Risk-based benefit-cost analysis of ecosystem-based disaster risk reduction with considerations of co-benefits, equity, and sustainability

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Ecosystem-based disaster risk reduction (Eco-DRR) measures are gaining attention as creative solutions to reduce community vulnerability against risks while providing multiple co-benefits. We evaluate an Eco-DRR, an afforestation effort, Boca de Sapo (hereafter, BdS), in a marginalized community in peri-urban Lima where we perform household surveys and key informant interviews. To estimate the economic viability, we design a benefit-cost analysis (BCA) and include probabilistically estimated DRR benefits and place-based economic and non-market co-benefits representing stakeholder values. Accounting for income differences, we incorporate equity weights to estimate social welfare benefits. We then evaluate BdS impacts based on BCA results and stakeholder responses along broader sustainability dimensions, and benchmark the project's contribution to urban sustainability using two international frameworks. Household surveys revealed high concern for rockfall risk, and a double-bounded contingent valuation indicated an average household willingness to pay (WTP) of $3.44 ± 0.49/month for BdS maintenance. The equity-weighted risk-based BCA using Monte Carlo simulations indicated BdS was unviable considering DRR benefits with a Benefit-Cost Ratio (BCR) of 0.06 ± 0.08. BCR estimates increased to 1.18 ± 0.42 with incremental integration of tangible property rights co-benefits, and to 1.70 ± 0.59 with addition of WTP representing non-market co-benefits. Our findings demonstrate that inclusion of the multiple Eco-DRR place-based, socio-cultural, and ecological co-benefits with primary DRR benefits is critical as they generate substantial wellbeing impacts for communities. Adapting a sustainability lens revealed holistic Eco-DRR outcomes including access to public green spaces, social inclusion, stronger resource governance, and health and wellbeing benefits, highlighting areas for improvement and pathways for adaptive governance.