Water resources significance of moisture recycling in the transition zone between Tibetan Plateau and arid region by stable isotope tracing

Moisture recycling, an important component of regional precipitation, is a key indicator of a region's ability to renew its water resources. Quantifying moisture recycling allows for a comprehensive understanding of the spatial and temporal structure of the regional water balance. Therefore, an observation and sampling network for precipitation, soil samples, plant stems, and surface water was established in the Qilian Mountains, a transition zone between the Tibetan Plateau and an arid region. Approximately 2749 samples were collected and analyzed for their isotopic compositions. Based on the Craig-Gordon model and the three-end-member mixing model, the evaporation, transpiration, and advection contributed 8%, 14%, and 78% to precipitation, respectively, and the total contribution to local moisture recycling was equivalent to 71 mm of precipitation. The evaporation fraction tended to decrease from the central Qilian Mountains to the surrounding areas, whereas the transpiration fraction exhibited a decreasing trend from south to north in the south-central Qilian Mountains. If all of the moisture recycling precipitation is produced in the flow, the water production is approximately 13 billion m3, which is approximately 87% of the average total annual runoff from the Qilian Mountains and twice the average total annual runoff of the three major inland river basins in the Hexi corridor. Additionally, altitude, topography, vegetation conditions, and meteorological factors influence local moisture recycling. The results showed that moisture recycling precipitation in cold regions is crucial to ecological stability and water resource supply. This study demonstrates that good ecological conditions enhance moisture recycling, improve the renewal capacity of water resources, and support the stability and sustainable use of regional water resources. Therefore, ecological protection remains an important support for sustainable development in the Qilian Mountains.