Reply on RC3

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.