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Comparing drag partition schemes over a herbaceous Sahelian rangeland
Author(s) -
Pierre C.,
Bergametti G.,
Marticorena B.,
Kergoat L.,
Mougin E.,
Hiernaux P.
Publication year - 2014
Publication title -
journal of geophysical research: earth surface
Language(s) - English
Resource type - Journals
eISSN - 2169-9011
pISSN - 2169-9003
DOI - 10.1002/2014jf003177
Subject(s) - environmental science , rangeland , vegetation (pathology) , atmospheric sciences , aeolian processes , drag , water content , hydrology (agriculture) , drag coefficient , partition (number theory) , soil science , geology , mathematics , agroforestry , medicine , physics , geotechnical engineering , pathology , combinatorics , geomorphology , thermodynamics
Modeling of dust emissions from the surface remains complex, especially in semiarid regions where vegetation must be accounted for because of its potentially important protective effect. Protection is directly linked to the fraction of the soil surface covered by vegetation, but it is also driven by the interaction of vegetation elements with the wind field. The sensitivity of simulated dust emissions to various drag partition schemes—mainly those proposed by Raupach (1992), Marticorena and Bergametti (1995), and Okin (2008)—is evaluated for a typical Sahelian rangeland, covered by a seasonal grass layer, over a complete vegetation cycle. The application of these schemes requires a fine characterization of the vegetation cover; field measurements from an ecological survey are used to derive the geometric dimensions of the grass patches. Models are run with meteorological forcing from automatic weather stations. As a result, the impacts of soil moisture and grass cover are estimated over April to September. Soil moisture inhibits dust emissions by 27% in mass. The different drag partition schemes exhibit distinctive limitations, mostly due to the properties of the Sahelian grass cover, which is composed of large and low patches of short grass, with a strong seasonal dynamics. However, the drag partition schemes result in remarkably coherent estimations of dust emissions. When soil moisture is taken into account, vegetation reduces the total vertical mass fluxes by 6 to 26% of the emissions of a bare soil, depending on the drag partition scheme.