Unrevealing past and future vegetation restoration on the Loess Plateau and its impact on terrestrial water storage

Vegetation restoration attributed to China’s Grain to Green Program (GTGP) exerts noticeable impact on the ecological-hydrological nexus. However, the vegetation restoration status associated with GTGP has been insufficiently studied and its effect on water availability remains controversial. This holistic study involved investigation of long-time satellite observations, outputs of a land surface model, and future projections to quantify the historical and future variations of gross primary productivity (GPP) on the Loess Plateau (China) and the associated effect on terrestrial water storage change (TWSC). The ensemble empirical mode decomposition (EEMD) model was employed to characterize the nonlinearity of interannual variability. Satellite-derived observations revealed a trend of increase of 8.162 TgC/year in GPP during 2003–2016, with the largest proportion attributable to grassland owing to its extensive coverage. Increased GPP is related to TWSC decline, as evidenced by both Gravity Recovery and Climate Experiment satellite observations and simulations from the modified Noah land surface model. In descending order, the magnitude of such negative impact varies with coverage of grassland, cropland, and trees. Ecological restoration is manifested as a critical anthropogenic stressor altering TWSC, which is further reinforced by prominent inverse correlation (R = − 0.31) after removing climatic impacts. The bias-corrected Coupled Model Intercomparison Project phase 6 dataset illustrates that increased GPP and reduced TWS are projected in the twenty-first century when considering the climate change and human interventions. Considering that past ecological benefits associated with revegetation measures could represent short-term gains and that TWS decline is most likely to continue, the government and local stakeholders should reconsider the current hydrological condition from the perspective of balanced socioeconomic benefit and terrestrial water storage cost.