Dividing the transit wind speeds into intervals as a favorable methodology for analyzing the relationship between wind speed and the aerodynamic impedance of vegetation in semiarid grasslands

Abstract

AbstractIn grassland ecosystems, the aerodynamic roughness (Z0) and frictional wind speed (u*) contribute to the aerodynamic impedance of the grassland canopy. Thus, they are often used in the studies of wind erosion and evapotranspiration. However, the effect of wind speed and grazing measures on the aerodynamic impedance of the grassland canopy has received less analysis. In this study, we monitored wind speeds at multiple heights in grazed and grazing-prohibited grasslands for 1 month in 2021, determined the transit wind speed at 2.0 m height by comparing wind speed differences at the same height in both grasslands, and divided these transit wind speeds at intervals of 2.0 m/s to analyze the effect of the transit wind speed on the relationship among Z0, u*, and wind speed within the grassland canopy. The results showed that dividing the transit wind speeds into intervals has a positive effect on the logarithmic fit of the wind speed profile. After dividing the transit wind speeds into intervals, the wind speed at 0.1 m height (V0.1) gradually decreased with the increase of Z0, exhibiting three distinct stages: a sharp change zone, a steady change zone, and a flat zone; while the overall trend of u* increased first and then decreased with the increase of V0.1. Dividing the transit wind speeds into intervals improved the fitting relationship between Z0 and V0.1 and changed their fitting functions in grazed and grazing-prohibited grasslands. According to the computational fluid dynamic results, we found that the number of tall-stature plants has a more significant effect on windproof capacity than their height. The results of this study contribute to a better understanding of the relationship between wind speed and the aerodynamic impedance of vegetation in grassland environments.