Modifying Wind for Cool Season Landscape Design Purposes

As wind moves through your landscape, it is modified by buildings, tree canopies and other solid and porous objects.  In cool season wind areas, the greater the difference in temperature between the air and the object, the greater the cooling effect and in winter when the temperature difference between a person and the air is at a maximum, modifying wind can reduce “windchill”.  This means that landscape designs for areas to be used in cool seasons, such as an outdoor living area, should focus on reducing wind speed by creating a wind block.

Of all the elements in a landscape to characterize and control through design, both biologically and physically, wind is probably the most difficult to control through design, however there are a few standard approaches that can help modify winds in your landscape design.  Once you have determined your cool season prevailing winds, orient your outdoor space away from these prevailing cool season winds and provide upwind barriers perpendicular to prevailing cool season winds.  A good example is to install a coniferous windbreak that deflects your cool season or winter winds.  By selecting the porosity of the object to utilize in your wind modification, you can control the amount of wind reduction and size of area, commonly referred to wind reflection zone.  Trees with 50 percent porosity that are low branched to the ground will reduce wind speed greater and create a wider wind reflection zone than open branched deciduous trees and conifers whose branches don’t reach to the ground.  As water will continue to flow after it encounters an obstruction, so will wind and will flow over and around.  Through design of properly placed vegetation, this wind can be reduced further or channeled to flow through areas that would benefit from increased winds. 

When modifying wind through proper design principles, we can also modify solar radiation to provide beneficial microclimates, a landscape that has been designed to modify both the wind and solar radiation to provide a thermally comfortable place for people.  In the upcoming blog we will discuss strategic modification of solar radiation and the benefits of active and solar heating, survival of plants and habitat for animals.  It will contain information on landscape design utilizing proper landscape vegetation that can modify and increase poor air quality in urban settings.  

Resources:  Brown, Robert D., and Terry J. Gillespie

Microclimatic Landscape Design:  Creating Thermal Comfort and Energy Efficiency

John Wiley and Sons, Inc.