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Water balance in a small endoreic Sahelian catchment

Congress: 2008
Author(s): B. Cappelaere, L. Descroix, N. Boulain, D. Ramier, J.P. Laurent, S. Boubkraoui, A. Koné, H. Alhassane, A. Alhassane, F. Métayer, F. Timouk, G. Favreau
Cappelaere B. (1), Descroix L. (2), Boulain N. (1), Ramier D. (1), Laurent J.P. (2), Boubkraoui S. (2), Koné A. (3), Alhassane H. (4), Alhassane A. (3), Métayer F. (3), Timouk F. (5), Favreau G. (1) (1) UMR HydroSciences Montpellier, France (2) UMR LTHE Grenoble, France (3) IRD Niamey, Rép. du Niger (4) Institut National de la Recherche Agronomique du Niger, Niamey (5) UMR CESBIO Toulouse, France

Keyword(s): semiarid, West Africa, Sahel, evapotranspiration, channel losses, pilot catchment
AbstractAmong key processes in Sahelian hydrology are evapotranspiration, which dominates the annual water balance, and infiltration in permeable hydrographic networks. Their importance is such that, in many areas, catchments are endoreic, but these components of the water cycle are not easily measured in the field. An experimental setup was therefore installed in the vicinity of Niamey in South-West Niger, as part of the AMMA (1) research program, to monitor as comprehensively as possible all major components of the water cycle at the scale of a typical, small endoreic catchment (~ 2 km²). Rainfall is measured by three tipping-bucket recording gauges and a network of twenty event-step pluviometers. Direct, continuous measurements of evapotranspiration fluxes are performed by the eddy-covariance method, at two locations that are representative of the dominant vegetation covers in the area, namely fallow savannah and millet crop. Additional equipment allows for the monitoring of the full energy balance at those sites, as well as at two additional sites including a typical plot with degraded vegetation and soil. Soil humidity profiles are captured using TDR sensor recording down to 2.5 meters, and neutron probing down to about 10 meters. Infiltration in the hydrographic network is approached thanks to a series of four gauging stations installed along the catchment’s ravine, and to several neutron probe access tubes in the ravine’s bed and alongside. This experimental setup has been operating since 2005, and provides a unique dataset for the characterization of the main components of the water balance at various time scales. Some of the major features recorded over the 2005 to 2007 rain seasons are highlighted. Consequences for water resources are discussed. (1) African Monsoon Multidisciplinary Analyses
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