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Northern Research Station
One Gifford Pinchot Drive
Madison, WI 53726
(608) 231-9200
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Urban Natural Resources Stewardship

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Tree Influences on Climate of Urban Areas

[image:] Map of predicted temperature differences across metropolitan Baltimore, MD on a clear, calm night.  Blue areas are up to 10 ˚C cooler than red areas, which are highly urbanized.  Trees account for up to 2 or 3 ˚C of cooling at some of the weather stations indicated by the black dots.  Research Issue

By influencing air temperature, urban forests indirectly affect air quality, human comfort and health, energy use in buildings, and growth of ornamental plants. The urban forest effects on temperature vary depending in a complex way on a variety of factors: current and recent weather conditions, number of buildings, amount of impervious cover over the ground, tree species, tree size, and planting arrangement or density. Methods are needed to quantify the urban forest influences on air temperature across urban areas.

Our Research

We are deriving statistical equations to relate temperature difference between weather stations in Baltimore to differences in tree cover, impervious cover, and water cover for distances up to 5 km in the upwind direction.  Other predictor variables are rainfall over periods from 1 day to 1 month previous and atmospheric stability (determined by sun, clouds, and wind speed).  The statistical equations are used to make maps of the temperature differences across the city hour by hour throughout representative days.  The effect on air temperature of adding trees in different land uses will be determined by predicted temperatures with simulated differences in tree cover.

Expected Outcomes

We expect to provide computer methods to predict the influence of added tree cover on temperature at people height in cities.  Preliminary results include maps of the combined influence on air temperature of tree canopy cover, impervious surface cover, elevation, antecedent precipitation, and atmospheric thermal stratification.

Research Results

Heisler, G., J. Walton, I. Yesilonis, D. Nowak, R. Pouyat, R. Grant, S. Grimmond, K. Hyde, and G. Bacon, 2007: Empirical modeling and mapping of below-canopy air temperatures in Baltimore, MD and vicinity. Seventh Urban Environment Symposium, San Diego, CA, American Meteorological Society, Boston, J2.7. 

Research Participants

Principal Investigator

Research Partners

  • David J. Nowak, US Forest Service - Northern Research Station
  • Kenneth Belt, US Forest Service - Northern Research Station
  • Ian Yesilonis, US Forest Service - Northern Research Station
  • Sue Grimmond, King’s College, London, U.K.
  • Richard H. Grant, Purdue University, West Lafayette, IN


Last Modified: 10/03/2019