Abstract
Accurate maps of surface water extent are of paramount importance for water management, satellite data processing and climate modeling. Several maps of water bodies based on remote sensing data have been released during the last decade. Nonetheless, none has a truly (90 ∘ N/90 ∘ S) global coverage while being thoroughly validated. This paper describes a global, spatially-complete (void-free) and accurate mask of inland/ocean water for the 2000–2012 period, built in the framework of the European Space Agency (ESA) Climate Change Initiative (CCI). This map results from the synergistic combination of multiple individual SAR and optical water body and auxiliary datasets. A key aspect of this work is the original and rigorous stratified random sampling designed for the quality assessment of binary classifications where one class is marginally distributed. Input and consolidated products were assessed qualitatively and quantitatively against a reference validation database of 2110 samples spread throughout the globe. Using all samples, overall accuracy was always very high among all products, between 98 % and 100 % . The CCI global map of open water bodies provided the best water class representation (F-score of 89 % ) compared to its constitutive inputs. When focusing on the challenging areas for water bodies’ mapping, such as shorelines, lakes and river banks, all products yielded substantially lower accuracy figures with overall accuracies ranging between 74 % and 89 % . The inland water area of the CCI global map of open water bodies was estimated to be 3.17 million km 2 ± 0.24 million km 2 . The dataset is freely available through the ESA CCI Land Cover viewer.
Highlights
Fresh surface water is one of the most precious resources on Earth, fulfilling social, economic and environmental services [1,2]
This global, void-free dataset consists of two separate layers: an inland water/ocean repartition at 150-m spatial resolution and an inland water fraction, in percent of the 150-m grid cell
This study demonstrated that the combination and consolidation of existing water body products leads to a global map of open water bodies that meets the climate modelers needs of adequate spatial resolution, maximal spatial extent and completeness along with high accuracy
Summary
Fresh surface water is one of the most precious resources on Earth, fulfilling social, economic and environmental services [1,2]. Climate change and population growth increasingly affect, with large spatial disparities, water resources’ availability, quality [3], hydrological flows [4] and related biodiversity [5]. Reliable assessment of the world water resources is of paramount importance for decision making, governance and mitigation [8]. Maps depicting the distribution and extent of surface water support hydrological simulation analyses, climate modeling and satellite data processing. Maps of open water bodies allow retrieving key climate variables, such as evaporation, water/land surface temperature, energy balance, selecting appropriate aerosol algorithms and sharing a common coastline map between processes
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