Critical Role of Groundwater Inflow in Sustaining Lake Water Balance on the Western Tibetan Plateau

It is difficult to quantify the amount of groundwater inflow on the Tibetan Plateau (TP), yet it can be critically important for sustaining lake water balance. Here we show that most endorheic lakes on the western TP exhibited considerable water level increase during the ice‐covered period, which contrasts with lakes in other regions of the TP. An analysis of lake water balance attributes this water surplus to significant groundwater inflow, which is estimated to be about 59%–66% of total inflow into lakes. The groundwater inflow occurred after the 2000s, which is consistent with the rapid lake expansion and significant increase in precipitation. We suggest that the groundwater inflow is mainly related to large‐scale active faults in the limestone bedrock and sufficient meltwater from high elevations. Our results imply that groundwater may be deeply involved in the water cycle and modify the seasonal and inter‐annual lake variations on the western TP. Plain Language Summary Although groundwater inflow can be critically important for maintaining lake water balance, it is difficult to quantify its contribution to endorheic lakes on the Tibetan Plateau (TP). Lake‐level changes during the ice‐covered period (December to May) can be taken as a good indicator of groundwater inflow into endorheic lakes because there is very limited snowfall, surface runoff, and sublimation. Here we show that most endorheic lakes on the western TP exhibited considerable water level increase during the ice‐covered period, which contrasts with lakes in other regions of the TP. An analysis of lake water balance indicates that this water surplus was mainly attributed to significant groundwater inflow. The occurrence of groundwater inflow is consistent with the significant increase in precipitation and rapid lake expansion after the 2000s on the western TP. The formation of groundwater inflow may be mainly associated with the regional geological setting. Large‐scale active faults in the limestone bedrock increases lake basin permeability, and together with sufficient meltwater from glaciers and snow in high elevations contribute to groundwater inflow into these lakes. Our results imply that groundwater may be deeply involved in the water cycle and modify the seasonal and inter‐annual lake variations on the western TP. Key Points Lake level increased considerably on the western Tibetan Plateau during the ice‐covered period, accounting for half of annual lake‐level increase Lake water su