Characterizing the spatial variations of wind velocity and turbulence intensity around a single Tamarix tree

Authors: MIRI, ABBAS - Watershed And Development Initiative(WADI); WEBB, NICHOLAS - New Mexico State University

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2022
Publication Date: 7/28/2022
Citation: Miri, A., Webb, N. 2022. Characterizing the spatial variations of wind velocity and turbulence intensity around a single Tamarix tree. Agricultural and Forest Meteorology. 414:Article 108382.

Interpretive Summary: Vegetation can be used to control wind erosion by blocking the wind and sheltering exposed soil surfaces. However, while wind speed is typically reduced downwind of vegetation, wind speed may increase around the sides of plants due to compression of the airflow. Understanding how different live plants influence wind speed in these ways is important for designing windbreaks and shelterbelts and is needed to improve the accurary of wind erosion models. In this study we characterize wind speed and turbulence patterns around a single Tamarix tree. We found that a half-ellipse shaped deceleration zone formed downwind of the tree and full-ellipse acceleration zones formed on the sides of the tree. The largest turbulence intensity was observed closer to the soil surface and in the leeside of the tree where wind speed was highest, and the smallest turbulence intensity was found on the sides where wind speed accelerated. On the sides of the tree the structure of wind speed and turbulence profiles was similar and no significant differences in wind speeds were found between identical locations. The sheltering effect of the tree extended to a downsind distance of 7 times the height of the tree. This study represents an important investigation of the plant effect on airflow and the results can be used to inform Tamarix management and support parameterization of drag partition schemes to improve the accuracy of aeolian transport models in landscapes with Tamarix aphylla.

Technical Abstract: Characterizing airflow and turbulence patterns around real vegetation is essential for predicting aeolian erosion. However, few studies have explored the airflow field around live plants. In this field study, airflow field and turbulence patterns were investigated around a single Tamarix tree. Wind speeds were monitored at 34 locations around the tree at the heights of z/h = 0.13 h, 0.5 h, 1.1 h, and 1.8 h (where h is the height of the tree) in a wind speed of 12 m s-1. The results showed that a half-ellipse deceleration zone formed downwind and full-ellipse acceleration zones on the sides of the tree. The largest turbulence intensity was observed at lower heights and in the leeside of the tree where wind speed was highest and the smallest was found on the sides where wind speed accelerated. On the sides of the tree the structure of wind speed and turbulence profiles was similar and no significant differences (P<0.001) in wind speeds were found between identical locations. The mean wind velocities measured downwind of the tree at 0.5 h - 7 h and DR1-DR4 (at the right side of the tree edge) were significantly different (P<0.001) to the approach flow (wind speeds at -7 h) but no statistical differences were observed between wind speeds in other locations and the approach flow. The values of ''_(''('','')) (wind velocity reduction coefficient) were higher in the wake of the tree than upwind and on the sides of the tree indicating that the sheltering effect of the tree extended to the distance of 7 times the height tree. This study represents an important investigation of the plant effect on airflow and the results can be used to inform Tamarix management and support parameterization of drag partition schemes to improve the accuracy of aeolian transport models in landscapes with Tamarix aphylla.