OasisMap30: a 30 m annual land cover dataset of China's oases from 1987 to 2024

Abstract. High spatio-temporal resolution maps of oasis land cover are valuable for understanding ecological and societal development processes in dryland regions. However, the relatively late development of oasis research, combined with the highly fragmented structure of oases and their frequent land cover transitions, has made it challenging to construct high spatio-temporal resolution land cover datasets for oases. As a result, dedicated data products of this kind are still lacking. Here, we developed a framework for annual 30 m land cover mapping that integrates Landsat satellite imagery, machine learning, a temporal segmentation approach (LandTrendr), and principal component analysis. Using this framework, we produced a 30 m resolution annual land-cover dataset for Chinese oases (OasisMap30) for the period 1987–2024 on the Google Earth Engine (GEE) platform. Accuracy assessment based on more than 6300 visually interpreted samples demonstrates high accuracy of OasisMap30 (overall accuracy > 90 %). In cross-product comparisons based on visually interpreted and third-party test samples, OasisMap30 exhibits considerable advantages in terms of classification accuracy and error reduction. Moreover, in comparison with several 30 m resolution thematic products for impervious surface, cropland, and surface water, we found an impressive consistency between OasisMap30 and these datasets. Using OasisMap30, we investigated the changes in land cover patterns of Chinese oases. The results show that oasis area expanded by 45.87 % (+7.75 Mha) between 1987 and 2024, primarily driven by cropland expansion and grassland restoration. Specifically, 4.04 Mha of desert were restored to grassland, and 3.19 Mha were converted from desert to cropland. In addition, OasisMap30 reveals the expansion of impervious surfaces (0.58 Mha) and surface water (0.35 Mha), as well as conversions among land cover types, such as the conversion of 3.12 Mha of grassland to cropland. Overall, the consistent, high-resolution OasisMap30 data can substantially support studies on the evolution of oasis landscape patterns, socio-ecological responses, and spatial pattern optimization, thereby contributing to the sustainable development of oasis regions. The full archive of OasisMap30 is freely available at https://doi.org/10.6084/m9.figshare.30798032 (Chen et al., 2025).