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Mamadou O., Cohard J. M., Galle Sylvie, Awanou C. N., Diedhiou Arona, Kounouhewa B., Peugeot Christophe. (2014). Energy fluxes and surface characteristics over a cultivated area in Benin : daily and seasonal dynamics. Hydrology and Earth System Sciences, 18 (3), 893-914. ISSN 1027-5606

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Lien direct chez l'éditeur doi:10.5194/hess-18-893-2014

Titre
Energy fluxes and surface characteristics over a cultivated area in Benin : daily and seasonal dynamics
Année de publication2014
Type de documentArticle référencé dans le Web of Science WOS:000334501700001
AuteursMamadou O., Cohard J. M., Galle Sylvie, Awanou C. N., Diedhiou Arona, Kounouhewa B., Peugeot Christophe.
SourceHydrology and Earth System Sciences, 2014, 18 (3), p. 893-914. ISSN 1027-5606
RésuméLatent and sensible heat surface fluxes are key factors of the western African monsoon dynamics. However, few long-term observations of these land surface fluxes are available; these are needed to increase understanding of the underlying processes and assess their impacts on the energy and water cycles at the surface-atmosphere interface. This study analyzes turbulent fluxes of one full year, measured with the eddy covariance technique, over a cultivated area in northern Benin (western Africa). The study site is part of the long-term AMMA-CATCH (African Monsoon Multidisciplinary Analysis-Coupling of the Tropical Atmosphere and Hydrological Cycle) hydrological observatory. The flux partitioning was investigated through the evaporative fraction (EF) and the Bowen ratio (beta) at both seasonal and daily scales. Finally, the surface conductance (G(s)) and the decoupling coefficient (Omega) were calculated and compared with specific bare soil or canopy models. Four contrasting seasons were identified and characterized by their typical daily energy cycles. The results pointed out the contrasting seasonal variations of sensible and latent heat fluxes due to changing atmospheric and surface conditions. In the dry season, the sensible heat fluxes were largely dominant (beta similar to 10) and a low but significant evapotranspiration was measured (EF = 0.08); this was attributed to a few neighboring bushes, possibly fed by the water table. During the wet season, after the monsoon onset, surface conditions barely affected the evaporative fraction (EF), which remained steady (EF = 0.75); the latent heat flux was dominant and the Bowen ration (beta) was about 0.4. During the dry-to-wet and wet-to-dry transition seasons, both EF and beta were highly variable, as they depended on the atmospheric forcing or the response to isolated rains. A complete surface-atmosphere decoupling was never observed in 2008 (0 < Omega < 0.6), which suggests a systematic mixing of the air within the canopy with the atmospheric surface layer, irrespective of the atmospheric conditions and the vegetation height. Modeling approaches showed a good agreement of soil resistance with the Sakaguchi bare soil model. Canopy conductance was also well reproduced with the Ball-Berry stomata model. We showed that the skin surface temperature had a large seasonal and daily amplitude, and played a major role in all the surface processes. Consequently, an accurate modeling of the surface temperature is crucial to represent correctly the energy and water budgets for this region.
Plan de classementHydrologie [062] ; Limnologie physique / Océanographie physique [032] ; Sciences fondamentales / Techniques d'analyse et de recherche [020]
Descr. géo.BENIN
LocalisationFonds IRD [F B010061925]
Identifiant IRDfdi:010061925
Lien permanenthttp://www.documentation.ird.fr/hor/fdi:010061925

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