Adapting densely populated deltas to the combined impacts ofclimate change and socioeconomic developments presents a major challenge fortheir sustainable development in the 21st century. Decisions for theadaptations require an overview of cost and benefits and the number ofstakeholders involved, which can be used in stakeholder discussions.Therefore, we quantified the trade-offs of common measures to compensate for an increase in discharge and sea level rise on the basis of relevant, butinexhaustive, quantitative variables. We modeled the largest deltadistributary of the Rhine River with adaptation scenarios driven by (1)?thechoice of seven measures, (2)?the areas owned by the two largeststakeholders (LS) versus all stakeholders (AS) based on a priori stakeholderpreferences, and (3)?the ecological or hydraulic design principle. Weevaluated measures by their efficiency in flood hazard reduction, potentialbiodiversity, number of stakeholders as a proxy for governance complexity,and measure implementation cost. We found that only floodplain lowering overthe whole study area can offset the altered hydrodynamic boundaryconditions; for all other measures, additional dike raising is required. LSareas comprise low hanging fruits for water level lowering due to thegovernance simplicity and hydraulic efficiency. Natural management ofmeadows (AS), after roughness smoothing and floodplain lowering, representsthe optimum combination between potential biodiversity and flood hazardlowering, as it combines a high potential biodiversity with a relatively lowhydrodynamic roughness. With this concept, we step up to amultidisciplinary, quantitative multi-parametric, and multi-objectiveoptimization and support the negotiations among stakeholders in thedecision-making process.
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