Study Proves Trees' Cooling Effect in Extreme Heat

Swiss researchers have made a remarkable discovery that challenges long-held assumptions about urban trees' cooling capabilities. The Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) has demonstrated that plane trees continue to provide significant cooling effects even in extreme heat conditions exceeding 39°C, contradicting previous beliefs that their cooling efficiency diminished at 30-35°C. This breakthrough finding has significant implications for urban heat management strategies, particularly as cities worldwide grapple with rising temperatures due to climate change.

The study, conducted in the Geneva suburb of Lancy during the summer of 2023, involved detailed monitoring of eight plane trees. Researchers from WSL and EPFL observed that water flow in tree trunks not only maintained its level but actually increased as temperatures rose above 39°C. The trees continued to evaporate substantial amounts of water through their leaves, effectively cooling their surroundings through a process similar to sweating. This discovery suggests that current models may significantly underestimate trees' cooling potential during heatwaves.

These findings have profound implications for urban planning and heat management strategies. As cities experience more frequent days with temperatures above 30°C, the confirmed cooling capacity of plane trees offers a natural and sustainable solution to urban heat islands. The research suggests that strategic urban forestry could be more effective than previously thought in combating extreme heat events. Swiss cities are now better positioned to make evidence-based decisions about green infrastructure investments.

Study leader Christoph Bachofen emphasizes that our understanding of trees' responses to extreme conditions is still evolving. The research team hypothesizes that deep-lying water reserves in the soil played a crucial role in maintaining the trees' cooling effect. Future research will focus on examining how other tree species perform under similar conditions and investigating the mechanisms behind this unexpected resilience. This ongoing work will be crucial for optimizing urban forest planning and management strategies.