From West to East: Tree Placement Differentially Affects Summertime Household Energy Consumption in a Semi-Arid City

Background: Urban tree canopy (UTC) is often proposed as a mitigation strategy for simultaneously decreasing carbon emissions and urban heating in cities. Not only can trees reduce outdoor temperatures through shading and transpiration, but research also suggests that microclimate regulation by trees surrounding buildings can lead to cooler indoor temperatures and a subsequent decrease in summertime energy use. Methods: We analyzed summertime cooling electricity consumption for 21,048 single-family homes in a semi-arid city in northern Colorado, USA. Using Pearson’s correlation coefficients and multiple linear regression models, we evaluated the potential impact of UTC on cooling electricity use in 16 different zones around each house. We hypothesized that trees closer to the home, and trees located on the west and south sides of homes, would have the greatest impact on cooling electricity use. Results: UTC in all 16 zones around residential buildings was associated with negative correlation coefficients, indicating that UTC may be having an impact on energy use. Our regression results showed that UTC on the east side of single-family homes had the greatest effect. Conclusions: Although our results indicated that trees in landscapes around residential buildings can lead to some decreases in household-level energy consumption, the reductions in electricity usage were not as substantial as previous studies have predicted. Past research has shown that tree location matters, and our results indeed show that where UTC is located in reference to a building can change how much impact trees have on energy use. However, our results also show that trees on the east side of buildings have the most impact on household energy consumption in a semi-arid city in Colorado during the summer months. These results directly contradict predictions offered by popular ecosystem service models that show trees on the west and south sides of buildings as having the most impact on energy use in the Northern Hemisphere. Furthermore, many studies have suggested that the energy benefits provided by urban trees outweigh their carbon sequestration potential, and our results indicated this assumption may not hold true in all cities.