Objectives Studying the spatiotemporal changes of groundwater storage（GWS） and its sustainable spatiotemporal evolution characteristics in the upper reaches of the Yellow River Basin can provide a valuable reference for the sustainable and rational development of water resources in the Yellow River Basin.
Methods The changes of terrestrial water storage (TWS) and GWS in the upper reaches of the Yellow River Basin from April 2002 to December 2022 were estimated using Masson data and spherical harmonic (SH) data from GRACE (gravity recovery and climate experience) and GRACE-FO (GRACE follow on) gravity satellites, combined with prior hydrological models, and their temporal and spatial variation characteristics were also analyzed. The sustainability index (SI) of water resources in the study area was further calculated to evaluate the sustainability of regional groundwater. And the correlation and contribution of precipitation change, normalized difference vegetation index (NDVI), evapotranspiration (ET) and regional GWS were discussed.
Results The change of GWS in the study area showed an overall downward trend at a rate of approximately －3.89 ± 0.37 mm / a, and showed obvious spatial characteristics of the difference between the southern and northern values, which was consistent with the monitoring results of the measured wells (correlation was approximately 0.73). During the study period, the regional groundwater was almost in a state of severe unsustainability, and the spatial sustainability also gradually decreased from south to north, with an average sustainability index of only 0.38. The size of the contribution measure shows that NDVI has the greatest impact on the change of GWS in the study area, ET has the second highest impact,and the rainfall has the smallest; there was a significant negative correlation between NDVI, ET and regional GWS changes (correlation coefficients were approximately －0.76 and －0.77, respectively). The rainfall in the south and north of the study area was positively correlated with the corresponding GWS changes (correlation coefficients were approximately 0.54 and 0.50, respectively).
Conclusions This study effectively evaluated the changes of TWS and GWS in the upper reaches of the Yellow River Basin over the past 20 years, and reasonably evaluated the spatiotemporal distribution characteristics of groundwater sustainability in the upper reaches of the Yellow River, as well as the correlation between external influences and GWS.
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