EGU2020-3881, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-3881
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

A forensic hydrometeorological and geomorphological reconstruction of the catastrophic flash flood occurred in Mallorca (Spain) on October 9th, 2018

Arnau Amengual1, Jorge Lorenzo-Lacruz2, Celso Garcia2, Enrique Morán Tejeda2, Víctor Homar1, Aina Maimó-Far1, Alejandro Hermoso1, Climent Ramis1, and Romu Romero1
Arnau Amengual et al.
  • 1Universitat de les Illes Balears, Grup de Meteorología, Departament de Ciències Físiques, Palma, Mallorca, Spain
  • 2Universitat de les Illes Balears, Grup de Geografia física, Departament de Geografia, Palma, Mallorca, Spain

An extraordinary convective rainfall event –unforeseen by most numerical weather prediction models– led to a devastating flash flood in the town of Sant Llorenç des Cardassar, eastern Mallorca, on 9th October 2018. Four people died inside the village, while the total death toll was of 13 and economic damages amounted to 91 M€. The observed flooded extension inside the town by the Copernicus Emergency Management Service –based on Sentinel-1 imagery– far exceeded the extension for a 500-year return period flood. This extreme event has been reconstructed by implementing an integrated flood modelling approach over the semi-arid and small-sized Ses Planes basin up to Sant Llorenç (23.4 km²). This procedure is based on three components: (i) generation of high spatial and temporal resolution radar-derived precipitation estimates; (ii) modelling of the hydrologic response based on post-flood peak discharge estimates; and (iii) hydraulic simulation and mapping of the affected areas based on high water marks. Radar-derived rainfall estimates and the simulated flooding extent and water depths highly correlate with observations. The hydraulic simulation has revealed that water reached a depth of 3 m at some points inside Sant Llorenç and that water velocity greatly increased at bridges’ locations close to the town centre. Even if the catastrophic flash flood was not a debris flow, the flood bore eroded enough material to change channel geomorphology. This study also highlights how the concurrence of the very low predictability of this type of extreme convective rainfall events and the very short hydrological response times typical of small Mediterranean catchments still challenges the implementation of early warning systems, which effectively reduce people’s exposure to flash flood risk in the region.

How to cite: Amengual, A., Lorenzo-Lacruz, J., Garcia, C., Morán Tejeda, E., Homar, V., Maimó-Far, A., Hermoso, A., Ramis, C., and Romero, R.: A forensic hydrometeorological and geomorphological reconstruction of the catastrophic flash flood occurred in Mallorca (Spain) on October 9th, 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3881, https://doi.org/10.5194/egusphere-egu2020-3881, 2020

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Presentation version 3 – uploaded on 02 May 2020
Just some minor and final amendments
  • CC1: Comment on EGU2020-3881, Maria-Carmen Llasat, 04 May 2020

    Congratulations, Arnau and the other authors, for your good and deep work! I have a last question: 

    Why have you used the FEST and KLEM models? They are not usual to flash floods modeling

    • AC1: Reply to CC1, Arnau Amengual, 04 May 2020

      Hi Carme,

      well, the idea was suggested by a reviewer pointing out this same interesting question as you do. So, we decided to test the model dependency to flash-flood response by using two different models. A complex one and simple one.  As both models account for a varying complexity in the description
      of the physical processes and model structure, we thought that a better quantification of the associated uncertainties should be expected when simulating the peak discharges and flow velocities for this extreme event. Why the choice of these two particular models?. Nothing in special, in fact. It is enriching to have available in the scientific community so much diversity of models in order to better encompass the uncertainties associated with their structures, numerical formulations and so on. We decided to work with these particular models, because we have already worked with them in the past.

       Cheers and take care!

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