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Lookup NU author(s): Dr Mohamed Akl, Dr Brian Thomas, Professor Peter ClarkeORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2025. The Author(s). The Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On missions have enriched global groundwater monitoring, forming the basis for tools that detect groundwater drought, including the GRACE-Groundwater Drought Index (GGDI). The reliability of GGDI is fundamentally tied to the accurate isolation of a representative groundwater storage anomaly (GRACE-GWA) signal from GRACE observations, a challenge heightened by the scarcity of direct water budget measurements and the diverse methodologies applied in GRACE data processing. In this global assessment, we integrate multi-model GRACE-GWA estimates into the GGDI framework to examine how variability among these estimates influences groundwater drought interpretation across 37 study aquifers. Results reveal substantial sensitivity of key drought indicators to input uncertainty, with maximum observed intra-basin discrepancies reaching 11 events, 122 months in maximum duration, 63.33 months in average duration, 24.47 in severity, and 5.4 in intensity. Aquifer memory, inferred from GGDI autocorrelation, reveals pronounced variability, most notably in the Nubian Basin where memory estimates range from 3 to 61 months amongst multi-model realizations. Aquifers with higher memory tended to experience fewer drought events, yet those droughts were typically longer and more intense. Our findings underscore that even modest discrepancies in GRACE-GWA methodologies can translate into considerable uncertainties in both drought indicators and aquifer memory, thereby compromising the reliability of groundwater drought assessments.
Author(s): Akl M, Thomas BF, Clarke PJ
Publication type: Article
Publication status: Published
Journal: Water Resources Research
Year: 2025
Volume: 61
Issue: 12
Online publication date: 06/12/2025
Acceptance date: 30/11/2025
Date deposited: 22/12/2025
ISSN (print): 0043-1397
ISSN (electronic): 1944-7973
Publisher: John Wiley and Sons Inc.
URL: https://doi.org/10.1029/2025WR040389
DOI: 10.1029/2025WR040389
Data Access Statement: CSR-SH (Landerer, 2021), JPL-SH (Landerer, 2021), GFZ-SH (Landerer, 2021), and JPL-M (Wiese et al., 2018) are accessible through JPL website at (https://grace.jpl.nasa.gov/data/get-data/monthly-mass-grids-land/; Last access: 03 December 2024). For the CSR-M (Save, 2020), visit CSR website (https://www2.csr.utexas.edu/grace/RL06_mascons.html; Last access: 03 December 2024). GLDAS (Rodell et al., 2004) and FLDAS (McNally et al., 2017) data sets are available from The NASA Goddard Earth Sciences Data and Information Services Centre (https://ldas.gsfc.nasa.gov/gldas/gldas-get-data; Last access: 09 December 2024). WaterGAP v2.2e (Müller Schmied et al., 2024) outputs can be retrieved from the Goethe University Data Repository (GUDe) at (https://gude.uni-frankfurt.de/entities/researchdata/7d500a84-9a36-4cd2-9f76-a4081f9ee94e/details; Last access: 09 December 2024). [Please see the article for the full data access statement.]
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