Mapping mangroves over decades
Mangroves are recognized for their valued ecosystem services provision while having the highest carbon density among forested ecosystems. Yet they are increasingly threatened by deforestation, conversion to agriculture and development, reducing the benefits they provide for local livelihoods, coastal protection and climate change mitigation. Accurate estimates of mangrove area and change are fundamental for developing strategies for sustainable use, conservation and Reducing Emissions from Deforestation and Degradation (REDD+).
Mapping mangroves with Landsat imagery
The Zambezi River Delta in Mozambique contains one of the largest mangrove forests in Africa, and deforestation has been reported to be substantial, however these estimates vary widely. We used Landsat imagery from 1994, 2000 and 2013, to estimate a total current mangrove area of 37,034 ha, which is a net increase of 3723 ha over 19 years. The land cover change assessment was also used to provide perspective on ecosystem carbon stocks, showing that the Zambezi Delta mangrove ecosystem acts as a large carbon sink. Our findings reinforce the importance of conducting land cover change assessments using coherent data and analytical models, coupled with field validation. Broader application of our approach could help quantify the rates of natural change from erosion and land aggradation contrasted with anthropogenic causes. We also developed a mangrove map from high resolution Digital Globe data, providing the first mangrove map for the Zambezi Delta at 1m resolution.
Field Validation
A total of 10 days of field work in difficult, muddy and crocodile-filled conditions allowed us to collect enough ground truthing data to validate the mangrove maps with over 85% accuracy.
Interactive outputs
The outputs from the project were published on GLOBIL for interactive visualization, comparison of different resolution products and mangrove extent over different years.
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