Climatology is the study of weather and its changes over long periods of time. The climate within a given location can be described from three aspects: macroclimate, mesoclimate, and microclimate. Macroclimate, mesoclimate and microclimate can be used to describe the climate of a given location. Macroclimate in general covers large geographical areas (e.g. continent). Mesoclimate covers the climate of areas many square miles and describes variations from the macroclimate due to the effects of water bodies, topographic features and other influences. Whereas microclimate covers climate in areas consisting of square feet (e.g. garden plot) and variations in elevation in the tens of feet.
Intercepting solar radiation
Solar radiation is reduced as it passes through the earth’s atmosphere. The atmosphere contains particles and gases, which affect the incoming radiation through the mechanism of scattering and absorption. Scattering causes changes in direction and intensity of radiation. Buildings, asphalt, and concrete absorb solar energy thus resulting in the emission of long-wave radiation that heat the atmosphere (air) in cities. Trees and other vegetation can affect urban mesoclimate and microclimate by intercepting solar radiation, directing air movement, and influencing air temperature. Trees, shrubs, and other plants shade buildings, intercept solar radiation, and cool the air through evapotranspiration. Specifically, evapotranspiration occurs when plants transpire or secrete water through pores in the leaves. Trees have a large water content and release water vapors into the atmosphere to keep cool. A mature street tree with a treetop of 30 feet can transpire about 40 gallons of water a day.
Trees can direct air movement
Trees can regulate temperature and climate by reducing the heat and redirecting wind. Wind can be guided during the summer months by designing walls of vegetation to direct air to sites where maximum cooling is desired. By accelerating wind through strategically placed vegetation, plantings can constrict airflow, thus creating a vortex effect. Wall(s) of vegetation can be used also to deflect wind away from targeted areas. Using the same concept of using vegetation as a barrier, air can be guided away from the targeted area rather than blocking it entirely. Additionally, windbreaks can be designed to slow the speed of the wind by filtration when some, but not all airflow is desired.
Examples
Trees for Energy Conservation with the feature article Windbreaks for Energy Conservation with tips for both summer and winter.
Decrease in Energy Costs “Trees can help reduce heating and cooling costs by shading buildings, acting as windbreaks, and cooling the air through evaporation that occurs through transpiration”.
Evergreen Conifers for Energy Conservation “A windbreak of trees slows down the wind speed so that a stable layer of slightly warmer air forms around the building exterior, minimizing the temperature difference between the building and the outside air”.
Literature Reference
R. W. Miller, Urban Forestry: Planning and Managing Urban Greenspaces. (1997) Long Grove, Illinois: Waveland Press Inc.
Article by: Sharon Jean-Philippe, University of Tennessee, Department of Forestry, Wildlife and Fisheries and Sarah Workman, University of Georgia, Warnell School of Forestry and Natural ResourcesSee also:
What is a windbreak? and How do I plant a windbreak?
effects on odor and air quality Wind Speed at Shelterbelt
What is a windbreak, and how can it help reduce my home energy bills?
and other related windbreak materials at eXtension.org.
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Additional Resources
Your local university Extension Service or Conservation District can provide you with suggested windbreak species for your area.
The University of Nebraska has many excellent materials about Windbreaks, including Windbreak Design, Windbreaks For Rural Living, Windbreak Establishment , and How Windbreaks Work.
The USDA National Agroforestry Center Notes on Windbreaks and the Windbreak Series that include works from University of Nebraska-Lincoln Extension (some of those above) and North Dakota State University.