Understanding the evolution of groundwater storage and its drivers is essential for groundwater conservation and sustainable management in arid regions. However, a comprehensive assessment of long-term groundwater storage changes in the Heihe River Basin (HRB), especially before and after the artificial water diversion scheme, remains lacking. Here, we developed a downscaling framework to produce a 1 km groundwater storage anomaly (GWSA) dataset spanning the past three decades. A random forest model and a modified interactive geographical and temporal weighted regression (mIGTWR) model were then used to characterize spatiotemporal evolution patterns and identify the driving mechanisms. The results showed that: (1) groundwater level anomalies from monitoring wells were reasonably consistent with the reconstructed GWSA, with a maximum Pearson correlation coefficient of 0.746; (2) groundwater storage in the HRB declined significantly during 1990-2019, at rates of -0.20 cm/yr, -0.21 cm/yr, and -0.25 cm/yr for the entire basin, the midstream, and the downstream, respectively; (3) nighttime light intensity (NTL) was identified as the dominant temporal driver of GWSA variations; and (4) spatially, the interactions TEM fl NTL (temperature x NTL), PET fl NTL (potential evapotranspiration x NTL), NTL fl NPP (NTL x net primary productivity), together with NDVI (Normalized Difference Vegetation Index), were the key explanatory factors of GWSA change. These results highlight the coupled human-climate impacts on groundwater dynamics and provide critical implications for adaptive basin management and sustainable groundwater use in arid regions.