Coastal cities such as Quelimane in Mozambique are highly vulnerable to sea level rise, cyclones, and associated flooding and erosion—while population and economic pressures lead people living along Mozambique’s coast to destroy naturally occurring mangrove forests that protect against these climate-related threats and provide ecosystem services. USAID/Mozambique funded the Coastal City Adaptation Project (CCAP), which included a pilot for mangrove restoration on 22 hectares near the low-income, coastal communities of Icídua and Mirazane in Quelimane. To inform scaling up of mangrove restoration efforts in Quelimane, the USAID/Washington Global Climate Change Office and USAID/Mozambique subsequently funded this cost-benefit analysis to compare economic and environmental costs and benefits of mangrove restoration with construction of an earthen dike to protect vulnerable communities from flooding.
The study considered the value of mangrove restoration for fishing, aquaculture, beekeeping, and greenhouse gas (GHG) mitigation based on ecological assumptions about mangrove growth and the related ecosystem services. A sensitivity analysis valued GHG mitigation benefits at alternative carbon prices, conducted at multiple discount rates to reflect the time value of money. However, this study did not quantify or value the effects of the two alternatives on human health and safety.
Results/Conclusions
Mangrove restoration had a positive financial and economic net present value (NPV) in all of the scenarios analyzed: the economic NPV ranged from $35,708 to $404,041 per hectare depending on the assumed price of carbon. The flood protection value of mangroves was a small part of the total economic benefits due to the low value of the informal sector houses in the community ($915 per house) and the lack of other built infrastructure. The largest economic benefits from mangrove restoration were from the value of fishing and aquaculture and carbon mitigation. The study highlighted that mangrove restoration would not generate the projected returns if mangrove survival rates were low due to poor maintenance, clearing mangroves for other land uses, unsustainable cutting of mangroves, or unfavorable hydrological conditions.
The earthen dike alternative was not financially or economically viable under any of the scenarios considered due to its high construction and maintenance costs and its low flood protection benefits because of the low value of housing. Their ecosystem service benefits made mangrove restoration the preferred alternative over gray infrastructure under the study assumptions.