“…The surface roughness has been shown to be a key indicator of wind-breaking and sand-fixation effect, and has been used in wind erosion equations (Yang 1996). The surface roughness acts to absorb part of the momentum of the wind which reduces the threshold friction speed and wind erosion (Ashrafi et al 2015). In our study, afforestation also increased the surface roughness significantly.…”
Wind erosion is a primary cause of desertification as well as being a serious ecological problem in arid and semi-arid areas across the world. To determine mechanisms for restoring desertified lands, an unrestored shifting sand dune and three formerly shifting sand dunes (desertified lands) that had been enclosed and afforested for 5, 15, and 25 years were selected for evaluation on the south edge of the Tengger Desert, China. Based on sampling heights between 0.2 and 3 m, the critical threshold average wind speed was 6.5 m s at 2 m where the sand transport rate was reduced from 285.9 kg m h on the unrestored dunes to 9.1 and 1.8 kg m h on the sites afforested and enclosed for 5 and 15 years, respectively. The percentage of wind eroded area was reduced from 99.9% on the unrestored dune to 94.5, 9.0, and 0.5% on the sites afforested and enclosed for 5, 15, and 25 years, respectively. Wind erosion was effectively reduced after 15 years. Although there were different driving factors for wind erosion mitigation on the different restoration stages, an increase in the vegetation cover, surface roughness, soil shear strength, soil clay content, organic matter, and reduction in the near-surface wind speed were the primary variables associated with the restoration chronosequence. We conclude that reducing the wind speed and developing a biological crust through vegetation restoration were the critical components for restoration of desertified land.
“…The surface roughness has been shown to be a key indicator of wind-breaking and sand-fixation effect, and has been used in wind erosion equations (Yang 1996). The surface roughness acts to absorb part of the momentum of the wind which reduces the threshold friction speed and wind erosion (Ashrafi et al 2015). In our study, afforestation also increased the surface roughness significantly.…”
Wind erosion is a primary cause of desertification as well as being a serious ecological problem in arid and semi-arid areas across the world. To determine mechanisms for restoring desertified lands, an unrestored shifting sand dune and three formerly shifting sand dunes (desertified lands) that had been enclosed and afforested for 5, 15, and 25 years were selected for evaluation on the south edge of the Tengger Desert, China. Based on sampling heights between 0.2 and 3 m, the critical threshold average wind speed was 6.5 m s at 2 m where the sand transport rate was reduced from 285.9 kg m h on the unrestored dunes to 9.1 and 1.8 kg m h on the sites afforested and enclosed for 5 and 15 years, respectively. The percentage of wind eroded area was reduced from 99.9% on the unrestored dune to 94.5, 9.0, and 0.5% on the sites afforested and enclosed for 5, 15, and 25 years, respectively. Wind erosion was effectively reduced after 15 years. Although there were different driving factors for wind erosion mitigation on the different restoration stages, an increase in the vegetation cover, surface roughness, soil shear strength, soil clay content, organic matter, and reduction in the near-surface wind speed were the primary variables associated with the restoration chronosequence. We conclude that reducing the wind speed and developing a biological crust through vegetation restoration were the critical components for restoration of desertified land.
“…In the arid and semi-arid regions, soil particles are susceptible to wind erosion, while vegetation coverage can directly prevent the surface from being eroded. Thus, vegetation is conducive to maintaining soil moisture, increasing surface roughness, blocking sand transport, reducing the turbulence of the wind, and increasing collisions between soil particles and between soil particles and plants, which can effectively lead to an increase in the deposition of soil particles (Bauer et al, 2004;Zobeck and van Pelt, 2006;Ashrafi et al, 2015). Our results showed that with increasing vegetation coverage, the amount of soil eroded by wind decreased sharply, and that the higher the wind speed was, the more efficient the protective effect of vegetation on the soil surface was.…”
The rapid desertification of grasslands in Inner Mongolia of China poses a significant ecological threaten to northern China. The combined effects of anthropogenic disturbances (e.g., overgrazing) and biophysical processes (e.g., soil erosion) have led to vegetation degradation and the consequent acceleration of regional desertification. Thus, mitigating the accelerated wind erosion, a cause and effect of grassland desertification, is critical for the sustainable management of grasslands. Here, a combination of mobile wind tunnel experiments and wind erosion model was used to explore the effects of different levels of vegetation coverage, soil moisture and wind speed on wind erosion at different positions of a slope inside an enclosed desert steppe in the Xilamuren grassland of Inner Mongolia. The results indicated a significant spatial difference in wind erosion intensities depending on the vegetation coverage, with a strong decreasing trend from the top to the base of the slope. Increasing vegetation coverage resulted in a rapid decrease in wind erosion as explained by a power function correlation. Vegetation coverage was found to be a dominant control on wind erosion by increasing the surface roughness and by lowering the threshold wind velocity for erosion. The critical vegetation coverage required for effectively controlling wind erosion was found to be higher than 60%. Further, the wind erosion rates were negatively correlated with surface soil moisture and the mass flux in aeolian sand transport increased with increasing wind speed. We developed a mathematical model of wind erosion based on the results of an orthogonal array design. The results from the model simulation indicated that the standardized regression coefficients of the main effects of the three factors (vegetation coverage, soil moisture and wind speed) on the mass flux in aeolian sand transport were in the following order: wind speed>vegetation coverage>soil moisture. These three factors had different levels of interactive effects on the mass flux in aeolian sand transport. Our results will improve the understanding of the interactive effects of wind speed, vegetation coverage and soil moisture in controlling wind erosion in desert steppes, and will be helpful for the design of desertification control programs in future.
“…3 e). The latter leads to a worsening of atmospheric horizontal and vertical dispersion, resulting in an accumulation of pollutants in a thin layer above the surface ( Ashrafi et al, 2009 ; Dai et al, 2020 ; Tiwari et al, 2016 ). Fig.…”
Section: Resultsmentioning
confidence: 99%
“…The ventilation coefficient (VC) is a good proxy to understand the accumulation and dispersion efficiency of air pollutants within the PBL ( Ashrafi et al, 2009 ; Dai et al, 2020 ; Tiwari et al, 2016 ). It is defined as the potential volume into which air pollutants are diluted per unit of time and can be calculated as the product of the MLH (vertical dilution of pollutants: m) and the mean wind speed (horizontal ventilation: m s −1 ) ( Dai et al, 2020 ; Tiwari et al, 2016 ): …”
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