Spatial–Seasonal Isotopic Variations in a Surface–Groundwater System in an Extremely Arid Basin and the Associated Hydrogeological Indications

Abstract. Climate warming accelerates the global water cycle. However, the relationships between climate warming and hydrological processes in the alpine arid regions remain unclear. Herein, high spatiotemporal resolution sampling of surface water and groundwater was performed at the Qaidam Basin, an extremely arid area in the northeastern Tibetan Plateau. Stable H-O isotopes and radioactive ³H isotopes were combined with atmospheric simulations to examine climate change and hydrogeological characteristics. The surface water heavy isotopes enrich during the wet season and deplete during the dry season. The contribution of precipitation to river discharge was considerably higher in the eastern region of the basin (approximately 45 %) than in the central and western regions (10 %–15 %). The H-O isotopic compositions showed a gradually negative spatial pattern from the west to the east in the Eastern Kunlun Mountains water system; a reverse pattern occurred in the Qilian Mountains water system. This distribution pattern was jointly regulated by the westerly water vapor transport intensity and local hydrothermal conditions. Increased precipitation and cryosphere shrinkage caused by climate warming mainly accelerated basin groundwater cycle. In the eastern and southwestern Qaidam Basin, precipitation and ice/snow meltwater infiltrate structural channels that favor water flow, such as fractures and fissures, facilitating rapid seasonal groundwater recharge and increased terrestrial water storage. However, under future increases in precipitation in the southwestern Qaidam Basin, compensating for water loss from long-term melting of ice and snow will be challenging, and the total water resources may show an initially increasing and then decreasing trend.