Publications related to the GRACE Missions (no abstracts)

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Integrating satellite gravimetry and ground–based SGI diagnostics for groundwater drought assessment in Greece (2002–2023)

Akşan, Gözde N., 2026. Integrating satellite gravimetry and ground–based SGI diagnostics for groundwater drought assessment in Greece (2002–2023). Acta Geophysica, 74(5):280, doi:10.1007/s11600-026-01995-1.

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@ARTICLE{2026AcGeo..74..280A,
       author = {{Ak{\c s}an}, G{\"o}zde N.},
        title = "{Integrating satellite gravimetry and ground-based SGI diagnostics for groundwater drought assessment in Greece (2002-2023)}",
      journal = {Acta Geophysica},
     keywords = {Groundwater drought, GRACE, Standardized Groundwater Index (SGI), Mann--Kendall and Sen's slope, KNN-GapFiller, Earth Sciences, Physical Geography and Environmental Geoscience},
         year = 2026,
        month = sep,
       volume = {74},
       number = {5},
          eid = {280},
        pages = {280},
     abstract = "{Groundwater is a critical component of water security in Mediterranean
        countries, yet it is increasingly threatened by climate
        variability, recurrent droughts, and anthropogenic pressures.
        This study presents an integrated groundwater drought assessment
        framework for Greece by combining GRACE/GRACE-FO-derived
        groundwater storage anomaly (GWSA) time series with Standardized
        Groundwater Index (SGI) diagnostics for the period 2002--2023.
        Monthly GWSA records were obtained for 13 observation points
        distributed across Greece, and missing observations, including
        the 2017--2018 GRACE/GRACE-FO mission gap, were reconstructed
        using a Python-based KNN-GapFiller algorithm. Cross-validation
        results demonstrated strong reconstruction performance (RMSE =
        7.90, NSE = 0.94, PCC = 0.97), confirming the reliability of the
        reconstructed time series. The resulting GWSA records were
        analyzed using an automated SGI workflow to identify groundwater
        drought events, quantify drought severity and duration, and
        evaluate long-term trends using the Mann--Kendall test and Sen's
        slope estimator. Results revealed widespread groundwater
        depletion across Greece, with 12 of the 13 observation points
        exhibiting negative groundwater trends. The strongest declines
        were observed in northeastern Greece, where Sen's slope values
        reached approximately -3.9 mm year⁻$^{1}$, whereas only one
        observation point showed a significant positive trend. SGI
        analyses further identified recurrent groundwater drought
        episodes, particularly during 2007--2009 and 2012--2013,
        together with increasing drought persistence in several regions.
        Overall, the proposed framework integrates machine-learning-
        based reconstruction of incomplete GRACE/GRACE-FO records with
        SGI-based groundwater drought diagnostics, providing a
        reproducible approach for groundwater drought monitoring and
        supporting sustainable groundwater management and climate
        adaptation in Mediterranean environments.}",
          doi = {10.1007/s11600-026-01995-1},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2026AcGeo..74..280A},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}

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