Wind Erosion Threshold Research Articles

Estimation of wind erosion threshold velocity using wind tunnel device in dust sources in Khuzestan, Iran (case study: Mahshahr, Omidiyeh, Hendijan)

Estimation of wind erosion threshold velocity using wind tunnel device in dust sources in Khuzestan, Iran (case study: Mahshahr, Omidiyeh, Hendijan)

Effect of pedestrian trampling on aeolian sand dynamics on beach surfaces: An experimental study

Wind tunnel experiments and measurements with the Portable In-Situ Wind Erosion Laboratory (PI-SWERL) were conducted to investigate the effect footprints on a sandy beach have on aerodynamic roughness, physical roughness, and the wind erosion threshold. Footprints parallel and footprints perpendicular to the wind were tested, for bare feet and walking shoes, for a lighter (63 kg) and a heavier (75 kg) person. The data were compared to a flat undisturbed surface, which served as control. Results show that footprints have a significant effect on aerodynamic roughness and on the wind erosion threshold. Aerodynamic roughness is higher, and the wind erosion threshold lower, for footprints parallel to the wind compared to footprints perpendicular to the wind, for footprints produced with bare feet compared to footprints produced by walking shoes, and for footprints made by a heavier person compared to footprints made by a lighter person. The differences with an undisturbed flat surface, for which aerodynamic roughness is small and the wind erosion threshold high, were found to be substantial. Of the measured physical roughness parameters of the footprints, surface area of the imprint showed the highest correlation with aerodynamic roughness. The effect of the volume and the average depth of the imprint on aerodynamic roughness was much smaller or even not statistically significant. The PI-SWERL measurements also suggested that on dry sandy surfaces foot imprints may rapidly disintegrate, even when the wind is only slightly above the erosion threshold. This study shows that when wind erosion models are used to describe and predict the initial phase of wind erosion on sandy beaches, the process of trampling with footprints should at least be considered.

Investigation of Wind Erosion Threshold in Different Land Cover and the Effect of Soil Properties on It (Case Study: Niatak Region of Sistan)

Investigation of Wind Erosion Threshold in Different Land Cover and the Effect of Soil Properties on It (Case Study: Niatak Region of Sistan)

Recent changes in physical properties of the land surface and their effects on dust events in different climatic regions of Iran

The physical characteristics of the Earth’s surface play an important role in controlling the velocity of the wind erosion threshold. Therefore, to reduce the risks of dust storms, it is necessary to determine the impact of changes in this characteristic on wind erosion events in different regions. In this regard, this study was carried out to examine the effects of soil moisture (SM), land surface temperature (LST), and vegetation cover (VC) on wind erosion phenomenon using a combination of satellite data and terrestrial observations from 2010 to 2018. In this work, the dust storm index (DSI) was selected to monitor the wind erosion across the country. The multivariate regression method was utilized to explore the effect of alterations in these parameters on changes in soil erosion at both local and regional scales in Iran. In the local scale, regression coefficients between LST-DSI, SM-DSI, and VC-DSI were estimated in the range of 0.002 to 0.77, −0.029 to −0.51, and − 0.001 to −0.82, respectively. On the regional scale, alterations in the LST and EVI could show about 40% of changes in the wind erosion activity over arid regions of Iran (R2 = 0.43; P value β2LST = 0.15). In semi-arid regions, 36% of changes in DSI was due to alterations in LST and SM (R2 = 0.36; P value 0.05). These results can be used by planners and managers to develop programs to combat wind erosion and reduce the risks posed by dust storms in arid and semi-arid regions of Iran.

Gravel-Desert Surface Properties and Their Influences on the Wind-Erosion Threshold Friction Velocity in North-West China

In north-west China, extensive areas of gravel desert exist, whose surface properties have an important effect on the wind-erosion threshold friction velocity $$ u_{*t} $$ . In this study, we use four models and field observations of gravel mass fraction, soil physical crust, and soil clay content to assess the effect of gravel-surface properties on the value of $$ u_{*t} $$ . Results show that gravel coverage in north-west China ranges between 0.07 and 1.00 (with a mean of 0.67), and about 81% of the sites investigated are covered by soil physical crust. Clay content is 2.4% on average in the study region, less than 2% in 52.1% of that region, and between 2 and 4% in the remaining study regions. The four regions where clay content is greater than the mean include the western Alxa Plain, the alluvial fan of the western Alxa Plain, the northern Alxa Plain, and the Hexi Corridor. In the study region, the value of $$ u_{*t} $$ ranges between 0.12 and 0.78 m s−1 (with a mean of 0.45 m s−1). Soil moisture, gravel coverage, and soil physical crust all affect the magnitude of $$ u_{*t} $$ . A principal component analysis indicates that the soil crust contributes of about 62% of the $$ u_{{*{\text{t}}}} $$ variations, soil moisture 25%, and surface roughness 9%. A variance analysis shows clear spatial differences in the magnitude of $$ u_{*t} $$ in north-west China due to the spatial variations in gravel land-surface properties.

Preferential transport of microplastics by wind

Contamination of terrestrial and marine environments by plastic waste has been widely documented. Most research into the distribution of microplastics has focused on water but here we show that wind transport can be very effective in mobilising microplastic particles. A series of wind tunnel experiments using two different substrates (sand and soil), two different microplastics (microbeads and fibres) and 5 different concentrations of microplastics (ranging from 0 mg kg−1dw to 1040 mg kg−1dw) is used to demonstrate that microplastics are preferentially transported by wind compared to sand and soil. When compared to either of the untreated substrate beds (0 mg kg−1dw), the inclusion of microplastics was not found to significantly affect the wind erosion threshold for any of the concentrations or geometric forms (fibres or beads) tested. Averaged over all concentrations of microplastics and both substrate types, microplastic enrichment was lower for microbeads than fibres. The enrichment of microplastic fibres within the entrained particulate matter was one to two orders of magnitude higher for both test bed substrates, ranging from 98 to 498 for the sand and 278 to 726 for the soil. This suggests microplastic shape needs to be carefully parameterized in models of atmospheric microplastic transport. We suggest that microplastic research could benefit from previous investigations into the wind erosion of soil organic carbon.

Retrieving the global distribution of the threshold of wind erosion from satellite data and implementing it into the Geophysical Fluid Dynamics Laboratory land–atmosphere model (GFDL AM4.0/LM4.0)

Abstract. Dust emission is initiated when surface wind velocities exceed the threshold of wind erosion. Many dust models used constant threshold values globally. Here we use satellite products to characterize the frequency of dust events and land surface properties. By matching this frequency derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue aerosol products with surface winds, we are able to retrieve a climatological monthly global distribution of the wind erosion threshold (Vthreshold) over dry and sparsely vegetated surfaces. This monthly two-dimensional threshold velocity is then implemented into the Geophysical Fluid Dynamics Laboratory coupled land–atmosphere model (AM4.0/LM4.0). It is found that the climatology of dust optical depth (DOD) and total aerosol optical depth, surface PM10 dust concentrations, and the seasonal cycle of DOD are better captured over the “dust belt” (i.e., northern Africa and the Middle East) by simulations with the new wind erosion threshold than those using the default globally constant threshold. The most significant improvement is the frequency distribution of dust events, which is generally ignored in model evaluation. By using monthly rather than annual mean Vthreshold, all comparisons with observations are further improved. The monthly global threshold of wind erosion can be retrieved under different spatial resolutions to match the resolution of dust models and thus can help improve the simulations of dust climatology and seasonal cycles as well as dust forecasting.

Optimal feature selection for prediction of wind erosion threshold friction velocity using a modified evolution algorithm

Threshold friction velocity (u⁎t) is a very important parameter, which represents wind erosion potential. Because of the difficulty of measuring u⁎t, it would be advantageous if u⁎t could be estimated indirectly from its effecting factors that can be easily measured. The main purpose of this research was to quantify relationships between u⁎t and various topsoil features using inexpensive approaches. To prepare a reliable dataset, we used a portable wind tunnel for measuring u⁎t at a total of 118 observation points in Kerman province, southeast Iran. We developed a non-dominated sorting genetic algorithm II (NSGA-II), specifically designed to operate with artificial neural network (ANN) to select the most determinant properties that influence u⁎t. A permutation of nine input features including surface crust (SC), gravel coverage (GC), very fine sand (VFS), fine sand (FS), very coarse sand (VCS), electrical conductivity (EC), sodium adsorption ratio (SAR), calcium carbonate equivalent (CCE), and mean weight diameter (MWD), was introduced as explanatory variables. We also examined the potential power of using a Multi-Layer Perception (MLP) neural network for prediction of u⁎t changes in response to spatial variation of the selected features. The results of constructed MLP model revealed the ability of the model for u⁎t prediction and showed that the coefficient of determination (R2) values were 0.91 and 0.89 for training and testing data, respectively. Furthermore, acceptable level of the statistical validation criteria verified reliable performance of the MLP model. This research provided a powerful basis for prediction of u⁎t from topsoil features and surface roughness in arid and semi-arid areas of Iran; however, its generic framework could be used to other arid and semi-arid regions with similar challenges.

How long does precipitation inhibit wind erosion in the Sahel?

AbstractSimultaneous measurements of saltation, wind speed, and rainfall performed in Niger before, during, and after 18 rain events are used to investigate how rain events affect wind erosion in the Sahel. The results show that the inhibition of saltation is rapid but progressive after the beginning of a rain event. The decrease of sand transport during the rain event is better linked to the time elapsed from the beginning of the rain event rather than to the cumulative rainfall. In the Sahel, after a rain event, less than 12 h is necessary to almost fully restore the sand transport potential. Our results suggest that assuming that no sand transport and dust emission occur during the 12 h following the end of a rain event could be a reasonable alternative to existing parameterizations of the influence of soil moisture on the wind erosion threshold, at least for the Sahelian conditions.

Research progress on wind erosion control with polyacrylamide (PAM).

Soil wind erosion is one of the main reasons for soil degradation in the northwest region of China. Polyacrylamide (PAM), as an efficient soil amendment, has gained extensive attention in recent years since it is effective in improving the structure of surface soil due to its special physical and chemical properties. This paper introduced the physical and chemical properties of PAM, reviewed the effects of PAM on soil wind erosion amount and threshold wind velocity, as well as the effect differences of PAM in soil wind erosion control under conditions of various methods and doses. Its effect was proved by comparing with other materials in detail. Furthermore, we analyzed the mecha-nism of wind erosion control with PAM according to its influence on soil physical characteristics. Comprehensive analysis showed that, although some problems existed in wind erosion control with (PAM), PAM as a sand fixation agent, can not only enhance the capacity of the soil resis-tance to wind erosion, but also improve soil physical properties to form better soil conditions. Besides, we proposed that combination of PAM and plant growth would increase the survival rate of plants greatly, control soil wind erosion in wind-erosive areas, and improve the quality of the ecological environment construction. Thus, PAM has practically important significance and wide application prospect in controlling soil wind erosion.

Wind erosion occurrence probabilities maps in the watershed of the Ningxia–Inner Mongolia reach of the Yellow River, China

The watershed of the Ningxia–Inner Mongolia reach of the Yellow River suffers serious wind erosion hazards and the areas with high wind erosion probabilities need to be identified to help in the building of the correct wind-sand blown hazard protection systems. In this study, the Integrated Wind-Erosion Modelling System model and Normalized Difference Vegetation Index (NDVI) data set were used to identify the distributions of threshold wind speeds and wind erosion occurrence probabilities. Through field observations, the relationships among NDVI, vegetation cover, frontal area (lateral cover), roughness length, and threshold friction velocity were obtained. Then, using these relationships, the spatial distributions of threshold wind speeds for wind erosion at a height of 10 m for the different months were mapped. The results show that the threshold wind speed ranged from 7.91 to 35.7 m/s. Based on the threshold wind speed distributions, the wind erosion occurrence probabilities of different months were calculated according to the current wind speed. The results show that the distributions of wind erosion occurrence probabilities and threshold wind speeds were related to each other. The resulting maps of threshold wind speeds and wind erosion occurrence probabilities would help environmental and agricultural researchers in determining some strategies for mitigating or adapting from wind erosion hazards.

Air density effects on aeolian sand movement: Implications for sediment transport and sand control in regions with extreme altitudes or temperatures

AbstractAeolian sand transport results from interactions between the ground surface and airflow. Previous research has focused on the effects on sand entrainment and mass transport of surface features and wind velocity, but the influence of air density, which strongly constrains airflow characteristics and the resulting sand flow, has not been widely considered. In the present study, entrainment, saltation characteristics and transport rates were examined at nine experimental sites ranging in elevation from −154 m below sea‐level (Aiding Lake) to 5076 m above sea‐level (Tanggula Mountain pass on the Qinghai–Tibetan plateau). At each site, a portable wind tunnel and high‐speed camera system were set up, and the friction wind velocity, threshold friction velocity and sand flow structure were observed systematically. For a given volumetric airflow, lower air density increases the wind velocity. Low air density also creates a high threshold friction velocity. The Bagnold wind erosion threshold model remains valid, but the value of empirical parameter A decreased with decreasing air density and ranged from 0·10 to 0·07, the smallest values reported in the literature. For a given wind velocity, increased altitude reduced total sand transport and creeping, but the saltation rate and saltation height increased. The present results provide insights into the fundamental mechanisms of the initiation and transport of sand by wind in regions with an extreme temperature or altitude (for example, alpine deserts and low‐lying lake basins) or on other planets, including Mars. These results also provide theoretical support for improved sand‐control engineering measures. The data and empirical equations provided in this paper improve the ability to estimate threshold and transport conditions for wind‐blown sand.

Estimating aerodynamic roughness over complex surface terrain

AbstractSurface roughness plays a key role in determining aerodynamic roughness length (zo) and shear velocity, both of which are fundamental for determining wind erosion threshold and potential. While zo can be quantified from wind measurements, large proportions of wind erosion prone surfaces remain too remote for this to be a viable approach. Alternative approaches therefore seek to relate zo to morphological roughness metrics. However, dust‐emitting landscapes typically consist of complex small‐scale surface roughness patterns and few metrics exist for these surfaces which can be used to predict zo for modeling wind erosion potential. In this study terrestrial laser scanning was used to characterize the roughness of typical dust‐emitting surfaces (playa and sandar) where element protrusion heights ranged from 1 to 199 mm, over which vertical wind velocity profiles were collected to enable estimation of zo. Our data suggest that, although a reasonable relationship (R2 > 0.79) is apparent between 3‐D roughness density and zo, the spacing of morphological elements is far less powerful in explaining variations in zo than metrics based on surface roughness height (R2 > 0.92). This finding is in juxtaposition to wind erosion models that assume the spacing of larger‐scale isolated roughness elements is most important in determining zo. Rather, our data show that any metric based on element protrusion height has a higher likelihood of successfully predicting zo. This finding has important implications for the development of wind erosion and dust emission models that seek to predict the efficiency of aeolian processes in remote terrestrial and planetary environments.

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

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. ► Below a threshold of 2% of crop residues cover, Z0 decreases dramatically fields. ► Crop residues cover of 2% corresponds to a residues density of 100 kg ha − 1 . ► Above this threshold, potential wind erosion is reduced by at least a factor of 3. ► Meteorological changes explain the end of erosion by mid July in the Sahel.

Modeling aeolian sediment transport thresholds on physically rough Martian surfaces: A shear stress partitioning approach

This paper explores the effect that large roughness elements (0.30 m × 0.26 m × 0.36 m) may have on entrainment of sediment by Martian winds using a shear stress partitioning approach based on a model developed by Raupach et al. (Raupach, M.R., Gillette, D.A., Leys, J.F., 1993. The effect of roughness elements on wind erosion threshold. Journal of Geophysical Research 98(D2), 3023–3029). This model predicts the shear stress partitioning ratio defined as the percent reduction in shear stress on the intervening surface between the roughness elements as compared to the surface in the absence of those elements. This ratio is based on knowledge of the geometric properties of the roughness elements, the characteristic drag coefficients of the elements and the surface, and the assumed effect these elements have on the spatial distribution of the mean and maximum shear stresses. On Mars, unlike on Earth, the shear stress partitioning caused by roughness can be non-linear in that the drag coefficients for the surface as well as for the roughness itself show Reynolds number dependencies for the reported range of Martian wind speeds. The shear stress partitioning model of Raupach et al. is used to evaluate how conditions of the Martian atmosphere will affect the threshold shear stress ratio for Martian surfaces over a range of values of roughness density. Using, as an example, a 125 µm diameter particle with an estimated threshold shear stress on Mars of ≈ 0.06 N m − 2 (shear velocity, u ⁎ ≈ 2 m s − 1 on a smooth surface), we evaluate the effect of roughness density on the threshold shear stress ratio for this diameter particle. In general, on Mars higher regional shear stresses are required to initiate particle entrainment for surfaces that have the same physical roughness as defined by the roughness density term ( λ) compared with terrestrial surfaces mainly because of the low Martian atmospheric density.

Feedbacks between fires and wind erosion in heterogeneous arid lands

Shrub encroachment, a widespread phenomenon in arid landscapes, creates “islands of fertility” in degraded systems as wind erosion removes nutrient‐rich soil from intercanopy areas and deposits it in nearby shrub‐vegetated patches. These islands of fertility generally are considered to be irreversible. Recently, fire has been observed to alter this pattern of resource heterogeneity through the redistribution of nutrients from the fertile islands of burnt shrubs to the surrounding bare soil areas. Despite the recognized relevance of both fires and wind erosion to the structure and function of arid ecosystems, the interactions between these two processes remains poorly understood. This study tests the hypothesis that fire‐induced soil hydrophobicity developing in the soils beneath burned shrubs enhances soil erodibility by weakening the interparticle wet‐bonding forces. To test this hypothesis, the effects of grass and shrub fires on changes in soil erodibility and on the intensity of fire‐induced soil water repellency are compared at both the field and patch scales in heterogeneous arid landscapes. Higher water repellency was observed in conjunction with a stronger decrease in wind erosion threshold velocity around the shrubs than in grass‐dominated patches affected by fire, while neither water repellency nor changes in threshold velocity was noticed in the bare soil interspaces. Thus, fires are found to induce soil hydrophobicity and to consequently enhance soil erodibility in shrub‐vegetated islands of fertility. These processes create temporally dynamic islands of fertility and contribute to a decrease in resource heterogeneity in aridland ecosystems following fire.

Enhancement of wind erosion by fire‐induced water repellency

The occurrence of fire and the subsequent increase in wind erosion are known to affect vegetation dynamics in dryland landscapes. Fires act as a disturbance on shrubs and trees and expose the soil surface to the erosive action of wind, thereby affecting the loss and redistribution of soil nutrients. Despite the relevance of wind erosion and fires to the dynamics of arid ecosystems, the interactions between these two processes remain poorly understood. We have investigated how a representative water repellent organic compound released by burning biomass and absorbed in the soil may enhance soil erodibility. To this end, we carried out a series of wind tunnel experiments, laboratory tests, and theoretical analyses to assess the effect of fire‐induced water repellency on the soil susceptibility to wind erosion. The experiments were carried out using clean, well‐sorted sand which was artificially coated with palmitic acid, a common water repellency inducing fatty acid found in most plants. The results indicate that fire‐induced water repellency enhances soil erodibility, causing a drop in wind erosion threshold velocity. The results are explained by the effect of water repellent compounds on soil‐water contact angle and on the strength of interparticle wet‐bonding forces.

An assessment of dust emission schemes in modeling east Asian dust storms

By implementing dust emission schemes developed by Marticorena and Bergametti (1995), Alfaro et al. (1997), Alfaro and Gomes (2001) (hereinafter referred to as MBA) and Shao (2001, 2004) into a regional climate model with a size‐distributed active aerosol algorithm, NARCM (Northern Aerosol Regional Climate Model), an assessment of dust emission schemes in the simulation of east Asian dust storms for March 2002 was carried out. Sensitivity of the parameters used for both the MBA and Shao schemes is first analyzed with a box version of the NARCM, where the wind erosion threshold friction velocities for both schemes are in good agreement for soil grain size range in diameter from 40 μm to 400 μm but differ for other size ranges. Although the impacts of clay, silt, loam and sand contents on vertical dust fluxes show a similar trend, their dependences on friction velocity vary substantially as the correction factors in each scheme to the threshold friction velocity, soil moisture and vegetation cover present a different degree of impact on vertical dust fluxes with wind friction velocity. One specific parameter, soil plastic pressure p, required by the Shao scheme varies between 103 Pa for loose surfaces and 105 Pa for hard crusted surfaces, which controls significantly emission flux. On the basis of the comparison of dust emission with the MBA scheme in the box model, the soil plastic pressure p applicable to Asian deserts for the Shao scheme is set to be 1000 Pa for sandy, 5000 Pa for loamy and silty and 10,000 Pa for clay soil in March 2002. In 3‐D simulations, both schemes captured the dust mobilization episodes during this period in east Asia and produced the similar spatial distributions of Asian dust column loading. Compared with the MBA scheme, the Shao scheme predicted much lower dust emission and surface concentration in eastern Mongolia and eastern and central north China and slightly higher with some additional dust emission sources in north western China, eastern Kazakhstan and western Mongolia. The key parameters responsible for the differences between the MBA and Shao emission schemes are the surface and soil‐related factors including soil moisture and vegetation coverage.

A field‐scale analysis of the dependence of wind erosion threshold velocity on air humidity

The wind‐forced detachment and movement of soil particles, is known for having important regional and global implications on climate change and biogeochemical cycles. The wind erosion process occurs when wind speed exceeds a certain threshold value, which depends on a number of factors, including surface soil moisture. In arid regions changes in atmospheric humidity contribute to most of the variability in surface soil moisture, which, in turn, has a significant influence on wind erosion threshold. This paper investigates the dependence of wind erosion threshold on air humidity in two arid regions in North America, the Mojave Desert (CA) and Canyonlands (UT). Field data are used to test existing models relating the threshold velocity for wind erosion to atmospheric conditions. The threshold velocity is found to be significantly dependent on the atmospheric relative humidity (RH) and to exhibit a well‐defined maximum for RH ≈ 35%. This result validates at the field scale recent theories and laboratory‐scale experimental results.

Parametrization of the increase of the aeolian erosion threshold wind friction velocity due to soil moisture for arid and semi-arid areas

Abstract. 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)