Assessing the Sustainability of Terrestrial Water Storage in the Pearl River Basin Using HUST-Grace2024 Model

Objectives: As a core indicator for water resource management, the sustainability assessment of terrestrial water storage (TWS) is crucial for addressing climate change and ensuring regional water security. Methods: This study employed the latest HUST-Graces2024 model developed by Huazhong University of Science and Technology to analyze the spatiotemporal characteristics of TWS changes (TWSC) across the Pearl River Basin (PRB) from 2003 to 2023. The results were compared with those derived from five internationally recognized GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (Follow-On) models. Using the Sustainability Index (SI) derived from HUST-Graces2024, we assessed the water resource sustainability in the PRB and its sub-basins. We also quantitatively evaluated the impact of precipitation, evapotranspiration (ET), runoff, and the normalized difference vegetation index (NDVI) on TWS using meteorological and hydrological data. Results: Findings indicate that the TWSC calculated by HUST-Graces2024 is highly consistent with that calculated by five commonly used international models. Its accuracy is second only to that of the CSR RL06 model, and it is comparable to the results of the COST-G model, indicating that the TWSC of the Pearl River Basin inverted by this model has higher reliability and accuracy. During the study period, TWS in the PRB increased at an average rate of 4.7 mm/year, 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 ET. 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-Graces2024 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.