Satellite Technology: Mapping Fiji's Mangrove Green Shield

The cover image is a map produced by Hatfield displaying the change in Soil Adjusted Vegetation Index (SAVI) around the Namarai village, Fiji, between the years of 2017 and 2022. An increase in SAVI (green) indicates that mangrove density increased between 2017-2022. The yellow areas are those where the SAVI, and consequently the mangrove density, remained the same over the period analysed. Background Image Data: ESRI Online Service.

The  Earth Observation for Sustainable Development Forestry Management  (EO4SD FM) project, financed by the European Space Agency (ESA), is supporting the Asian Development Bank (ADB) in Fiji. This involves the use of Earth Observation (EO) data for the  Knowledge and Support Technical Assistance (KSTA) 54212-001 Building Coastal Resilience Through Nature-based and Integrated Solutions . This application of EO is playing an important role in shaping the programme’s planning of grey and green solutions for enhancing coastal resilience and sustainable growth in Fiji.

The EO4SD FM approach involves creating annual, cloud-free Sentinel-2 composite images of the islands using advanced cloud and shadow masking. This Sentinel-2 image is then analysed with Sentinel-1 radar data to map the mangrove extent and condition, within the potential mangrove landscape, areas with favourable conditions for mangrove growth. The diagram below shows the described workflow.

The Copernicus-driven mangrove products were used to help assess the changes in mangrove extent and condition at numerous candidate village locations around the country, whereby the mangrove products could also be compared against multiple dates of very high resolution (50 cm) images obtained for specific locations and dates.

The strategic application of EO information presents considerable benefits for International Financial Institutions (IFIs) and their client countries. In the medium to long term, the detailed mangrove maps can inform the planning and execution of nature-based seawall developments. They provide key insights into the evolution of mangrove extent and condition over the years, which can help assess the impact of different interventions.

This methodology can be replicated in other regions, providing IFIs or client states with a valuable tool in their quest for to strengthen coastal resilience. The combination of free and open Copernicus imagery and very high-resolution images, offering more detailed mangrove maps than most existing products, underlines the cost-effectiveness and utility of this approach.

Through interactions with the ADB project team, future improvements in the products have been identified, which will be implemented in the next EO4SD-FM mangrove use case.