04 Aug 2021

04 Aug 2021

Review status: this preprint is currently under review for the journal HESS.

Compound flood impact forecasting: Integrating fluvial and flash flood impact assessments into a unified system

Josias Ritter1, Marc Berenguer1, Francesco Dottori2, Milan Kalas3, and Daniel Sempere-Torres1 Josias Ritter et al.
  • 1Center of Applied Research in Hydrometeorology, Universitat Politècnica de Catalunya, BarcelonaTech, Jordi Girona 1-3 (C4-S1), 08034 Barcelona, Spain
  • 2European Commission, Joint Research Centre, Space, Security and Migration Directorate, Via E. Fermi 2749, 21027 Ispra, Italy
  • 3Freelance consultant, Sladkovicova 228/8, 01401 Bytca, Slovakia

Abstract. Floods can arise from a variety of physical processes. Although numerous risk assessment approaches stress the importance of taking into account the possible combinations of flood types (i.e. compound floods), this awareness has so far not been reflected in the development of early warning systems: Existing methods for forecasting flood hazards or the corresponding socio-economic impacts are generally designed for only one type of flooding. During compound flood events, these flood type-specific approaches are unable to identify the overall hazards or impacts. Moreover, from the perspective of the end-users (e.g. civil protection authorities), the monitoring of separate flood forecasts – with potentially contradictory outputs – can be confusing and time-consuming, and ultimately impede an effective emergency response. To enhance the decision support, this paper proposes the integration of different flood type-specific approaches into one compound flood impact forecast. This possibility has been explored by combining the simulations of two impact forecasting methods (representing fluvial and flash floods) for a recent catastrophic episode of compound flooding: the DANA event of September 2019 in Southeast Spain. The combination of the two methods identified well the overall compound flood extents and impacts reported by various information sources. For instance, the simulated economic losses amounted to about 670 million Euros against 425 million Euros of reported insured losses. Although the compound impact estimates were less accurate at municipal level, they corresponded significantly better to the observed impacts than those generated by the two methods applied separately. This demonstrates the potential of such integrated approaches for improving the decision support.

Josias Ritter et al.

Status: open (until 12 Nov 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-387', Mario Rohrer, 02 Sep 2021 reply
  • RC2: 'Comment on hess-2021-387', Anonymous Referee #2, 14 Oct 2021 reply

Josias Ritter et al.

Josias Ritter et al.


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Short summary
During flood events, emergency managers such as civil protection authorities rely on flood forecasts to make informed decisions. In the current practice, they monitor several separate forecasts, each one of them covering a different type of flooding. This can be time-consuming and confusing, ultimately compromising the effectiveness of the emergency response. This work illustrates how the automatic combination of flood type-specific impact forecasts can improve the decision support.