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In WP1 (ISPA, iEES Paris, IRA, LISA), the preliminary version of the wind erosion model of Dupont et al. (2015), including saltation and dust suspension, and coupled with a Large-Eddy Simulation (LES) airflow model, will be generalized to multimodal dust distribution. This model will be tested on bare soils against a dedicated field experiment performed in Tunisia where wind dynamics, saltation and dust fluxes per size class will be measured. The dust flux will be deduced from the traditional gradient method with the measurement of dust concentration at two levels (from optical particle counters), and from the eddy-covariance method, with the high frequency measurements of the vertical wind velocity (from sonic anemometers) and the dust concentration.

In WP2 (LMFA, ISPA), the near-surface resolution of the LES model developed in WP1 will be improved by performing Direct Numerical Simulation (DNS) and wind-tunnel experiments of the wind gust – particle interaction near the surface. To that purpose, a DNS model coupled with an immersed boundary method will be developed to simulate saltation on a bare soil. The coupling will be validated against a wind-tunnel experiment and compared with the LES model.

In WP3 (ISPA, iEES Paris, IRA, LISA), the protective effect of the vegetation will be quantified by performing simulations and field experiments over different arrangements of vegetation. Simulations will be performed with the model developed in WP1, extended here to vegetated environment. The field experiments will be similar in terms of measurements and strategy as in WP1 but with two different vegetation arrangements. Once the simulations will be in fair agreement with the experimental observations, the model will be used to deduce a specific parameterization of the impact of the vegetation on erosion fluxes for regional dust models. Finally, during the last year of the project, a workshop will be organized at IRA Médenine (Tunisia) with local representative of agricultural sector to present model results for different vegetation arrangements and to discuss on potential improvement and feasibility of crop organization to limit soil erosion and to sustainably manage soil.

In WP4 (iEES Paris, IRA, LISA), a parameterization of the chemical composition of particles according for the fractionation they experiment along the soil-saltation-suspension continuum, will be developed based on the size resolved chemical/mineralogical characterization of the saltation and dust fluxes measured during the Tunisian experiments. The composition of the soil will be also fully characterized for two types of size segregations: after minimal dispersion (dry sieving) to obtain the composition of the soil aggregates available for saltation and after complete dispersion to obtain the composition of the individual particles composing the soil aggregates.

In WP5 (iEES Paris, IRA, LISA), the new parameterizations of erosion fluxes and their chemical composition developed in WP3 and WP4, following wind conditions and vegetation main characteristics will be implemented in the 3D regional dust-transport model CHIMERE-Dust. Dust emission-transport-deposition will be simulated in southern Tunisia for two years and validated against available in-situ measurements of the saltation flux and surface wind speed. Simulations performed with the standard dust emission scheme and with the new one will be compared in order to estimate the benefit provided by these new parameterizations as a function of land use and wind conditions.

References:

Dupont S., Alfaro S., Bergametti G., Marticorena B. (2015). Dust flux enrichment in small particles during erosion event and with increasing wind velocity. Geophysical Research Letter, 42, doi:10.1002/2015GL063116.