Introduction Sea level rise is a harsh reality in the Pacific, directly affecting coastal environments and communities. The Intergovernmental Panel on Climate Change predicts that Pacific Island Countries will experience higher sea level rise rates, which according to the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Secretariat of the Pacific Regional Environment Programme (SPREP) are projected to increase by roughly 0.32 meters–0.47 meters by 2070. Elevated sea levels regularly inundate numerous villages in Fiji, highlighting the need for coastal adaptation measures to protect coastal communities from climate change impacts. Nature-based solutions are an effective tool to enhance ecosystem-based adaptation and support the development of green and gray infrastructures. Context From 1992 to 2024, sea level rise around Fiji, as measured by satellite altimeters, was between 4 millimeters (mm)/year to 5 mm/year, with sea level monitoring confirming a localized measurement of 4.1 mm/year in 2024. When comparing these values with the global mean sea level rise of 3.2 mm/year, it is no surprise that low-lying villages are experiencing flooding and coastal erosion. The Government of Fiji has received support to understand how to best address these issues through the Asian Development Bank’s (ADB) Building Coastal Resilience through Nature-based and Integrated Solutions Technical Assistance. The proposed coastal engineering intervention encompasses a blend of green-gray infrastructures, featuring a rock seawall (with locally sourced material), to be complemented by mangrove restoration. Mangroves not only contribute to food security by providing a habitat for fish and birds to nest and live, but they also have a unique ability to capture and retain sediments by reducing the force of water flowing through their dense vegetation. They also enhance shoreline protection by providing a buffer against wave energy. However, mangroves alone cannot prevent flooding from occurring. Significant erosion or accretion of the shoreline frequently leads to the loss of mangroves at both individual tree and forest levels. Villages where the green-gray infrastructure will be developed are deemed suitable to sustain mangrove growth. Site Selection for Green-Gray Infrastructure Development Mangrove mapping The Earth Observation for Sustainable Development Forestry Management project, financed by the European Space Agency, supported ADB in mapping mangrove extent changes at the candidate village sites. The project workflow started by generating yearly, cloud-free Sentinel-2 composite images of the islands, enabling the joint analysis of Sentinel-2 optical and Sentinel-1 radar data using machine learning to map the mangrove extent and condition. This approach was utilized to create maps highlighting changes in mangrove coverage at a resolution of 10 meters. Additionally, it examined variations in the size and density of mangrove areas between 2017 and 2022. Information from the Sentinel satellites was overlaid on very high-resolution 50-centimeter satellite base maps for each village under consideration. Shoreline evolution The KSTA Empowering Developing Member Countries to Use Multi-Spectral Satellite Images and Artificial Intelligence for Land Use and Coastal Planning funded this component of the assessment. A multi-phase algorithm using advanced deep learning techniques analyzed sets of optical satellite images spanning the past 13 years to evaluate changes in the coastline. Namarai Village The village of Namarai, located in the Ra province of Viti Levu, is one of the villages selected for implementation. Along the shoreline fronting the village, there was notable mangrove degradation between 2015 and 2017, attributed to the impact of Tropical Cyclone Winston in 2016. In Namarai, the cyclone destroyed 30 of the 36 houses when it swept through the community on 20 February 2016. Mangrove forests at the southern end of the village were largely destroyed. However, the high-resolution detailed mangrove maps reveal that between 2017 and 2022, mangrove density and coverage increased. This ongoing pattern of growth over the past 5 years suggests that mangroves are expected to persist in their upward trajectory. Mangrove restoration is occurring in the village, with a seedling nursery in place and active selling to nearby villages. Concept design Multiple community consultations were undertaken to ensure that people’s concerns were considered in the design. The community noted that coastal erosion and flooding of the access road and around the village meeting house were the main issues, with coastal erosion along the main extent of the village assessed to be between -0.1 and -0.3 meters/year. A simplified drawing of the proposed hybrid green-gray infrastructure is used during community consultations. Illustration from O2 Marine. Seawalls were designed to prevent erosion and reduce wave over-topping during high wave events. The seawall crests will be stabilized by vetiver grass to further improve the structure. Mangrove planting fronting the structure will provide a shield for wave energy reduction. The community endorsed the final design and redefined the area selected for the mangrove plantation to make sure it will not impact their rugby training field. Additional design features include one-way valves and swales to assist with the removal of stormwater to the sea during heavy rainfall events, thus, reducing floodwater levels. A proposed raised road can further enhance village connectivity. Site selection The success of adding a nature-based solution component to a standard seawall development relies heavily on the suitability of the selected sites where natural environmental conditions will likely to sustain mangrove growth, a crucial element of the project. A direct relationship exists between the growth of coastal mangrove forests and the buildup of shoreline land. Mangrove vegetation can stabilize the substrate, thereby increasing retention, availability, and supply of sediment. Implications The development of seawalls, alongside the restoration of mangrove habitats, will enhance living conditions and increase the resilience of Fijian communities living along the coast. The design of these structures followed an iterative process of consultation with the local community and stakeholders for their endorsement and approval. The construction will soon begin at the pilot sites that have been visited and analyzed in detail, like Namarai, but a longer list of villages waits to be selected for implementation. Resources C. Cameron et al. 2021. Landcover Change in Mangroves of Fiji: Implications for Climate Change Mitigation and Adaptation in the Pacific. Environmental Challenges. 2. 100018. Commonwealth Scientific and Industrial Research Organisation, and Secretariat of the Pacific Regional Environment Programme. 2021. Current and Future Climate for Fiji: Enhanced 'NextGen' Projections. Technical report. EP2021–2149. Melbourne. Government of Fiji, Ministry of Public Works, Transport and Meteorological Services, Fiji Meteorological Service. 2024 Annual Climate Summary. University Corporation for Atmospheric Research. 2025. Global Mean Sea Level from TOPEX & Jason Altimetry Climate Data Guide. Ask the Experts Sira Tecchiato Coastal Resilience Consultant, Asian Development Bank and Principal Coastal Geomorphologist, O2 Marine Sira Tecchiato is a coastal scientist with expertise in coastal resilience and nature-based solutions. She is currently engaged as the Technical Coordinator of ADB’s technical assistance “Building Coastal Resilience Through Integrated and Nature-based Solutions” and contributes to coastal adaptation projects in Southeast Asia and the Pacific. She has a PhD in Marine Geosciences and works as a principal consultant in the Australian industry, with a focus on supporting coastal management for ports, government, and the private sector. Follow Sira Tecchiato on Geoffrey Wilson Senior Water Resources Specialist, Sectors Department 2, Asian Development Bank Geoff Wilson contributes to implementing ADB's Strategy 2030 by providing advice on strategic directions, conducting activities on water issues, and producing water knowledge products and publications. He has over 30 years' experience in the consulting engineering market, where he focused on hydraulic and hydrological studies, including sustainable development and climate change. He obtained his master’s in Civil Engineering from Canterbury University, NZ and continued toward a master’s in HydroInformatics from UNESCO IHE in Delft, The Netherlands. Follow Geoffrey Wilson on Asian Development Bank (ADB) The Asian Development Bank is a leading multilateral development bank supporting sustainable, inclusive, and resilient growth across Asia and the Pacific. Working with its members and partners to solve complex challenges together, ADB harnesses innovative financial tools and strategic partnerships to transform lives, build quality infrastructure, and safeguard our planet. Founded in 1966, ADB is owned by 69 members—49 from the region. Follow Asian Development Bank (ADB) on Leave your question or comment in the section below: View the discussion thread.