The protective role of mangroves in safeguarding coastal populations through hazard risk reduction: A case study in northeast Brazil

Coastal and estuarine ecosystems such as mangroves provide coastal protection services, safeguarding coastal communities and economies. However, sea-level rise can affect mangroves' protective role by increasing exposure to coastal hazards and economic costs. To better understand the role of mangroves as coastal protective barriers against hazards and their importance for conservation planning in the face of sea-level rise, we first analyzed temporal changes in the coastal landscape by measuring the erosion/accretion rates on the shoreline. We assessed coastal exposure to hazards with the presence and absence of mangroves. Finally, we estimated the economic losses and costs from the long-term retreat in the shoreline and mangrove loss. This study was carried out along the western coast of the South Atlantic, in the northeast Brazilian region. Coastal exposure indices were estimated using the Integrated Valuation of Environmental Services and Tradeoffs (InVEST) software, and the multitemporal analysis of shoreline was developed using the Digital Shoreline Analysis System (DSAS) software. Finally, the economic losses produced by those shoreline changes and social costs were estimated by predicting economic losses in terms of private property and by calculating societal costs in mangrove restoration and rockfill building. The results show that nearly a third of the shoreline is experiencing erosion and the coast could lose an additional 118 ha by 2030. In terms of the value of property loss, this translates to US$38,800 and would increase to US$72,000 under the maximum erosion rate scenario. Based on our coastal vulnerability assessment, almost 50 km of the coastline (20%) would transition to intermediate-high exposure levels if the current distribution of mangroves were to be lost. It is expected to cost about US$145 million in rockfill works and US$21 million in forest restoration to mitigate the impacts from human activities and sea-level rise on mangroves ecosystem services. At the national level, a total loss of mangroves in Brazil could mean mangrove forest restoration costs of nearly US$4000 million. More robust conservation policies are needed to conserve mangrove forests and safeguard the ecosystem-service co-benefits they provide. The latter is essential in low- and middle-income nations where the economic and welfare losses from coastal hazards are more challenging due to dependence on nature for livelihoods and well-being.