Surface water expansion due to increasing water demand on theLoess Plateau

Land surface water bodies are important to ensure water security for agricultural, industrial, domestic, and environmental sectors. Especially in dryland areas, such as the Loess Plateau in China, changes in land surface water bodies as a response to climate change and human activities have been the subject of great concern. Many dams and reservoirs have been constructed on the Loess Plateau to combat serious soil erosion and water resource shortages. These projects are widely recognized as an effective measure to enhance soil conservation, but little is known about the dynamics of surface water bodies. In this study, we employ a long-term satellite water product to detect the spatial-temporal variability in surface water at the regional scale on the Loess Plateau and identify the potential cause of climate change and human activities. The results show that the area of permanent water has increased by approximately 800 km² during the past two decades. Surface water expansion is primarily associated with small water bodies (< 1 km²), as their number has roughly doubled, while the number and area of large water bodies have remained stable. We found that surface water expansion has little correlation with precipitation variation but is highly correlated with water withdrawal for agricultural, industrial, and other sectors. Thus, the surface water expansion on the Loess Plateau is primarily contributed by hydraulic project construction as a response to the increasing water demand. The above findings imply the positive role of hydraulic projects, but it is essential to note that the continuous expansion of surface water might not be sustainable because of constraints from natural conditions.