Dredging versus hedging: Comparing hard infrastructure to ecosystem-based adaptation to flooding

- We estimate costs and benefits of options to mitigate flooding in Fiji.
- Ecosystem-based adaptation often yields higher net benefits than conventional options.
- Afforesting upper catchments provide greatest overall net benefits.
- Riparian buffers most cost-effective with benefit-cost ratios between 2.8 and 21.6.
- Benefits increase by 100% or more when accounting for climate change

Efforts to ameliorate flooding have historically centred on engineered solutions such as dredging rivers, building levees, and constructing spillways. The potential for ecosystem-based adaptation (EbA) options is becoming increasingly apparent; however, implementation is often limited by a poor understanding of their costs and benefits.This study compares the costs and benefits of a range of hard infrastructure and ecosystem-based adaptation options to mitigate flooding under climate change using data from two catchments in Fiji. We employ unique survey data to document the costs of flooding under various climate change scenarios. We then use a hydrological model to simulate the potential benefits of a range of hard infrastructure and EbA options and conduct a comprehensive cost-benefit analysis.We find that under reasonable economic assumptions, planting riparian buffers is the most cost-effective option, yielding benefit-cost ratios between 2.8 and 21.6. However, the absolute level of protection provided by this strategy is low. Afforestation provides greater overall benefits, yielding net present values between 12.7 and 101.8 million Fijian dollars, although implementation costs would be substantial. Planting floodplains and reinforcing riverbanks provide some monetary benefits that are lower than riparian and upland planting. Elevating houses is not economically viable under any climate scenario.