Geomorphologic approach for modelling the surface features of arid environments in a model of dust emissions: application to the Sahara desert

Abstract

Mineral dust emissions from arid regions are influenced by the surface features encountered in the source regions. These surface features control both the erosion threshold and the intensity of the dust flux. Recently, a soil-derived dust emission scheme has been designed in order to provide an explicit representation of the mineral dust accounting for the influence of the surface features on the dust emissions. This physical scheme has been validated with micro-scale field measurements. Its large scale application has required the development of additional relations to estimate the input parameters from more accessible data: the mean height and the covering rate of the roughness elements and the mineralogical soil type. The determination of these surface data has been based on a geomorphologic approach which describes the surface features of arid areas in a 1 x 1 0 grid. Inside each square degree, up to five different areas characterised by different surface features have been distinguished. However, these areas have not been located inside the square degree. Each area can be constituted by several combined surface features, including roughness, vegetation, granulometry. Five m?in types of landscapes and eight main types of surface features have been distinguished. This approach is based on the combination of various data, mainly topographical, geological maps and climatological analysis. In addition to the problem of scale transfer, the main constraints to obtain a quantitative assessment are the confidence level of the existing data and the number of parameters to document. On the opposite, with this method, the fine scale required by the dust modelling can be separated from the scale accessible by the mapping approach, of the order of the square degree. This method can also be easily improved by aggregating new data and can be extended to other deserts. An example of application is given for the north-west of the Algerian Sahara where the method has been elaborated. The data provided by the modelling of * Correspondence and reprints.

Particle size distributions of South Tunisian soils erodible by wind

“…The presence of this fine mode is also ubiquitous whatever the land use since it is observed both on natural surfaces such as steppic vegetation and on agricultural fields (like olive trees). However, in some regions of the Dahars, Matmatas and more generally in regions close to the mountains, the presence of small pebbles or aggregates at the soil surface, as frequently observed in arid regions [6], could increase the wind erosion threshold and thus reduce the erodability of these surfaces.…”

Modelling of primary aerosols in the chemical transport model MOCAGE: development and evaluation of aerosol physical parameterizations

“…The Marticorena et al (1997) scheme covers Africa, Arabia and the Middle East (13-36 • N, 17 • W-77 • E) with a resolution of 1 • × 1 • . The input soil properties and aerodynamical surface parameters are based on available pedological, topographical, geological and climatological data and analysis (Marticorena et al, 1997;Callot et al, 2000). The main sources were from the French National Geographic Institute (IGN) and Soviet topographic maps.…”

Estimation of air quality degradation due to Saharan dust at Nouakchott, Mauritania, from horizontal visibility data

“…Indeed, it is estimated that the Sahara and its margins inject amounts of dust varying between 600 and 900 10 6 tons into the atmosphere every year (D'Almeida, 1986;Marticorena et al, 1997;Callot et al, 2000). This represents about half of annual global mineral dust production (Ginoux et al, 2004).…”