Review on Eco-hydrological Processes of Groundwater-dependent Vegetation in NW China: Progress and Outlook

The relationship between groundwater and vegetation is crucial to achieve a harmonious balance between human and the natural environment. Groundwater-dependent vegetation (GDV) is extensively distributed in the arid and semi-arid regions of Northwest China. In certain areas, the decline in water table levels due to human activities has fallen below ecological water level thresholds, leading to the degradation of ecological functions and, in some cases, widespread vegetation die-off. Therefore, the sustainable development of the region's economy and society is under significant threat. A comprehensive review was conducted concerning GDV mapping, ecological resilience assessment, groundwater-vegetation co-evolution, and ecological water table. Through this review, the main challenges and urgent issues that need to be addressed in current research have been summarized, and future research directions were outlined. The review revealed limited research on GDV mapping at the watershed scale in Northwest China, highlighting the need for further refinement on the stable isotope method for ground validation of mapping results. Current studies on resilience focus on surface ecology and ecological indicators overlook underground indicators, such as groundwater and root distribution, and lack a comprehensive evaluation based on resistance, recovery, and adaptability. Qualitative assessments of ecological resilience prevail in current research, falling short of meeting the requirements for effective ecological conservation and restoration. Challenges in researching the co-evolution of vegetation and groundwater arise from the difficulty in accurately detecting changes in root systems. Further studies are warranted to develop root detection methods and three-dimensional models for simulating the co-evolution of roots and water sources. Concerning ecological water tables, the focus remains on static water levels determined by current conditions, with insufficient consideration of spatial variations in precipitation and lateral groundwater flow as well as plant self-adaptation. Additional research is essential to establish dynamic ecological water levels under varying external conditions. This review aims to summarize the progress and future prospects of research on eco-hydrological processes of GDV, addressing the weak research areas. By doing so, it aims to provide a robust scientific foundation for further theoretical research and practical applications on eco-hydrology in NW China.