Causes, consequences and control of wind erosion in Sahelian Africa: a review

Abstract

Sahelian Africa is one of the poorest regions of the world, where approximately 90 per cent of the population depends on subsistence agriculture. Due to the high population growth, with annual growth rates of about 3 per cent during recent decades, farmers have expanded their cropping areas to increase production. At the same time the traditional bush fallow system collapsed and more land became subject to soil degradation processes. Wind erosion is one of the main degradation processes that has received much scientific attention since the 1980s. The objective of this paper is to review the latest research results on wind-erosion causes, consequences, perceptions and control in the Sahel. First the main processes involved in wind erosion (creep, saltation and suspension) are described and related to the Sahelian climate, soils and farming systems. Then the agricultural consequences of wind erosion are evaluated. Three types of damage are distinguished: undesired sedimentation, crop damage and soil degradation. Several studies were done to determine farmers knowledge and perceptions of wind erosion. In general the Sahelian farmers have a good qualitative understanding of wind-erosion processes, and they are concerned about the consequences, especially about crop damage and soil productivity decline. Finally, the possibilities and constraints for winderosion control are evaluated. The most widely applied control measure is mulching with crop residues, but the quantity of residue is insufficient due to low biomass yields and multiple uses. It is concluded that regeneration and exploitation of natural, scattered vegetation is a promising control strategy that needs more research.

A spatially explicit methodology to quantify soil nutrient balances and their uncertainties at the national level

“…Wind erosion may be more important for dry Sahelian countries. However, results of wind erosion and deposition measurements are highly variable and difficult to compare due to a variety of research methods (Sterk 2003). Besides, at the national level fluxes due to wind erosion are negligible and only Harmattan dust should be accounted for (Schlecht and Hiernaux 2004).…”

Dynamical mechanisms controlling the vertical redistribution of dust and the thermodynamic structure of the West Saharan atmospheric boundary layer during summer

“…Dust devils, which form in convective boundary layers with sheared but relatively light winds, may also be important in some regions (Koch and Renno, 2005). Dust uplift by density currents is also important in many locations (Sterk, 2002;Flamant et al, 2007 hereafter F07; Knippertz et al, 2007;Bou Karam et al, 2008;Marsham et al, 2008b). After uplift, very coarse particles (with diameter d > 30 µm) settle down quickly in the proximity of the sources.…”

Multi‐platform observations of a springtime case of Bodélé and Sudan dust emission, transport and scavenging over West Africa

“…This is related to: (i) the presence of the intertropical discontinuity (ITD) over the Sahel which has been shown to favour the uplift of dust during the night-time when the leading edge of the monsoon flow exhibits the characteristics of a density current (Bou Karam et al, 2008), (ii) the occurrence of the first MCSs over Sahel (south of the ITD) and their associated cold pools which offer an efficient mechanism for dust lifting and injection to altitudes favourable for long-range transport, before the growing vegetation rapidly inhibits local dust emission (e.g. Sterk, 2002;Flamant et al, 2007;Marsham et al, 2008), and (iii) the strong harmattan winds to the north of the ITD which can generate large uplift of dust from the North African sources in the form of discrete outbreaks (Knippertz, 2008).…”