Drastic water volume changes in mega lakes can pose considerable impacts on regional water storage

The widely distributed surface water bodies (e.g., lakes and reservoirs) are important components of water resources on Earth, their spatial–temporal dynamics can pose significant effects on regional water resources. Previous studies generally attributed variability in terrestrial water storage (TWS) to groundwater dynamics, hardly considering surface water changes, making the influence of the changing surface water storage on TWS unclear. Here, by taking Hulun Lake as an example, which occupies 94.0 % of the total water areas in the target basin, we quantitatively revealed the impacts of changes in lake water volume on TWS. Using cloud computing-based water body monitoring and altimetry satellite-based water level measurements, we found continuous lake shrinkage (25 km2/yr) before 2012 while rapid expansion after that. By coupling water areas with levels, annual lake volumes were estimated. We showed that lake volumes also significantly declined (−0.52 km3/yr) before 2012, and then rapidly restored (0.65 km3/yr) due to the increasing water recharge from rivers. The increasing rate of lake water volume was higher than that of TWS (0.15 km3/yr), indicating the great contribution of lake volume increases to TWS gains. Our study highlights the considerable impacts of the changing surface water bodies on regional water resources and it is essential to consider storage changes in surface water when attributing the drivers of TWS variability in regions experiencing dramatic lake changes. Our method proposed is also applicable to evaluating the impacts of surface water changes on TWS in other similar areas around the world.