Comparison of GRACE gravity anomaly solutions for terrestrial water storage variability in arid and semi-arid Botswana

Abstract

The Gravity Recovery and Climate Experiment (GRACE) terrestrial water storage anomalies (TWSA) estimations provide valuable information for the monitoring of the variability of water resources. Explorations of the differences between GRACE solutions in local regions and basins is fundamental in determining their suitability and applicability in these environments. Because of the different mathematical inversions used by the different processing centers, individual solutions exhibit discrepancies in terms of mass increase or loss which makes it difficult for users to select the best model for studying TWSA. This study compares TWSA trends as derived from different GRACE solutions over the arid and semi-arid Botswana (2002-2019), where both storage and flux from CSR, JPL, GFZ, TUGRAZ, AIUB, and COST-G were compared. The results show that the six solutions are fairly correlated with the least correlation of R=0.829 between JPL and AIUB and a maximum R=0.921 between CSR and TUGRAZ. The TWSA analyses between 2002-2019 indicate that TWS is increasing in Botswana with the least linear trend of +0.11cm/yr detected from the TUGRAZ inversion model and the highest linear trend at +0.43cm/year from the COST-G model. On comparison with rainfall, all solutions had a correlation coefficient of more than 0.5 showing that the two signals have nearly the same response. Over the 18-years, the overall rainfall trend is observed to be decreasing, which was only detected by the TUGRAZ model in terms of the recorded equivalent water height (EWH) of -0.008cm/yr from the monthly trend observations. Overall, despite the relatively high correlational similarity between the inversion models for the case study, users should investigate to determine the suitable inversion model.