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Engineering ToolBox > Wind Shear
Wind moving across the Earth's surface is slowed by obstructions like buildings, trees and similar and the wind velocity increases with altitude.
The wind shear can be expressed as
v / vo = (h / ho)α (1)
where
v = the velocity at height h (m/s)
vo = the velocity at height ho (m/s)
α = the wind shear exponent
The wind shear exponent varies with the terrain.
| Terrain | Wind Shear Exponent |
| Open water | 0.1 |
| Smooth, level, grass-covered | 0.15 |
| Row crops | 0.2 |
| Low bushes with a few trees | 0.2 |
| Heavy trees | 0.25 |
| Several buildings | 0.25 |
| Hilly, mountainous terrain | 0.25 |
If the wind velocity at level 10 m is measured to 5 m/s, the wind velocity at level 40 m can estimated by transforming (1) to
v = (h / ho)α vo (1b)
Substituting with values
v = (40 / 10)0.2 5
= 6.6 m/s