Flood risk curves and uncertainty bounds

Abstract

Although flood risk assessments are frequently associated with significant uncertainty, formal uncertainty analyses are the exception rather than the rule. We propose to separate two fundamentally different types of uncertainty in flood risk analyses: aleatory and epistemic uncertainty. Aleatory uncertainty refers to quantities that are inherently variable in time, space or populations of individuals or objects. Epistemic uncertainty results from incomplete knowledge and is related to our inability to understand, measure and describe the system under investigation. The separation between aleatory and epistemic uncertainty is exemplified for the flood risk analysis of the City of Cologne, Germany. This flood risk assessment consists of three modules, (1) flood frequency analysis, (2) inundation estimation, and (3) damage estimation. By the concept of parallel models, the epistemic uncertainty of each module is quantified. The epistemic uncertainty associated with the risk estimate is reduced by introducing additional information into the risk analysis. Finally, the contribution of different modules to the total uncertainty is quantified. The flood risk analysis results in a flood risk curve, representing aleatory uncertainty, and in associated uncertainty bounds, representing epistemic uncertainty. In this way, the separation reveals the uncertainty (epistemic) that can be reduced by more knowledge and the uncertainty (aleatory) that is not reducible.

Adaptability and transferability of flood loss functions in residential areas

“…The model is applicable on the microscale, i.e., on the object level, as well as on the mesoscale, i.e., on homogeneous land use units. For both scales it was successfully validated ) and applied or modified in different studies (e.g., Kreibich and Thieken, 2008;Apel et al, 2009;Merz and Thieken, 2009;Wuensch et al, 2009;Elmer et al, 2010;Kreibich et al, 2011b;Merz et al, 2013).…”

“…Even if the full range of the underlying asset values (i.e., the minimum (EUR 224 per m 2 ) and maximum (EUR 353 per m 2 ) values) is applied, none of these two functions is within the confidence interval in one of the two hydraulic-simulation runs. Some of these three standard functions were already used in different geographical regions before like in the German federal states of Saxony (Schwarz et al, 2005;Thieken et al, 2008) and Baden-Württemberg Apel et al, 2009;Merz and Thieken, 2009) but it has also been reported that these models tend to under-or overestimate observed damage to buildings (e.g., Schwarz et al, 2005;Thieken et al, 2008;Apel et al, 2009).…”

“…The maximum range of these specific combinations is only EUR 0.3 m (factor of 1.3) and illustrates the remaining deviation between the most accurate models as far as two hydraulic-simulation runs are applied for the flood loss model validation. However, for a complete assessment of the associated uncertainty for flood risk curves also the uncertainty of the flood frequency estimates has to be taken into account (e.g., Merz and Thieken, 2009).…”

Assessment of the effectiveness of flood adaptation strategies for HCMC

“…There are many studies that quantify flood hazard and expected changes in the hazard due to sea-level rise (Nicholls and Cazenave, 2010). Other studies use flood risk assessment models, focusing both on the flood hazard, and on flood exposure and vulnerability (Apel et al, 2008;Merz and Thieken, 2009;Ward et al, 2011a). Some of these studies use catastrophe risk models to calculate risk reduction for different flood adaptation measures on local to regional scales (e.g.…”

Modelling flood damages under climate change conditions – a case study for Germany

“…There exist many different methodologies to derive flood losses (Merz and Thieken, 2009;Apel et al, 2009a), typically in the suite: discharge (stage) -damage, or discharge -return period -damage, developed for a range of scalesfrom local to national or continental. However, the issue of Cammerer et al (2013) examined adaptability and transferability of stage-damage functions for the estimation of direct flood damage to buildings.…”