Extreme heat reduces effectiveness of urban trees, study finds

A study conducted by the Institute of Environmental Science and Technology at the Universitat Autònoma de Barcelona (ICTA-UAB) warns that extreme heat and drought are diminishing the ability of urban trees to cool cities.

Research published in the journal ‘Urban Climate’ analyzed street trees in dense areas of Barcelona. The findings indicate that when soil moisture is low, plant transpiration is severely restricted, reducing the thermal relief trees typically provide during heatwaves.

Under optimal soil moisture conditions, tree transpiration can reduce air temperatures by an average of 1.2 °C to 1.7 °C from midday to late afternoon. Furthermore, trees can reduce pedestrian thermal stress by up to 3.2 °C and lower mean radiant temperature by as much as 12.3 °C in sun-exposed areas.