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| Titel |
Energy fluxes and surface characteristics over a cultivated area in Benin: daily and seasonal dynamics |
| VerfasserIn |
O. Mamadou, J. M. Cohard, S. Galle, C. N. Awanou, A. Diedhiou, B. Kounouhewa, C. Peugeot |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 3 ; Nr. 18, no. 3 (2014-03-07), S.893-914 |
| Datensatznummer |
250120297
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| Publikation (Nr.) |
 copernicus.org/hess-18-893-2014.pdf |
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| Zusammenfassung |
Latent 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
(β) at both seasonal and daily scales. Finally, the surface
conductance (Gs) and the decoupling coefficient (Ω) 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 (β ~ 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 (β) was about 0.4. During the dry-to-wet and
wet-to-dry transition seasons, both EF and β 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 < Ω < 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. |
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