Surveys in Geophysics

, Volume 37, Issue 2, pp 471–502 | Cite as

Subsurface Hydrology of the Lake Chad Basin from Convection Modelling and Observations

  • T. LopezEmail author
  • R. Antoine
  • Y. Kerr
  • J. Darrozes
  • M. Rabinowicz
  • G. Ramillien
  • A. Cazenave
  • P. Genthon


In the Lake Chad basin, the quaternary phreatic aquifer (named hereafter QPA) presents large piezometric anomalies referred to as domes and depressions whose depths are ~15 and ~60 m, respectively. A previous study (Leblanc et al. in Geophys Res Lett, 2003, doi: 10.1029/2003GL018094) noticed that brightness temperatures from METEOSAT infrared images of the Lake Chad basin are correlated with the QPA piezometry. Indeed, at the same latitude, domes are ~4–5 K warmer than the depressions. Leblanc et al. (Geophys Res Lett, 2003, doi: 10.1029/2003GL018094) suggested that such a thermal behaviour results from an evapotranspiration excess above the piezometric depressions, an interpretation implicitly assuming that the QPA is separated from the other aquifers by the clay-rich Pliocene formation. Based on satellite visible images, here we find evidence of giant polygons, an observation that suggests instead a local vertical connectivity between the different aquifers. We developed a numerical water convective model giving an alternative explanation for the development of QPA depressions and domes. Beneath the depressions, a cold descending water convective current sucks down the overlying QPA, while, beneath the dome, a warm ascending current produces overpressure. Such a basin-wide circulation is consistent with the water geochemistry. We further propose that the thermal diurnal and evaporation/condensation cycles specific to the water ascending current explain why domes are warmer. We finally discuss the possible influence of the inferred convective circulation on the transient variations of the QPA reported from observations of piezometric levels and GRACE-based water mass change over the region.


Lake Chad Piezometric anomalies Vertical permeability Infrared data Convection GRACE 



This research has benefited from the support by the French Space Agency CNES and TOSCA (Terre, Océan, Surfaces continentales, Atmosphère) support. It has also benefited from the support of Commissariat Général au Développement Durable (CGDD) from the French Ministry of Environment, as part of the CEREMA internal research project HYDROGEO. Thanks are due to the “Bureau Gravimétrique International (BGI)/International Association of Geodesy” for providing the EGM model. We thank G. de Marsily and G. Vasseur for their constructive criticisms, and the Editor in Chief for editorial suggestions, which significantly improved the paper. This paper arises from the ISSI Workshop on Remote Sensing and Water Resources.


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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  • T. Lopez
    • 1
    Email author
  • R. Antoine
    • 2
  • Y. Kerr
    • 1
  • J. Darrozes
    • 3
  • M. Rabinowicz
    • 3
  • G. Ramillien
    • 4
  • A. Cazenave
    • 4
    • 5
  • P. Genthon
    • 6
  1. 1.Centre d’Etudes Spatiales de la Biosphère, Unité mixte de Recherche Université Toulouse 3, Centre National d’Etudes Spatiales, Centre National de la Recherche Scientifique, Institut de Recherche pour le DéveloppementToulouseFrance
  2. 2.Centre d’Etudes et d’Expertise sur les Risques, l’Environnement, la Mobilité et l’Aménagement, Laboratoire Régional de Rouen, Groupe Sciences de la TerreLe Grand QuevillyFrance
  3. 3.Géosciences Environnement Toulouse, Unité mixte de Recherche Université Toulouse 3, Centre National d’Etudes Spatiales, Centre National de la Recherche Scientifique, Institut de Recherche pour le DéveloppementToulouseFrance
  4. 4.Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, Unité mixte de Recherche Université Toulouse 3, Centre National d’Etudes Spatiales, Centre National de la Recherche Scientifique, Institut de Recherche pour le DéveloppementToulouseFrance
  5. 5.International Space Science Institute (ISSI)BernSwitzerland
  6. 6.Laboratoire Hydrosciences Montpellier, Unité mixte de Recherche Université Montpellier, Institut de Recherche pour le Développement, Centre National de la Recherche ScientifiqueMontpellierFrance

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