Assessment of global land cover changes using satellite data: intermittent and long-term land cover changes from 2001 to 2020

Global land cover has changed during the past decades, influencing biogeochemical cycles and the global climate system. This study aimed to improve understanding of global land cover dynamics to enable more effective future land management practices and conservation actions. This study quantified interannual changes in global land cover types from 2001 to 2020 and distinguished intermittent transitions from stable gains and losses. From the interannual perspective, we found that global barren lands, forests, shrublands, and snow-covered areas decreased by 5281, 1804, 952, and 188 kha yr-1, respectively. In contrast, grasslands, croplands, urban areas, and water bodies increased at 6529, 1407, 237, and 51 kha yr-1, respectively, from 2001 to 2020. According to the definitions provided in this paper, of the global forest areas, 75% was Stable (no change), 4% was Gain, 5% was Loss, and 16% was Unstable. Of the cropland areas, 56% was Stable, 9% was Gain, 9% was Loss, and 26% was Unstable. Hotspots for forest loss were Brazil, the Rest of South America, and Sub-Saharan Africa, and grassland was the most common land cover classification following forest loss. The global cropland expansion hotspots were Brazil, Canada, China, India, and the Rest of South America. The cropland gains were mainly converted from grasslands. On the other hand, barren areas in China and Middle Eastern and North Africa were changed to grasslands. A certain amount of shrublands were changed to forest in temperate regions. This paper provided land cover changes at a 500 m spatial resolution as a benchmark for future assessments. The findings showed that unstable pixels play an important role in determining the sources of uncertainty when assessing land cover changes using satellite data. Land cover assessments are sensitive to the time steps used for analysis and the definition of changes.