- Wetlands, the most biologically diverse ecosystem on Earth, cover around 12.8 million km2 globally. Their economic value – based on the food, freshwater and building materials they provide, along with services such as water treatment, flood protection and erosion control – is estimated to be USD 70 billion per year. Yet, mapping and monitoring wetlands in order to manage their resources is challenging because of their shifting nature.
Wetlands are fundamentally dynamic. They move, change shape, and expand and contract with the seasons, often to varying extents from year to year. A wetland can sometimes be dryland, depending on when it is observed. The surface area of Cambodia’s Tonle Sap combined river-lake system, for example, expands by 12,000 km2 each year due to the influence of the monsoon on the Mekong River, while the Sudd wetland in South Sudan averages 30,000 km2 in extent, but can swell to 130,000 km2 during the wet season.
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IWMI, in collaboration with McGill University, Canada, has helped
to develop a new map of the world’s wetlands, using an innovative
method for measuring their extent. Generated from satellite images
taken over a 12-year period, the high-resolution map distinguishes
between permanent and temporary wetlands, and measures patterns
of inundation: the extent to which water remains in an area over time. For the first time, users are able to query whether or not an area is a wetland on a scale of probability.
“A snapshot of what a wetland is at a particular point in time holds little value,” explained Lisa-Maria Rebelo, Senior Researcher - Remote Sensing and GIS at IWMI, who helped to develop the map. “Data which characterize the dynamic nature of wetlands are crucial for studying large floodplain and wetland ecosystems, and for accurately assessing global freshwater resources. Without them, it is impossible to guide policies related to the wise use of wetlands or to ensure that the ecosystem services wetlands provide are not being compromised.”
The dataset underpinning the new map addresses a large information gap, and is already being put to good use. For example, it will inform the Ramsar Convention’s analyses on the State of the world’s wetlands and their services to people, and is included as an inventory option among technical guidance provided for SDG indicator 6.6.1 (change in the extent of water-related ecosystems over time).
The dataset also provides essential input to the water accounting framework developed by IWMI, UNESCO-IHE Institute for Water Education, and FAO, through WLE, for assessing hydrological ecosystem services in the Volta, Nile and Mekong river basins.
