According to the non-profit organizations "Cool Communities and American Forests", trees, shrubs, and other plants shade buildings, intercept solar radiation, and cool the air by "evapotranspiration". Planting programs that group and effectively place trees can help reduce urban temperatures and make cities greener. Within ten to fifteen years–the time it takes a tree to grow to a useful size–trees placed in strategic locations can reduce heating and cooling costs by an average of 10-20%.

  • Direct Effect:
    • Light colored roofs: reflect solar radiation; reduce air-conditioning use
    • Trees that shade buildings: reduce air-conditioning use
  • Indirect Effect:
    • Light-colored surfaces: result in lower ambient temperature
    • Vegetation in a neighborhood reduces ambient temperature by evapotranspiration
Annual Electric Energy Savings from Heat Island Measures
Houston Metropolitan Area
Energy
Use & Savings (GWh)
Residential Office Retail Total
Base
Case
(alb edo is 0.2, no trees)
4,873 912 1,445 7,230
Savings        

shade trees

351 21 49 421

cool roofing

393 41 90 524

indirect

185 24 28 237
Total Savings 929 86 167 1,182
%
Savings of base case energy consumption:
  19.1% 9.4% 11.6% 16.3%

Total energy savings amounted to 16.3% of the base case energy consumption. This analysis shows that the heat island measures would achieve a 14% reduction in peak power use.

Preliminary estimates of NOx reductions for heat island measures in the Houston Metroplex as determined by David Hitchcock of the Houston Advanced Research Center:

Emission
Reductions Tons Per Day

Heat Island
Measure
Residential Office Retail Total

direct shade trees

1.06 0.06 49 421

cool roofing

393 41 90 524

indirect

185 24 28 237
Total Savings 929 86 167 1,182

These estimates are based on county information provided by EPA for Reliant Energy; the pounds of NOx per MWh varies by electricity provider from 1.59 to 3.66 depending on the amount of generation fueled by coal.