EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Ensemble generation strategies for the short-range forecast of flash floods: the 12-13 September 2019 event in Eastern Spain

Alejandro Hermoso, Victor Homar, and Arnau Amengual
Alejandro Hermoso et al.
  • Universitat de les Illes Balears, Physics, Palma de Mallorca, Spain (

The Mediterranean region is frequently affected by heavy precipitation and flash flooding during the extended warm season. A precise meteorological forecast of socially relevant aspects of these phenomena such as location, timing and intensity is crucial to prevent personal and material losses. However, forecasting these aspects becomes extremely challenging due to small-scale processes involved in the triggering, development and subsequent evolution of convective systems.


On 12 and 13 September 2019 widespread flash flooding caused devastating effects across Murcia and Valencia, eastern Spain. Seven fatalities were reported, hundreds of homes were flooded and economic losses were estimated at 200 M€. The performance of various ensemble generation strategies for short-range convection-permitting ensemble prediction systems (EPS) are evaluated for this episode. Different sources of error are coped by the implemented ensemble generation approaches.  Uncertainty in the initial and lateral boundary conditions uncertainty is sampled in two ways: (i) the dynamical downscaling of the ECMWF global EPS and, (ii) a new tailored breeding technique that accounts for perturbations across the multiple scales of interest for short-range forecasting. Additionally, errors in mesoscale model formulation are encompassed by combining different parameterization schemes and stochastic physics.


This study contributes to the identification of the most relevant sources of uncertainty hampering an accurate spatial and temporal forecasting of heavy precipitation resulting in flash flooding over the Spanish Mediterranean region. These cutting-edge EPS can contribute to implement more reliable and effective hydrometeorological prediction chains with lead times up to 24 h, providing a valuable support to civil protection and emergency management authorities.

How to cite: Hermoso, A., Homar, V., and Amengual, A.: Ensemble generation strategies for the short-range forecast of flash floods: the 12-13 September 2019 event in Eastern Spain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10453,, 2020

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Presentation version 2 – uploaded on 02 May 2020
Version description: The size of some figures has been increased and some descriptions of the methodology are further developed.[...]
  • CC1: Comment on EGU2020-10453, Maria-Carmen Llasat, 04 May 2020

    Congratulations for your nice work, Alejandro! I have another question. Why do you say that the third phase is dominated by a MCS? Was its duration above 3h and the size the required to be a MCS? 

    • AC1: Reply to CC1, Alejandro Hermoso, 05 May 2020

      Hi Carme, thank you for your interest.

      The duration of the mesoscale convective system displayed on the radar image in slide 8 is well above 3h. It begins to form on 12 September 21 UTC approximately and remains stationary over Murcia for approximately 6 hours. Afterwards, the system advances northwards affecting the area of Cap de la Nau with smaller precipitation intensities than those recorded during phase 1.

      The size of the convective system is around 100 km at the time when the precipitation is more intense.

      Best regards!


      • CC2: Reply to AC1, Maria-Carmen Llasat, 05 May 2020

        Dear Alejandro

        Thank you very much for your information. As you explain it acomplishes the requirements about MCS. As you probably know I work on this topic with Tomeu Rigo (Rigo and Llasat, 2004; Rigo et al, 2005, 2007, 2019 are devoted to MCS)

        Congratulations for your research! We have started to analyse this event but we don't have enough human resources to do it and we have stopped it. When we will re-start we wil contact you

        Best Regards

        Maria Carmen

Presentation version 1 – uploaded on 01 May 2020 , no comments