Validation of a dust production model from measurements performed in semi-arid agricultural areas of Spain and Niger

Models of two processes (saltation and sandblasting) that lead to fine dust release in and areas have recently been combined to form a dust production model (DPM), the physical bases of which are summarized. In order to validate DPM at field scale, its predictions in terms of horizontal and vertical mass fluxes are compared to direct measurements made in natural conditions on a silt loam soil in north-east Spain during Wind Erosion and Loss of SOil Nutrients in semi-arid Spain (WELSONS) experiment and a sandy soil in Niger during the PROgramme Soil and Erosion (PROSE) experiment. In the Spanish case, due to the formation of a coalescing crust after rainfall, a limited supply of loose particles on the soil surface restricts the availability of soil aggregates for saltation. Once this supply limitation is taken into account in the saltation submodel, the vertical fluxes, predicted by DPM with the binding energies previously determined in a wind tunnel experiment, agree well with the measured ones. In the Niger case, the agreement is found to be directly satisfactory for unlimited saltation, even in crusted conditions. However, in order to retrieve measured vertical fluxes, the aggregate binding energies that constitute key factors involved in the sandblasting computation must be divided by 3. These results validate the sandblasting part of DPM but show that saltation has to be adequately tuned when a coalescing crust forms on loamy soils. These results also show that the potential of soil for fine-dust production does not increase with its clay content which rather tends to slightly reduce sandblasting efficiencies. A high clay content favours formation of a coalescing crust that efficiently traps formerly loose soil aggregates. The supply limitation resulting from this crust formation controls the importance of saltation, and hence, of fine-dust production. Finally, saltation clearly appears as the limiting factor for fine-dust production. (C) 2003 Elsevier Science B.V All rights reserved.