The trajectory of wetland change in China between 1980 and 2020: hidden losses and restoration effects.

Understanding wetland change is critical to establishing and implementing international conservation and management conventions. With such knowledge, supporting sustainable development, making management decisions, improving policies, and conducting scientific research become possible. However, consistent information on changes in Chinese wetlands has been unavailable. We applied the hybrid object-based and hierarchical classification approach to ∼53,000 scenes of Landsat images acquired between 1980 and 2020 and created a national wetland mapping product (China_Wetlands) for six periods (e.g., 1980, 1990, 2000, 2010, 2015, and 2020). China_Wetlands revealed diverse changes in Chinese wetlands and their trajectories in response to climate change and human impacts over the past four decades. Specifically, there was a substantial shrinkage in wetland area before 2015, with a small rebound between 2015 and 2020. The net loss was ∼60.9 × 10 ³  km ² , which represents 12% of the area in 1980. However, the loss of natural wetlands was hidden by human-made wetland gain with an offset of 15.6 × 10 ³  km ² . Additionally, the expansion of surface water extent approximately 14.0 × 10 ³  km ² obscured the loss of vegetated wetlands. Wetland loss in hotspot areas (e.g., Sanjiang Plain and Yangtze River Delta) should not be neglected. The sustainable management and effective conservation of wetlands in China should target wetland areas, landscape structures, and small wetlands delivering important ecosystem services. Moreover, the conversion of wetland types and the invasion of alien species need to be monitored and regulated. China_Wetlands will be a critical wetland dataset for ecological research and the assessment of national and global environmental objectives (e.g., the United Nation's sustainable development goals).
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