The reduction in wind speed behind a windbreak modifies the environmental conditions, or microclimate, in the sheltered zone. Within this protected zone, the structural characteristics of a windbreak, especially density, determine the extent of wind speed reductions. Windbreak density is the ratio of the solid portion of the barrier to the total area of the barrier. Wind flows through the open portions of a windbreak. Thus, the more solid a windbreak, the less wind that passes through.
Low pressure develops on the leeward side of very dense windbreaks.
The low pressure area behind the windbreak pulls air coming over the windbreak downward, creating turbulence and reducing protection downwind. As density decreases, the amount of air passing through the windbreak increases, moderating the low pressure and turbulence, and increasing the length of the downwind protected area. While this protected area is larger, the wind speed reductions are not as great. By adjusting windbreak density, different flow patterns and areas of protection are established. A windbreak density of 40 to 60 percent provides the greatest downwind area of protection and provides excellent soil erosion control.