Analysis of the groundwater flow system in a high-altitude headwater region under rapid climate warming: Lhasa River Basin, Tibetan Plateau

Study region: Lhasa River Basin (LRB) on the Tibetan Plateau, China. Study focus: Tibetan Plateau has been undergoing climate warming in the past five decades. The hydrological processes in the LRB, a representative alpine headwater region basin on the Tibetan Plateau, are changing in response to climate warming. However, characteristics of groundwater recharge and discharge and response of the groundwater flow system to future climate change in this region remain unclear. This study constructed a three-dimensional numerical model to simulate the groundwater flow variations under different future climate change scenarios. New hydrological insights for the region: Approximately 13.6 % (∼71.6 mm/yr) of annual precipitation recharges groundwater. Glacier meltwater recharge is 10 % of the total groundwater recharge across the entire LRB, and this proportion increases to 34.8 % in the Yangbajing subbasin. More than 80 % of the groundwater circulates within 0∼0.3 km below ground surface. The groundwater flow system is dominated by travel times between 10–100 years and flow path distances less than 10 km. The baseflow shows an increasing trend in response to future climate change, and the increasing trends range from 0.07 to 0.21 m/s per year under different future climate change scenarios. The baseflow variation indicates that wet year will become wetter and dry year will become drier in the future.