Article

# Impact of very low crop residues cover on wind erosion in the Sahel

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## Abstract

In the Sahel, with average annual precipitation in the order of 500 mm yr − 1 , wind erosion occurs mainly on cultivated millet fields whose surfaces are only partially covered by crop residues. The impact of these residues on wind erosion was not clearly established. The objective of this study is thus to quantify the actual amount of crop residues in traditional Sahelian fields and to determine their impacts on wind erosion by reference to a bare surface throughout the seasonal cycle over several years. At the beginning of the year during dry season, Sahelian farmers use to "clean" their fields, i.e. cut and lay flat on the soil surface any millet stalks still standing and yearly sprouts of shrubs. After this clearing, the crop residues cover (CRC) regularly decreases passing from 12% to less than 2% four months later. On traditional cultivated plot, crop residues efficiently prevent soil losses by wind erosion during the dry season and considerably reduce erosion fluxes at the beginning of the rainy season. However, for CRC lower than 2%, wind velocities were sufficient to produce important erosion even during dry season. A minimal cover rate of about 2% (100 kg ha − 1) thus appears as critical to reduce wind erosion. This reduction is driven by the higher aerodynamic roughness length which increases the wind erosion threshold velocity. If field clearing is made in January, as currently done, the CRC just after clearing should be about 800 kg ha − 1 to maintain CRC above 2% at beginning of the rainy season when wind velocities are the highest and wind erosion the most intense. Our results also demonstrate that during the second part of rainy season wind erosion is reduced, not so much due to vegetation development but rather to a decrease in the number and the intensity of high winds events.

## Supplementary resources (2)

... In Southwest Niger, several studies (Abdourhamane Touré et al., 2011Touré et al., , 2013Touré et al., , 2018Bielders et al., 2002;Rajot, 2001) have highlighted the contribution of cultivated surfaces to wind erosion. In this region, these authors show that wind erosion is mainly due to the high surface wind velocities produced by convective systems associated with the onset of the monsoon. ...
... The horizontal flux, Fh, was computed as the integral of Eq. (1) from 0 to 40 cm for each period of sampling (Abdourhamane Touré et al., 2011;Bielders et al., 2002;Fryrear et al., 1991;Michels et al., 1995;Rajot, 2001;Sterk and Raats, 1996;Stout and Zobeck, 1996). ...
... The Harmattan season is a dry season known as a "dusty" season; the highest monthly mean dust concentrations are recorded in March-April as a consequence of dust transport from Saharan sources (Kaly et al., 2015;Marticorena et al., 2010). At Banizoumbou (70 km east of Niamey), the recorded wind speeds do not exceed the erosion thresholds, and no significant wind erosion (Abdourhamane Touré et al., 2011;Rajot, 2001) or local dust emissions (Marticorena et al., 2010) are observed at that period. On the other hand, short duration events associated with extremely high wind speeds are recorded at the beginning of the monsoon season, leading to the highest dust concentrations (Kaly et al., 2015;Marticorena et al., 2010). ...
Article
In the Sahel, wind erosion increases the vulnerability of sandy soil through the removal of the finest and most fertile fraction of the soil, including nutrients, potentially limiting vegetation development. To provide experimental evidence of the role of different land uses on wind erosion, measurements of horizontal sand fluxes and associated meteorological parameters were taken for four years in Kilakina (southeast of Niger), where large rangeland surfaces coexist with cultivated surfaces and moving dunes in a typical Sahelian semiarid regime (average annual precipitation in the order of ± 300 mm yr −1). The horizontal sand fluxes were monitored using BSNE sediment traps on the three sandy surfaces representative of the main land uses in the region: a cultivated field, a pastured land and a mobile dune. In addition, a meteorological station was installed to monitor the wind speed and direction and rainfall. Saltation flux on the bare mobile dune appeared to be an excellent proxy for wind erosivity in this region. The mobile dune produced saltation fluxes 2 to 40 times higher than the cultivated field and the rangeland. The annual fluxes on the dune varied from 2000 to 6000 kg m −1 due to the variability of the winds from year to year. The sediment fluxes are higher in the millet field than those on the pastured land due to a larger fraction of bare surface compared to the relatively homogeneous grass cover that exists on pastured surfaces. The vegetation produced in a given year affects the wind erosion of the following year through the effect of dry vegetation and litter cover. These results highlight the sensitivity of wind erosion to dry vegetation, even for low cover rates. This outcome suggests that any agricultural practice that decreases dry vegetation cover, such as the uptake of vegetation residues from the fields and the pastured land, has a strong impact on wind erosion. Wind erosion in East Niger can be higher during the Harmattan season than during the monsoon season, while similar measurements in West Niger showed that saltation fluxes were higher during the monsoon season. This outcome suggests that the intensity of the Harmattan surface winds could decrease from east to west. In addition to land use changes, the regional pattern of the surface winds and its future evolution clearly deserve further investigation based on relevant long-term in situ measurements.
... Moulin & Chiapello (2006) have also suggested that land use change has modified Sahelian dust emission at a regional scale during the 20th century. To date, studies dedicated to the effects of agropastoral practices on Sahelian wind erosion have been mostly provided by experiments at the plot scale, focusing on crop residue management and on deposition of wind-blown particles into fallows (e.g., Michels et al., 1995;Bielders et al., 2002;Sterk, 2003;Abdourhamane Touré et al., 2011). Some studies provided recommendations on the amount of crop residue that should be left on the field after harvest to reduce wind erosion (Michels et al., 1995;Buerkert et al., 1997). ...
... Some studies provided recommendations on the amount of crop residue that should be left on the field after harvest to reduce wind erosion (Michels et al., 1995;Buerkert et al., 1997). Approximately 2,000 kg ha À1 of crop residue clearly inhibited wind erosion, but effects of 500 kg ha À1 were also acknowledged (see also Abdourhamane Touré et al., 2011). However, the application of 2,000 kg ha À1 was considered hardly achievable by farmers due to plant production limitation (Sterk, 2003;Ikazaki et al., 2011). ...
... Mean annual precipitation ranges between 100 and 600 mm; most of it is brought by a few mesoscale convective systems that induce strong winds just before the start of the rain. Thus, most wind erosion occurs during the late dry season and beginning of the rainy season, when vegetation cover is low and strong winds are frequent (Abdourhamane Touré et al., 2011;Marticorena et al., 2016). ...
Article
In the Sahel, climate change and demographic growth are raising major concerns about the ability of crop yields to support the local population. Agro-pastoral management affects wind erosion (e.g. through crop residue management and tillage practices, which modify surface characteristics), which itself substantially affects the soil fertility, and thus crop yields. There is therefore a need to assess the potential impact of the main Sahelian cropping practices – like sowing, manuring and crop residue management - on wind erosion. Using a modelling approach adapted to an experimental site located in southwestern Niger over the period 2006-2012, and scenarios that describe a set of agro-pastoral practices, the impacts of these practices on wind erosion are simulated and compared. The results indicate that horizontal fluxes differ by a factor of 10 among scenarios, with annual horizontal fluxes ranging from 121 kg.m-1 to 1317 kg.m-1. Modeled wind erosion is most sensitive to the mass of crop residues in the late dry season, but different practices dealing with crop growth or with crop residue management may result in fluxes of the similar magnitude. The collection of the crop residues after grain harvest increases wind erosion, whereas grazing might have mixed effects, probably further mediated by the mobility of livestock as a response to forage availability. The seasonal dynamics of the monthly cumulated horizontal fluxes vary depending on practice; however, the annual cumulated horizontal fluxes are closely correlated with meteorological conditions such as wind speed and rainfall in the previous year.
... The most important method for preventing wind erosion from agricultural fields is the maintenance of a residue and vegetation cover [12][13][14][15][16][17][18]. The erodibility of a surface can furthermore be influenced by the presence of a soil crust that increases cohesion and thus in turn by the tillage operations that disturb the crust [19][20][21]. ...
... The efficiency of the BSNE correlates positively with the grainsize [44,45,49]. Since the efficiency of saltating grains is described to be near 100% [18,44], we will assume this efficiency for the horizontal mass flux samples. ...
... The mass data from the BSNEs is transformed to a horizontal sediment flux. For these calculations, we will use a power relationship as proposed by Zobeck and Fryrear [57] as well as others, Abdourhamane Toure et al. [18], Sharratt et al. [49], and Webb et al. [58]. Therefore, the sediment flux Q (g m −2 ) with height z (m) is described as: ...
Article
Full-text available
Minimizing wind erosion on agricultural fields is of great interest to farmers. There is a general understanding that vegetation can greatly minimize the wind erosion taking place. However, after harvest, a low vegetation cover can be inevitable, whereby the amount of stubble that remains on a field is dependent on the crop type and land management. This study aims at quantifying the vulnerability to wind erosion of different crops, and the possibility to predict the vulnerability based on high precision aerial images. The study area was the semi-arid Free State, which holds large intensive agriculture on sandy soils. These croplands have been identified as the largest emitter of dust in South Africa. The main crop in the region is maize, but also sunflower, peanut and fallow fields are common land-use types. On these fields, the horizontal sediment flux, the saltation threshold, and aerodynamic roughness length were measured, and the soil cover was assessed using Unmanned Aerial Vehicle (UAV) imagery. The results showed a strong relationship between the soil cover and the sediment flux, whereby fallow and groundnut fields have the highest wind erosion risk. These results emphasize the great importance of soil cover management to prevent wind erosion.
... Au Niger, la production de mil, principale culture vivrière, est supportée par des sols sableux particulièrement sensibles à l'érosion éolienne (J.L. RAJOT, 2001 ;C.L. BIELDERS et al., 2002 ;A. ABDOURHAMANE TOURÉ et al., 2011). ont montré, par exemple, qu'une perte de sol par hectare de 38 tonnes en seulement deux événements érosifs sur un champ de mil s'est accompagnée d'une perte de 57,1 kg de potassium, 79,6 kg de carbone, 18,3 kg d'azote et 6,1 kg de phosphore. Ces pertes équivalent approximativement, en termes de potassium et phosphore, aux quantités néc ...
... Entre 2006et 2008, A. ABDOU-RHAMANE TOURÉ et al. (2011 ont mis en évidence une baisse du recouvrement par les résidus de culture, les quantités présentes passant de près de 800 kg/ha en février-mars à 220 kg/ha environ en mai, puis à moins de 100 kg/ha en juillet (A. ABDOURHAMANE TOURÉ et al., 2011). La parcelle PI a été mise en jachère en 2010. ...
... YREAR, 1986). Huit mâts de BSNE, espacés de 30 m les uns des autres, sont disposés suivant une ligne est-ouest (N94° - Fig. 3). Cette orientation était censée correspondre à la direction dominante des vents convectifs (lignes de grains) qui provoquent les intenses érosions dans l'Ouest du Niger (K. MICHELS et al., 1995 ;C.L. BIELDERS et al., 2002 ;A. ABDOURHAMANE TOURÉ et al., 2011). Les mâts de BSNE ont permis de suivre le flux horizontal de manière quasi continue de 2006 à 2014 (excepté en 2011, où les observations ont été interrompues dans l'attente de nouveaux financements). Chaque mât supporte trois BSNE superposés, le centre des ouvertures se trouvant respectivement à 5, 15 et 30 cm du sol (Photo 2). ...
Article
Full-text available
In the Sahel, under 500 mm of annual rainfall, wind erosion is an important factor leading to the degradation of the environment. It causes soil losses and reduces soil productivity. This work, conducted in the southwestern Niger, aims at quantifying wind erosion fluxes using BSNE sand traps. The study was conducted, from 2006 to 2014, on a plot first in cultivation, then set in fallow. It emerges that the cultivated areas are very sensitive to erosion, particularly at the beginning of the rainy season (May-July), when more than 90 % of the fluxes are recorded. Once the plot in fallow, the progressive densification of the vegetation cover caused a sharp reduction of fluxes. Compared to the results obtained during the cultivated period, they decreased by 28 % in the first year of fallowing and by 94 % in the fifth.
... Goutorbe et al. 1997;Warren et al. 2003;De Rouw and Rajot 2004;Cappelaere et al. 2009;Hiernaux et al. 2009). Several field measurements were dedicated to the dynamics of wind erosion (Rajot 2001;Bielders et al. 2004), some of which included the monitoring of crop residue degradation and land use effects (Abdourhamane Touré et al. 2011). Measurements of meteorological data and dust concentration and deposition fluxes were also collected since 2006 (Marticorena et al. 2010(Marticorena et al. , 2017. ...
... Bergametti et al. 2017), a large proportion of the annual wind erosion occurs during this period (e.g. Abdourhamane Touré et al. 2011). ...
... The mean annual rainfall over the used time-series is 505 mm with a standard deviation of 144 mm. The proportion of high wind speeds (greater than 7 m s -1 , at 5-min resolution, 6.5 m height, corresponding to wind erosion threshold for the bare soil at the study site, see Abdourhamane Touré et al. 2011) was also highly variable through years with a mean of 1.35% and a standard deviation of 0.63%. ...
Article
Full-text available
ContextWind erosion plays a major role in land degradation in semi-arid areas, especially in the Sahel. There, wind erosion is as sensitive to land use and land management as to climate factors. Future land use intensification may increase wind erosion and induce regional land degradation.Objective We aimed to estimate wind erosion responses to changing land management in a Sahelian region.Methods We defined land use intensification scenarios for a study site in southwestern Niger for two historical situations (1950s and 1990s), and two alternative prospective scenarios (2030s: extensive or intensive). We simulated vegetation growth and horizontal sediment flux of wind erosion for the corresponding landscapes.ResultsAnnual amounts of horizontal sediment flux increased with land management changes from 1950s (nil flux) to 1990s (176 kg m−1 yr−1) and 2030s (452 to 520 kg m−1 yr−1), mostly because of differences in land use, declining soil fertility, and practices decreasing the dry vegetation. For 2030s, intensive scenario exhibited larger vegetation yields than extensive conditions, but similar large values of horizontal sediment flux, thus questioning the sustainability of both scenarios. Realistic sets of practices had as large an influence as the largest theoretical range of practices on the variability of annual horizontal sediment flux. This variability was as large as that due to meteorological conditions.Conclusions This study demonstrates that the environmental impact of land use and management practices, of which wind erosion is an aspect, must be assessed at the landscape scale to account for the variability in land cover and associated land management.
... Ainsi, des impacts néfastes liés à l'érosion éolienne sont souvent enregistrés: le déchaussement de la végétation, et l'appauvrissement en nutriments des sols conduisant à la réduction de leur fertilité et de leur productivité. Les sols sableux sur lesquels repose la production du mil, principale culture de la région sahélienne, sont particulièrement sensibles à l'érosion éolienne [7][8][9][10][11]. Celle-ci, par processus sélectif, affecte spécifiquement l'horizon de surface et conduit à l'exportation des fines particules du sol où l'essentiel des réserves en nutriments pour les plantes est stocké [8]. ...
... Le flux horizontal (Fh) est calculé (équation 2) en intégrant la densité de flux en fonction de la hauteur (0 à 40 cm) [7][8][9][20][21][22][23]. ...
... Sur la parcelle cultivée Pc, le couvert végétal constitué principalement de résidus de récolte est la plus faible passant de 2,25 % (±0,66) en mai à 2,13 (±0,94) en juillet 2014. Ces taux de recouvrement par la litière sont du même ordre de grandeur que ceux déterminés, en juin (~2%), sur des surfaces cultivées du même terroir entre 2006 et 2008 [9]. La densité de recouvrement sur la jachère Pj est relativement plus importante variant entre 6,20 % (±4,4) en mai à 6,19 (±3,2) en juillet 2014. ...
Article
Full-text available
Au Sahel, l'érosion éolienne cause des pertes en terres et en nutriments. Au Niger méridional, cette orme érosion est une cause majeure de la dégradation de l'environnement. Le paysage de ce milieu est dominé par une juxtaposition de surfaces exploitées sous culture pluviale, et de jachères d'âges différents. L'objectif de ce travail est de quantifier les flux d'érosion éolienne et les transferts de nutriments associés en fonction du type d'occupation du sol sur une saison entière. Il apparaît que l'érosion éolienne est faible dans la jachère ancienne (Pi) du fait d'un fort couvert végétal (80%). Cette occupation du sol a respectivement émis près de 7 et 3 fois moins de flux d'érosion que le champ (Pc) et la jachère d'une année (Pj). De même, la somme des bases échangeables sur la jachère ancienne (2,669 Mèq/100g) est supérieure à celles sur le champ (2,085 Mèq/100g) et la jachère jeune (2 Mèq/100g). Ceci est lié, en particulier, au piégeage des particules et des nutriments associés transportés depuis les surfaces très sensibles à l'érosion éolienne (champ et jachère jeune) par le couvert végétal de la jachère ancienne.
... 2. 1. Mesure de la vitesse du vent et de la pluviométrie L"érosion éolienne est un phénomène à seuil contrôlé par la rugosité de surface et la vitesse du vent. Au Sahel, la dynamique de l"érosion éolienne est intimement liée à celle de la vitesse du vent [12,13]. Ainsi, la vitesse du vent a été mesurée à l"aide d"un anémomètre installé à 250 cm de hauteur sur un champ cultivé situé à Banizoumbou (13°54"N ; 2°66"E ; 50 km à l"Est de Bangou Bi). ...
... Sur les sols sableux cultivés de la région de Niamey, la vitesse seuil d"érosion éolienne des sols est de 7,2 m s -1 pour des vents mesurés à 2,5 m du sol [12]. Relativement à cette valeur seuil, les vitesses journalières maximales de vent ont présenté une dynamique saisonnière marquée (figure 2) :  pendant la saison des pluies (mai à septembre), les vitesses maximales ont été largement au-dessus de ce seuil : ces vents violents précèdent les systèmes convectifs qui produisent 100 m a b ...
... Les ordres de grandeur mesurés ici sont tout à fait comparables à ceux obtenus par [17], mais atteignent le double de ceux mesurés par [16,18]. Ces différentes périodes de dépôt de poussière sur Bangou Bi coïncident avec les périodes d"érosion observées sur les surfaces cultivées et nues de Banizoumbou [12,13]. Ces périodes sont en effet déterminées par la météorologie, particulièrement, par les vitesses de vent ( figure 2). ...
Article
Full-text available
In Niamey region, ponds and lakes formed in the past six decades are being filled with a sedimentation rate of 4 cm per year. The cultivated sandy soils covering their watershed are prone to wind and water erosions. This work aimed to estimate the proportion of aeolian deposits in the filling of one of these lakes, Bangou Bi, by the means of aeolian deposition flux measurements on the lake and wind erosion flux measurements on cultivated and bare soils. It appeared that more than 70% of aeolian deposits on Bangou Bi were provided by locale wind erosion that is controlled by the annual cycle of cultivated and bare soils erosion. Anyway, these deposits only reached a maximum thickness of 500μm per year which appears negligible in the filling of the lake.
... Ainsi, des impacts néfastes liés à l'érosion éolienne sont souvent enregistrés: le déchaussement de la végétation, et l'appauvrissement en nutriments des sols conduisant à la réduction de leur fertilité et de leur productivité. Les sols sableux sur lesquels repose la production du mil, principale culture de la région sahélienne, sont particulièrement sensibles à l'érosion éolienne [7][8][9][10][11]. Celle-ci, par processus sélectif, affecte spécifiquement l'horizon de surface et conduit à l'exportation des fines particules du sol où l'essentiel des réserves en nutriments pour les plantes est stocké [8]. ...
... Le flux horizontal (Fh) est calculé (équation 2) en intégrant la densité de flux en fonction de la hauteur (0 à 40 cm) [7][8][9][20][21][22][23]. ...
... Sur la parcelle cultivée Pc, le couvert végétal constitué principalement de résidus de récolte est la plus faible passant de 2,25 % (±0,66) en mai à 2,13 (±0,94) en juillet 2014. Ces taux de recouvrement par la litière sont du même ordre de grandeur que ceux déterminés, en juin (~2%), sur des surfaces cultivées du même terroir entre 2006 et 2008 [9]. La densité de recouvrement sur la jachère Pj est relativement plus importante variant entre 6,20 % (±4,4) en mai à 6,19 (±3,2) en juillet 2014. ...
... Ainsi, des impacts néfastes liés à l'érosion éolienne sont souvent enregistrés: le déchaussement de la végétation, et l'appauvrissement en nutriments des sols conduisant à la réduction de leur fertilité et de leur productivité. Les sols sableux sur lesquels repose la production du mil, principale culture de la région sahélienne, sont particulièrement sensibles à l'érosion éolienne [7][8][9][10][11]. Celle-ci, par processus sélectif, affecte spécifiquement l'horizon de surface et conduit à l'exportation des fines particules du sol où l'essentiel des réserves en nutriments pour les plantes est stocké [8]. ...
... Le flux horizontal (Fh) est calculé (équation 2) en intégrant la densité de flux en fonction de la hauteur (0 à 40 cm) [7][8][9][20][21][22][23]. ...
... Sur la parcelle cultivée Pc, le couvert végétal constitué principalement de résidus de récolte est la plus faible passant de 2,25 % (±0,66) en mai à 2,13 (±0,94) en juillet 2014. Ces taux de recouvrement par la litière sont du même ordre de grandeur que ceux déterminés, en juin (~2%), sur des surfaces cultivées du même terroir entre 2006 et 2008 [9]. La densité de recouvrement sur la jachère Pj est relativement plus importante variant entre 6,20 % (±4,4) en mai à 6,19 (±3,2) en juillet 2014. ...
Article
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At south Niger, wind erosion is the main factor of the environmental degradation. The landscape of this area is a juxtaposition of field and follow of different age. This work aimed to quantify wind erosion fluxes and nutrient transfer in relation of soil usage during an entire season. Thus it appeared that wind erosion had an important role in the soil fertility restauration of the old follow (Pi). This follow emitted respectively near of 7 and 3 times less of flux than field (Pc) and youth follow (Pj). Besides, the amount of exchangeable bases on the old follow (2,669 Mèq/100g) was superior to on field (2,085 Mèq/100g) and youth follow (2 Mèq/100g). This is particularly linked to the trapping of particles and exchangeable bases transported since the surfaces more sensible to wind erosion (field and youth follow) by the vegetation cover of the old follow.
... One of the most spectacular consequences of such changes is the huge increase in dust concentrations measured at Barbados in connection with the drought that the Sahel has undergone in the 1970-1980s (Prospero & Nees, 1986). Moreover, in contrast to the arid Sahara Desert, a significant part of the Sahelian region is used for agropastoral activities, which highly modify the surface cover at certain periods of the year (e.g., Abdourhamane Touré et al., 2011;Mulitza et al., 2010;Pierre et al., 2014;Sterk, 2003). Thus, it is thought that the combined effects of climatic changes and of the increasing anthropogenic pressure could lead to significant changes in the dust amount emitted into the atmosphere from the Sahelian belt during the next decades (e.g., Evan et al., 2016;Prospero & Lamb, 2003;Ridley et al., 2014).The high wind speed events able to produce wind erosion, and dust emissions in the Sahel are known to be strongly connected to two main processes: . ...
... In order to check if the choice of a TWV of 7 m s À1 at 6.5 m height is reasonable, we compare the weekly cumulative DUP computed from the 5 min wind speed data in Banizoumbou with the cumulative horizontal fluxes of windblown sediment measured at the same location from 2007 to 2010 over a bare soil by using BSNE (Big Spring Number Eight, Fryrear, 1986) catchers mounted on poles at heights of about 5, 15, and 35 cm, that is, in the saltation layer (see for details, Abdourhamane Touré et al., 2011). The BSNE were continuously sampling throughout these years and were collected after each observed event. ...
... This timing has strong implications for wind erosion since these highest wind speeds blow when the agricultural fields have been cleared by the farmers in order to be ready for the new planting season. At that time agricultural soils are bare, and thus, it is the time of the year during which they are the most erodible (Abdourhamane Touré et al., 2011;Pierre et al., 2014). In the same way, during this period, due to pasture and/or natural decomposition, rangelands exhibit a minimum residue of the vegetation of the previous year and thus are also potentially more erodible than at any other time of the year (Kergoat et al., 2017;Pierre et al., 2015). ...
Article
Full-text available
A 10-year data set of wind speed and precipitation recorded in two Sahelian stations located in Niger and Mali is used to investigate the duration and the diurnal and seasonal cycles of high wind speeds and Dust Uplift Potential (DUP). The results indicate that high wind speeds, those greater than the threshold wind velocity required to initiate wind erosion (TWV) over a bare soil occurred in the mid and late morning during the dry and wet seasons but also at nighttime during the wet season. However, the morning wind speeds are only slightly greater than TWV leading to low DUP. On the opposite, the high wind velocities associated to the nocturnal mesoscale convective systems crossing the Sahel during the wet season are responsible for the highest potential wind erosion events. This leads to a strong seasonality of DUP with more than 70% occurring in less than 90 days, from mid-April to mid-July. The duration of the high wind speed events is very short since more than 80% last for less than 3 hours, suggesting that the frequency of the observations performed in SYNOP meteorological stations is not sufficient to correctly quantify the contribution of such events to DUP. Finally, by combining precipitation and DUP we estimated that precipitation should have a relatively limited role in terms of inhibition of wind erosion in this region with precipitation only affecting 25% of total DUP.
... The sandy soil was almost bare: At the time of the experiment (mid-June), most of the plant residues from the previous year have been decomposed or grazed. Indeed, as observed by Abdourhamane Touré et al. (2011), the crop residue estimated at the end of the dry season was very low on this field, less than 100 kg/ha, covering about 1% of the surface. ...
... In the Sahel, most of the wind erosion events occur from May to mid-July when the protection of the soil surface by vegetation and crop residues is the lowest and episodes of high wind velocities the most frequent (e.g., Abdourhamane Touré et al., 2011;Bergametti et al., 2017;Bielders et al., 2004;Rajot, 2001). At that time, in West Africa, most of the humidity comes from the South Tropical Atlantic Ocean and is transported northward by the African monsoon. ...
Article
Full-text available
Bulk and size-resolved particle concentrations were measured at 2.1 and 6.5 m above the soil surface during an intense dust deposition event that occurred in June 2006 in Niger. Bulk concentration measurements were performed using two tapered element oscillating microbalance instruments, and the size-resolved particle concentrations (from 0.3 to 20 μm) using two optical particle counters. The deposition fluxes derived from the bulk concentrations and those derived from the size-resolved ones are in very good agreement. The largest deposition fluxes are recorded when the dust concentrations are maximal. The temporal evolution of the dust deposition flux follows that of the dust concentration. This is not the case of the dry deposition velocities that are most of the time controlled by the wind friction velocity. The results also show that large particles are strongly sensible to rebound when the wind friction velocity is the highest. Size-resolved dry deposition velocities are compared with the rare measurements of dust deposition velocities over bare sandy soils and are confronted to existing parameterizations of the dry deposition velocity. The parameterization of Zhang and Shao (2014, https://doi.org/10.5194/acp-14-12429-2014) appears to be the only one able to reproduce satisfyingly the measured dry deposition velocities on sandy soils in the 1- to 10-μm particle size range. Indeed, unlike others, this scheme considers the desert sandy surfaces as rough surfaces, allowing the interception of dust particles by the sand grains and/or by the small roughness elements present on the surface.
... Thus, from October to the next wet season, the remaining dry vegetation controls the percentage of cover of the surface: It continuously decreases due to agricultural practices, soil trampling, grazing, and consumption by termites and gradually uncovers the surface until the start of the next wet season (e.g., Pierre et al., 2015). As a result, dry vegetation plays a major role in protecting the surface against wind erosion during the dry season and the beginning of the following wet season: Abdourhamane Touré et al. (2011) estimated that a percentage of cover of agricultural fields by vegetation residues higher than 2% could be sufficient for significantly reduce wind erosion and dust emission. On an interannual time scale, Kergoat et al. (2017), using an indicator of the dry-season nonphotosynthetic vegetation cover in the Sahel based on Moderate Resolution Imaging Spectroradiometer (MODIS), suggested that 43% of the year-to-year variance in Sahelian-mean dry-season aerosol optical depth can be explained by the change in dry vegetation cover as a consequence of differences in precipitation patterns occurring during the previous wet season. ...
... In the cultivated field most of the surfaces remains bare due to the repeated weeding all along the first part of the rainy season maintaining the surface highly erodible (e.g., Klaij & Hoogmoed, 1996). Then, after the first phenological stage of vegetation, when the millet begin to grow it tends to increase the TWS despite the vegetation cover remain low (Abdourhamane Touré et al., 2011). This suggests that the impact of growing vegetation on dust emission could vary in time and space in the Sahel according to land uses. ...
Article
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Based on 10 years of continuous measurements of wind speed, rainfall and PM10 concentrations (i.e., concentrations of the particulate matter having a diameter lower than 10 μm) performed in two Sahelian stations, we examine how wind speed and vegetation interact during the wet season to control the dust concentration when it is due to local dust emissions. The results clearly show that the frequency of the high wind speeds is higher at the beginning of the wet season and is the main driver of the seasonal dust emission. During the second part of the wet season, the frequency of high wind speeds is much lower and, in addition, their efficiency for wind erosion and dust emission is strongly affected by the vegetation whose growth reduces progressively PM10 concentrations up to 80%.
... Surface coverage at the field observation sites on this sediment trap; five aeolian-flux trap samplers were installed in the study region ( Fig. 1). The horizontal aeolian-flux trap has been widely used to measure dust transport under field conditions (Gillette et al. 1972;Gillette 1974;Gillette and Blifford 1974;Abdourhamane Touré et al. 2011;Bhattachan et al. 2013;Yang et al. 2013). Previous investigations have used different trap heights (Abdourhamane Touré et al. 2011;Yang et al. 2013;Bhattachan et al. 2013), and for our purposes, we installed the flux traps at heights of 0.25, 0.5, 1.0 and 1.5 m. ...
... The horizontal aeolian-flux trap has been widely used to measure dust transport under field conditions (Gillette et al. 1972;Gillette 1974;Gillette and Blifford 1974;Abdourhamane Touré et al. 2011;Bhattachan et al. 2013;Yang et al. 2013). Previous investigations have used different trap heights (Abdourhamane Touré et al. 2011;Yang et al. 2013;Bhattachan et al. 2013), and for our purposes, we installed the flux traps at heights of 0.25, 0.5, 1.0 and 1.5 m. The main reason for selecting these heights was due to the large quantity of transported dust (to avoid the lowest trap being filled very quickly) for the long-time field transport under field conditions. ...
Article
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Year-long field observations have shown that there are spatial and temporal variations in the quantity of dust emissions for particulate matter $${<}$$10 $$\upmu \hbox {m}$$ (PM10), particulate matter $${<}$$63 $$\upmu \hbox {m}$$ (PM63) and vertical dust flux over different gravel surfaces (with loose sand, without loose sand, with a crust, and without a crust), with the greatest emissions occurring in the spring. The largest quantity of PM10 and PM63 emissions occurred over gravel with a loose sand surface ($$1.1 \times 10^{-3}$$ and $$10.2 \times 10^{-3 }\hbox { kg m}^{-1}\hbox { day}^{-1}$$, respectively). The gravel surface without loose sand and without a crust presents the lowest values of PM63 ($$1.6 \times 10^{-3 }\hbox { kg m}^{-1}\hbox { day}^{-1}$$) and PM10 ($$3.3 \times 10^{-4}\hbox { kg m}^{-1}\hbox { day}^{-1}$$). However, the vertical dust flux was largest at over sandy surface ($$373 \times 10^{-3 }\hbox { kg m}^{-2}\hbox { day}^{-1}$$). Multivariate correlation analysis indicates that the quantity of PM10 is strongly negatively correlated to gravel coverage ($$R^{2 }= 0.55$$). The quantity of PM10 dust emissions over a gravel surface with loose sand is approximately three times greater than that of a gravel surface with a crust. The mean quantity of PM10, PM63 and vertical dust flux over a gravel surface decreased with increasing gravel coverage. By comparing the quantity of PM10 dust emissions over gravel and sandy deserts, we found that gravel deserts and sandy deserts are both major sources of dust for dust storms in this region.
... Ainsi, la région de Tillabéry, à laquelle appartient administrativement le site d'étude, a connu un quadruplement de sa population en 35 ans entre 1977 et 2012 [7]. Une telle croissance démographique implique l'exploitation quasi-régulière des ressources foncières et forestières [8] avec, dans certains cas, des pratiques peu conservatrices [9,10]. D'où le déclenchement des processus d'érosion hydrique et éolienne qui se manifestent par l'encroûtement [11 -13] et ou par le ravinement [14 -16]. ...
... A B Figure 10 : Impact de ré-encroûtement de la parcelle sous solée sur la production de ruissellement L'encroûtement de la parcelle sous-solée traduit aussi la nécessité d'un élément structurant empêchant la compaction du sol. Il est ainsi montré qu'une proportion des résidus de culture de l'ordre de 2 % est suffisante pour limiter la déflation et la compaction des sols [9] dans le secteur de cette étude. Donc la réalisation d'un sous-solage couplé à l'épandage de résidus permettrait de maintenir durablement les fonctions du sol. ...
... By contrast, at a smaller spatial scale, field studies in the Sahel have repeatedly underlined the importance of land surface conditions, especially vegetation cover and soil moisture, in controlling wind erosion [Nickling and Gillies, 1993, Sterk, 2003, Maurer et al., 2009, Bielders et al., 2002, Ikazaki et al., 2011. Toure et al. [2011] suggested that a value as low as 10 g/m 2 of crop residues (~2% cover) may significantly inhibit wind erosion in southwestern Niger. The comparison of wind erosion over fallow fields and millet fields, with or without millet residues left over in the dry season, also points toward the importance of Sahelian vegetation to limit dust emission, especially in the late dry season (April-June). ...
... The strong persistence of STI anomalies until the next rainy season (Figures 2 and S1) implies that the drivers of vegetation decay in the dry season, namely, grazing, bush fires, residues management, decomposition, and oxidation are not fluctuating enough to generate noticeable interannual variability at the Sahel scale over 2002-2014. This persistence also supports the use of previous summer's NDVI as an indicator of dry-season vegetation variability for two reasons: First, the correlation of NDVI and dry-season STI with AOD are fairly close, and second, from a physical process point of view, the dry-season cover fraction identified here is close to plausible thresholds of inhibition of dust emission [Toure et al., 2011]. The shape of the persistence time series also calls for using a calendar starting in July and ending in June, rather than January to December, when studying at vegetation impact on dust emissions with annual data. ...
... Vegetation, whether native or exotic, has been widely reported to be effective in reducing dust storms (e.g. Goudie and Middleton 2006;Micklin 2007;Mendez and Maier 2008;Toure et al. 2011;Li and Sherman 2015;Ahmed, Al-Dousari, and Al-Dousari 2016;Dong 2017, 2019;Torshizi et al. 2020b;Al-Dousari et al. 2020). Native plants and green belts have also contributed to the reduction in the annual rates of mobile sand by 94% and 95.3%, and dust by 64.5% and 68.4%, respectively (Al-Dousari et al. 2019). ...
... Native plants and green belts have also contributed to the reduction in the annual rates of mobile sand by 94% and 95.3%, and dust by 64.5% and 68.4%, respectively (Al-Dousari et al. 2019). Even when vegetation cover is as low as 2%, the potential for wind erosion and SDS is reduced (Toure et al. 2011). In addition to the presence of vegetation, Li and Sherman (2015) showed that the efficiency of dust stabilization is related to the height of vegetation. ...
Article
Sand and dust storms (SDS) are a natural phenomenon dominantly originating in arid and semi-arid regions. The vastness and changing distribution of the SDS hotspots, their inaccessibility, and financial limitations are the greatest challenges to projects combating SDS. To boost project success, a prioritized site-selection method which incorporates the physical and human variables interacting with SDS is applied in this paper. This ensures that potential economic and health impacts of SDS on human populations are also included. Six variables were selected for analysis: within-region sand and dust hotspots, changing distribution of the hotspots, residential areas, vegetation cover, soil texture, and the maximum drought-inundation of the Hamoun wetland. SDS hotspot sites for possible stabilization were identified and prioritized using the multi criteria evaluation (MCE) method. Such prioritization assists the practical management of hotspots under conditions of resource and budgetary constraints which are especially common in developing countries. This paper thus provides a template for site selection and prioritization of SDS hotspots for remediation. It also highlights the importance of variables other than SDS source areas for selection of rehabilitation sites. The proposed method, using the Sistan region as an example, is applicable to other regions of the world as a means of reducing the negative effects of known dust storm hotspots.
... However, under the climate condition of low temperature in northeast China, the corn cobs decompose slowly after returning to the field, which causes short-term soil acidification [7], affects crop root development, aggravates pests and diseases, and reduces the quality of spring sowing [8,9]. Therefore, in order to improve soil physical and chemical properties [10], combat soil erosion [11], promote crop growth, and increase crop yield [12,13], it is of great significance to explore the field decomposition characteristics of corn cobs under the conditions of corn kernel harvesting technology in northeast China. ...
... Agriculture 2021, 11, 556 ...
Article
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Returning corn cobs to the field during corn kernel harvesting is an effective way to improve soil properties and increase crop yield. However, seasonally frozen soil seriously hinders the field decomposition process of corn cobs. To explore the decomposition characteristics and promote field decomposition, in this study, the nylon mesh bag method was used to perform field decomposition tests for 150 days. Fiber composition analysis and microstructure observation were carried out. The results showed that the field decomposition of corn cob was influenced by temperature, precipitation, and frozen soil environment. The 150-day cumulative decomposition rates of the pith, woody ring, and glume were 40.0%, 24.2%, and 36.3%, respectively. Caused by the difference in fiber compositions, the decomposition speeds of pith and glume were much higher than that of the woody ring. The complex microstructures of the pith, woody ring, and glume led to differences in the accessibility of cellulose, which indirectly influenced the field decomposition characteristics. The homogeneous sponge-like structure of the pith and glume increased the accessibility of cellulose and ultimately accelerated the field decomposition, while the compact lignocellulosic structure of the woody ring hindered the decomposition process. Compared with corn stalk, corn cob had similar or even better field decomposition characteristics and excellent application prospects.
... Cependant, au cours de la saison sèche, le flux mesuré au sommet des dunes a été inférieur à celui mesuré sur le flanc d'en moyenne 3,7 (± 4,8) fois. Cette phase d'érosion au coeur de la saison sèche a été également observée sur les sols nus de l'Ouest du Niger [13]. Ces mesures montrent ainsi la complexité de l'appréhension de la dynamique des dunes vives. ...
... Sahel. Il apparait, ainsi, que les vitesses de vent max ont régulièrement été au-dessus de la vitesse seuil d'érosion déterminée sur les surfaces sableuses nues (5,8 m / s) du Sud -Ouest du Niger[13]. ...
Article
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Dans le Manga (Sud-est du Niger), l'un des effets de la pression anthropique et de la variation climatique se traduit la disparition de la végétation qui a pour principale conséquence la mobilisation du sable dunaire. L'objectif de ce travail est de caractériser l'érosion éolienne au niveau des dunes vives. Spécifiquement, il s'agit de i) mesurer le flux d'érosion éolienne sur les dunes vives et ii) déterminer les vitesses et les périodes optimales de déplacement de ces dunes. La méthodologie utilisée a consisté baliser dans le sens de l'avancée des fronts dunaires avec les piquets en fer 22 dunes répartie au sud du 14 e parallèle, à installer une station météorologique automatique et des capteurs de sédiments de type BNSE sur le flanc et au sommet de la dune vive. Les résultats obtenus montrent que l'érosion éolienne est fonction de la vitesse du vent dont les phases de vents extrêmes s'observent avec le passage des tempêtes convectives des débuts de la saison des pluies. Le reste du temps, les vents restent inférieurs à 10 m / s mais régulier. Les fronts dunaires dépourvus de système de fixation sont les plus mobiles. La vitesse moyenne de l'avancée de leurs fronts a été de 5,60 ± 2,02 m / an. La mesure des flux éoliens montre que l'érosion se produit sur les dunes vives toute l'année du fait de l'existence des vents très souvent largement au-dessus de la vitesse seuil d'érosion. Elle connait, cependant, une baisse d'intensité entre août et octobre. Le flux d'érosion mesuré au sommet de la dune vive a atteint en moyenne 1,61 fois (± 0,6) celui mesuré sur le flanc durant la saison des pluies. Cependant, au
... Presently, several practices and techniques are available for potentially reducing wind erosion hazard (Tibke 1988, Fryrear & Skidmore 1985, Toure et al. 2011). One of the most effective tools is controlling erosion length by planning the orientation, size and shape of the arable plot. ...
Article
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Wind erosion is a problem not only in the arid and semi-Arid parts of the Earth but also in the temperate climates. Long-Term wind erosion of plots decreases the nutritional content and deteriorates the upper soil's physical properties. Shelterbelt planting and plot size planning are effective tools for wind erosion control. Our new method combines two already existing model functions to determine the effect of erosion length and windbreak systems on wind erosion hazard potential: The WEPS windbreak subroutine and the TEAM length factor function. By combining the windbreak subroutine and length factor, a new GIS tool was developed which easily modelled the windbreak system airflow control and erosion length effect of the potential wind erosion hazard. A strong (15 m/s at 10 m height) wind event was modelled, and it was found that the windbreak system could decrease the deflation potential. Significant result was the extent to which erosion length and windbreak systems influenced the potential wind erosion hazard. In the study area, the simulations showed that the windbreak system had a greater influence on potential wind erosion control than plot size. This paper's main contribution is to demonstrate how windbreak system planting and plot size and shape planning can influence wind direction distribution and draw attention to the role of preventive agriculture management in controlling wind erosion hazard areas. © 2017 Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, Germany.
... The relationship between soil loss and vegetation cover (live or dead) is generally exponential: the soil loss ratio is at a maximum of 1 on a bare unprotected surface but decreases rapidly to a value of approximately 0.2 with 40% soil cover [72]. However, work in Sahelian Africa has shown that maintaining a crop residue cover of just 2% on a field reduces the potential wind erosion by at least a factor of three [73]. ...
Article
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Sand and dust storms (SDS) play an integral role in the Earth system but they also present a range of hazards to the environmental and economic sustainability of human society. These hazards are of considerable importance for residents of dryland environments and also affect people beyond drylands because wind erosion can occur in most environments and desert dust events often involve long-range transport over great distances (> 1000 km). This paper makes an assessment of the scale of SDS impacts by totalling the countries affected using an appraisal of peer-reviewed published sources, arriving at a conservative estimate that 77% of all parties to the United Nations Convention to Combat Desertification (UNCCD) are affected directly by SDS issues. We then present a synthesis of the environmental management techniques designed to mitigate SDS hazards for disaster risk reduction and review policy measures, both historical and contemporary, for SDS impact mitigation. Although many SDS hazards are well-known, the processes involved and their impacts are not all equally well-understood. Policies designed to mitigate the impacts of wind erosion in agricultural areas have been developed in certain parts of the world but policies designed to mitigate the wider impacts of SDS, including many that are transboundary, are geographically patchy and have a much shorter history. Further development and wider implementation of such policies is advocated because of the recent marked increase in wind erosion and associated dust storms in several parts of the world.
... Tillage ridges trap aggregates transported by saltation effectively, but do not usually reduce erosion rates in soils where aggregates transported in suspension dominate [16]. Vegetation lessens soil loss from wind by slowing down the wind speed and thereby reducing soil erodibility, and also traps more eroded material [3,20,24,31]. In their wind tunnel experiments, [32] arrived at the conclusion that in addition to density, plant height and flexibility favor effectiveness in reducing material transport by wind. ...
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The purpose of this study was to analyze the influence of wind erosion on the productivity of citric crops over gypsiric Fluvisols in Gador area (Almeria, SE Spain) by blowing air through a wind tunnel. Wind erosion varies considerably depending on time since the last tillage. This is because a physical crust forms after tilling which protects the soil from wind. Crust formation in the study area is strongly favored by dew, which causes them to form in around a week. The repeated measurements ANOVA, as a nonparametric alternative to the ANOVA, using the Geiiser method and the Friedman test shows significant differences (P ≤ 0.05) in the fractions of very fine sand and coarse silt, which confirmed that very fine sand and coarse silt are the fractions most susceptible to loss from wind. The same statistical analysis for fertility showed smaller differences in organic carbon and K2O content, while N and P2O5 increased. Nutrients lost from wind imply an additional fertilization cost for a crop to be economically feasible. The cost of this restoration of nutrients lost from the soil because of wind erosion was based on experimental data taken in crusted soil and immediately after tilling. Losses in organic matter (O.M.), N, P2O5 and K2O were estimated based on the cost of fertilizers most commonly used in the area.
... With advances in research and application, agricultural by-products have been identified as a significant potential for bioenergy production. In addition, incorporation of straw into the soil plays a positive role in protecting the soil's ecological environment and combating soil erosion [5,6]. Some studies also found that continuing straw return will improve crop yield in the long term [7]. ...
Article
Straw return has positive effect on improving soil ecological environment, and now there are serious ecological problems of arable land in China. Therefore, the concept of basic straw returning amount (BSRA) was put forward based on soil protection functions, and literature review and scenario analysis method were adapted to design BSRA. Based on this, a bottom up dynamic accounting model was built, which considering the changes of sown area, unit crop yield, planting structure and crop straw utilization. Then, the model was applied to assess the potentials of straw resources for bioenergy production. Usable straw resources in low, middle and high BSRA scenario are 265.70, 180.25 and 117.51 Tg respectively in 2030, mainly composed of paddy rice (Oryza sativa L.) stalk, maize (Zea mays L.) stalk and potato (Solanum tuberosum L.) stalk in low and middle scenario, and maize stalk, potato stalk and sugarcane (Saccharum officinarum) stalk in high scenario. Available crop residues mainly distribute in Sichuan, Henan, Heilongjiang and Shandong Province under the three scenarios. There will be interzone spatial transfer of usable straw resources, over time, mainly transferring to Northeast China, North China and Northwest China. The usable straw amount will have shape decrease in August and September as the increase of BSRA.
... The strong persistence of STI anomalies until the next rainy season (Figures 2 and S1) implies that the drivers of vegetation decay in the dry season, namely, grazing, bush fires, residues management, decomposition, and oxidation are not fluctuating enough to generate noticeable interannual variability at the Sahel scale over [2002][2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013][2014]. This persistence also supports the use of previous summer's NDVI as an indicator of dry-season vegetation variability for two reasons: First, the correlation of NDVI and dry-season STI with AOD are fairly close, and second, from a physical process point of view, the dry-season cover fraction identi- fied here is close to plausible thresholds of inhibition of dust emission [Toure et al., 2011]. The shape of the persistence time series also calls for using a calendar starting in July and ending in June, rather than January to December, when studying at vegetation impact on dust emissions with annual data. ...
Article
The drivers of dust emission inter-annual variability in North Africa, the largest dust source on earth, are still debated. Early studies outlined the role of previous-season rainfall and vegetation growth, while some recent studies emphasize the role of wind variability. Here, we use a newly-developed estimation of dry-season nonphotosynthetic vegetation cover in the Sahel based on MODIS short-wave infrared bands over the 2002-2015 period. The vegetation growth anomalies caused by variability of rainfall in June-September translate to anomalies of dry vegetation cover that persist throughout the dry season until May. These vegetation anomalies explain 43% (50%) of the year-to-year variance in Sahelian-mean dry-season Aerosol Optical Depth (AOD) as derived from MODIS Deep Blue (sun-photometers). Similar explained variance is found with 10 m wind speed and Dust Uplift Potential. The central Sahel proves more important than the western Sahel for dry-season AOD variability.
... Threshold velocity was determined with statistic method which has been successfully applied and verified by Park and In (2003), Kurosaki and Mikami (2007) and Toure et al. (2011). The equation is as follows: ...
Article
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A field experiment was conducted from 2 May 2010 to 1 May 2012 in the Gurbantunggut Desert, the second largest desert in China, to investigate saltation activity and its threshold velocity, and their relations with atmospheric and soil conditions. The results showed that saltation activity occurred more frequently during 08:00–20:00 Local Standard Time in spring and summer, with air temperatures between 20.0 and 29.0 �C, water vapor pressures between 0.6 and 0.9 kPa, soil temperatures between 25.0 and 30.0 �C, and a soil moisture lower than 0.04 m3/m3. At 2 m height, the saltation threshold velocity varied between 11.1 and 13.9 m/s, with a mean of 12.5 m/s. Threshold velocity showed clear seasonal variations in the following sequence: spring (11.7 m/s) \autumn (12.7 m/s)\summer (13.6 m/s). Affected by soil conditions, aeolian sand transport was weak, with an average annual aeolian sand that transported across a section (1.0 m 9 2.0 m) of less than 6.0 kg.
... The results play an important role in increasing the ability to control soil wind erosion and in realizing sustainable development of agriculture and grassland farming. Due to the increase in aerodynamic roughness that controls the threshold speed of aeolian erosion, even very low crop residue density of standing stalks (approximately 400 plants m −2 ), essentially in the form of millet stalks, can be a simple and sufficient method to reduce wind erosion (Amadou, Jean, Zibo, et al., 2011). ...
Article
Crop residues, particularly standing stubble, can reduce soil erosion by wind in conservation tillage. To determine the optimum architecture of standing stubble for effective reduction of wind speeds near the soil surface, we quantitatively analyzed the interception effect of standing stubbles on soil erosion particles through pure wind experiments and sand‐bearing wind experiments. The relationship between stubble height, row number and interception rate was also revealed. The study was conducted in a wheat field under conservation tillage. Three representative heights of standing stubble were tested: 10, 20 and 30 cm. All had an average plant density of 400 plants m‐2, row spacing of 20 cm, and an average stubble cover of 52 %. A wind tunnel was placed over the stubble, and the central wind speeds were selected at 6, 9, 12, 15, and 18 m s‐1. During the experiments, the blowing time was set for 10min, and 1,404 g of local soil from the experimental area was fed into the wind tunnel. A sand collector was placed at the 16th, 19th, 23rd, 27th, and 31st stubble row away from the air inlet of the wind tunnel to measure the amount of soil eroded by wind at different stubble heights under conditions of blank and sand‐bearing winds. The concept of “interception rate” and its corresponding formula were proposed. The interception rates of 10‐cm and 20‐cm high stubbles were lower than those of 30‐cm stubble and decreased sharply, particularly at wind speeds > 12 m s‐1. Even at the wind speed of 18 m s‐1, the interception of wind erosion particles with 30‐cm high stubble at 16th, 19th, 23rd, 27th, and 31st rows were 20.85%, 41.55%, 60.46%, 80.59% and 85.96%, but only 5.75%, 24.76%, 39.32%, 62.39% and 76.04% with 10‐cm high stubble at the same positions. The interception effect was similar at the 27th and 31st rows. However, more than 31 rows would be required of the 10‐cm stubble and 20‐cm stubble to intercept the same amount of wind erosion particles as with 27 rows of the 30‐cm stubble. The soil particle interception rate increased with an increase in the number of rows of standing stubble and decreased with an increase in wind speed. As expected, with additional rows of stubble, the amount of soil intercepted increased. Therefore, for a farmland that uses 400 plants m‐2, leaves 30‐cm high stubble with 52 % cover, and has row spacing ≤ 20 cm, the effective amount of standing stubble should be more than 27 rows.
... Threshold velocity was determined with statistic method which has been successfully applied and verified by Park and In (2003), Kurosaki and Mikami (2007) and Toure et al. (2011). The equation is as follows: ...
Article
Full-text available
A field experiment was conducted from 2 May 2010 to 1 May 2012 in the Gurbantunggut Desert, the second largest desert in China, to investigate saltation activity and its threshold velocity, and their relations with atmospheric and soil conditions. The results showed that saltation activity occurred more frequently during 08:00–20:00 Local Standard Time in spring and summer, with air temperatures between 20.0 and 29.0 °C, water vapor pressures between 0.6 and 0.9 kPa, soil temperatures between 25.0 and 30.0 °C, and a soil moisture lower than 0.04 m3/m3. At 2 m height, the saltation threshold velocity varied between 11.1 and 13.9 m/s, with a mean of 12.5 m/s. Threshold velocity showed clear seasonal variations in the following sequence: spring (11.7 m/s) < autumn (12.7 m/s) < summer (13.6 m/s). Affected by soil conditions, aeolian sand transport was weak, with an average annual aeolian sand that transported across a section (1.0 m × 2.0 m) of less than 6.0 kg.
... Zhang [38] indicated that this ability is related to air pressure and influenced by the interaction between near-surface wind flow and roughness elements. Toure [39] pointed out that the potential for wind erosion decreases for aerodynamically-rougher surfaces. The results of the present study indicate that z 0 is correlated with the surface roughness properties of the underlying vegetation conditions (e.g., vegetation height), and decrease with increases in wind speed. ...
... Crop residue on the agricultural land generally protects the soil from wind erosion (Hagen, 1996;Sterk and Spaan, 1997;Toure et al., 2011;Gao et al., 2014;Jia et al., 2015). According to its character, crop residue can be divided into two types: standing residue and flat residue. ...
Article
Atmospheric particulate matter and dust from agricultural land significantly affect air quality and human health in nearby residential areas. To quantify these air pollutants, it is important to estimate the vertical atmospheric particulate matter PM2.5, PM10, and dust flux using observations and validated models. To the authors´ knowledge, this has previously not been performed for semi-humid agricultural areas in China. For this purpose, we used wind tunnel tests together with field observations and the validated WEAM simulation model to assess vertical PM2.5, PM10, and dust flux from an experimental agricultural area. Four maize residue management procedures were included in the experiments, namely, conventional tillage (CT), remaining flat residue (FR), remaining standing stubble (MS), and a combination of flat residue and standing stubble (SR). Results showed that: (1) the modified WEAM model adequately simulated the vertical PM10 and dust flux from agricultural land with the four residue managements and the vertical PM2.5 flux from soils of CT and MS; (2) the vertical PM2.5, PM10, and dust flux decrease with increase of density and height of standing maize residue >10 cm, and increase with increase height of standing maize residue <10 cm; (3) the vertical PM2.5, PM10, and dust flux decrease with increase of flat residue coverage, and the threshold coverage of flat maize residue varies linearly with the wind speed; and (4) a combination of standing and flat maize residue is needed to prevent vertical PM2.5, PM10, and dust flux at wind speed 12−24 ms⁻¹. It can be concluded that flat or standing maize residue may reduce dust emission to the National Environment Air Quality Standard when the wind speed is <16 ms⁻¹. A combination of flat and standing maize residue (>30 cm, denser than 5 cm, and coverage >45 %) is needed for higher wind speed. The study provides an approach to control PM2.5, PM10, and dust emission from agricultural areas and ways to better manage of crop residue.
... Our results reaffirmed previous findings representing the potential of vegetation to reduce the rate of soil loss (Youssef et al., 2012), as indicated by the decreased soil loss of zigzag and random vegetation patterns. The results obtained from our experiment with the wind tunnel are consistent with the findings of Van De Ven, Fryrear, andSpaan (1989, Sterk, Jacobs, andVan Boxel (1998), Cornelis and Gabriels (2005), Udo and Takewaka (2007), Abdourhamane Toure et al. (2011), Leenders, Sterk, Van Boxel (2011), Munson, Belnap, and Okin (2011 and Youssef et al. (2012) who reported the capacity of vegetation to decrease the rate of soil loss by wind, through reducing the wind speed and wind erosivity and increased entrapment of eroded material. The greater coverage at upwind positions of the zigzag vegetation pattern was crucial in intercepting wind and delaying soil loss as compared to random and raw vegetation pattern. ...
Article
Full-text available
Dust emission from wind erosion is a widespread phenomenon in arid and semi‐arid areas having considerable implications for ecosystems and human well‐being. However, few studies have examined the efficiency of biochar amended to soil on wind erosion control. Aimed at studying the effect of biochar on resistance of soils against wind erosion, a wind tunnel experiment was conducted. We tested (i) soils amended with hard waste walnut wood biochar and soft maize cob biochar, (ii) soils amended with powdery waste wood and powdery maize cob, and compared them with (iii) non‐treated soil, in their susceptibility to wind erosion and also the additional effect of various patterns of vegetation cover. Amending soil with biochar and powdery material did significantly increase their resilience to wind erosion because of increased soil aggregation. In comparison with the non‐treated control, the mass flux of un‐vegetated soil reduced from 4.42 to 1.86 g/m2/s for the waste walnut wood biochar, from 4.28 to 1.50 g/m2/s for maize cob biochar, from 4.11 to 1.44 g/m2/s for powdery maize cob and from 3.97 to 1.14 g/m2/s for powdery waste walnut wood. When combining amendments with vegetation, there was still a substantial improvement, though the soil treatments responded differently in terms of soil loss to different vegetation patterns. A single row vegetation pattern had the highest mass flux, while a zigzag vegetation pattern had the lowest. In conclusion, waste wood or maize cobs, whether applied as biochar or as powdery material are able to fix soil and reduce wind erosion.
... One of the primary goals of this study is to generate region-specific information that will help the growers in the desert southwest to select appropriate cover crops to protect the soil surface from wind erosion under deficit and full irrigation conditions. Most of the previous studies have evaluated the effects of crop residues on wind erosion control in agricultural lands (Unger et al., 1991;Michels et al., 1995aMichels et al., , 1995bToure et al., 2011). Soils are highly vulnerable to wind erosion in arid and semiarid regions because of limited or no residue cover during the wind erosion events. ...
Article
Highlights Four summer cover crops under two irrigation regimes were tested for soil wind erosion control. Soil aggregate stability and wind erosion losses were improved with plant cover in the peak summer. Sorghum sudan is a prominent summer species for wind erosion control in the arid southwest. Abstract . Cover crops can have significant impacts on minimizing soil erosion by wind, which is a common problem in the arid southwest. A study was conducted at NMSU Leyendecker Plant Science Center, Las Cruces, New Mexico, to evaluate the impacts of selected summer cover crops on soil loss during wind erosion events. Four summer grass species [Japanese millet (Echinochloa esculenta), pearl millet (Pennisetum glaucum), brown top millet (Urochloa ramosa (L.) Nguyen), and sorghum sudangrass (Sorghum bicolor × S. bicolor var. Sudanese)] were randomly assigned to four blocks under two irrigation regimes (full-irrigation and deficit-irrigation). Results showed significant effect of grasses on horizontal soil flux compared to control under both irrigation regimes. When comparing the grasses, sorghum sudan grass performed better than the other tested summer cover crops for soil surface protection from wind erosion with its higher ground coverage, higher plant density, taller plant height and higher amount of biomass, while brown top millet was least effective in terms of plant and erosion control characteristics (P=0.05). Pearl millet and Japanese millet performed better than brown top millet, but was as effective as sorghum sudan as barriers against the wind erosion. Therefore, sorghum sudan is a prominent cover crop for summer in the arid zones of desert southwest. Producers of this region can be significantly benefited from the current research recommendations about cover crops choices for summer season. Keywords: Arid climates, Cover cropping, Summer grasses, Wind erosion control.
... Wind erosion influences soil drying and nutrient loss (Molchanov et al, 2015), both of which are conditioned by soil surface compaction. Vegetation protects the soil from wind erosion by reducing wind speed, it also reduces soil erodibility, and traps eroded material (Touré et al., 2011;Leenders et al., 2011;Asensio et al., 2015b). Plant cover acts like a windbreak, forcing air to flow through it more slowly and faster over the top (Molina-Aiz et al., 2006). ...
... Standing residue can result in sediment accumulation, as observed by Jia et al. (2015) in corn fields of northern China. The required amount of crop residues to mitigate wind erosion can be relatively low, even for litter (Abdourhamane Touré et al., 2011). However, critical standing and prostrate residue cover levels required to control wind erosion have only been established for a few crop types, sowing densities and wind conditions. ...
Chapter
Human land uses and land management systems have created anthropogenic environments that influence rates of wind erosion and dust emission. This article begins by reviewing the sensitivity of aeolian processes to anthropogenic land use and management. It reviews the latest research addressing anthropogenic wind erosion, including impacts on agroecosystems, human health and built infrastructure. Conceptual frameworks underpinning assessments are critically evaluated relative to the state-of-the-science and support for wind erosion management. The article then explores how future research can connect anthropogenic wind erosion mitigation to broader land management and air quality objectives.
... Vegetation provides an effective agent in reducing dust storms (Toure et al., 2011;Miri et al., 2017Miri et al., , 2018Miri et al., , 2019Miri et al., , 2021Torshizi et al., 2020aTorshizi et al., , 2020b. Tan (2016) found a clear relationship between the Normalised Difference Vegetation Index (NDVI) and dust storms in China. ...
Article
Dust storms cause a wide range of impacts on environment, economy and human health in the Sistan region of southeastern Iran. This paper investigates long-term variability of dust activity over 23 years (1997-2019) using the Dust Storm Index (DSI) and the frequency of dust-storm days (DSD, visibility <1000 m) and assesses the associated importance of various terrestrial and climatic drivers. A dust storm corridor was identified, based on the prevailing wind direction at Zabol, including parts of the Hamoun lakes and surrounding desert in order to study the effects of vegetation cover and lake water levels on dust activity. The results show maximum intensity of dust storms occurred at 10:30 a.m. and in the summer, consistent with the highest wind speeds – associated with the regionally important Levar wind – and highest air temperatures and lowest precipitation and relative humidity. Strong positive correlations were demonstrated between DSI and wind speed, particularly in summer. The 2000-2004 period saw severe dust-raising activity with a DSI of 530.6. Mean wind speeds were greater and precipitation, humidity, vegetation and water coverage were lower during this severe dust-activity period than in other periods. Comparing 2000-2004 with 1997-1999, DSI was five times higher and DSD eight times higher. The dust storms with the longest duration occurred in July 2001 and June 2008 (114 h and 78 h respectively). The July 2001 event, in which wind speed peaked at 25 m/s and visibility dropped to 100 m on several occasions, may be the longest continuous dust storm on record. The key role of water and vegetation cover in the Hamouns was highlighted, indicating the importance of protecting the Hamoun ecosystems and sustainably managing their water resources in efforts to mitigate dust storm hazards in the Sistan region
... As well, crop residues may form small dams which retard runoff and create localized puddles which absorb raindrop energy, reducing both the detachment and the transport of soil particles (Nalatwadmath et al. 2006). The frontline defence measures to reduce and stop soil erosion from cultivated fields are the reduction or elimination of tillage combined with the retention of residues and/or the application of mulches (Toure et al. 2011;Alliaume et al. 2014). Bhatt and Arora (2019) reported that treatments under ZT or NT combined with a weed mulch had only 3 Mg ha À1 of soil loss, whereas treatments under CT with the weed mulch or under ZT without mulch had 7 and 12 Mg ha À1 soil loss, respectively. ...
Chapter
... This clearly suggests that most of the high wind speed associated with such rainy events are the most efficient dust producers since they generally occur before the rain inhibits the erodibility of the surface. Moreover, the prevalence of the highest wind speed in May/June has large consequences in terms of dust emission since this period of the year is that during which the soil surface is the less protected by the vegetative residues from the previous year (e.g., Abdourhamane Touré et al., 2011;Bergametti et al., 2020;Pierre et al., 2015). Thus, it can be concluded that meteorological conditions and surface characteristics converge to favor the genesis of intense wind erosion and dust emission events during the premonsoon period and the beginning of the monsoon. ...
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The Sahel is a dust source region where dust emission could be drastically modified in the future due to climatic and land use changes. Based on observations of meteorological parameters and dust concentration for about 1,000 rain events, we investigated the processes leading to dust emission during the rainy season when Mesoscale Convective Systems (MCSs) regularly cross the Sahel. We show that the highest wind speed is strongly linked to the MCS cold pool intensity, which is characterized by a drop in surface temperature. This is observed during the premonsoon period (∼May to June) when the midtroposphere is still sufficiently dry to allow intense evaporation of raindrops. Because this coincides with the time of the year that the surface is the least protected by the vegetative residue, the premonsoon wind speed leads to the highest observed dust concentration in our record. Most of the highest wind speed occur before or just at the beginning of a rainy event allowing a large part of the dust raised to be transported ahead the rain limiting dust removal by wet scavenging. Finally, we show that the number of 5‐min dust concentration higher than 5,000 μg m⁻³ is almost only occurring during the rainy season. These results suggest that until the dust models fail to correctly resolve MCS, it will be difficulty to obtain reliable estimates of dust emission from the Sahel for the present or future scenarios.
... Standing residue can result in sediment accumulation, as observed by Jia et al. (2015) in corn fields of northern China. The required amount of crop residues to mitigate wind erosion can be relatively low, even for litter (Abdourhamane Touré et al., 2011). However, critical standing and prostrate residue cover levels required to control wind erosion have only been established for a few crop types, sowing densities and wind conditions. ...
... In the absence of tillage, there is more natural vegetation and soil aggregation, which reduce soil loss from wind by slowing down wind speed, further increasing the capacity for capturing lost material [6,7]. Climate and the spatial and temporal variability in threshold wind velocity strongly influence the prediction of the amount and type of wind-blown particles [8,9]. ...
Article
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We tested an efficient, easily and economically manufactured wind-transported particle collector of our own design, called a multidirectional trap (MDt), on fine-tilled Anthrosols. Results from the logs of nine vaned masts, each with four MDt collectors at different heights, showed a clear predominance of northeast and south winds. After analyzing sediment transport rates and their balance, we found that sediments from the south were being deposited rather than lost. A large amount of phyllosilicates, which are highly adhesive sediments, and therefore, increase aggregation, decreasing erodibility, were captured in the upper traps. Moreover, they are rich in calcium carbonate, mainly calcite, which is a powerful aggregate, and therefore, also decreases their wind erodibility. Sediments from the northeast, however, with almost double the total mass transport, contained the largest amount of captured quartz, promoting abrasion and increasing soil erodibility. Nevertheless, large amounts of organic matter found in sediments from the NE led to some aggregation, which balances material lost.
... This research is supported by the extensive literature on momentum partitioning over different roughness arrays (e.g., Raupach et al., 1993;Crawley and Nickling, 2003;Pierre et al., 2014;Webb et al., 2014). Recent studies have sought to establish more integrative effects of residue management on wind erosion for different crop production systems from field measurements and mechanistic models (e.g., Touré et al., 2011;Funk and Engel, 2015;Pierre et al., 2018;Rakkar et al., 2019). Results from these studies can inform wind erosion management and provide references to managers to identify critical crop residue amounts for controlling wind erosion (Rakkar et al., 2019). ...
Article
Crop residue is an important factor influencing wind erosion of cultivated soils. Establishing soil surface protection afforded by standing crop residue is critical for land managers seeking to reduce or prevent soil loss by wind erosion and the impacts of blowing dust from agricultural lands. The objectives of this study were to evaluate the effect of standing residue on soil wind erosion in the inland Pacific Northwest (iPNW), USA, and test the performance of the plant factor algorithm of the Agricultural Policy/Environmental eXtender (APEX) and Revised Wind Erosion Equation (RWEQ) models in influencing soil loss. The effect of standing winter wheat (Triticum aestivum L.), spring canola (Brassica napus L.), and chickpea (Cicer arietinum) residue on wind erosion, remaining from major commodity crops in the region, was tested in a laboratory wind tunnel using four levels of residue density. The impact of standing residue in controlling wind erosion was compared and analyzed in terms of residue density and their respective frontal area index. Our results show that residue at a density characteristic of the production environment (110 standing residue elements m −1 for winter wheat, 20 standing elements m −1 for canola, and 16 standing elements m −1 for chickpea) provided significant protection to the soil surface from wind erosion. Soil loss at this level of residue density was reduced by 73.3, 53.4, and 60.9% for respectively winter wheat, spring canola, and chickpea (frontal area indexes are 0.172, 0.104, and 0.026 respectively) compared with a surface without residue. The soil surface was found to be at significant risk from wind erosion when residue densities of the three crop types were < 50% of the typical production amounts. Although not consistently significant, soil loss decreased as wind direction shifted from parallel to perpendicular with the standing residue row. The APEX model adequately simulated winter wheat and spring canola residue protection but had low accuracy in representing chickpea residue effects relative to the wind tunnel experiments. In contrast, the RWEQ model appeared inadequate in simulating soil loss for the winter wheat and canola treatments but adequately represented chickpea residue effects. Differences in model accuracy for different crop types must be considered by producers and managers to determine whether model information used to select practices to control wind erosion are likely to result in under-or over-protection of soil resources.
... Several studies have demonstrated that vegetation has the ability to increase the entrapment of mobile sand and dust, and decrease soil loss by the wind as a result of reduction of soil erodibility and wind speed [9,10,11,12]. Lancaster and Baas [13] revealed that vegetation increases both the threshold wind shear velocity and the aerodynamic roughness length. According to Fryrear et al. [14] theory for the transport phenomenon over a bare land, the absolute maximum particle transport rate is reached after a certain distance under the condition of no limited field length. ...
Article
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This study deals with the vegetation change in Kuwait from 1974 compared to recent vegetation map and their capabilities on trapping mobile sand, dust and carbon dioxides (Co2). The average cost of one cubic meter removal of encroached sand around infrastructures in Kuwait is 1.32 USD. The capability of trapping sand is much higher for Haloxylon sp. than Stipagrostis sp. by 100%. The areas that were covered by Haloxylon in 1974 lose recently 4385 km2 for the benefits of Stipagrostis causing the formation of a new mobile sand corridor. The total estimated annual cost for the vegetation change is 35,429,379 USD obtained from the costs of sand encroachment, CO2 consumption loss and solar energy efficiency loss. Rehabilitation for areas that were occupied with large size canopy vegetation will surely cause a decrease in the aeolian activities and air temperature, lower the albedo and increase the precipitation and solar energy production.
... evidence, high agreement)(Touré et al. 2019;Amundson et al. 2015; Borrelli et al. 2017;Pierre et al. 2017).Amadou et al. (2011) note that even a minimal cover of crop residues (100 kg ha -1 ) can substantially decrease wind erosion. ...
... When vegetation is sparse, standing residue is significantly more effective than flat residue for wind erosion control (Hagen, 1996). Wind erosion studies have focused on the effects of sparse vegetation after harvesting (Wolfe and Nickling, 1993;Lancaster and Baas, 1998;He et al., 2017), land degradation and conversion (Li et al., 2005), and dry land conditions (Musick and Gillette, 1990;Toure et al., 2011). These are all conditions that make the soil surface vulnerable to wind erosion. ...
Article
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Maintaining vegetative cover on the soil surface is the most widely used method for control of soil loss by wind erosion. We numerically modeled airflow through artificial standing vegetation (i.e., simulated wheat plants) using computational fluid dynamics (CFD). A solver (simpleFoam within the OpenFOAM software architecture) was used to simulate airflow through various three-dimensional (3D) canopy structures in a wind tunnel, which were created using another open-source CAD geometry software (Salomé ver. 7.2). This study focused on two specific objectives: (1) model airflow through standing vegetation using CFD, and (2) compare the results of a previous wind tunnel study with various artificial vegetation configurations to the results of the CFD model. Wind speeds measured in the wind tunnel experiment differed slightly from the numerical simulation using CFD, especially near positions where simulated vegetation was present. Effective drag coefficients computed using wind profiles did not differ significantly (p <0.05) between the experimental and simulated results. Results of this study will provide information for research into other types of simulated stubble or sparse vegetation during wind erosion events. Keywords: 3-D canopy structure, OpenFOAM, Wind erosion, Wind tunnel studies. Highlights Keywords: 3-D canopy structure, OpenFOAM, Wind erosion, Wind tunnel studies. Measured airflow through a simulated canopy was successfully modeled using CFD software. Keywords: 3-D canopy structure, OpenFOAM, Wind erosion, Wind tunnel studies. Effective drag coefficients did not differ between the experimental and simulated results. Keywords: 3-D canopy structure, OpenFOAM, Wind erosion, Wind tunnel studies. Results of this study provide 3-D simulation data of wind flow through a plant canopy. Keywords: 3-D canopy structure, OpenFOAM, Wind erosion, Wind tunnel studies.
... Threshold velocity was determined with statistic method which has been successfully applied and verified by Kurosaki and Mikami (2007), Abdourhamane Touré et al. (2011) and Bergametti et al. (2016). The equation is as follows: ...
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Soil and the atmospheric conditions are important factors that affect wind speed threshold of surface dust emissions. Based on the observed data of surface dust emissions in the Taklimakan Desert collected from March 2008 to February 2018, the effects of soil moisture, air humidity (vapor pressure), and air temperature on wind speed threshold were analyzed in this study. The results showed that the accumulated time of dust emissions over the decade was 3609.8 h, thereby accounting for 4.1% of the total observation time. In addition, the duration of dust emission in the four seasons were consistent with the pattern of summer > spring > autumn > winter. When the soil moisture is above 3.0–4.0%, the wind speed threshold for dust emission increases with increasing soil moisture. When the vapor pressure is above 10–15 kPa, the wind speed threshold for dust emission increases with increasing vapor pressure. There was a negative correlation between air temperature and the wind speed threshold for dust emission. When the air temperature was higher than 0.0 °C, the soil moisture decreased with increasing air temperature, and the wind speed threshold for dust emission was lower.
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Based on a large number of in‐situ measurements performed over a 9‐years period in two Sahelian stations, we investigate the drivers of the dust wet deposition in relation to the meteorological situations and the PM10 (Particulate Matter with diameter lower than 10 μm) surface concentrations. Precipitation associated with cold pools (CP) contribute to more than 90% of the precipitation amount associated with the collected wet deposition samples. The wet deposition events associated with these CP control by far the wet deposition, that is, 66% and 81%, depending on the station. The dust washout ratios (WR) corresponding to the most convective events under high level of dust concentrations were found to be in the range of 319–766 while WR of other kind of events are depending on the dilution effect. This range of value are in the lower range of WR previously estimated and used in dust modeling studies (200–2000).
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The observed increase of the catchments flow values in the Sahel during the drought years has exacerbated the interest for the studies on the superficial hydrodynamic properties of soils and their impact onto runoff volumes. This work focuses on the processes responsible for the flow production within two experimental catchments situated in the granitic basement of Western Niger. It aims at characterizing the hydrodynamical functioning at three nested spatial scales. At point scale (50 cm²), soil surface infiltrability (0-10 cm) is determined for different surface features through hydraulic conductivity (Ks) measurements carried out in situ. At the plot scale, runoff is measured from 10 m² experimental plots while at catchment scale (5 ha), stream flow is controlled by stream gauges at the exutories. Measurements show low values of hydraulic conductivity ranging from 10 mm.h-1 (minimal value measured on erosion crusts ERO) to 40 mm.h-1 (maximal value measured on cultivated sites in seasonal average). Runoff coefficients are inversely ranked, from 0.60 on ERO to 0.25 on cultivated surface. Catchment scale runoff coefficients are 0.41 and 0.28 for the not cultivated and the cultivated basins, respectively. Results obtained at these three scales are consistent and reveal the strong runoff production ability of these granitic catchments resulting from both low point scale infiltrability and small re-infiltration of runoff water within the stream network. This last component represents only 4% of annual rainfall while it may reach more than 50% for sedimentary catchments of similar size. Within these catchments, thus, a 2-4 mm rainfall is sufficient to generate a flow at the outlet due to rather small (less than 20 cm) sand deposits covering the stream beds. Finally, both at the plot and at the catchment scales, hydrodynamical functioning was found quasi independent on the initial water content.
Article
In arid and semiarid areas with frequent dust storms, reasonable planting modes and crop residue measures could prevent dust storms that originate from local farmlands and address key factors for wind erosion control. The considered crop residue modes included all harvesting with no residue in a Cyperus esculentus L. (C.) monoculture setting (AH), retention of 1 ridge and harvesting of 3 ridges in a C. monoculture setting (RH), and all harvesting with retention of Setaria italica (L.) Beauv. var. germanica (Mill.) Schrad (S.) residue in an intercropping setting of 6S. ridges and 9C. ridges (ARS). The aerodynamic roughness z0 and friction velocity u* were measured with handheld anemometers, and sediment fluxes were measured by combining multichannel sand collectors under different crop residue modes. The results indicated that the total aeolian sediment flux increased with distance away from the final belt of crop residue under both the RH and ARS modes. S. residue reduced the total aeolian sediment flux by more than 50% compared to C. residue at a distance of 4.5 m away from the residue belt during the dust storm. The sand transported height under both the RH and ARS modes was lower than that under the AH mode, and the distance required for sand to be transported to the same flux behind the S. residue belt was more than that behind the C. residue belt. The frontal area index (FAI) is a parameter that can better reflect the wind erosion control ability of C. and S. residues. S. residue attained a higher wind weakening ability than C. residue according to the positive relationship between z0, u* and FAI. During the dust storm, the relationship between the total aeolian sediment flux and FAI changed from significant to insignificant as the sand transported height exceeded C. residue height. Using standing crops intercropping with C. can provide both income from C. and wind erosion control from standing crop residues. The results can provide useful guidance for local C. harvest and planting design.
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The endemic argan woodlands cover large parts of South Morocco and create a characteristic landscape with areas of sparsely vegetated and bare soil surfaces between the single trees. This unique ecosystem has been under extensive agrosilvopastoral management for centuries and is now at risk of degradation caused by overgrazing and increasing scarcity and variability of rainfall. To investigate susceptibility to wind erosion, we conducted an experimental-empirical study and quantified wind erodible material on five different associated surface types. The highest emission flux was measured on freshly ploughed surfaces (1875 g m-2 h-1), while older ploughed areas with a re-established crust produced a much lower emission flux (795 g m-2 h-1). Extensive tillage may have been a sustainable practice for generations, but increasing drought and uncertainty of rainfall now leads to an acute risk of severe soil erosion and dust production. The typical crusted surfaces characterised by residual rock fragment accumulation and wash processes produced the second highest emission flux (1354 g m-2 h-1). Collected material from tree-shaded areas (933 g m-2 h-1) was revealed as a considerable source of organic material possibly affecting substrate conditions positively on a larger regional scale. Lowest flux was measured on rock fragment covered surfaces (301 g m-2 h-1). The data show that open argan woodland may be a considerable source for wind erosion and dust production, depending on surface characteristics strongly related to management. An adapted management must include the conservation of the argan trees to offer a promising approach to prevent severe wind erosion and dust production and mitigate possible impacts of land-use change and climate-change related shifts in wind and rainfall patterns.
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An accurate threshold velocity ut for sand movement is essential for predicting wind erosion events and calculating the magnitude of horizontal sand flux. We compared various approaches for determining ut using data observed during 4–31 July 2009 in the hinterland of Taklimakan Desert. We used the Gaussian time fraction equivalence method developed by Stout with an interval of 1 day to obtain ut values of 3.03–5.62 m/s (the approach of observations through field experiments). The Kurosak (ut50%) method yielded values of 3.71–5.74 m/s (the approach of statistical calculations). The Marticorena and Shao models gave ut values of 4.87–4.90 and 5.82–6.78 m/s, respectively (the approach of model parameterizations). To test the accuracy of these threshold velocities above, we estimated the total horizontal sand flux and the duration of sand saltation. Estimates of the total horizontal sand flux were 1311.9, 1166.4, 1279.9, and 661.6 kg/m for the Stout, Kurosak, Marticorena, and Shao methods, respectively, while the observed value was 732.9 kg/m. The correlation coefficient between observed and estimated values based on the Stout, Kurosak, Marticorena, and Shao methods was 0.75, 0.79, 0.77, and 0.83, respectively. The estimated duration of sand saltation using the ut been as Stout, Kurosak, Marticorena, and Shao was 8211, 6575, 7567, and 3463 min, of which 6208, 5646, 5986, and 3346 min were correct reports, respectively, and the observed value was 7663 min. We discuss the advantages and disadvantages of these methods combining those results above, which can be used to advise researchers to improve the threshold velocity used in future studies.
Chapter
It is common to distinguish two main types of erosion: natural erosion and accelerated erosion by human action. Erosion can also be classified into mechanical erosion and chemical erosion based on the processes. This chapter focuses on the accelerated and mechanical erosion of continental soils and the main principles of soil conservation. It briefly discusses three consequences of erosion, distinguishing between on‐site and off‐site effects, and historical consequences. On‐site effects mainly concern soil quality. Off‐site impacts concern impacts downstream of detachment areas, and therefore transport and deposition. Any erosion process involves three mechanisms: soil particle detachment, transport and deposition. Streambank erosion is also an important source of sediment. Wind erosion affects the climate, geochemical cycles, as well as air quality and human health. The main difficulty of modeling arises from the multiplicity of scales and processes that must be clearly defined each time. There are a variety of approaches: statistical, physically based, and hybrid.
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A household survey, combined with an extensive literature search of baseline studies, complemented on-station research on spatial soil and crop growth variability with a farmer's viewpoint. Farmers explained spatial variability in crop growth in terms of differences in soil types, soil fertility and degradation, as well as their cultivation and management practices. Farmers counteract spatial crop growth variability by within-field fallow; kraaling; spot applications of manure, crop residuals and household waste; by internationally moving their settlements; and by exploiting the micro-environmental differences around specific tree and shrub species.
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Field studies conducted at Owens Lake, California, provide direct measurements of sand flux on sand sheets with zero to 20 per cent cover of salt grass. Results from 12 different sand transport events show that aerodynamic roughness length and threshold wind shear velocity increase with vegetation cover as measured by vertically projected cover and roughness density (lambda). This results in a negative exponential decrease in sediment flux with increasing vegetation cover such that sand transport is effectively eliminated when the vertically projected cover of salt grass is greater than 15 per cent. A general empirical model for the relation between sand flux and vegetation cover has been derived and can be used to predict the amount of vegetation required to stabilize sand dune areas. (C) 1998 John Wiley & Sons, Ltd.
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Wind erosion is regarded as a major contributor to the desertification process in the Sahel, yet little quantitative information is available for that region on soil losses by wind erosion under different land management practices. A 3-yr, on-farm experiment was, therefore, set up to assess the effect of ridging and either banded or broadcast millet stover mulches (2000 kg ha-1) on soil loss in a millet-cowpea intercrop. For wind directions approximately perpendicular to the orientation of ridges and residue bands, sediment mass balances were calculated from the change in horizontal sediment mass fluxes measured across the experimental plots with Big Spring Number Eight sand traps. Mass balance calculations for 16 events over 3 yr indicated an average soil loss of 17.5, 15.4, and 18.0 Mg ha-1 on control plots, and deposition of 15.5, 15.3, and 7.4 Mg ha-1 on banded residue plots in 1995, 1996, and 1997, respectively. Broadcast and banded residue mulches were not significantly different (P = 0.05) in terms of their sediment trapping efficiency. During the same time period, ridges reduced soil losses by an average of 57% compared with the control plots, but their efficiency was reduced to less than 15% after 100 mm of cumulative rainfall as ridges collapsed. Linear regression analysis using the incoming sand fluxes as the independent variable was used to estimate potential soil losses for all events with sediment fluxes <25 kg m-1 irrespective of wind direction. The calculations indicated potential soil losses of up to 79 Mg ha-1 on control plots and deposition of 41 Mg ha-1 on broadcast residue plots in a single year. For wind erosion control, broadcast millet stover mulching constituted the most effective control technique because it effectively protected the soil against erosion and its trapping efficiency is expected to be independent of wind direction.
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The effect of turbulent flow structures on saltation sand transport was studied during two convective storms in Niger, West Africa. Continuous, synchronous measurements of saltation fluxes and turbulent velocity fluctuations were made with a sampling frequency of 1 Hz. The shear stress production was determined from the vertical and streamwise velocity fluctuations. The greatest stress-bearing events were classified as turbulent structures, with sweep, ejection, inward interaction, and outward interaction described according to the quadrant technique. The classified turbulent structures accounted for 63·5 per cent of the average shear stress during the first storm, and 56·0 per cent during the second storm. The percentage of active time was only 20·6 per cent and 15·8 per cent, respectively. High saltation fluxes were associated with sweeps and outward interactions. These two structures contribute positively (sweeps) and negatively (outward interactions) to the shear stress, but have in common that the streamwise velocity component is higher than average. Therefore, the horizontal drag force seems primarily responsible for saltation sand transport, and not the shear stress. This was also reflected by the low correlation coefficients (r) between shear stress and saltation flux (0·12 and 0·14, respectively), while the correlation coefficients between the streamwise velocity component and saltation flux were much higher (0·65 and 0·57, respectively). © 1998 John Wiley & Sons, Ltd.
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For the study of field wind erosion, detailed observations of wind-blown sediment transport in the field are needed. The objective of this study was to determine the best method to quantify the mass of wind-blown material moving past a fixed point during four storms. Twenty-one Modified Wilson and Cooke (MWAC) sediment catchers were installed in a pearl millet [Pennisetum glaucum (L.) R. Br.] field in the Sahelian zone of Niger, on a sandy, siliceous, isohyperthermic Psammentic Paleustalf. Each catcher trapped materials at seven heights between 0.05 and 1.00 m. The vertical profiles of measured horizontal mass fluxes were described by two different models, a three-parameter power function and a five-parameter combined model, which is a combination of an exponential function and a power function. For all four storms, both models described accurately the mass fluxes between 0.05 and 0.26 m, but fitted mass fluxes at 0.50, 0.75, and 1.00 m deviated from measured fluxes. Deviations were 21.1, 45.2, and 60.6% for the power function and 12.4, 18.5, and 30.0% for the combined model. Mass transport rates were calculated by integrating the mass flux profiles across height. The differences in calculated mass transport rates were small, but because of the better fit, the combined model was preferred. Correcting for the trapping efficiency of the MWAC catchers (0.49) and multiplying by the storm duration resulted in total mass transport values, which are equal to the mass of soil passing a strip of 1-m width perpendicular to the mean wind direction. The average mass transport values were 102.7, 15.5, 31.8, and 149.8 kg m-1, respectively, for the four storms.
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Large-scale simulation of the soil-derived dust emission in semi-arid regions needs to account for the influence of the soil moisture on the wind erosion threshold. Soil water retention consists of molecular adsorption on the soil grain surface and capillary forces between the grain. Interparticle capillary forces (characterized by the moisture tension) are the main factor responsible for the increase of the wind erosion threshold observed when the soil moisture increases. When the soil moisture content is close to but smaller than the maximum amount of adsorbed water, w' (depending on the soil texture), these capillary forces are considered as not strong enough to significantly increase the erosion threshold. An expression of the moisture tension as a function of soil moisture and w' is derived from retention curves. From this expression, a parametrization of the ratio of the wet to dry erosion thresholds has been developed as a function of soil moisture and soil texture. The coefficients of this parametrization have been determined by using experimental data from the literature. An empirical relationship between w' and soil clay content has been established. The erosion threshold ratios simulated for different soil textures were found to be in good agreement with the experimental data.Key words. Atmospheric composition and structure (Aerosols and particles) · Hydrology (soil moisture)
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In the Sahel, sandy soils are widespread and support not only most of the pearl millet production, the major staple crop in the region, but also grass production for livestock. Parent sediments of these soils have an aeolian origin and are hence prone to wind erosion. Still, their clay content, even though very low, allows physical crust formation during rainfall leading to runoff and water erosion. Squall lines, major rainfall events of the rainy season, are usually preceded by intense wind. Wind and water erosions are therefore closely associated in both time and space, but they are rarely studied simultaneously. Erosion measurements were performed for two years (2001, 2002) on a small catchment of grazing land (1,4 ha) at Katchari, Burkina Faso, a location typical of the Sahel area with under 500 mm annual rainfall. Wind erosion occurs at the onset of the rainy season, from May to 15th of July, when soil cover is the lowest and before the growth of vegetation. On this non-cultivated area, the same dynamic unfolds as that recorded in millet fields in other sahelian studies. Water erosion occurs throughout the rainy season, but certain intense events produce most of the total annual erosion. Wind causes the largest sediment fluxes leading to both erosion (up to 20 Mg/ha per year) and deposition (up to 30 Mg/ha per year) depending on the area in the catchment. Water erosion is one order of magnitude lower than wind erosion and is more intense where wind erosion is highest. Hence, the same area is eroded by both wind and water. Conversely, areas where aeolian deposition occurs are less affected by water erosion and correspond to fertile islands where vegetation grows. From this study, it comes out that there is on the whole no land degradation at the catchment scale, but an intense aeolian and water dynamic leading to substantial spatial variability typical of sahelian landscapes.
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During the 2006 and 2007 special observing periods of the African Monsoon Multidisciplinary Analysis campaign an original experimental system has been implemented in Banizoumbou (Niger) for measuring the size-resolved dust emission flux in natural conditions and documenting the possible influence of wind speed on its size distribution. The instrumental set-up, associated methodology, and the quality tests applied to the data set are described before the results acquired during 2 events of the Monsoon type and 1 of the convective type are analyzed in detail. In good agreement with the theory of sandblasting, it is found in all cases that saltation must take place for a vertical emission flux to be detected. During a particular erosion event, the magnitude of the vertical flux is controlled by the surface roughness, which conditions the saltation threshold, and by the wind friction velocity. The dust flux released by the high energy convective event is also found to be much richer in very fine (*. This is interpreted as a possible result of the rather long duration (15&apos;) over which wind fluctuations must be averaged for computing u*, which could make it an inadequate parameter for representing the very short response-time physical processes that are at the origin of fine dust emission at the measurement sites.