Aeolian dust, resulting from wind erosion, is controlled by two major factors: aeolian erosivity (i.e., wind speed) and aeolian erodibility (i.e., land surface conditions). Erodibility factors include a number of land surface parameters that interact in complicated manners. Thus far, the extent to which each of the factors contributes to dust outbreaks, which vary regionally and seasonally, remains unclear. As such, we present a novel map of the controlling factors for dust outbreaks in dryland of East Asia by quantifying the relative contributions of the erosivity and various erodibility parameters to inter-annual dust variations on a station basis during the period of 1999 to 2013. Erosivity controls dust outbreaks in the Taklimakan Desert, west of the Hexi Corridor, and on the north side of the Altai Mountain. On the other hand, dust outbreaks are dependent on erodibility in steppe regions: lower precipitation or less abundant vegetation during the previous summer was found to be related to dusty springs in the Mongolian steppe, whereas the less abundant spring vegetation and reduced snow cover enhanced dust outbreaks in the Inner Mongolian steppe. Anthropogenically restored vegetation in desertified areas was found to be likely to suppress dust outbreaks in the Loess Plateau.(Citation: Wu, J., Y. Kurosaki, M. Shinoda, and K. Kai, 2016: Regional characteristics of recent dust occurrence and its con-

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We used a compact boundary layer wind tunnel equipped with a turbulence generator and a piezoelectric blown-sand meter to investigate the effects of the surface coverage of fine gravel on wind-blown sand flux. The vertical profile of wind-blown sand over a flat sand surface showed an exponential distribution at all wind speeds, whereas the profile over gravel surfaces of 20% or greater coverage showed a non-monotonic vertical distribution. At 20% to 30% gravel coverages, a peak of wind-blown sand flux developed between 6 and 10 cm above the ground at all wind speeds because of less energy loss due to grain-bed collisions at that level. To analyze the erosional state of wind-blown sand, we used the Wu–Ling index (λ) of the mass-flux density of sand-bearing wind. Values of λ for all gravel coverages were greater than 1 at all wind speeds, indicating an unsaturated (erosional) state. Moreover, we found that the wind-blown sand flux at 4 cm height accounted for about 20% of the total flux regardless of wind speed and gravel coverage. This finding can simplify future estimations of total near-surface wind-blown sand flux based on field observations because such measurements can be taken at just one height.

Aeolian dust is dependent on erosivity (i.e., wind speed) and erodibility (i.e., land surface conditions). The effect of erodibility on dust occurrence remains poorly understood. In this study, we proposed a composite erodibility index (dust occurrence ratio, DOR) and examined its interannual variation at a typical steppe site (Abaga-Qi) in Xilingol Grassland, China, during spring of 1974–2018. Variation in DOR is mainly responsible for dust occurrence (R2 = 0.80, p-value < 0.001). During 2001–2018, DOR values were notably higher than those during 1974–2000. There was also a general declining trend with fluctuations. This indicates that the land surface conditions became vulnerable to wind erosion but was gradually reversed with the implementation of projects to combat desertification in recent years. To understand the relative climatic and anthropogenic impacts on erodibility, multiple regression was conducted between DOR and influencing factors for the period of 2001–2018. Precipitation (spring, summer, and winter) and temperature (summer, autumn, and winter), together with livestock population (June) explained 82% of the variation in DOR. Sheep and goat population made the greatest contribution. Therefore, reducing the number of sheep and goat could be an effective measure to prevent dust occurrence in Xilingol Grassland.

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