Objectives As a core indicator for water resource management, the sustainability assessment of terrestrial water storage is crucial for addressing climate change and ensuring regional water security.

Methods We employed the latest HUST-Grace2024 model developed by Huazhong University of Science and Technology to analyze the spatiotemporal characteristics of terrestrial water storage change (TWSC) across the Pearl River Basin (PRB) from 2003 to 2023. The results were compared with those derived from five internationally recognized gravity recovery and climate experiment (GRACE) and GRACE Follow-On (GRACE-FO) models. Using the sustainability index (SI) derived from HUST-Grace2024, we assessed the water resource sustainability in the PRB and its sub-basins. We also quantitatively evaluated the impact of precipitation, evapotranspiration, runoff, and the normalized difference vegetation index (NDVI) on terrestrial water storage using meteorological and hydrological data.

Results Comparison results indicate that the TWSC calculated by HUST-Grace2024 is highly consistent with that calculated by five commonly used international models. Its accuracy is comparable to the results of the international combination service for time-variable gravity field model, indicating that the TWSC of the PRB inverted by this model has higher reliability and accuracy. During the study period, terrestrial water storage in the PRB increased at an average rate of 4.7 mm/a, with significantly faster growth in the Nanpan and Hongliu River sub-basins compared to others. Overall, although the water resources in the PRB are in a mildly unsustainable state (SI=0.36), with the Yujiang River Basin and Nanpan-Beipan River Basin having the highest (0.39) and lowest (0.34) SI values respectively, their sustainability is continuously improving. Among the influencing factors, NDVI has the greatest impact on the TWSC in the PRB, followed by runoff, precipitation and evapotranspiration. This indicates that vegetation coverage plays a significant role in regional soil and water conservation. Although the ranking of the contribution rates of these four influencing factors is consistent across all sub-basins, there are significant differences in their numerical values.

Conclusions These results demonstrate that the HUST-Grace2024 model effectively monitors and evaluates the spatiotemporal evolution and sustainability of TWSC in the PRB, providing valuable insights for regional water resource management and informed decision-making.