on 29 October were about 36 % higher in the Factual scenario, exceeding the Clausius–Clapeyron (CC) scaling expected from the mean warming between scenarios. These findings indicate that anthropogenic warming can intensify EPEs in the WMed even when synoptic drivers alone would generate extreme rainfall, highlighting thermodynamic amplification as a key mechanism in Mediterranean flood events. High-resolution, physically consistent storyline simulations offer a robust framework for event-based attribution and improve understanding of future climate risks in vulnerable coastal regions.
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Status: open (until 19 Jan 2026)
- RC1: 'Comment on egusphere-2025-5929', Anonymous Referee #1, 17 Dec 2025 reply
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RC2: 'Comment on egusphere-2025-5929', Anonymous Referee #2, 05 Jan 2026
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Review of: “The October 2024 Extreme Precipitation Event over Valencia: Storyline Attribution of the Synoptic-Scale Thermodynamic Drivers” by Campos et al.
Recommendation: Minor revisions
This study presents an event-based attribution analysis of the extreme precipitation event that affected Valencia in October 2024, utilizing the "storyline" approach with spectrally nudged simulations. The authors employ the coupled IFS-FESOM model within the Destination Earth (ClimateDT) framework at a relatively high global resolution (~9 km). By comparing Factual (present-day) and Counterfactual (1950s) scenarios, the manuscript quantifies the thermodynamic amplification of the event, reporting significant increases in precipitation (~20-36%), CAPE (~25%), and moisture transport due to anthropogenic warming.
The manuscript is well-structured and addresses a topic of high scientific and societal relevance. While recent literature has begun to address this specific event (e.g., Huang et al., 2025; Barriopedro et al., 2025; Calvo-Sancho et al., 2026), the present study offers a distinct and necessary contribution through its methodological framework. Unlike other studies that may rely on uncoupled simulations or purely statistical attribution, this work leverages a coupled atmosphere-ocean system (IFS-FESOM) with high-resolution global coverage. This setup allows for a more physically consistent representation of the thermodynamic and dynamic drivers.
The results regarding the "Super-CC" scaling of precipitation intensity on the peak day are particularly interesting, suggesting non-linear amplification mechanisms that warrant further discussion. The methodology is robust, particularly the use of spectral nudging to isolate the thermodynamic signal while preserving the large-scale circulation.
However, to fully distinguish this work from the rapidly growing body of literature on the Valencia 2024 event and to clarify some physical mechanisms, I suggest several improvements. Detailed comments are provided below, which require Minor Revisions before it can be considered for publication WCD.
General comments:
- While the authors cite recent works like Barriopedro et al. (2025) and Calvo-Sancho et al. (2025), the manuscript would benefit significantly from a more explicit discussion on how the IFS-FESOM coupled results complement these studies. Most existing studies use different attribution protocols or regional models. Does the coupled nature of IFS-FESOM (resolving SST feedbacks dynamically) offer a different perspective on the moisture supply compared to studies using prescribed SSTs? Highlighting this methodological distinction is crucial to justify the publication of this paper in a landscape where other attribution studies already exist. The "storyline" approach with a coupled Digital Twin is a strong point that should be emphasized further in the Introduction and Discussion.
- The finding that precipitation rates increased by ~36% (far exceeding Clausius-Clapeyron scaling) is a key result. The authors mention this could be due to convective microphysics or dynamics. Could the authors provide a more in-depth physical argument here? For example, is there a change in the convective efficiency or dynamic feedback where the stronger latent heat release in the Factual scenario intensifies the local updrafts (beyond just the large-scale nudging)? Calvo-Sancho et al. (2026) suggest the non-linearity in the storm dynamics changes promotes the Super-CC behavior. A brief comparison with the vertical velocity profiles (or heating rates) between Factual and Counterfactual during the peak intensity hours would strengthen this argument.
- The simulation runs at ~9 km. While impressive for a global run, this is still within the "gray zone" for deep convection and arguably coarse for the complex orography of the Valencia region. The paper acknowledges the underestimation of peak rainfall compared to observations. The authors should add a discussion regarding the limitation of parameterized convection at 9 km versus convection-permitting models used in other studies (e.g., Calvo-Sancho et al., 2025).
- Figure 5 shows the evaporation evolution. Since this is a coupled model experiment, it would be interesting to know if the enhanced evaporation in the Factual scenario is purely thermodynamic (warmer SST) or if there are differences in the surface wind stress between scenarios (even with nudging). The evaporation difference seems to peak before the event (Oct 27-28). Please clarify the lag/lead relationship between the local Mediterranean evaporation peak and the precipitation peak on the 29th. Is the moisture locally sourced "pre-loaded" days in advance?
Citation: https://doi.org/10.5194/egusphere-2025-5929-RC2
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The authors have highlighted research work on one of the most catastrophic events in Spain in recent years. Cut-off Lows (COLs) are events that require our dedication and in-depth research to understand them as thoroughly as possible and comprehend their role in a changing climate in the Mediterranean area, a climate change hotspot region.
The work is well-organised and well-written. However, the immediacy and impact of the event have meant that multiple studies have already been published by different scientific groups.
The initial part of the article, the synoptic characterisation of the event, can already be seen in the article entitled "Synoptic background conditions and moisture transport for producing the extreme heavy rainfall event in Valencia in 2024", published in Atmospheric and Oceanic Science Letters, 2025, https://doi.org/10.1016/j.aosl.2025.100666, by Huang et al. And, in the same paper, an in-depth analysis of moisture transport, using the same model (HYSPLIT), was done.
On the other hand, in this recent paper by Barriopedro, D. et al., 2025: A Multimethod Attribution Analysis of Spain’s 2024 Extreme Precipitation Event. published in the BAMS, 106, E2440–E2460, https://doi.org/10.1175/BAMS-D-25-0049.1, a multi-method attribution analysis is carried out, one of which is similar to the methodology and results of the paper under evaluation.
That is why, much to my regret, the authors must reformulate the article, given that the information provided is no longer new at this point.