Independent Evaluation of GPCC and GPCP Precipitation Products and G3P and JPL Mascon TWS Products

This study aimed to independently evaluate precipitation and terrestrial water storage (TWS) products by analyzing hydrological drought characteristics across various climate zones. Hydrological drought characteristics were estimated using two TWS and two precipitation products as the hydrological drought recovery time (DRT). The TWS data were obtained from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO). The Global Gravity-based Ground Product (G3P) spherical harmonic solution and JPL mascon solution (RL06) were utilized as GRACE/GRACE-FO TWS products. Precipitation data were obtained from the Global Precipitation Climatology Center (GPCC) Full Data Monthly Product version 2022 and the Global Precipitation Climatology Project (GPCP) version 3.2 monthly analysis product. Köppen-Geiger Climate Classifications were utilized in the presentation of the results of the study. Two methods were used to estimate DRT: (1) storage deficit, using the detrended TWS anomaly (dTWSA), and (2) required precipitation amount, using the detrended smoothed precipitation anomaly (cdPA) and the dTWSA. The storage deficit method is based on the calculation of the residuals of the dTWSA from its climatology. The required precipitation amount method is based on the linear relationship between the cdPA and dTWSA. The end of a hydrological drought was determined when the residuals of the dTWSA turned positive for the storage deficit method and when observed precipitation amount exceeded absolute required precipitation amount for the required precipitation amount method. Results indicated that the mean DRT estimations from GPCC and GPCP were similar. However, the mean DRT obtained from G3P was approximately three months shorter than that from the JPL mascon. For precipitation products, the results of the consistencies in mean DRT estimations between the two methods were similar to those of the mean DRT estimations, showing no significant difference between GPCC and GPCP. Conversely, the consistency in DRT estimations obtained from G3P was 5.0% higher than the consistency in DRT estimations obtained from JPL mascon. Among climate zones, the equatorial zone had the shortest DRT estimation (~10 months) and the highest consistency (~98%). In contrast, the polar zone had the most extended DRT estimation (~16 months) and the lowest consistency (~75%). Overall, findings demonstrate that GPCC and GPCP are closely aligned in terms of mean DRT estimations and consistency. Additionally, G3P exhibited slightly more consistent DRT estimations with precipitation products than did JPL mascon. By analyzing hydrological drought characteristics, this study provides a basis for a better understanding of meteorological and hydrological processes as well as assessing the accuracy of the precipitation and TWS products.