Flaounas et al. (2025) Dynamics, predictability, impacts and climate change considerations of the catastrophic Mediterranean Storm Daniel (2023)

Identification

• Journal: Weather and Climate Dynamics
• Year: 2025
• Date: 2025-11-24
• Authors: Emmanouil Flaounas, Stavros Dafis, Silvio Davolio, Davide Faranda, Christian Ferrarin, Katharina Hartmuth, Assaf Hochman, Aristeidis Koutroulis, Samira Khodayar, Mario Marcello Miglietta, Florian Pantillon, Πλάτων Πατλάκας, Michael Sprenger, Iris Thurnherr
• DOI: 10.5194/wcd-6-1515-2025

Research Groups

• Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
• Institute of Oceanography, Hellenic Centre for Marine Research, Greece
• National Observatory of Athens, Institute for Environmental Research and Sustainable Development, Greece
• Dipartimento di Scienze della Terra, Università di Milano, Italy
• Institute of Atmospheric Sciences and Climate, National Research Council, Italy
• Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212 CEA-CNRS-UVSQ, Université Paris-Saclay & IPSL, France
• London Mathematical Laboratory, UK
• LMD/IPSL, ENS, Université PSL, École Polytechnique, Institut Polytechnique de Paris, Sorbonne Université, CNRS, France
• CNR – National Research Council of Italy, ISMAR – Institute of Marine Sciences, Italy
• Fredy and Nadine Herrmann Institute of Earth Sciences, Hebrew University of Jerusalem, Israel
• School of Chemical and Environmental Engineering, Technical University of Crete, Greece
• Mediterranean Centre for Environmental Studies (CEAM), Spain
• LAERO, Université de Toulouse, CNRS, IRD, France
• Department of Physics, National and Kapodistrian University of Athens, Greece

Short Summary

This study provides a comprehensive, interdisciplinary assessment of the catastrophic Mediterranean Storm Daniel (2023), linking its atmospheric dynamics, predictability, and impacts in Greece and Libya to climate change considerations. It highlights distinct predictability challenges for the storm's cyclogenesis versus its mature medicane phase and evaluates the capacity of numerical models to forecast such extreme events.

Objective

• To analyze how Storm Daniel's cyclone development stages related to flooding in Greece and Libya.
• To assess the reliability and accuracy of numerical models in predicting weather conditions and river discharges at various lead times.
• To determine if numerical weather prediction models can adequately simulate climate extremes.
• To investigate potential links between Storm Daniel's characteristics and human-driven climate change.

Study Configuration

• Spatial Scale: Mediterranean Sea, Greece (Thessaly, Pelion, Peneus catchment: 11,063 km²), Libya (Benghazi, Derna basin: 575 km²), Ionian Sea, Aegean Sea, Black Sea, central/eastern Europe, North Atlantic Ocean. Model resolutions ranged from 9 km (ECMWF EPS) to 0.05° (GloFAS, approx. 5 km) and 1.5 km (EFAS).
• Temporal Scale: Storm Daniel event (4-11 September 2023). Forecast lead times up to 15 days. Climatological periods: 1990-2020 (ERA5), 1993-2023 (GloFAS), 1993-2021 (wave reanalysis), 1979-2000 (ClimaMeter counterfactual), 2001-2022 (ClimaMeter factual). Lagrangian trajectories calculated 10 days backward.

Methodology and Data

• Models used:
  • ECMWF Ensemble Prediction System (EPS)
  • LISFLOOD hydrological model (within GloFAS and EFAS)
  • COSMO Local Ensemble Prediction System (COSMO-LEPS)
  • LAGRANTO tool (for air parcel backward trajectories)
  • ClimaMeter framework (analogue-based climate change attribution)
• Data sources:
  • ECMWF operational analysis and ensemble prediction system products
  • ERA5 reanalysis (hourly atmospheric fields, 0.25° grid spacing)
  • Global Flood Awareness System (GloFAS) river discharge data (v4.0, 0.05° resolution)
  • European Flood Awareness System (EFAS) forecasts (1.5 km resolution)
  • Mediterranean Sea Waves Analysis and Forecast system (Copernicus Marine Service, CMEMS)
  • Mediterranean Sea wave reanalysis dataset (1993–2021, CMEMS)
  • MSWX database (surface pressure, 2 m temperature, total precipitation, wind speed)
  • NOAA/ERSSTv5 (ENSO, AMO, PDO indices)
  • Copernicus Sentinel-2 satellite data (flooded areas)
  • National Observatory of Athens (NOAAN) weather station network (rainfall)

Main Results

• Storm Daniel caused extreme precipitation in Greece (up to 1235 mm in 4 days in Thessaly) and Libya (up to 414.1 mm in 24 hours in Bayda), leading to river discharges exceeding historical maxima by 300-500%.
• Moisture sources for Greece were primarily the Aegean and Black Seas and continental Europe, while for Libya, the Mediterranean Sea was a major source, with both events showing a southwest-to-northeast orientation of large-scale moisture transport.
• Predictability of cyclogenesis in Greece was low at lead times greater than 4 days, improving significantly at shorter lead times (< 72 hours) as the upper-level potential vorticity (PV) streamer intrusion became clearer.
• The medicane's track and landfall in Libya were more predictable (reliable at 4-day lead times), but numerical models generally underestimated its intensity.
• Numerical weather prediction models demonstrated the capacity to capture the extreme character of precipitation and floods, providing crucial information on expected severity, despite underestimating localized magnitudes due to resolution limitations.
• Analogue-based attribution (ClimaMeter) indicated that while similar cyclone systems impacting Greece had comparable pressure minima to the past, temperatures increased by approximately 2 °C. For Libya, Daniel's pressure pattern was exceptional, with no good analogues found.
• Anomalously warm sea surface temperatures (SSTs) in the Mediterranean and Black Sea likely enhanced evaporation, contributing to the extreme precipitation.
• The frequency of circulation analogues conducive to such extreme Mediterranean cyclones has increased in recent decades, suggesting a heightened background risk.
• The disaster in Derna, Libya, was significantly exacerbated by dam failures and societal factors, not solely the extreme rainfall.

Contributions

• Provides a unique interdisciplinary assessment of a catastrophic Mediterranean cyclone, integrating atmospheric dynamics, predictability, hydrological and oceanographic impacts, climate extremes, and attribution theory.
• Offers detailed insights into the differential predictability of cyclone formation versus mature-stage track and intensity, crucial for improving early warning systems.
• Quantifies the specific moisture sources contributing to extreme precipitation events in both Greece and Libya, enhancing understanding of regional hydrological cycles during extreme weather.
• Demonstrates the capability of operational numerical weather prediction systems to forecast the extreme nature of high-impact events, even with limitations in resolving localized magnitudes.
• Applies an advanced analogue-based attribution framework to contextualize Storm Daniel within a changing climate, suggesting that human-driven climate change likely amplified precipitation through warmer SSTs, despite no major shifts in large-scale atmospheric patterns.

Funding

• Italian Ministry of University and Research (MUR) – "Dipartimenti di Eccellenza 2023/2027"
• EU's Horizon Europe program, OCEANIDS (G.A. no. 101112919)
• Next Generation EU, Mission 4, Component 1, CUP B53D23007360006, "Thunderstorm outflows measurements and modeling for strong WIND nowcast and RISK mitigation (WIND RISK)"
• Israel Science Foundation (grant no. 978/23)
• Planning and Budgeting Committee of the Israeli Council for Higher Education – "MedWorld" Consortium
• European Space Agency (ESA) – "Earth observations as a cornerstone to the understanding and prediction of tropical-like cyclone risk in the Mediterranean (MEDICANES)" project (ESA Contract 4000144111/23/I-KE)
• COST actions: CA19109 "MedCyclones" and CA22162 "FutureMed"

Citation

@article{Flaounas2025Dynamics,
  author = {Flaounas, Emmanouil and Dafis, Stavros and Davolio, Silvio and Faranda, Davide and Ferrarin, Christian and Hartmuth, Katharina and Hochman, Assaf and Koutroulis, Aristeidis and Khodayar, Samira and Miglietta, Mario Marcello and Pantillon, Florian and Πατλάκας, Πλάτων and Sprenger, Michael and Thurnherr, Iris},
  title = {Dynamics, predictability, impacts and climate change considerations of the catastrophic Mediterranean Storm Daniel (2023)},
  journal = {Weather and Climate Dynamics},
  year = {2025},
  doi = {10.5194/wcd-6-1515-2025},
  url = {https://doi.org/10.5194/wcd-6-1515-2025}
}