A comparison of the aerodynamic characteristics of four kinds of land surface in wind erosion areas of northern China

Aerodynamic characteristics is a crucial factor influencing soil wind erosion, which is closely related to the properties of surface roughness elements. In the expansive arid and semi-arid northern China, grassland, farmland, mobile sandy land, and gobi are the main land surface types that suffer wind erosion to varying degrees. To investigate the aerodynamic characteristics of different surfaces, we used three-dimensional ultrasonic anemometers to observe the near-surface wind speed above grassland, farmland, mobile sand, and two types of gobi surfaces in areas of northern China (a total of five observation sites). We compared the aerodynamic characteristics of the five surfaces and their causes (i.e., the surface roughness length, wind speed pulsation, turbulence intensity, and drag coefficient), and analyzed how surface roughness elements weakened the airflow. The roughness length was greatest for grassland, followed by farmland, sand, fine gobi, and black gobi. The pulsation intensity of near-surface wind speed increased linearly with increasing wind speed at all sites. At a given wind speed, increasing roughness length increased the pulsation intensity of wind speed. The probability distributions for the drag coefficient and turbulence intensity of the five surfaces followed a positively skewed distribution. The drag coefficient and turbulence intensity were greatest for grassland, followed by farmland, sand, fine gobi, and black gobi surfaces. The drag force exerted on the roughness elements increased with increasing wind speed, but the ratio of drag force exerted on the roughness elements to the total drag force (tau R/tau) for flexible roughness elements (i.e., plants) increased as the wind speed increased; for rigid roughness elements, tau R/tau decreased with increasing wind speed. This confirms that the shelter capability of flexible roughness elements against soil wind erosion increases with the increase of wind speed, while that of rigid roughness elements is opposite.

Automated summary

This study investigated the aerodynamic characteristics of different land surface types in northern China and analyzed the effects of surface roughness elements on the airflow. The results showed that the roughness length, wind speed pulsation, turbulence intensity, and drag coefficient varied among different land surfaces. Furthermore, the shelter capability of flexible roughness elements increased with increasing wind speed, while that of rigid roughness elements decreased.