Characterization of Groundwater Storage in the Heihe Headwater Watershed, Qinghai Province, China

A warming climate has led to decreases in permafrost extent and water insecurity in the Qinghai-Tibet Plateau in China. It is speculated that this will cause large-scale changes water resource availability. These speculations bring up questions: At what amount does groundwater storage contribute to stream flow in these headwater watersheds? How does groundwater storage change with increasing temperatures and decreasing permafrost extent? How will changes in permafrost and thus, groundwater storage, change seasonally? To address these questions, we have: (1) Developed a three-dimensional, groundwater flow and energy model for the Hulugou Watershed, the headwaters of the Heihe River located on the northern edge of the Qinghai-Tibet Plateau; (2) Analyzed seasonal base flow contribution to streamflow for the Hulugou Watershed using the two-parameter Kalinin method; and (3) Compared model results to geochemical data from the Hulugou Watershed. We derive a transient three-dimensional finite element coupled flow and energy transport model to characterize the groundwater and energy systems and quantify groundwater storage under long-term climatic conditions. The coupled hydrogeologic model incorporates the physics of water phase change, allowing for modeling of pore water freeze and thaw and permeability dependence on ice saturation. Major outcomes of the model include: spatial and temporal distributions of subsurface temperature, fluid pressure, groundwater storage, and discharge to the land surface. Model results highlight that groundwater recharges mainly at high elevations and discharges to springs and streams at low elevations. Results from base flow extraction of observed discharge data suggest that within the Hulugou Watershed, stream discharge is primarily from groundwater contributions in the form of base flow (53%). These results corroborate with geochemical data, highlighting temporal changes in groundwater storage.