Abstract
The monitoring of Global Aquatic Land Cover (GALC) plays an essential role in protecting and restoring water-related ecosystems. Although many GALC datasets have been created before, a uniform and comprehensive GALC dataset is lacking to meet multiple user needs. This study aims to assess the effectiveness of using existing global datasets to develop a comprehensive and user-oriented GALC database and identify the gaps of current datasets in GALC mapping. Eight global datasets were reframed to construct a three-level (i.e., from general to detailed) prototype database for 2015, conforming with the United Nations Land Cover Classification System (LCCS)-based GALC characterization framework. An independent validation was done, and the overall results show some limitations of current datasets in comprehensive GALC mapping. The Level-1 map had considerable commission errors in delineating the general GALC distribution. The Level-2 maps were good at characterizing permanently flooded areas and natural aquatic types, while accuracies were poor in the mapping of temporarily flooded and waterlogged areas as well as artificial aquatic types; vegetated aquatic areas were also underestimated. The Level-3 maps were not sufficient in characterizing the detailed life form types (e.g., trees, shrubs) for aquatic land cover. However, the prototype GALC database is flexible to derive user-specific maps and has important values to aquatic ecosystem management. With the evolving earth observation opportunities, limitations in the current GALC characterization can be addressed in the future.
Highlights
Aquatic land cover refers to land cover types that are significantly influenced by the presence of water over extensive periods in a year [1], including open water, and wetlands in transitional zones of terrestrial upland and open water systems [2]
The total area of Global Aquatic Land Cover (GALC) is estimated as 27.5 million km2, of which 15.3 million km2 is on the land (i.e., 11.4% of the global land area)
At Level-2, the persistence of water map is good at characterizing permanently flooded areas, while weak in waterlogged areas without evident surface flooding and temporarily flooded areas with greater water variations—the presence of vegetation map tends to underestimate the vegetated aquatic land cover while overestimating the non-vegetated ones; natural aquatic types are sufficiently mapped while artificial aquatic lands are poorly represented
Summary
Aquatic land cover (excluding open oceans) refers to land cover types that are significantly influenced by the presence of water over extensive periods in a year [1], including open water, and wetlands in transitional zones of terrestrial upland and open water systems [2]. Knowledge about the global distribution of aquatic land cover is critical to manage and protect aquatic ecosystems. Remote sensing provides an efficient way to monitor the spatial distribution of aquatic land. As there is a lack of uniform and comprehensive aquatic land cover classification schemes, current Global Aquatic Land Cover (GALC) datasets have often been narrowed down to specific classes [4], most of which focus on providing the information of water bodies [5,6] while missing the vegetation and wet soils that are key components of aquatic ecosystems [2]. The most comprehensive GALC product that describes a variety of aquatic classes is the Global Lakes and Wetlands Database (GLWD) [7]. Aquatic classes mapped in Global Land Cover (GLC) products have often been underrepresented
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