Aerodynamic properties of agricultural and natural surfaces in northwestern Tarim Basin

Abstract

Friction velocity (u*) and aerodynamic roughness (z0) are atmospheric parameters that influence the flux of windblown dust. These parameters have not been quantified for different land use types in the Tarim Basin of China, one of the largest sources of atmospheric dust in the world. Wind speed profiles were measured and used to determine d, u* and z0 of a cotton (Gossypium hirsutum L.) field, red date (Ziziphus jujuba L.) orchard and native desert during the spring wind erosion season of 2012 and 2013. In addition, d, u* and z0 were estimated using Raupach's model. During periods of high winds sufficient to cause erosion in spring, d averaged 0.28, 0.067 and 0m; u* averaged 0.39, 0.51 and 0.35ms−1; and z0 averaged 7.0, 17.0 and 1.2mm for respectively the cotton field, red date orchard and desert. Estimates of d, u* and z0 according to Raupach's model during the same periods of high winds were 0.10, 0.16 and 0m; 0.56, 0.73 and 0.49ms−1; and 12.6, 21.9 and 1.8mm for respectively the cotton field, red date orchard and desert. The Raupach model, which depends on canopy height and area index, overestimated u* and z0 for the three land use types during most high wind events. The desert had the greatest potential for flux of windblown dust (due to the lowest z0) while the red date orchard has the lowest potential for dust flux (due to the highest z0).