Roughness Length

The roughness classes are defined as roughness length in meter (z0), which results to the height above ground level where the wind speed is theoretical zero.

Roughness ClassRoughness  Length, z0 in mEnergy Index (%)Land  Scape

0

0.0002

100

Water surface

0.5

0.0024

73

Open terain with smooth surface i.e. runways

1

0.03

52

Agricultural area, no fences or hedges, scattered buildings,

1.5

0.055

45

Agricultural area, some houses, hedges with min. 1250m/¾ mile distance

2

0.1

39

Agricultural area, couple of houses, hedges with min. 500m/¼ mile distance

2.5

0.2

31

Agricultural area with houses, shrubs, trees and hedges with min. 250m distance

3

0.4

24

Villages, small towns forests or very rough and uneven terain

3.5

0.8

18

Lager cities with tall buildings

4

1.6

13

Very large cities with tall buildings