Publications related to the GRACE Missions (no abstracts)

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Detecting hydrologically induced seasonal stress variations in Ethiopia from GPS, GRACE, and rainfall observations

Koji, Abdisa Kawo and Elemo, Abdulkadir Gemachu, 2026. Detecting hydrologically induced seasonal stress variations in Ethiopia from GPS, GRACE, and rainfall observations. Journal of African Earth Sciences, 234:105911, doi:10.1016/j.jafrearsci.2025.105911.

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@ARTICLE{2026JAfES.23405911K,
       author = {{Koji}, Abdisa Kawo and {Elemo}, Abdulkadir Gemachu},
        title = "{Detecting hydrologically induced seasonal stress variations in Ethiopia from GPS, GRACE, and rainfall observations}",
      journal = {Journal of African Earth Sciences},
     keywords = {GPS, GRACE, TWS, Deformation, Hydrological stress},
         year = 2026,
        month = jan,
       volume = {234},
          eid = {105911},
        pages = {105911},
     abstract = "{Seasonal redistribution of water exerts a strong influence on Vertical
        Crustal Deformation (VCD) in Ethiopia, a region marked by
        pronounced rainfall gradients, active rifting, and increasing
        water stress. This study quantifies hydrologically induced
        deformation between 2012 and 2021 using two independent
        datasets: (i) daily millimeter-scale positions from 35 GPS
        stations processed with the GAMIT/GLOBK Global Kalman Filter,
        and (ii) monthly terrestrial water storage (TWS) anomalies from
        the GRACE and GRACE-Follow On (GRACE-FO) JPL RL06.2 mascon
        solution, which were converted to vertical displacements using
        Green's function convolution. To validate the hydrological
        stress signals, we first compared GPS- and GRACE-derived
        vertical displacements with local rainfall gauge records at the
        ADIS station (2012─2020). GPS displacements correlated strongly
        with rainfall (r = 0.72, zero lag). GRACE-TWS anomalies also
        showed a strong correlation with rainfall (r = 0.80), confirming
        that both geodetic techniques consistently capture the seasonal
        hydrological cycle. The close agreement in timing and magnitude
        among GPS, GRACE, and rainfall strengthens confidence in using
        these complementary datasets to monitor hydrologically induced
        crustal deformation. On the other hand, the comparison between
        GPS- and GRACE-derived vertical displacements reveals pronounced
        spatial variability across Ethiopia. In the northern and western
        highlands (e.g., Shimsheha, Debark and Asosa), the two datasets
        show strong agreement, with correlations exceeding 0.80 and
        phase lags below 3 weeks, indicating that large-scale seasonal
        hydrological loads are the dominant drivers of elastic crustal
        deformation. In contrast, at sites such as Arba Minch, near
        Lakes Abaya and Chamo, GPS amplitudes are up to five times
        greater than GRACE estimates, reflecting localized lake-level
        fluctuations that fall below GRACE's spatial resolution. At
        Djibouti, additional mismatches are observed, likely caused by
        tectonic activity and coastal thermal effects that obscure
        hydrological signals. Together, these spatial patterns
        demonstrate that while GPS is highly sensitive to localized
        loading effects, GRACE provides robust constraints on basin-to
        regional-scale water redistribution.}",
          doi = {10.1016/j.jafrearsci.2025.105911},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2026JAfES.23405911K},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}

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