92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Tuesday, 24 January 2012: 8:45 AM
Impact of Urban Trees on the Urban Heat Island and Air Quality
Room 339 (New Orleans Convention Center )
Christopher P. Loughner, Univ. of Maryland, College Park, MD; and D. Allen, D. L. Zhang, K. E. Pickering, R. R. Dickerson, and L. Landry

An urban heat island (UHI) can magnify heat waves and air pollution episodes. The impact of urban trees dampening UHI effects during an extreme heat wave in the Washington, DC and Baltimore, MD metropolitan area is examined. Currently, the Weather Research and Forecasting model coupled with an urban canopy model (WRF-UCM) does not include trees, soil, or grass in urban areas. The WRF-UCM is modified to include parameterizations of the effects of these natural surfaces alongside roadways and buildings in an urban environment to investigate how urban trees, soil, and grass dampen UHI effects. The model is run with 50% tree cover over urban roads and a decrease in the width of urban streets by 10% to make space for soil and grass alongside roads and buildings. Averaged over all urban areas, the added vegetation decreases the (subgrid scale) surface air temperature above urban streets by 4.1 K and road and building wall surface temperatures by 15.4 and 8.9 K due to tree shading and evapotranspiration. This work implies that urban trees can decrease building surface temperatures, reduce the electrical demand needed to cool buildings during the summertime, and therefore result in lower anthropogenic emissions. The added vegetation also decreased surface temperatures downwind of the urban areas near the Chesapeake Bay modifying the strength of the bay breeze. A bay, lake, or sea breeze can magnify air pollution events by causing pollutants to re-circulate and converge over land. Future work integrating the modified WRF-UCM with urban trees with air quality and climate models and alternate anthropogenic and biogenic emissions scenarios to account for urban tree planting strategies can be used to investigate how urban vegetation can impact air quality and climate.

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