Abstract
This study presents a new global baseline of mangrove extent for 2010 and has been released as the first output of the Global Mangrove Watch (GMW) initiative. This is the first study to apply a globally consistent and automated method for mapping mangroves, identifying a global extent of 137,600 km 2 . The overall accuracy for mangrove extent was 94.0% with a 99% likelihood that the true value is between 93.6–94.5%, using 53,878 accuracy points across 20 sites distributed globally. Using the geographic regions of the Ramsar Convention on Wetlands, Asia has the highest proportion of mangroves with 38.7% of the global total, while Latin America and the Caribbean have 20.3%, Africa has 20.0%, Oceania has 11.9%, North America has 8.4% and the European Overseas Territories have 0.7%. The methodology developed is primarily based on the classification of ALOS PALSAR and Landsat sensor data, where a habitat mask was first generated, within which the classification of mangrove was undertaken using the Extremely Randomized Trees classifier. This new globally consistent baseline will also form the basis of a mangrove monitoring system using JAXA JERS-1 SAR, ALOS PALSAR and ALOS-2 PALSAR-2 radar data to assess mangrove change from 1996 to the present. However, when using the product, users should note that a minimum mapping unit of 1 ha is recommended and that the error increases in regions of disturbance and where narrow strips or smaller fragmented areas of mangroves are present. Artefacts due to cloud cover and the Landsat-7 SLC-off error are also present in some areas, particularly regions of West Africa due to the lack of Landsat-5 data and persistence cloud cover. In the future, consideration will be given to the production of a new global baseline based on 10 m Sentinel-2 composites.
Highlights
IntroductionFound in the coastal zones of more than 118 countries in the tropics, subtropics and temperate regions [1,2,3], mangroves have (for centuries) provided natural resources to local populations, including food ( fish and invertebrates) and timber
Mangroves are forested wetlands that are uniquely adapted to the intertidal zone
The new global mangrove baseline has been generated using a combination of Synthetic Aperture Radar (SAR) from the Advanced Land Observing Satellite (ALOS) Phased-Array L-band Synthetic Aperture Radar (PALSAR) and optical satellite data from Landsat-5 Thematic Mapper (TM) and Landsat-7 Enhanced TM (ETM+)
Summary
Found in the coastal zones of more than 118 countries in the tropics, subtropics and temperate regions [1,2,3], mangroves have (for centuries) provided natural resources to local populations, including food ( fish and invertebrates) and timber. Through processes such as population increases, industrialisation, urban expansion and globalisation, their extent has been reduced [4] and many have been fragmented or degraded [5], in Southeast Asia, where about one third (32%) of the world’s mangroves are located [6]. While critical for informing efforts that support conservation, sustainable management, and restoration of these ecosystems, data on mangrove status and extent are necessary to meet reporting requirements for signatories to the Ramsar Convention on Wetlands and other countries with mangroves in their territories who are striving to meet the Sustainable Development Goals [5,9]
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