Publications des scientifiques de l'IRD

Lopez T., Antoine R., Kerr Y., Darrozes J., Rabinowicz M., Ramillien G., Cazenave A., Genthon Pierre. (2016). Subsurface hydrology of the Lake Chad Basin from convection modelling and observations. In : Cazenave A. (ed.), Champollion N. (ed.), Benveniste J. (ed.), Chen J. (ed.). Remote sensing and water resources. Cham : Springer, p. 281-312. (Space Sciences Series of ISS ; 55). ISBN 978-3-319-32448-7.

Titre du document
Subsurface hydrology of the Lake Chad Basin from convection modelling and observations
Année de publication
2016
Type de document
Article référencé dans le Web of Science WOS:000390418000012
Auteurs
Lopez T., Antoine R., Kerr Y., Darrozes J., Rabinowicz M., Ramillien G., Cazenave A., Genthon Pierre
In
Cazenave A. (ed.), Champollion N. (ed.), Benveniste J. (ed.), Chen J. (ed.), Remote sensing and water resources
Source
Cham : Springer, 2016, p. 281-312 (Space Sciences Series of ISS ; 55). ISBN 978-3-319-32448-7
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 basinwide 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.
Plan de classement
Hydrologie [062] ; Géologie et formations superficielles [064]
Localisation
Fonds IRD [F B010072211]
Identifiant IRD
fdi:010072211
Contact