Air Temperature Reductions at the Base of Tree Canopies

Area of Science:

• Urban forestry
• Environmental science
• Climate studies

Background:

• Urban trees play a crucial role in regulating hydrologic cycles and mitigating urban heat.
• While their aesthetic and cooling benefits are recognized, quantitative long-term data on temperature mitigation is limited.
• Urban trees are increasingly utilized as a stormwater management tool.

Purpose of the Study:

• To quantitatively assess the temperature mitigation effects of urban trees using temperature sensors across a large urban area.
• To investigate the influence of tree size, canopy type, street orientation, and time of day on urban air temperature.
• To provide long-term data on urban tree temperature regulation.

Main Methods:

• Air temperature was monitored using logging thermistors at various locations in Camden, New Jersey, from August to November 2017.
• Sensors were placed under tree canopies of different sizes and compared to control sites (poles, parking lots).
• Data was analyzed using analysis of variance, categorizing days into hot, average, and cool based on maximum control site temperatures.

Main Results:

• On hot days (max temp > 30°C), a statistically significant temperature difference was observed between areas under intersecting tree canopies and control sites.
• Daytime temperatures on east-west streets were higher than north-south streets during hot and average days.
• Nighttime temperatures showed the opposite trend, with north-south streets being hotter than east-west streets.

Conclusions:

• Urban trees, particularly those with intersecting canopies, offer significant temperature mitigation during hot conditions.
• Street orientation and time of day are critical factors influencing the effectiveness of urban tree cooling.
• Further research is needed to fully understand the long-term impact of urban trees on microclimates.