Obstacles to the fluid movement of air change wind characteristics. The obstacles may absorb some wind energy, redirect the wind flow and create areas of stronger and weaker winds. The next two pages describe how the wind flows over dunes and around objects. A common obstacle to flow in dune environments is vegetation.

The effects on wind flow depend on the characteristics of the obstacle. For vegetation, the height, width, spacing, branch/leaf characteristics, and flexibility will determine the changes to the wind. The effects of a fence depend on its height and porosity. A useful approximation is that an obstacle changes wind characteristics at the ground to a downwind distance that is 10 times the height of the obstacle. For example, a 3-m (10-ft) high tree disturbs the wind for approximately 30-m (100 ft) in the downwind direction.