Terrestrial water storage variations and drought characteristics in the upper yellow river basin revealed by joint GNSS-GRACE analysis

The Upper Yellow River Basin (UYRB) This study integrates Global Navigation Satellite System (GNSS) and Gravity Recovery and Climate Experiment (GRACE) observations from 2011 to 2023 to jointly invert terrestrial water storage (TWS) changes. By combining these results with multi-source meteorological and hydrological datasets, we characterize the spatiotemporal evolution of hydrological droughts in the UYRB and, through correlation analysis and a robust machine-learning framework supported by SHAP interpretation, identify their dominant drivers. In the UYRB, TWS seasonal variability decreases from southwest to northeast, with overall storage increases in the southern basin and gradual declines in the north. Due to the basin’s elongated geometry and uneven GNSS station distribution, neither GNSS nor GRACE alone can reliably capture basin-wide variations; however, the joint inversion framework effectively overcomes these limitations. The analysis reveals distinct spatial heterogeneity in drought behaviors, identifying nine events (2–12 months) in the northern sub-regions and six events (2–24 months) in the south. Interpretation of these patterns suggests that northern droughts are primarily driven by groundwater extraction and evapotranspiration, whereas southern droughts are predominantly regulated by multi-year precipitation variability associated with large-scale atmospheric circulation. Notably, we identify a long-term drought propagation timescale (e.g., 37 months in the south) that governs TWS-based drought evolution, distinguishing it from rapid surface-water propagation. These findings highlight the pronounced spatial differences in TWS dynamics and drought drivers across the UYRB, demonstrating the potential of GNSS–GRACE integration for fine-scale drought monitoring and sustainable water-resource management in climate-sensitive basins. • Joint GNSS–GRACE framework developed to assess TWS and drought in the UYRB. • TWS variations exhibit diverging trends with southern increases and northern declines. • Southern TWS driven by precipitation; northern loss dominated by groundwater depletion.