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.