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@ARTICLE{2026ISPAr49B3..859U,
       author = {{Udoka}, Ubong Paulinus and {Pavelka}, Karel},
        title = "{Estimating Long-Term Groundwater Storage Change in the Chad Basin, Nigeria, Using GRACE/GRACE-FO and GLDAS Terrestrial Water Storage Anomalies}",
      journal = {ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences},
         year = 2026,
        month = jul,
       volume = {49B3},
        pages = {859-864},
     abstract = "{The Chad Basin is the main source of fresh water to over 30 million
        people in the semi-arid Sahel region, and long-term evaluation
        of groundwater resources is crucial for sustainable abstraction
        of fresh water, water security for the region, and humanitarian
        resilience. Using the GRACE/GRACE-FO satellite gravimetry and
        GLDAS land surface modelling, this study was used to assess the
        hydrological variations in one of the least data-rich and most
        water-drafted transboundary basins in the world. Results show an
        important hydrogeological paradox. The overall trend in the
        basin-scale water mass, as revealed by Total Water Storage
        Anomaly (TWSA), is a strong increase of +5.91 mm/year
        (R{\texttwosuperior} = 0.70). However, recoverable water
        components are diminishing, with surface water, soil moisture,
        and Groundwater Storage Anomaly (GWSA) decreasing at
        {\ensuremath{-}}1.04, {\ensuremath{-}}1.02, and 0.02 mm/year,
        respectively. This means that a higher absolute amount of water
        stored does not necessarily lead to an increase in groundwater
        recharge, probably because of high evaporation, extraction
        pressures, and hydrogeological conditions. Spatial analysis also
        reveals areas of critical groundwater depletion along the
        western boundary of the basin, especially across the
        northeastern part of Nigeria, where groundwater extraction is
        high. Rainfall trends are weak (+1.65 mm/year) and not
        significantly correlated with groundwater storage (r =
        {\ensuremath{-}}0.176), indicating that recharge efficiency to
        the deep aquifers is poor. The overall conclusion is that the
        anthropogenic pressures on water scarcity are growing, and the
        use of evidence-based transboundary governance, regulation of
        groundwater abstraction, and targeted Managed Aquifer Recharge
        strategies is needed.}",
          doi = {10.5194/isprs-archives-XLIX-B3-2026-859-2026},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2026ISPAr49B3..859U},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}