Increasing urban tree cover to at least 30 percent across the entire urban area could significantly reduce the impact of heat waves in Italian cities. This is the key finding of a study conducted on a sample of ten Italian cities by researchers from the Institute of Research on Terrestrial Ecosystems of the National Research Council of Italy and the State University of New York College of Environmental Science and Forestry, published in the journal npj Urban Sustainability.
The research team analyzed data from Bari, Bologna, Bolzano, Cagliari, Florence, Genoa, Palermo, Rome, Turin, and Verona, representing a range of urban sizes and geographic settings. They simulated what would have happened during the historic summer 2003 heat wave if every neighborhood had achieved at least 30 percent tree canopy cover. According to their estimates, the impact of the heat wave—measured in terms of excess heat-related mortality among people aged 65 and older—could have been reduced by approximately 36 percent.
The authors—Theodore Endreny, Marco Ciolfi, Anna Endreny, Francesca Chiocchini, and Carlo Calfapietra of CNR-IRET and State University of New York College of Environmental Science and Forestry—used the sophisticated urban climate model i-Tree Cool Air, which combines data on temperature, humidity, land cover, and vegetation to estimate how trees cool the environment through shading and evapotranspiration, the process by which plants release water into the atmosphere, helping to dissipate heat.
“The benefits would be particularly significant in the most densely built-up and populated neighborhoods, where the urban heat island effect is strongest,” explain Marco Ciolfi and Francesca Chiocchini. “The cooling effect also depends on water availability: in Mediterranean climates, which are increasingly affected by drought, it may be necessary to combine green infrastructure with efficient water management systems to keep trees healthy without excessively increasing humidity.”
“In light of the urgent need to prepare cities for extreme heat, this research offers a practical solution,” adds Theodore Endreny of CNR-IRET and the State University of New York College of Environmental Science and Forestry. “Urban forests can become a key tool for climate resilience, improving public health and quality of life alongside increased permeable surfaces and rainwater management systems. We also plan to develop more detailed models to identify the neighborhoods best suited for planting new trees.”
The study also highlights additional benefits, including lower air pollution, reduced stormwater runoff thanks to more permeable surfaces, and increased carbon dioxide (CO₂) sequestration. Overall, expanding urban tree cover would generate additional environmental benefits through ecosystem services, estimated at an average value of approximately US$56,000 per square kilometer per year.
Figure caption:
Left: Estimated heat exposure and risk. Darker colors indicate higher exposure to heat waves and a greater risk of heat-related mortality among people aged 65 and older.
Right: Estimated reduction in heat exposure and risk. Darker colors indicate greater benefits resulting from increased urban tree cover.
