Spatio-temporal patterns of oasis dynamics in China's drylands between 1987 and 2017

Oases are among the most productive and vulnerable ecosystems on drylands as well as central areas of human life and economic development. In China, oasis expansion and degradation are directly related to the survival and development of tens of millions of inhabitants who live within them, profoundly affecting human well-being. However, our understanding of the spatiotemporal dynamics of China's oases has been limited. This creates a challenge to accurately assess the environmental impacts of oasis dynamics and sustainable oasis development. Here we analyzed Landsat images (5 TM, 7 ETM+, and 8 OIL, similar to 61 900 images) over the period 1987-2017, and we produced annual maps of China's oases (30 m spatial resolution) using trajectories and spectral-temporal segmentation algorithm (LandTrendr) and machine-learning methods (Random Forest). We found that oasis areas increased significantly between 1987 and 2017 (+8.82 Mha). Grasslands and croplands expanded the most, and reclamation of deserts and grasslands made cropland the largest gainer. At the provincial scale, oasis expansion in Inner Mongolia and Qinghai was mainly attributed to grassland restoration. In Xinjiang, Gansu, and Ningxia, reclamation of croplands was also an important factor in addition to grassland restoration. With the expansion of the oasis similar to 73.36% of areas showed decreasing trends of soil moisture, and even desertification in some areas. The overexpansion of oases might cause a great challenge to regional water security. Our dataset and results can provide a basis for identifying trade-off areas/regions between development benefits and environmental impacts, helping policymakers to identify high-priority areas for intervention and reasonably plan land-use spatial structure in oasis areas for sustainable development of oases.