Thomas Van Der Pol (Germany) 1; Jochen Hinkel (Germany) 1; Jan Merkens (Germany) 2; Leigh Macpherson (Germany) 3
1 - Global Climate Forum; 2 - Kiel University; 3 - Siegen University
A wide range of economic methods is available to support local decision-making on coastal flood protection investments or standards under changing flood risks. However, comparisons of these methods are either qualitative in nature or limited in scope, which makes it difficult to select an appropriate subset of methods in a given coastal decision context. To contribute to addressing this limitation, this paper applies an adapted Dutch cost-benefit analysis (CBA) method and six loss- and regret-based methods for robust decision-making (RDM) to the German Baltic Sea coast. The CBA results suggest that a share of the Baltic Sea coast of Schleswig-Holstein (18.2-23.3% of total km) and Mecklenburg-Vorpommern (8.6-10.3 % of total km) with no or limited flood protection, is currently under-protected from a social welfare perspective. Efficient investment strategies, however, diverge across sea-level rise and socioeconomic scenarios, and are greatly affected by extreme sea-level uncertainty.
The robust performance of strategies, in turn, differ across robustness metrics and are sensitive to the specified scenario set. The minimax criterion is shown to yield most conservative solutions, followed by minimisation of maximum absolute regret, and minimisation of maximum relative regret or average regret. Low regret (B/C>1) solutions tend to be least conservative. A scenario version of info-gap analysis is proposed to analyse sensitivity to defined lower and upper scenarios.
The paper concludes that CBA and the applied methods for RDM are complementary: combining these methods can help decision-makers to narrow down the number of ‘good’ solutions, i.e. solutions that are both potentially efficient and sufficiently robust, as well as to show efficiency-robustness trade-offs beyond a selected set of plausible futures. Local policy recommendations include further harmonising flood defence heights, revisiting the existing (“H200+50 cm”) design height policy, and increasing preparedness for future investments in the region. The analyses performed suffer from important data and model limitations, for example on protection type, estimated monetary flood exposure and vulnerability.