Integration of flood-induced benefits in flood risk optimization analysis in South-Central Bangladesh

Flooding is a recurrent distress in Bangladesh, yet conventional risk mitigation strictly aims to keep water away, often disregarding the socio-ecological benefits of floodplain utilization. This study presents a spatial risk–benefit analysis in Bangladesh’s flood-prone coastal regions. By overlaying two-dimensional hydrodynamic model-simulated flood depths (utilizing the F0–F5 scale) with land-use maps and economic valuation curves, we quantitatively integrate benefit and damage functions into a risk optimization framework. Participatory appraisals (PCMs, FGDs, KIIs) further contextualized local stakeholder coping mechanisms. Our findings demonstrate that while extreme inundation drives severe losses, moderate flood depths (0.3–0.9 m depth) enhance aquatic habitats and generate crucial fisheries benefits. It necessitates a strategic trade-off with agricultural submergence. Quantitatively, an extreme 50-year flood event (under 2023 land-use) causes over USD 43 million in agricultural damage, exceeding ecosystem benefits by approximately USD 16 million. Conversely, floods with recurrence intervals under five years yield net positive outcomes, with a 2.33-year flood generating the optimal economic benefit. Simulated 2041 scenarios, incorporating land-use predictions, show a similar trend, though planned infrastructure reduces the net damage gap of extreme events by 28%. These results emphasize a necessary policy shift for deltaic environments. Rather than relying solely on hard-engineered, 'full-flood-free' concept, flood management in Bangladesh must embrace ecosystem-based adaptation. Strategically allowing tolerable inundation (up to a 5-year return period) optimizes the balance between structural protection, sustainable livelihoods, and vital ecosystem services, offering a pragmatic framework for future national delta management interventions.