Publications des scientifiques de l'IRD

Bouchez C., Goncalves J., Deschamps Pierre, Vallet-Coulomb C., Hamelin Bruno, Doumnang J. C., Sylvestre Florence. (2016). Hydrological, chemical, and isotopic budgets of Lake Chad : a quantitative assessment of evaporation, transpiration and infiltration fluxes. Hydrology and Earth System Sciences, 20 (4), p. 1599-1619. ISSN 1027-5606.

Titre du document
Hydrological, chemical, and isotopic budgets of Lake Chad : a quantitative assessment of evaporation, transpiration and infiltration fluxes
Année de publication
2016
Type de document
Article référencé dans le Web of Science WOS:000377856100017
Auteurs
Bouchez C., Goncalves J., Deschamps Pierre, Vallet-Coulomb C., Hamelin Bruno, Doumnang J. C., Sylvestre Florence
Source
Hydrology and Earth System Sciences, 2016, 20 (4), p. 1599-1619 ISSN 1027-5606
In the Sahelian belt, Lake Chad is a key water body for 13 million people, who live on its resources. It experiences, however, substantial and frequent surface changes. Located at the centre of one of the largest endorheic basins in the world, its waters remain surprisingly fresh. Its low salinity has been attributed to a low infiltration flow whose value remains poorly constrained. Understanding the lake's hydrological behaviour in response to climate variability requires a better constraint of the factors that control its water and chemical balance. Based on the three-pool concep-tualization of Lake Chad proposed by Bader et al. (2011), this study aims to quantify the total water outflow from the lake, the respective proportions of evaporation (E), transpiration (T), and infiltration (I), and the associated uncertainties. A Bayesian inversion method based on lake-level data was used, leading to total water loss estimates in each pool (E + T + I = ETI). Sodium and stable isotope mass balances were then used to separate total water losses into E, T, and I components. Despite the scarcity of representative data available on the lake, the combination of these two geochemical tracers is relevant to assess the relative contribution of these three outflows involved in the control of the hydrological budget. Mean evapotranspiration rates were estimated at 2070 +/- 100 and 2270 +/- 100 mm yr(-1) for the southern and northern pools, respectively. Infiltration represents between 100 and 300 mm yr(-1) but most of the water is evapotranspirated in the first few kilometres from the shorelines and does not efficiently recharge the Quaternary aquifer. Transpiration is shown to be significant, around 300 mm yr(-1) and reaches 500 mm yr(-1) in the vegetated zone of the archipelagos. Hydrological and chemical simulations reproduce the marked hydrological change between the normal lake state that occurred before 1972 and the small lake state after 1972 when the lake surface shrunk to a one-tenth of its size. According to our model, shrinking phases are efficient periods for salt evacuation from the lake towards the phreatic aquifer.
Plan de classement
Hydrologie [062] ; Géologie et formations superficielles [064]
Description Géographique
TCHAD ; CAMEROUN ; NIGERIA ; NIGER ; CENTRAFRIQUE ; ZONE SAHELIENNE ; TCHAD LAC
Localisation
Fonds IRD [F B010067587] ; Niamey (LASDEL)
Identifiant IRD
fdi:010067587
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