The hidden risk in China's cropland conversion from the perspective of slope.

• Distinct slope features of China's cropland conversion were detected. • Cropland conversion in flat areas and steep areas triggered diverse risks. • "Grain for Green project" should be adjusted based on slope features of sub-regions. • Upslope reclamation and downslope loss of cropland indicated develop conflicts. Cropland conversion is a significant theme of the influence of human activities on ecological systems and global food security. Conventionally, cropland conversion in China has been deemed to match the dynamic balance of cropland resources well and to ensure food security for the whole country. However, local studies have presented some conflicting signs that call for an integrated analysis from a national viewpoint. In this paper, by considering the significance of slope in cropland-related natural and socioeconomic issues, we explore the slope features of China's cropland conversion during 2000–2015 and endeavor to identify some potential risks hidden in the process. High-resolution remotely sensed images, digital elevation model and spatial analytical methods are adopted to conduct the analysis. The results show that, the features of cropland conversion in diverse slope division areas are all distinct. Some risks indicated by these conversion features can be identified as follows: (1) unsuitable reclamation of cropland in flat areas causes ecological damage, (2) the invasion of sparsely populated construction land on cropland in steep areas has a dramatic impact on the local area, (3) excessive greening in Northwest and Northeast China, and insufficient greening in Southwest China are not healthy for regional sustainability, (4) cropland's upslope reclamation and downslope loss pose potential risks for food security. In the context of dynamic balance management and other related national policies, cropland conversion in China is not as optimistic as former surveys have indicated, and promoted measures should be elaborately adjusted based on local conditions. [ABSTRACT FROM AUTHOR]