Dune sand transport as influenced by wind directions, speed and frequencies in the Ordos Plateau, China

The Ordos Plateau in China is a region with extensive wind erosion, severe desertification and various aeolian sand hazards. In order to determine aeolian sand transport in this region, the relationship between the sand transport rate and wind speed at 10 min frequencies was established by field observation in both the Qubqi Sand Desert and the Mu Us Sandy Land. Threshold wind speeds (2 m above the ground) for mobile, semi-fixed and fixed dune surfaces were estimated by field observations. The sand transport rate increased with the increase of the bare land ratio and near-bed wind speed. High-resolution meteorological 10 min average wind velocity data at 10 m above the ground were converted into velocity values at a height of 2 m to calculate sand transport potential based on three specific parameters decisive for sand transport: wind speed, duration and direction. The quantity of aeolian sand transported was calculated for various wind speed levels and directions, and the overall characteristics of sand transport on different dune surface types were determined by vector operation techniques. Sand transporting winds took place mainly in springtime. The prevailing wind directions were W, WNW and NW, with a frequency of more than 60% in total, and sand transport in these directions made up more than 70% of the total transport, corresponding to a general southeastward encroachment of aeolian sand in the study area. The relationship between wind frequency and speed can be expressed by a power function. High magnitude strong winds had a low frequency, but they played a dominant role in aeolian sand transport.