Preparing for future flood risk now. An expanded understanding of forward-looking disaster risk reduction in the face of increasing coastal and riverine flood risk.

Flooding is one of the most destructive natural hazards worldwide, with risks expected to rise sharply under climate change, sea-level rise, population growth in vulnerable areas, and unsustainable resource extraction. Global flood risk assessments have become essential tools for guiding international investments, policymaking, and disaster risk reduction (DRR) strategies. Yet, these models often privilege financial performance and engineered defences, while neglecting alternative solutions, social inclusivity, and the lived realities of marginalised groups. This thesis investigates how global flood risk assessments can evolve to incorporate a wider range of measures, decision-making metrics, and equity considerations, ultimately contributing to more effective and inclusive strategies for reducing flood risk.
The study first evaluates global coastal flood risk, revealing that without intervention, annual damages could exceed USD 1 trillion by 2080. While traditional dykes and levees achieve the greatest risk reduction in monetary terms, alternative measures such as zoning restrictions, dry-proofing, and foreshore vegetation offer significant benefits when assessed through benefit-cost ratios. Importantly, all four measures studied return positive investment outcomes at the global scale, highlighting the economic viability of diverse DRR strategies.
Riverine flood risk is then examined, with damages projected to increase nearly 50-fold by the end of the century in the absence of adaptation. Analysis across 180 sub-national regions shows striking differences in the cost-effectiveness of dykes, zoning restrictions, and dry-proofing depending on the metric applied. Notably, benefit-cost analysis and efficacy analysis often point to different “best” solutions, with three-quarters of regions arriving at different recommendations depending on the chosen metric. This finding underscores the importance of incorporating multiple approaches to decision-making rather than relying on a single evaluative lens.
The role of Nature-based Solutions (NbS) is further explored through a global review of rural coastal contexts, which are typically overlooked in flood modelling despite being home to highly vulnerable populations. Evidence from 28 peer-reviewed cases illustrates that while NbS face significant barriers—including resource constraints and governance challenges—they can deliver co-benefits such as agricultural support, aquaculture opportunities, and ecotourism. Many successful examples emphasise the importance of local knowledge and community participation in implementation, suggesting that future global assessments should integrate these perspectives alongside economic metrics.
Beyond technical measures, the thesis also addresses social vulnerability in global flood risk assessments. Current frameworks often ignore or inadequately capture the experiences of sexual and gender minorities, treating gender as a binary and excluding sexual orientation altogether. By combining global flood risk data with indicators of legal and social protections, this research highlights that tens of millions of people exposed to flood risk currently live without recognition or legal safeguards. These numbers are expected to rise significantly by 2050 if social and legal conditions remain static. This omission represents a major blind spot in international DRR frameworks and demonstrates the need for more inclusive, human rights-based approaches to flood resilience.
The synthesis chapter argues for a redefinition of global flood risk assessments. Future models must account for a broader spectrum of adaptation measures evaluated with multiple decision-making metrics that move beyond financial efficiency alone. They must also reflect the diversity of exposure and vulnerability across societies, incorporating marginalised groups and overlooked regions. By embedding inclusivity, pluralism, and hybridised strategies into global frameworks, flood risk assessments can better inform equitable and sustainable pathways for reducing disaster impacts worldwide.
In sum, this thesis demonstrates that global flood risk assessments are powerful tools, but only if they evolve to reflect the complex realities of climate change, societal vulnerability, and adaptation potential. Expanding their scope to include multiple strategies, diverse decision metrics, and equity considerations can enable more effective, just, and forward-looking disaster risk reduction in the decades ahead.